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__
..
GenRad
,
\
Mic
r
op
h
o
n
es and Accessories
In cl u des
Ceramic Microphones
Electret-Condenser Microphones
J560 P42 Preamplifier
J560 P62 Power Supply
1972-9600 Preamplifier/Adaptor
1560 P 4 0 Preamplifier
1945 9730 Weathe r p r oof Microphone
F orm N o . 19610 1QO-I
...
Instruction Manual
Contents
SPECIFICATIONS
INTRODUCTION -SECTION 1
SOUND FIELDS- SECTION 2
CHARACTERISTICS OF MICROPHONES- SECTION 3
TYPE 1560-P42 PREAMPLIFIER- SECTION 4
TYPE 1560-P62 POWER SUPPLY- SECTION 5
TYPE 1972-9600 I;>REAMPLIFIER/ADAPTOR- SECTION 6
TYPE 1560-P40 PREAMPLIFIER- SECTION 7
TYPE 1945-9730 WEATHERPROOF MICROPHONE SYSTEM- SECTION
8
NOTE
Details for Federal Mfg. Code column in parts lists given on page 7-13.
Microphones
and
Accessories
Includes
Ceramic Microphones
Electret-Condenser Microphones
1560-P42 Preamplifier
1560-P62 Power Supply
1972-9600 Preamplifier/Adaptor
1560-P40 Preamplifier
1945-9130 Weatherproof Microphone
Form No. 1961-0100-1
©
Gen Rad 1977
Concord, Massachusetts, 01 742
July, 1979
GenRad
WARRANTY
We warrant that this product is free from defects in material and workmanship and, when properly used, will perform in accordance with applicable GenRad specifications.
If within one year after original shipment it is found not to meet this standard, it will be repaired or,
at
the option of GenRad, replaced
at
no charge when returned to
a
GenRad service facility. Changes in the product not approved by GenRad shall void this warranty, GenRad shall not be liable for any indirect, special, or consequential damages, even if notice has been given of the possibility of such damages.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES,
EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED
TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE:
GenRad policy is to maintain product repair capability for
a
period of ten years after original shipment and to make this capability available at the then prevailing schedule of charges.
Handbook of Noise Measurement
This book , by Or. A . P. G . Peterson and Ervin E . Gross. Jr .
, of the GenAad Engineering
Staff covers thoroughly the subject of noise and vibration meas uremen t. Copies are avail · able from GenAad at $9 .00 each, postpaid in the United States and Canada
Specifications
1971-9601 1-INCH CERAM I C MICROPHONE,
1971-9605 1-INCH CERAMIC MICROPHONE (1560 P5) and 1971-9606 MICROPHONE ASSEMBLY (1560-P6).
Frequency: Curve shows typ ical response and guaranteed lim i ts ; individual response curve supp lied with each m i cro · pho ne . Below 20 Hz, the microphone is typ ica lly flat
~ 1 dB down to 5 Hz . Time constant of pressure -equa lizing le ak is ty pically 0 .
08 s .
Sensitivity Level: NOMINAL: -40 dB re 1 V/Pa (-60 dB re 1 V/J.tbar) ; MINIMUM : 42 dB re 1 V/Pa (-62 dB re
1 Vi TEMPERATURE COEFFICIENT :
=
0 .
01 dB/ • c .
KEY SOUND PRESSURE LEVELS : <1% distort io n at 150 dB; a t 184 and + 174 dB pe ak, m i crophone may fail.
Impedance: Fo r 1 97 1 960 1 and 9605, 385 pF
±15 ~{, at
23 • C; for 1560 9606, 405 pF
~ 15 % at 23 • C . TEMPERA -
TURE COEFFICI ENT of
Z . for both : 2 .
2 pF
I
•c from 0 to 50 • c .
Environment: TEMPERATURE : 40 to +6o•c operating . HU -
MIDITY: 0 to 100% RH operating .
Terminals: 1971 9601 Coaxial with 0.46·60 thread for mount · ing on 1560.P42 or 1972 · 9600 preamplifiers . Center terminal is sig na l, outer terminal (shell) is ground. T hreaded adaptor may be rem oved for mounting on 156Q.P4
0 preamplifier.
1971-9605 Mic rophone cartridge fitted with 3 terminal audio connecto r .
1971 · 9606 Microphone cartridge with flexible conduit and 3terminal au dio connecto r.
Mechanical: DIMENSI ONS: Cartridge only, 1 .
13 in . (29 mm) long.
0.936
±
.
002 in. ( 23.7 mm
±50 J.tm) dia
; 1560-P5 assemb l y, 2 .
31 in.
(59 mm) lo ng. 0.94 in. (24 mm) dia ; 1560-P6 assembly. 11 .75 in.
(298 mm) long, 0 .
94 in . (24 mm) dia. WE IG HT : 1560-P5. 0 .2 l b
(0.1 kg) net. 1 lb (0.5 kg) shipping ; 1560 P6, 0. 7 lb (0 .
3 kg) net,
2 l b (0.9 kg) shipping.
Typ ica l performance with the 1560-P42 and 1 972-9600 Preampliers (Unity Gain)
Frequenc
Range y
"Systernu
Sensitivity re 1 V/Pa
Dynamic
Range* re20,.1Pa
5 Hz to 12.5 kHz
-40dB
22 to 145d8
*A weighted n oise level tu maximum rms s l newave signa l without clipping . iii
iv
19611-lnch Electret-Condenser Microphones
Frequency: Curves show typical r esponse and gua r anteed limits; individual response curve supp li ed with each microphone . Below 20 H z, the microphone is typically f lat ±1 dB do w n to 15 Hz . M ic rophone is essentially omnid ire ct i ona l .
Sensitivity Level: NOMINAL : -38 dB re 1 V/Pa ( 58 dB re 1 V/ J.tba
r). TEMPERATURE COEFFICIENT::::::+ O.Q1 dBf C f r om 0 to +55°C. MAXIM UM SOUND-PRESSURE
LE VE L: 160 dB absolute max.
Impedance: Nominally 63 pF at 23°C and 1 kHz.
Environment: -2 0 to +60°C and 90% RH operating; 1 -y ear exposure in an environment of +55 ° neglig i ble sensitivity change. c and 90% RH causes
Vibration Sensitivity: 83 dB equivalent
SPL from 1 g .
(pe r pendicu l ar to diaphragm) a t 20 and 100 Hz .
Mechanical:
TERMINALS:
Coaxial, w ith 0.907-60 thread, adapted to 0.
460-60 ( t hreads per in .
).'
D I MENSIONS :
0 .9
36
±0.001 in . dia x 0.670 in. long (1.060 in . lo ng with adaptor)
(23 .
77 ±0 .
025x 17 mm). WEIGHT: 1 oz (28g) net, 11b
(0.5' ·
-
•.
----,-
Typ i cal performance with 1560-P42 and 1972-9600 Preamplifiers (Unity Gain )
1eG:.e&10 '
.
19tf 1 ·
U.S. Patent No. 4,070,741
1962 Y:rlnch Electret-Condenser Microphones
Frequency: Curves show typical response and guaranteed limits : individual response curve supplied with each microphone . Below 20Hz. the microphone is typically flat ±1 dB down to 15 Hz . Mic ropho n e is esse n tially omnidire c t i onal.
Sensitivity Leve l : NOMINAL: -40 dB re 1 V/Pa ( 60 dB re 1 V/1-'bar). TEMPERATURE COEFF I CIENT : +.01 dBfC from 0 to +55°C . MAXIMUM SOUND PRESSURE LEVEL: 170 dB absolute max .
I mpedance: Nominally 22 pF, at 25°C and 1 kH z .
Environment: 20 to +60 ° C and 9 9 % RH operat i ng ; 1 year exposure in an environment of +55 ° neg li g i b l e sens i tiv i ty change .
C and 90% RH causes
VIbration Sensitivity: 83 dB equivalent SPL from 1 g (perpen dicu l ar to d i aphragm) at 20 and 100 Hz .
Mechanical: TERM I NALS : Coaxial, with 0.460-60 thread. DI-
MENS I ONS: 0 .
500± .
001 i n .
d ia x 0 .
6 15± ( 12 .
70± .
012x 15 .
6 mm ) .
WE I GHT: 0.25 oz (7 g) net, 1 lb (0 .
5 kg) shipping .
Hl 'J'l-1 0 iii""' QtM-'M:.tDI:toe: l
~t e, S ~ s.t
~ ~ ~ t
1 1
0
:
.
...
.
•
I
I .
-·~
170
~
T ypical l)«formance with 1560 P42 and 1972-9600 Preamplifiers (Unity Gain)
Microohone
Frequency
Aanoe
"System
Sensitivity re 1 V/Pa
Dynam1e
Range•
111
20uPa
1 962-9610
1962 961 1
1 5Hz
15Hz to 19kHz to 24kHz
40dB
-40dB
30to
30 to
1
1 ·
45
45 dB dB
• A weighted no i se level to maximum r ms sinewave signa l without c l ipping
Catalog Number Description
1962 Electret-Con--..
Microphones
-Flat random-incidence response, %·1nch
P l at perpendicular-incidence response, % indl
1962
1962
·
-
96 1 0
9611
U .
S . Patent No . 4.070
, 741
vi
TYPE 1560-P42 PREAMPLIFIER (CAT. NO. 1560-9642)
Gain: 1:1 or 10:1 (20 dB) ±0.3 dB at 25°C, slide-switch controlled; <±0.3-dB gain change, from that at 25°C, from -30 to +65°C.
Frequency Response (at 1-V rms open-circuit output behind
600 n,
-30 to +55°C}:
20Hz 100 kHz 300 kHz 500 kHz
Z:l gain
10:1 gain
Impedance: INPUT: ::::::: 2 G.Q in parallel with
<
6 pF; driven shield reduces input-capacitance loading for condenser microphones. OUTPUT: ::::::: 15 S1 in series with 10
J.J.F.
Output: SIGNAL: Up to 11 V pk-pk to 10 kHz into open circuit with 15-V supply, decreasing to 2 V pk-pk for 1:1 gain and 1 V pk-pk for 10:1 gain at 100kHz. Up to 10-mA rms output with
1560-P62 Power Suroly. POLARIZING VOLTAGE: +200 V
.±5% behind 1.2 G.Q de source resistance; on-off slide-switch. controlled; temperature coefficient 0.1%/ °C; frequency
>50 kHz.
Noise:
<3.5-~V equivalent input with 390-pF source capacitance, C-weighted, 10-kHz effective bandwidth.
Distortion: <0.25% harmonic distortion at 1 kHz with 1-V rms open-circuit output; <1% at 10 kHz with 1-V rms output into
0.1
~F
(equivalent to 2000ft of cable).
Terminals: INPUT: 0.460 x 60 thread for direct connection to
%-in. microphones and adaptors. ACCEPTS INSERT CALIBRA-
TION SIGNAL: 10 n
± 20% insert resistance, <0.5-dB nominal loss between connector and microphone terminals, 1-V rms max insert voltage. OUTPUT: 10-ft cable with 3-pin A3 mike connector, separate ground and shield reduce sensitivity to i.oterference.
Power: +15 to +25 Vdc, 1 to 2 mA idling (200 V off) or 3 to
5 mA idling (200 V on). Available directly from 1523, 1558,
1568, 1564, 1909, 1911, 1913, 1921, or 1925 Analyzers,
1525 Recorder, 1561 Sound-Level Meter, 1934 Noise-Exposure Meter, 1566 Multichannel Amplifier, or from 1560-P62 power supply when preamplifier is to be used with 1565 or
1551 Sound-Level Meter, 1553 Vibration Meter, and 1900 or
1910 Analyzer.
Mechanical: DIMENSIONS (less cable): 6.75 in. (170 mm) long x 0.5 in. (13 mm) dia. WEIGHT (with cable): 1 lb (0.5 kg) net, 3 lb (1.4 kg) shipping.
1972-9600 PREAMPLIFIER/ADAPTOR (CAT. NO. 1972-9600)
Gain: 0 dB, +0 -0.25 dB, at 1kHz.
Frequency Response: ±1 dB, 5 Hz to 100 kHz; ±3 dB, 3 Hz to 500 kHz (at 0.1 V rms output into an open circuit, driven trom 600-u source).
Input
Impedance: ::::::: 3 pF in parallel with 2 G.Q, at low audio frequencies.
Output
Impedance: Less than 20 fi in series with 6.8 ,F.
Output:
MAXIMUM VOLTAGE AVAILABLE: ;;,:10 V pk-pk, open circuit, at frequencies
~100 kHz, with + 15-V supply. CUR-
RENT (available): >1 mA, pk, with +15-V supply.
Noise: <2.5
,v equivalent input noise voltage, with 39CJ.,pF source capacitance, C weighted.
Distortion: 0.1% total harmonic distortion for frequencies qoo kHz, at 1 V rms output level, open circuit, +15-V supply.
Terminals: INPUT: Coaxial, with 0.460 x 60 thread for direct connection to most microphones. OUTPUT: Switchcraft type A3M microphone connector, mates with 3-wire extension cables 1560-9665, -9666, -9667.
Power: 9 to 25 V
(1 mA at 9 V). Available from most GR analyzers or 1560-P62 power supply. (See list with 1560-P42.)
Mechanical: DIMENSIONS: 0.75 in. dia x 3.44 in. long (19x
87 mm). WEIGHT: 3 oz {85 g) net.
vii
viii
1560-P62 POWER SUPPLY
Input:
100 to 125 or 200 to 250 V, 50 to 60 Hz.
Output:
18 to 21 V de, 15 mA max; automatic limiting protects supply and prevents deep battery discharge. BATTERIES: Two rechargeable Ni-Cd batteries provide up to 225 mA-hours operation at room temperature between charges. RIPPLE: <5 mV rms in CHARGE-OPERATE mode. CHARGE TIME: 14 to 16 h for completely discharged battery, constant 22-mA batterycharging current. Rear-panel slide switch selects internal or external battery.
Interface:
INPUT (from preamp): Power to, and signal from, preamplifier. Use Switchcraft type A3M microphone connector. OUTPUT (to analyzer): Signal from preamplifier and remote power control. Use Switchcraft type A3F microphone connector. ADDITIONAL OUTPUT: Miniature phone jack for connection to 1933 sound-level meter
I
analyzer and patch cable fitted with miniature phone plugs (listing follows).
Supplied:
1560-9665 4-ft cable to connect to 1551, 1561,
1564, etc; 1560-9668 4-ft adaptor cable to connect to 1900,
1910, etc, and cable to connect to 1561 charging terminals.
Remote Operation:
With line voltage not connected, preamplifier can be set to Operate-Only mode by signal of+ 15 to 25 V at 300 f.LA.
Environmental:
Mechanical:
TEMPERATURE: -15 to +50°C operating.
Convertible Bench cabinet. DIMENSIONS (wx hxd): Bench, 8.5x3.84x5.5 in. (216x98x140 mm); rack, 19x
3.84x6.02 in. (483x98x153 mm). WEIGHT: Bench, 3 lb
(1.4 kg) net, 5 lb (2.3 kg) shipping; rack, 5.5 lb (2.5 kg) net, 8 lb
(3.7 kg) shipping.
1560-P40 PREAMPLIFIER (CAT. NO. 1560-9640)
Frequency Response:
1:1 gain
10:1 gain
3Hz 5Hz 250kHz 500kHZ
Gain: 1:1 or 10:1 (20 dB) ±0.3 dB at 25°C, slide-switch controlled; <±0.3-dB gain change (from that at 25oC) from -30° to +55°C.
Impedance: INPUT: 6 pF, >500 Mn at low audio frequencies.
OUTPUT: =20 n in series with 3.3 ,Fat 1:1 gain, =100 n in series with 3.3 ,Fat 10:1 gain.
Noise: <2.5-,V equivalent input with 400-pF source capacitance. C weighted, 10-kHz effective bandwidth.
Distortion: <0.25% harmonic distortion at audio frequencies with 1 V pk-pk open-circuit output; 1% at 1 kHz with 5 V pk-pk into 0. Ol,F (equivalent to 200ft of cable); 1% at 1kHz with
2 V pk-pk into 0.01 ,F.
Available: Ceramic microphones, vibration pickups, tripod, cables, and adaptors. 1560-P96 adaptor converts input to accept 3-pin mike connectors.
Power: + 15 to +25 V de, 1 to 2 mA. Available from same sources as 1560-P42.
Mechanical: DIMENSIONS: 6.88 in. (175 mm) long x 1.56 in.
(30 mm) dia. WEIGHT: 0.6 lb (0.3 kg) net, 3 lb (1.4 kg) shipping.
ix
X
1945-9730 WEATHERPROOF MICROPHONE SYSTEM
The 1945-9730 is a complete weatherproof microphone system for outdoor noise monitoring. It is designed to protect its integral
1560-P42 Preamplifier and a microphone (not included) in an outdoor environment. The windscreen system provided protects the microphone from damage and reduces the effect of wind on the noise measurement. One of the following microphones should be used with the system:
1961 1-in. (23.81 mml Electret-Condenser Microphone
1962 %-in. (12.70 mm) Electret-Condenser Microphone
1972 1-in. (23.81 mm) Ceramic Microphone
Gain:
1:1 or 10:1 (20 dB) ±0.3 dB at 25°C, slide switch selected;
<±0.3 dB change from that at 25°C, from -30 to +65°C.
Frequency:
Measured at 1 V rms output into open circuit with
600 n source, -30°C to +55°C.
20Hz 100kHz 300kHz
±2dB
±1 dB
I
Input Impedance:
Approximately 2 GU in perallel with less than
6 pF. Driven shield reduces input capacitance loading for condenser microphones.
Output Impedance:
Approximately 15 n in series with 3.3 .uF. Up to 11 V pk-pk into open circuit with 15 V supply. at frequencies up to 10kHz. Decreasing to 2V pk-pk for 1:1 gain and 1 V pk-pk for
10:1 gain at 100 k!"Jz. Up to 10 mA rms output (sinewave) with
1560-9575 Power Supply.
Distortion:
<0.25% harmonic distortion at 1 kHz with 1 V rms into open circuit load: <1% at 10 kHz with 1 V rms into 0.1 IJ.F (equivalent to 2000 ft. (600 m) of cable).
Polarizing Voltage:
+200 V ±5% behind approximately 1.2 Gil (DC source resistance.) slide-switch selected. Temperature coefficient approx. +0.1%(C.
Noise:
<3.5 JJ.V equivalent input noise with 390 pF source capacitance, C-weighted (10kHz effective bandwidth).
Insert Terminals:
Accepts insert calibration signal. Insert resistance 10 n
±20"A>.
Nominal loss between connector and microphone terminals <0.5 dB. Maximum insert voltage 1 V rms.
Power:
+15 to 25 Vdc 1-2mA idling (200-V polarizing supply off),
3-5mA idling (200 Von).
Connectors:
Input connector 0.460-60 thread for direct connection to 1/2 in. microphones and adaptors. Output (signal) connector
(male) 4-pin shielded GR type 1933-0410. Supplied with 1560-10-ft
(3 m) cable with switchcraft type A3, 3-terminal microphone connector on opposite end. Type 1933-9601 60-ft. ( 18.5 m) extension cable (not supplied) may be connected between preamplifier output and 10-ft. (3m) cable.
Wind:
30-mph wind typically produces 65-dBA reading.
15-mph wind typically produces 55-dBA reading.
Rain:
Saturation of windscreen from heavy rain typically reduces sensitivity.;; 2 dB for frequency.;; 20kHz.
Humidity:
99% relative humidity at 50°C for a period of two weeks will not affect performance.
Mechanical Data:
HEIGHT WIDTH DEPTH
NET
WEIGHT
SHIPPING
WEIGHT in mm
23.68 601 kg
5
Introduction-Section 1
1.1 DESCRIPTION .
1 .2 ACCESSOR IE S SUPPLI ED
1.3 ACCESSORIES AVA IL ABLE
1 · 1
1 · 5
1 6
~ · ~
1972 9600
I
--· ·
PREAMPLIFIER / ADAPTOR
Figure 1-1 . A complete line o f microphones and accessories is available from GenRad. A f ew a re s h ow n above.
1 .
1 DESCRIPTION .
1 .
1.1
General.
This book c ontains a comp lete descrip t ion of the GenRad ceramic and electret-<:ondenser microphones (Figure 1-1). The many ava il ab l e accessories are a l so desc ribed and details of their uses are g i ven. Among the accesso ries are the GR Type
1560-P42 Prea mp lifi er and the 1 56(}P62 Power Supp l y. which is required with the
Prea mp li fier when it i s u sed w it h sound measur ing inst ru men ts th a t do not inc l ude a source of power to operate the Preamp l ifier. Other avai l able accessories described i nclude the 1972 9600 Preamplifier / Adaptor, 1 56(}P40 Preamplifier. 156()..9590 Tri· pod , microp h one windscreens and miscellaneous adap tors and cable .
1-1
- - - - - - - - - - - - - - - -
- - - - - - -
T~e1 · 1----------------------
TYPICAL CHARACTERISTICS
FOR MICROPHONES
GR
Catalog
Microphone
Number Type
Response
Characteristic
Open-Circuit
Sensitivity dB re 1 V/N/m
2
Cart· Lower Upper ridge Fr eFre-
Capaci· quenc:y quenc:y tance limit pF
Hz li mit kHz
1971-9605 GR 1 in.
Ceramic
1961
·
9610
GR
1 in.
Electret
1961
-
9611
GR
1 i n.
E l ec tr e t
1 962 · 9610
GR
1/2 in.
E lectr et
196 2
·
9611
GR
1/2 in.
E l ectret
Flat
Random In cidence
F la t
Random I ncidence
Flat
Perpendicular
\ncidence
Flat
Random Incidence
F l at
Perpendicular
I ncidence
-40
38
38
-40
-
40
380
65
65
24
2 4
15
1
5
15
15
15
12.5
1 2
15
19
24
1
.
1
.2 Ceramic
Microphones.
Ceramic mic r op hones are noted for their rugg'ldn ess . stabi
l
itY and re
l
iabilitY. Their l ow impedance resu
l
ts in low preamplifier noise and high sensitivity, and contributes to good performance under conditions of relatively high humidity. Complete detai
l
s of th e GR ce ramic microp
h
ones are given in Section 3.
1
.
1.3
E
l
ectret-Conde
n
ser
Microphones.
Thes e microp
h
ones feature very uniform high frequency performance in both flat random
-
and perpendicular-incidence versions. Avai
l
ab
l
e in 2 sizes, t
h
ey do not require a po
l
ar
i
zat
i
on voltage
. Th
us, they can be used with inexpensive preamplifiers, such as the
1
972-9600, described in Section 6. The electret-condense
r
mic
r
ophones are fully described in Section 3.
Figure 1-2 . Type 1560-P42
Preamplifier with mi crophone attac:hecf.
1
.
1
.4 Preamplifier.
The Type 1560-P42 Preamp
l
ifier (Figur e 1 ·2) is specifica lly designed to amplify the outpu t from a capacitive source, such as an ai r -conde n se r, elect ret-condenser or
1
·
2
ceramic microphone, or a piezoelectric vibration pickup. It also provides step-down impedance so that long cables can be used between the microphone/preamplifier combination and GR sound-level meters or analyzers without signal loss. It can be used to increase the sensitivity and input impedance of amplifiers, analyzers, counters, recorders, and similar instruments; it can also serve as a general-purpose audio preamp! ifier for resistive or capacitive sources.
The Preamplifier incorporates a 3-stage amplifier with a low-noise FET input stage and class AB output stage. Excellent stability is obtained with ac and de feedback. A slide switch offers a choice of X1 or X10 gain, controlled by ac feedback. A self-contained oscillator/rectifier circuit supplies the polarizing voltage (+200 V) for air-condenser microphones that can be switched off when ceramic or electret condensor microphones are used. The oscillator operates at approximately 60 kHz.
The Preamplifier is housed in a stainless-steel tube 6 1/2 in. long with a 1 /2-in. diameter. A detachable 10-ft output cable is furnished. Details of the Preamplifier are given in Section 4.
1.1.5 Power Supply.
Power for the Preamplifier (15-25 V de, 15 mA maximu'm) can be obtained from most GR sound-level meters and analyzers. as noted in Table 1-2. The 1560-P62 shielded. battery-powered supply is available for use with other instruments or where more supply current is required for driving large signals through long cables. The
1560-P62 includes 2 nickel-cadmium batteries with charging circuitry. Load-current is limited to prevent damage to the Preamplifier in the event of shorted lines. Provision has been made to tum the -P62 power on or off from a remote analyzer.
For the description and use of the 1560-P62 Power Supply, refer to Section 5 of this book.
B
E
L
5
D
E c
I
FREQUENCY IN H7.:
Figure 1·3. The microphone response curve is included with each GR Microphone.
1-3
-------------------------------------T~e1·2---------------------------------------
Type No.
1523
1525
1551-C
1553
1558
1560-P62
1561-A. R
1564
1565
1566
1568
1569
1900
1921
PHEAMPLIFIER POWER FROM GR ACOUSTICAL INSTRUMENTS
Instrument
Level Recorder
Data Recorder
Sound-Level Meter
Vibration Meter
Octave-Band Analyzer
Power Supply
Precision Sound-Level
Meter
Sound and Vibration
Analyzer
Sound-Level Meter
Multi-Channel Amplifier
Wave Analyzer
(1% Bandwidth)
Automatic Level
Regulator
Wave Analyzer
Real-Time Analyzer
Open-Circuit
Voltage
16 v
±5%
20 v
Requires
Power Supply
Requires
Power Supply
---
- -
---
--
RB<.luires
Power Supply
16 v
±5%
176Vmin
25 v ±5%
Requires
Power Supply
19 v ±5%
Source
16
V
Reg.
20 V Reg
--
- -
2-9 6-V NiCd
2-9 6-V NiCd
2-9 6V NiCd
3-9.0-V CZn
1-19.2-V NiCd
- -
16 V Reg
2-9.6V NiCd
25 V Reg
- -
19 V Reg
Source
Resistance
100n
2.5Hl.
--
- -
1kn
Current Limited
15mA
1.3 kn
240 n
- -
100 n s2o n
Current Limited
Less than 1 l2
- -
300 l2
Max. Available
Current To ·P42*
10mA
4mA
--
--
2.6-6 mA
15mA
0 85-8 3 mA
3 5 mA
--
10mA
3-5 mA
25 mA
--
10 mA
Notes
--
Use 1560-P62 Power Supply
Use 156<J P62 Power Supply
--
--
{ Not recommended for use with air-condenser microph ones
--
{Use 1560-P96 Adaptor and
1560-P62 Power Supply
--
Use 156Q..P62 Power Supp ly
--
Use 1560-P62 Power Suppl y
--
1925
Multifilter 19 v ±5% 19 V Reg
300 n 10mA
1933
1934
Precision Sound-Level
Meter and Analyzer
9V
15 v
±5%
--
15 V Reg
--
<2n
--
20 mA
- -
{Preamplifier included. For use with
156Q..P42, requires 156Q..P 62 Power
Supply and 1933-9602 cab I e.
--
1981 B
1982
1983-9730
Walsh-Healey Noise·
Exposure Meter
Pr~cisi on SLM
Precision SLM
Sound-Level Meter
(Require
Power Supply
- -
--
--
--
--
--
--
-
--
{Preamplifier included. For use with
Supply
and 1933-9602 cab
/e.
*I ndtcates range for ht!!h and low-voltage battertes.
Note 1: For reliable performance, load current multiplied oy sou:ce
re~1stance
(total supply and cable between the supply source voltage and
+
15 V supply rating of the 1560-P42. In other words, E
50 resistance) must not exceed the difference urce
~
( ltoadX A source + cable) must be> 15 V
Note 2: Refer to Figure 4-2 to relate these maximum currents to the permissible signal levels in output cables. The quiescent current of the Pre· amplifier (
1·2 mA for ceramic microphones and 3-5 mA for condenser microphones) must be subtracted from the supply current to deter mine the signal current available to drive long cables.
1.2 ACCESSORIES SUPPLIED.
1.2.1 General.
Each GR microphone is shipped with a Microphone Calibration Certificate, showing the response curve for the microphone (Figure 1-3) and the open-circuit sensitivity and capacitance of the cartridge.
The GR electret-condenser microphones are supplied with adaptors to 'h-in. in addition to the above-mentioned Certificate.
The adaptors supplied and available. are described in para 1.2.2.
The Preamplifier is shipped with the input connector protected by a plastic insu Ia tor cap.
A small stainless-steel clamp is provided, to serve as a hanger for the Preamplifier.
The clamp is shipped attached to the output cable, ready for use. It can be placed at any desired point along the cable. The hole in the clamp is used to hang the microphone and Preamplifier (by the cable). for mounting, such as "free" suspension in an anechoic chamber.
~
8
~
i;
-g_
11
1-in. Electret-Condenser
1961-9610; 1961-9611
L
J
11/2-in.
Electret-Condenser
L
~ .~ w~
I
1-in. Ceramic
I
1-in. Ceramic
1971-9601
I
I
U
Preamplifier/1
I
Adaptor
I
Adaptor
r-
I
1972-96oo l
1/2-in. Air-Condenser
l
B&K4133; B&K4134 *
l t - - - - - - - - - - - - - 1
l
1/4-in. Air-Condenser
B&K 4135; B&K 4136.
I
I
Available as set
I
Adaptor
I -
11----+---1
Preamplifier
I I
1560-P42. r-l1~/:;;:8-
-;A.,-ir-;·C::-o-nd e-n-se-r .....,l1560·9536
I
B&K4138.
1-in. Air-Condenser
I
I j,.-A_,d,-ap-t-or.....,L---
I
r--
Adaptor
Microphones
*
I
Vibration Pickup
I
1560-P52; -P53; -P54
I
Adaptor
11560·9669
• Air-condenser microphones can not be used with the 1972-9600
Preamplifier. because they require polarization voltage; use the
1560-P42.
Figure 1-4. Recommended combinations of transducers, adaptors and preamplifiers.
1-5
1.2.2 Adaptors.
As shown in Figure 1-4, the Y,-in. microphones connect directly to the input of the
Preamplifier. The 1971-9601 1-in. ceramic microphone is supplied as a cartridge with a built-in adapter for direct connection to the -P42. The 1-in. electret microphone also comes supplied with an adaptor, to convert to the Y2-in. thread. This 1961-3200 adaptor is avai I able separately from Gen R ad.
Adaptors are sup pi ied with the 1562 and 1567 Sound Level Calibrators to mate with the 1and Y2-in. electret-condenser microphones and the 1-in. ceramic microphone. The calibrators are accurate self-contained devices for checking the calibration of sound-measuring instruments or systems. The 1562 sup pi ies a known sound-pressure level at 5 different frequencies and the 1567 supplies a known level at
1 kHz.
1.3 ACCESSORIES AVAILABLE.
1.3.1 Preamplifier Cables
There are 2 types of preamplifier cable available from GenRad, namely 4-conductor and 3-conductor. The 4-conductor shielded cables are used with later model sound-level meters and analyzers to extend the distance between the preamplifier and measuring instrument. They are terminated in GR 4-pin male and female connectors.
The 3-conductor cables are used between the 1560-P40 Preamplifier, or the end of the 1560-P42 cable, and older sound-level meters, analyzers, and recorders. They also mate directly with the input and output connectors of the 1560-P62 Power Supply.
They are made of shielded, 3-wire cable and are terminated in Switchraft type 3A
3-pin connectors on each end (one male, one female).
All cables contain a conductor to carry power to the preamplifier.
PREAMPLIFIER CABLES
Description
4-term. 3 m ( 10 tt)
4-term. 18m (60ft)
3-term. 1.2 m ( 4ft)
3-term. 7.5 m (25ft)
3-term. 30 m ( 1 00 ft)
Part No.
1933-9600
1933-9601
1560-9665
1560-9666
1560-9667
1-6
1 .
3 .
2 Adaptors Available.
(Refe r , a l so, to pa r a. 1.3
.
3.)
The f ollowing adap t ors are availab l e separately, for use with the microp h ones :
An adaptor is supplied with the 1 971-9601 Microphone to allow direct connec ti on to the P42 preamplifier.
Adaptor, P/N 1560-9669, mates the P r eamp l i fier i nput co nnector with a Switch· craft, 3-pin, female, microp hone connector . fo r use with GR vibration pickups and the 1 97 1 9605 Ceramic Microphone .
Figure 1-5 . Use of Preamplifier Cables in a field application for sou nd -leve l measurements .
1-7
The 1-in. GR electret microphones come supplied with an adaptor to connect to the -P42 input. An adaptor is not needed for the Y2-in. electret microphone.
The 1560-9696 Adaptor converts the inputs of the 1560-P40 Preamplifier and 1565
Sound-Level Meter to an A3, 3-pin female, microphone connector.
1.3.3 Type 1972-9600 Preamplifier/Adaptor.
This inexpensive Preamplifier/Adaptor (refer to Section 6) is used to mate GR 1-in. ceramic microphones 1971-9601 and GR 1-in., and '/2-in electret-condenser microphones ( 1961 and 1962, respectively) to cables connecting to the input of a measuring instrument. The Preamplifier provides unity gain and sufficient current to drive more than 50 feet of cable. The internal preamplifier can be bypassed to allow the microphone terminals to be mated directly to a standard Switchcraft A3 connector.
Complete details of the use of the 1972-9600 Preamplifier/Adaptor are given in
Section 6 of this manual.
1.3.4
Patch Cables.
Shielded patch cords and adapting cables are available for general use (refer to
Table 1-4). They are 3 ft long and weigh approximately 2 oz (57 g), except
1560-9680, which is 2ft long and weighs 1.4 oz (40 g).
The microphone-plug adapting cables terminate in a microphone plug, such as the
Switchcraft type 850-P2, on one end. Various versions have, at the other end, a double
(in-line) banana plug or other regular-size connector, as listed in the table.
Cables with a %-in. phone plug at one end and a similar plug or a hammerhead double banana plug at the other end are also available (see table).
The BNC- and banane1-plug cables have identical connectors on both ends, as listed.
1-8
AVAILABLE PATCH CABLES
Connectors
Miniature Phone-Plug Patch Cords
1560-P77, with Double Banana Plug, 3ft
1560-P78, with Y.-in. Phone Plug, 3ft
1560-P79, with BNC Plug, 3ft
1560-PSO, with Y.-in. Phone Jack, 2ft
1560-P76 Patch Cord, Phone Plug, 3ft
1560-P95 Patch Cord, with Double Banana Plugs, 3ft
776-C Patch Cord, with BNC plugs, 3ft
274-NO Patch Cord, with Double Banana Plugs, 3ft
Catalog No.
1560·9677
1560-9678
1560-9679
1560-9680
1560-9676
1560-9695
0776-9703
0274-9860
1.3.5 Microphone Windscreens .
M i crophone windscreens (Figure 1 -6) are used to reduce the e f fects of ambient w ind noise. Wind flowing ac r oss t h e surface of the m i c r ophone genera t es lowfrequency noise, which can l ead t o erroneous measu r emen ts . The windsc r een a l so pro t ec ts the m i c r ophone from accumulat i ons o f vapor and dust in the work env ir on ment. Figure 1-7 shows the no i se reduc ti on for the 1 in . m icr ophone .
This accessory fits snug l y
ave r
the m i crophone . It is made of reticu l ated po l y u r e th ane foam and can be conven i ent l y removed and washed, or replaced, if it becomes soiled. This is in add it ion to th e obvious advantage of attenuating up to 20 dB o f amb i ent wind noises, such as might emana t e from a fan blowing cooling a i r o r outdoor winds a c ross the site being mon i tored .
Figure 1-6 . The Preamplif i er and microphone mounted on the Tripod, with th e windscreen in place.
40
-
..,
30
...
I
~
...
~ zo
4( m
10
~
--
"
0
~..-;;-""'"
~
WIND NO IS E REDUCTION
~
~
\
0
100 zoo
400 1 000 zooo
4000 f-Hz (1/3· OCTAVE)
Figure 1 7. Typical noise reduction by windscreen in 25 mp h breez e.
"'
+ 1
~
:>
< v a:
0 a: a:
~
"'
::l
0
:l;
~ a: z
~
~ a:
~
~
0 z
~ w a: u
· 1
"'
0 z i
•2
>
0
· 1
I
I
I
I
I I N . MICRO P HONE
V
W IND SCREE N
-
"1 \N
: .
~ ~~~ ~ ~~ ~
\
~
.......
.......
500 1 1(
2 K
FR EQ UE N C Y Hz
5 1( 101(
10K
30 1(
Figure 1-8. Effec:t of windscreens on microphone response.
1 9
Any attenuation of monitored noise resulting from use of the windscreen occurs over only a portion of the frequency spectrum being monitored. The loss of system sensitivity occasioned by use of the windscreen is 0 dB to 3 kHz,~
0.5 dB to 5kHz, and~
2 dB to 12kHz (see Figure
1-8).
The windscreens are available in packs of four, P/N 1560-9522 to fit 1/2-in. microphones and P/N 1560-9521 for 1-in. microphones.
1.3.6 Tripod.
The 1560-9590 Tripod (Figure 1-6) is designed to accept a variety of sound equipment, including the '12-in. and 1-in. microphones, the 1560-P42 Preamplifier, and the 1972-9600 Preamplifier/Adaptor. The 1-in. ceramic microphone can be mounted on the Tripod either with or without the Preamplifier. All electretcondenser microphones require either the 1560-P42 Preamplifier, the 1972-9600
Preamplifier/Adaptor, to mount them on the Tripod. The preamplifier supplied with the sound-level meter or analyzer can likewise meet this need.
The tilting head can be swiveled through 360° by rotating the center post of the tripod. The head can be tilted 90° (vertical to horizontal) in one direction and in the opposite direction as far as 20° from the vertical. The latter position is the proper mounting angle for a preamp with a flat-random-incidence microphone when the sound source is at the same elevation in a free field. (A free field is typically found outdoors away from obstructions or ·In an anechoic chamber.)
Height Adjustment.
Each of the tripod legs and its center post are telescoping for compact storage and versatility in use. Adjust the tripod for the desired height, from
14.5 to 56 in. (37 to 140 em) as follows: a. Extend the legs by loosening the knurled locking nuts (smallest first) and pulling out the telescoping sections. T1ghten securely (largest nut first) at the desired length. b. Extend the center post by loosening the thumb screw at its side, pulling it up, and clamping it at the desired height with the thumb screw. c. Keep the tilting sleeve adaptor (see below) in place to retain the inner tube of the center post as you loosen the locking nut on the center post. Swivel the very top assembly, and if necessary raise it, to the desired position before retightening this locking nut.
CAUTION
Be sure the 9 knurled locking nuts in the legs of the tripod are tightened securely so it will not collapse in use.
A
Figure
1-9:
Tilting sleeve adaptor. A= top stud.
B =smaller clamping nut, C = larger clamping nut,
D =bottom stud which screws onto top of tripod,
E =set screw for adjusting friction in: F =pivot.
1560·2560
1-10
Sleeve Adaptor (Head). With this tripod are included a tilting Sleeve Adaptor
1560-2560 and 2 sleeves. This adaptor usually serves as the head of the tripod center post. At the bottom end is a set screw with which you can vary the tightness ot the tilting pivot. This end is threaded to fit the center post of the tripod. Mounting instructions follow:
1972-9600 Preamplifier/Adaptor.
a. Ti It Sleeve Adaptor (head) to approx 20° from vertical. In one direction of tilt there is a stop at this angle. b. Remove each sleeve after loosening its knurled clamping nut, 1/4 turn. c. Tighten the smaller clamping nut gently, by hand. (If inadvertently removed, be sure to replace each nut with its split locking ring oriented so beveled edge is down.) If the larger clamping nut has been tightened without its sleeve in place, loosen 1 turn. d. Insert non-slotted end of larger sleeve into the clamping nut as far as it will go
(5/8 in.). Orient slot where you want the extension cable to pass through (downward\.
Tighten the clamping nut. e. Connect cable to 1972-9600 Preamplifier/Adaptor. (Always connect or disconnect with both parts in your hands, never in the tripod sleeve.) Observe the latch, which must be depressed when you disconnect. f. With cable in slot, slide preamp backwards into sleeve about 1/2 in., with latch in slot. /Sleeve will grip cable connector as well as preamp, for added support.) DO
NOT insert so far that cable is stressed.
CAUTION
Do not allow the edges of the slot to pierce the cable insulation.
1560-P42 Preamplifier.
a. Tilt Sleeve Adaptor (head) to approx 20° from vertical. In one direction there is a stop at this angle. b. Remove larger sleeve after loosening its clamping nut 1/4 turn. Tighten nut gently by hand (see step c, above). If the smaller clamping nut has been tightened without its sleeve in place, loosen 1 turn. c. Insert non-slotted end of smaller sleeve into clamping nut as far as it will go (3/8 in). Orient slot where you want cable to pass through (downward). Tighten clamping nut. d. With its cable in slot, slide preamp backwards into sleeve far enough for firm support but NOT so far that its cable is stressed.
Tightness of the Pivot. The stiffness of the pivot in the sleeve adaptor is adjustable as follows: a. Raise the inner tube of the tripod center post, so you can get a good grip on it.
Unscrew the tilting Sleeve Adaptor 1560-2560 from its top. b. Tighten or loosen the set screw, E, using a 0.125-in. hex wrench, a small fraction of a turn, until the pivot is free enough for convenience but tight enough for reliable support. c. Replace securely on center post.
1-11
1.3. 7 Miscellaneous Accessories.
The 1962-321 0 Microphone Attenuator attenuates the output of the 1962 %-in.
Electret-Condenser Microphones by 10 dB, to allow operation of microphones at high levels.
Also available is the 1962-9620 Dummy Microphone, a shielded 24-pF capacitor, used to simulate a 1962 %-in. Electret-Condenser Microphone, to determine i nstrument noise floor. BNC input connector is also provided to connect a signal source, simulating a sound signal. BNC shorting plug is supplied.
The 1560-9635 Permanent-Magnet Clamp can be used for firm holding of a vibration pickup to a ferrous metal surface.
1-12
Sound Fields-Section 2
2.1 FREE FIELDS . .
2.2 DIFFUSE (REVERBERANT) FIELDS
2.3 SEMI-REVERBERANT FIELDS
2.4 PRESSURE FIELDS .
2.5 SOUND INCIDENCE .
. 2-1
. 2-1
. 2-1
. 2-1
. 2-2
2.1 FREE FIELDS.
A sound field is said to be a free field if it is uniform, free from boundaries, and is undisturbed by other sources of sound. In practice, it is a field in which the effects of the boundaries are negligible over the region of interest. At any given point in a free field, the sound wave can be approximated by plain sound waves that have a given direction of propagation; the flow of sound energy is in one direction only.
A free field can be simulated in an enclosed environment by applying acoustic absorbing materials, usually in the form of wedges, to the boundaries. These anechoic
(echo-free) chambers can be built to make free-field measurements possible over much of the acoustic frequency range. The field in an anechoic chamber is a free field above the lower cut-off frequency of the absorbing wedges. (The cut-off frequency is the point at which the wavelength of the sound wave is equal to four times the depth of treatment.)
Another approximation to a free field occurs outdoors, in particular, in open spaces, well above the ground.
2.2 DIFFUSE (REVERBERANT) FIELDS.
A diffuse or reverberant sound field is one in which the time average of the mean square sound pressure is everywhere the same and the flow of energy in all directions is equally probable. The sound is reflected from the boundary surfaces; there is no particular direction of propagation to the sound wave. At any given point in the diffuse field, sound is arriving equally from all directions (random incidence).
2.3 SEMI-REVERBERANT FIELDS.
A semi-reverberant field is one in which sound energy is both reflected and absorbed. The flow of sound energy is in more than one direction. Much of the energy is truly from a diffused field; however, there are components of the field that have a definable direction of propagation from the noise source. The semi-reverberant field is encountered in the majority of noise-measurement situations.
2.4 PRESSURE FIELDS.
A pressure field is one in which the instantaneous pressure is everywhere uniform.
There is no direction of propagation. The pressure field exists primarily in cavities
2-1
(commonly called couplers). where the maximum dimension of the cavity is less than
1/6 of the wavelength of the sound. A pressure field is used in couplers for the calibration of microphones and earphones.
2.5 SOUND INCIDENCE.
2.5.1
Free-Field Sensitivity (Response)*
The free-field response of a microphone is the open-circuit output voltage caused by the free-field sound pressure in the
undisturbed
sound field; i.e., the pressure that existed at the location of the microphone prior to the introduction of the microphone into the sound field. For free-field sensitivity, the angle between the direction of sound propagation and the plane of the microphone diaphragm, as well as the frequency, must be specified.
2.5.2 Free-Field Response.
The free-field response of a microphone is the voltage output divided by the pressure that existed at the location of the microphone prior to the introduction of the microphone into the sound field. Free-field responses are typed according to the angle between the direction of sound propagation and the plane of the microphone diaphragm.
Perpendicular-Incidence Response (0°).
With this type of response, the direction of sound propagation is perpendicular to the plane of the diaphragm (at an angle of 0° to the normal of the diaphragm). The sound wave is moving in one direction only, directly into the microphone. This condition occurs only in a free-field environment
(or, under very special circumstances, in certain semi-reverberant environments).
Grazing-Incidence Response (90° ).
In this case, the direction of sound propagation is parallel to the plane of the microphone diaphragm (at 90° to the normal of the diaphragm). The sound wave can approach the microphone from any side, but its direction must be parallel to the diaphragm surface. This type of incidence occurs mostly in free-field environments.
The directions of sound propagation for perpendicular- and grazing-incidence responses are shown in Figure 2-1.
2.5.3
Random-Incidence Response.
The random-incidence response of a microphone is its voltage output when subjected to a diffuse sound field. The flow of energy in any direction is almost equally probable. Because of nearby reflecting surfaces, this is the most common type of sound field.
2.5.4
Pressure Sensitivity.
The pressure sensit';vity of a microphone is the voltage output when the diaphragm is excited with a pressure that is uniform over the entire surface of the diaphragm. The accuracy and repeatability of a pressure calibration are more easily controlled than with free-field methods. For this reason, the standard calibrations determined by the
National Bureau of Standards are pressure-sensitivity (pressure-response) calibrations.
•Technically, "sensitivity" and "response" have the same meaning. However, "sensitivity" is commonly used for a single-frequency statement, and "response" is used when the sensitivity as a function of frequency is intended.
2-2
2.5.5 Diffraction.
The physical size of the microphone causes diffraction of sound waves when the wavelength is not appreciably greater than the dimensions of the microphone, and gives rise to differences between the responses defined above. At low frequencies, all responses of a microphone are the same and the microphone is truly an omn idirectional receiver of sound. The various responses start to diverge at the frequency at which the diameter of the microphone is equal to approximately 1/10 of the wavelength of the sound. The curves of figure 2-2 show typical response characteristics for a microphone of 1-in. diameter. To a first approximation, the differences between the curves would hold for any measurement microphone of this size. For the
1/2-in. microphone, the frequency scale would be approximately double that for the
1-in. microphone. For a 1/4-in. microphone, the frequency scale would be increased by approximately a factor of 4, and for a 1/8-in. microphone, by a factor of 8.
MICROPHONE
DIAPHRAGM
Figure 2-1. Direction of sound propagation for perpendicular- and grazing-incidence responses.
+10
+8
+6
+4
"'+
....
~ u z
0
....
0 z
-4
-6
-8
-1 0 zo
I 1 T
1
FREE-FIELD PERPENDICULAR
RESPONSE CHARACTERISTIC.....___ l
I
I T
RANDOM -INCIDENCE
)\
"
rl
\
RESPONSE CHARACTERISTIC:::::::---.
./
_.,.
~
f'}
1\
GRAZING -INCIDENCE
RESPONSE CHARACTERISTIC
17
1'
~
\\
\
\
50 70 100
ZOO 500 700 I k
FREQUENCY IN HERTZ
Zk
5k 7k
IOk ZOk
156(>40
Figure 2-2. Typical response characteristics for the 1-in. ceramic microphone.
2-3
Characteristics of Microphones
Section 3
3.1 TRANSDUCERS .
3.2 CLASSIFICATIONS OF SOUND-MEASUREMENT MICROPHONES.
3.3 EQUIVALENT CIRCUITS .
3.4 MICROPHONE SELECTION
3.5 MINIMIZING DIFFRACTION.
3.6 GR CERAMIC MICROPHONES
3.7 GR ELECTRET-CONDENSER MICROPHONES.
..3-1
.3-1
.3-2
.3-3
.3-5
.3-5
.3-11
3.1 TRANSDUCERS.
A transducer transforms energy from one form to another. In the case of microphones, it changes the pressure variation of an acoustic wave into an electrical signal proportional to that pressure variation. Vibration pickups, specifically accelerometers, transform the motion of a vibrating body into an electrical signal proportional to their acceleration.
3.2 CLASSIFICATIONS OF SOUND-MEASUREMENT MICROPHONES.
3.2.1
General.
Sound-measurement microphones are divided into two main classes: condenser and ceramic microphones. Others, such as dynamic and controlled-reluctance types, lack the frequency-response control and stability necessary to make them usable as measurement m"1crophones. The most important requirements tor a measurement microphone are reliability and stability. Stated simply, this means that, between calibrations, accurate measurements can be made with a measurement microphone, and the conditions normally encountered in making sound measurements will not have a detrimental effect on the microphone or its calibration. Ceramic and condenser microphones meet these two requirements.
3.2.2
Ceramic Microphones.
Ceramic microphone use a piezoelectric ceramic (lead-titanate, lead-zirconate} as the voltage-generating element. The piezoelectric material produces a voltage when it is stressed. A diaphragm fastened to the ceramic transfers the sound-pressure variations into a corresponding varying force that bends the ceramic element.
3.2.3
Conventional Air-Condenser Microphones.
The conventional air-condenser microphone uses the variation of an electrical capacitance to generate an electrical signal. The original high-quality measurement microphone was this type, developed by Bell Telephone Laboratories. This microphone, known as the Western Electric 640AA, remains the standard of measurement and calibration.*
The advantages of air-condenser microphones are: smooth frequency-response characteristic, good sensitivity, and wide availability in various sizes and styles. However, condenser microphones of this type require a polarizing voltage, to bias them properly.
•e.
C. Wente,
"I>.
Condenser Transmitter as a Uniformly Sensitive Instrument 1or the l>.bsolute
Measurement of Sound Intensity,"
Physical Review,
M. S. Hawley, "The Condenser Microphone as an l>.coustlc Standard,"
Vol 33, No 1, January 1955, pp 6-10.
Vol10, 1917, pp 39-63.
Bell Laboratories Record,
3-1
Also, their relatively high output impedance makes them more susceptible to problems caused by high humidity. The high impedance also results in greater preamplifier noise.
3.2.4 Electret-Condenser Microphones.
A more recent type is the electret-condenser microphone. Its basic design is similar to the conventional air-condenser microphone, but it has a permanently charged. diaphragm and does not require a polarizing voltage. The electret-condenser microphone retains the advantages of conventional air-condenser microphones with high sensitivity, flat frequency response and wide dynamic range. It also provides some additional benefits: Its output capacitance is much higher and it does not become noisy in a humid environment, since no free electrostatic charge exists at the surface of the diaphragm. The electret charge is trapped inside a polymer film and there is an exceptionally strong bond between charged particles and molecules of the polymer.
The temperature coefficient of sensitivity of an electret-condenser microphone is fairly constant over its entire frequency range. This is a significant advantage over the air-condenser microphone, whose sensitivity changes markedly at frequencies above 16Hz, increasing by a factor of 4-to-6 at 4kHz and 5kHz.
A diaphragm of an electret-condenser microphone is shown in Figure 3-1 (b).
The electret layer is bonded to the backplate. The mechanical ruggedness and high stability of microphone parameters are ensured by a unique design of diaphragm supporting elements, which are bonded to the diaphragm.
3.3
EQUIVALENT CIRCUIT.
The equivalent circuit for both the condenser and ceramic microphones is shown in
Figure 3-1 (a). The open-circuit voltage, e, is the single-frequency voltage appearing at the microphone terminals when working into an infinite electrical impedance. If p is the sound pressure at the diaphragm, the pressure response of a microphone is
e
M p = p
The pressure response level relative to a reference response, Mr (in V /Pa) is
Useful relationships to remember are that the value of e is 1 mV when M = -40 dB re 1 V /Pa (or-60 dB re 1 V /IJ.bar) and P = 74 dB SPL or 1 11bar (or 1 dyne(cm2).
*
At the threshold of hearing of 20 J..LPa, a -40 dB microphone produces a voltage output of 0.2 J..LV. The voltage delivered to the measuring instrument is dependent upon the instrument input impedance.
If the microphone is connected directly to a Icing cable (capacitive load) without a preamplifier, the long cable merely reduces the sensitivity of the microphone by
Cm
Xe where Cin =input capacitance of the instrument and the cable; E·
1 n =instrument input voltage.
•1n the international system of units (SI), the unit of pressure is the pascal (Pa); 1 Pa
= 10 dynes/em
2
•
=
1 N/m
2
Ref: "The International System of Units (SI)", U.S. Dept. of Commerce, National Bureau of
Standards, NBS Special Publication 330. SO Cat. No. C 13.10:330/2, U.S. GPO, Wash., D.C., 20402.
3-2
The cable does not affect the frequency response because the microphone and cable capacitances change the impedance in the same proportion with changing frequency.
A preamplifier is usually used between the microphone and measuring instrument, to provide impedance transformation (very high to very low). This results in no loss in microphone sensitivity and, hence, no cable correction. In addition, preamplifiers usually provide some gain (20 dB), thus permitting the instrument to measure to lower levels.
The high input resistance of the preamplifier makes possible good low-frequency response with a high source impedance. The low input capacitance of the preamplifier minimizes loading of the microphone, thereby maintaining good sensitivity.
,---------,
: E-------<> ~ ~
,-----
PREAMPLIFIER
---,
l
~
DIAPHAAGM
SUPPORT
I
I
Cm a.l~e
:
I I
>500 r \
Mfi
ll~l'
MICROPHONE :
I
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J
I I b.
AIR LEAK HOLE
INSULATOR
Figure 3-1. a. Equivalent circuits for a microphone and preamplifier; b. Electret section view.
3.4 MICROPHONE SELECTION.
3.4.1 General.
Measurement microphones are designed to have either a flat pressure-response characteristic, a flat random-incidence response characteristic, or a flat free-field perpendicular-response characteristic. For the measurement of noise, in general, a microphone with a flat random-incidence response should be selected. The American
National Standard for sound-level meters is based on a flat random-incidence response.
The International Specification for precision sound-level meters permits other responses, but it stipulates that the supplier must give calculations and corrections for deriving the random-incidence response. As stated above, the random-incidence response of a microphone is its voltage output when subjected to a diffuse sound field.
The fields encountered in noise measurements are not truly diffuse. However, this is the closest approximation for nearly all indoor and most outdoor applications. An exception is aircraft flyover or automotive passby noise. In these applications, the noise signature of the vehicle is best measured with a microphone having a flat grazing-incidence response. For a vehicle passby on the ground, the microphone is placed with its diaphragm facing upward, so that the angle of incidence from the sound source to the microphone remains constant at grazing incidence. For aircraft flyover, the angle of incidence is kept constant by mounting the microphone with its axis parallel to the ground and perpendicular to the surface described by the arc of the fly over.
As shown in Figure 2-2, the difference between the grazing-incidence or pressure response and the random-incidence response of a 1-in. microphone is small, so that either a flat random-incidence microphone or a flat pressure microphone gives a good approximation to a flat grazing incidence. Sound-power measurements in a diffuse room are an ideal application for a microphone with a flat random-incidence response.
If one is making sound-pressure (sound-power) measurements of a device in an anechoic chamber, the sound wave is radiating outward from the source and there are
3-3
no reflections. For this application, use a microphone with flat perpendicular-incidence response, with the microphone pointed directly at the sound source.
If one is measuring the response in a coupler of small diameter compared with the wave length, use a microphone with a flat pressure response. Likewise, for measurement of the pressures at the ear drum, a microphone having a flat pressure response should be used.
In general, select the largest microphone that has adequate frequency response for the intended application.
Figure 3-2 is a plot of the response of various 1-in. microphones.
(/)
0
~ w m -z u w
0
-4
+6
+4
+Z
-6 /----
-a
20
·--·
DESIGNED FOR FLAT PRESSURE RESPONSE
I
100 50 70 ZOO
I
500 700 I kHz
I
ll
ELECTRET~
CONDENSER~
---
-
,_.. !"'.
....c
~ r'-
~/
1\\
1\
\~
CERAMIC~\
\
Zk 5k 7k
11
J
IOk 2.0k
FREQUENCY -Hz
1560-65
Figure 3-2. Random-incidence response of various types of microphones.
3.4.2
Sensitivity.
Until recently. the sensitivity level of a microphone was referenced to 1 V /JJ.bar.
The International System of Units (SI) has changed the reference to 1 V /Pa and
Sensitivity Level
= x dB re 1 V /Pa.' Because 1 Pa
=
10 JJ.bar, the new reference is merely 20 dB higher than the old reference.
Say we have a microphone with a sensitivity level of -40 dB re 1 V /Pa. What output voltage will it generate for a sound pressure of 1 Pa?
For the same sound-pressure level (SPL), 40 dB gives a voltage that is 100 times smaller. Thus, the voltage for an SP L of 1 V /Pa is 10 m V.
A sound pressure of 1 Pa is an SPL of 94 dB, where
SPL
=
20 log
1 0
• 20 log.,
(
1 Pa
\ dB
20 JJ.Pa
J
(ooo6
2
~
• 94 dB.
Thus, a microphone with a sensitivity level of -40 dB re 1 V /Pa will generate an output voltage of 10 mV for a sound pressure level of 94 dB.
By remembering this simple relationship, one can calculate the output voltage of
3-4
any microphone, with any sens1t1v1ty, for any sound pressure. This is particularly useful for determining signal-to-noise ratio relationships.
For example, for the same sound-pressure level, a -40 dB microphone generates
3.16 times the voltage generated by a -50 dB microphone (20 log
1 0
3.16
=
10 dB). A
-50 dB microphone will generate 3.16 mV for a 94-dB SPL, and if we subject it to a
114-dB sound-pressure level, the voltage generated is 20 dB higher or 31.6 mV. For quick reference, these calculations are already carried out in Figure 4-11.
3.4.3 Dynamic Range.
The low end of the dynamic range of a microphone/preamplifier system is determined by the self noise of the preamplifier when its input is terminated by the capacitance of the microphone. The noise level of the preamplifier is a function of the microphone capacitance. As a result, the low end of the dynamic range is limited by both preamplifier self noise and microphone sensitivity.
The upper end of the dynamic range is usually limited by the output-voltage amplitude or the output-current level at which the preamplifier no longer amplifies linearly. The maximum voltage swing is a function of the power-supply or battery voltage for the preamplifier and the current level is a function of the length of cable attached to the preamplifi~ output (cable reactance). Microphone sensitivity is a\so a limitation here, as the more sensitive the microphone, the more voltage it generates for a given SPL.
The range for the GR 1-in. ceramic microphone is 22 to 145 dB SPL.
The A-weighted dynamic range for the GR %-in. electret-condenser microphone with the -P42 Preamplifier is approximately 30 to 145 dB SPL. For the 1-in. electret microphone, the range is 22 to 140 dB SP L.
3.5 MINIMIZING DIFFRACTION.
The occasion often arises when one wishes to use a microphone with a smaller diameter, to provide a more omnidirectional characteristic or to enable one to select the response to be used. Another important consideration, however, is the size of all the material intercepting the sound field. This includes the microphone, preamplifier, and their supports. Figure 3-3 shows the free-field perpendicular-incidence response characteristic of a 1 /2-in. microphone mounted in line on a 1 /2-in. rod. This rod, in turn, connects to a 3/4-in. rod at a point 1 in. from the diaphragm of the microphone.
Note that variations of approximately ±1 dB occur because of the diffraction produced by the larger-diameter rod. A good rule to follow is to maintain the diameter of the microphone for a distance equal to 5 times the larger diffracting diameter.
Beyond the 5-diameters point, a gradual taper to the larger diameter should be employed. In the figure, the controlling diameter is the 3/4-in. support rod. Therefore, the 1-in. distance from the diaphragm to the larger rod should be increased to approximately 4 inches.
3.6 GR CERAMIC MICROPHONES.
3.6.1 General.
The G R ceramic microphone is offered in a 1-in. size (refer to Table 1-1).
3-5
•2
0 l I ! I H J ~J::C :tL ~-L
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., _ ,,..
moun ttnt
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H
~
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! f-1 l
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so
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$00 700
FREQUENCY Hz
, .
·sr
: ~i
;;: ~i H
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~ -
:'
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:
:
~ -
=
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:=: =:--:::: r :::;
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:=
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): :k
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-
',.
~
::: k
-:-:-
I• ·
I I
--:::::
--
-~ -
:;-
..
.
1560'")
Figure 3-3. Free-field perpendicular-i n cide n ce response character istic of a %-i n . microphone
(see
text).
The 1560 2131 Micropho n e Cartridge is used in the G R 1 in . ceramic microphones, in clud ing the 1 97 1 960 1 and 1971 9605 Microphones a nd the 1971 9606 Microphone
Assembly (see F igu r e s 3 4 and 3-5) . In this car t ridge, on e lead is connec te d to the shell .
1660-2131
MICROPHONE
CARTR I DGE
\
Figure 3 4 . The 1 in. ceramic microphone 1971-9601.
The Cartridge is a high-quality. measurement type unit, suitab le for use with many high input impedance preamplifiers. decade amplifiers. or sensitive voltm ete rs. The input impedance requ i red for response down to 20 H z is 20 MSL or higher .
The shell of the 1 in . Cartridge and one lead are connected together through th e base or adaptor. The red dot on the Cartridge identifies the signal terminal, which is also the positive-potential termina l when a posit i ve pressure pu lse is applied to the diaphragm of the Cartridge .
3-6
In the 1971-9605 Microphone. the Cartridge i s fix ed to a 3 p in , male, microp hone connector . To connect the 1971 9605 Mic r op ho ne Assembly to the P42 P r eamplifier. the 1560-9669 adap t or i s required .
The 1971 9601 Microphone Assembly contains the Cartridge and an adaptor, thus permitting its direct connection to the 1560 P42 .
3 .6.
2 Calibration .
The 1 in. GR c eramic microph on es are designed for a flat random incidence response ( r efer to Specifications). Wh en t h e r e is a possibility that the s o und w<Ne ma y h ave some di r ect ivity , th e microphone should be tipped at an angle of
70° to the di r ection of the sou n d sou r ce. This gives a f l at res ponse cha r acter i stic for any direct r adiated sound. The 70° in cidence response c l osely app r oxima t es the random incidence response.
Figure 3-5 . 1-in . ce ramic microphone 1971 9605.
+10
•8
•6
+4 en
...
"'+2
....
0
0
-2
-4
-6
20 50 70 100 200 ~00 700 h
FREQUENCY I N HERTZ
NA#INDIWlA.H
'
) vv
E
-
~
........ ...,
/)' -~~~
"'~
5 k 7k I O k 2k
\
20 k
F igu re 3-6 . Corrections to be added to the random incidence response of the 1 ·i n . ceramic microphone to obtain the perpend ic ular · and grazing-incidence r espo n ses or p ressure response.
3-7
10kHz
2kHz
4kHz
+
D
15kHz
6kHz
Figure 3-7. Directional patterns of the
1-in. ceramic microphones (2-6kHz).
3-8
20kHz
Figure 3-8. Directional patterns of the 1-in. ceramic microphones (10- 20kHz).
...
,.
The curves given with the Specifications show the random-incidence response characteristics for the two microphones. Figure 3-6 gives the corrections to be added (algebraically) to the random-incidence responses, to obtain the perpendicularincidence and grazing-incidence responses for the microphones.
3.6.3 Mechanical Description.
The diameter of the 1-in. Microphone is 0.936
± .002 in. This diameter is identical to the Western Electric 640AA; thus the microphone can be used interchangeably with the 640AA in couplers designed for earphone and hearing-aid calibrations, etc. For this use, the equivalent volume of the 1-in. microphone is 0.5 cc; the equivalent volume of the 640AA is 0.7 cc with the grid off and 0.3 cc with the grid on. For practical purposes, the GR 1-in ceramic microphone is totally interchangeable with the Western
Electric 640AA.
3.6.4 Diffraction Characteristics.
Diffraction of the sound waves by the 1-in ceramic microphone starts at approximately .1 kHz. Below this frequency, it is truly omni-directional. Figure 3-7 shows the directional characteristics ot the microphone to 20kHz.
-0.5
J
Iii
I: lj
I i
I• :; I!
I!
II IIi Iiiii I
~~IIi
I!
!{I
0
6207
Cllii=:==R
.
__
11E!IIii····lil
-f-'--;--- ·-·
STABILI~~~
:
3609
~
-i+i-+-.
-1-+-~
, 1 YEAR
'. f--
' '-·+c-
·-+
·-1-·
1969
·+.
1970
1560·P5·2
1966
1967
1966
Figure 3-9. Stability record for several sampla microphones.
3.6.5 Stability.
Work with the GR ceramic microphones over the years has proved that they have excellent short- and long-term stability. Figure 3-9 shows the record for several sample microphones over various periods of time, up to 4 1/2 years. Stability tests, started in
3-9
1966-1969, immediately upon production of the microphones, show a small initial drift (up to 0.3 dB), after which the microphones stabilize as shown in the figure.
Other evidence indicates that this drift is completed after 5 days. The normal manufacturing and testing cycle at G R guarantees that this initial drift is completed before the microphones are calibrated for sale.
The microphones were also evaluated for stability according to the procedures outlined in the American National Standard Institute (ANSI) S 1.12-1967 for
Laboratory Standard Microphones. Table 3-1 shows the average results for several 1-in. ceramic G R Microphones.
STABILITY RATING OF 1971 MICROPHONES
PER PROCEDURE OUTLINED IN ANSI S1.12 · 1967
STANDARD
REQUIREMENT
TYPE 1971
SHORT-TERM
STABILITY,
5-DAY PERIOD lml
dB/day SdB
.04 0.1
LONG-TERM
STABILITY,
1-YEAR PERIOD lml
dB/yr.
SdB
0.4 0.15
.0075 .032 .085 .07
WHERE: lml:
MAGNITUDE OF THE SLOPE OF CURVE OF SENSITIVITY VS TIME
S :STANDARD DEVIATION OF RESIDUALS.
1560·P5·6
3.6.6 Temperature Effects.
The GR ceramic microphones are stable up to 60°C (140°F). If the microphones are used above this temperature, there is a permanent loss of 1 dB in sensitivity
(following the initial exposure) up to 100°C (212°F). If the microphones are to be used above 60°C, they should be heat-treated previously for several hours at the highest temperature of operation. They should then be allowed to cool to room temperature and, after 24 hours, the sensitivity should be measured. The rr~icrophones are thus stabilized for operation at any temperature up to that at which they were heat-treated. However, use of the microphones above 60°C is not recommended and when so used the warranty is no longer valid.
3.6.7 Humidity Effects.
The impedance of the ceramic microphones is approximately an order-of-magnitude lower than that of the condenser microphones of equivalent size and no polarizing voltage is required; therefore, they are much less susceptible to the effects of humidity. Under most normal conditions of humidity, the mi~rophones are totally unaffected. However, under conditions of severe humidity with condensation of
3-10
MOD~L 1~2131
DAT~
4-16-11
HOURS
1560-P5·1
Figure 3-10. Change in leakage resistance with humidity changes.
1971 EVALUATIONS
VIBRATION SENSITIVITY'
1 g ACCELERATION AT 20 & 100Hz "' 100dB SPL
TEMPERATURE RANGE'
OPERATES AT 85'C & -55'C
THERMAL SHOCK'
-55'C FOR
5 CYCLES
y,
HR; TRANSFER WITHIN 5 MIN TO +85'C FOR
Y,
HR.
MECHANICAL SHOCK PER MIL 202 C METHOD 202'
50 g HALF SINE SHOCK (2 AXES!
VIBRATION PER Ml L 202 C METHOO 204'
60 MILS P TOP OR 10 g
10·500 Hz 15 MIN SWEEP 12 TIMES, I 3 AXES!
HUMIDITY & MOISTURE PER MIL 202 C METHOD 106·8·1'
60 MILS P-to-P
10-SS Hz
1560·P5·5
Figure 3-11. Results of environmental tests according to MIL-STD-202C, Method 106-81.
3-11
moisture, the leakage resistance will decrease, as shown in Figure 3-10, causing a low-frequency roll-oft. This roll-oft is determined by the characteristic capacitance of the microphone and the value of the leakage resistance. Humidity and moisture tests were made on a 1971 1-in. ceramic microphone according to MIL-STD-202C, Method
106-81 (see Figure 3-11 ), after which the leakage resistance had dropped to approximately 300 kD, making the microphone unusable below 1000 Hz. Within 24 hrs., under normal room conditions, the microphone had recovered.
3.6.8 Ruggedness.
The 1-in. ceramic microphone was subjected to several environmental tests, to evaluate its ruggedness. The tests are shown in Figure 3-11. The net result of the entire evaluation procedure was a negligible change in sensitivity and frequency response.
3.6.9 Pressure-Equalization Air Leak.
A controlled air leak is built into the terminal plate of the GR ceramic microphones, to equalize the static pressure on the back and front of the diaphragm when the ambient pressure changes. At very low frequencies, the air leak equalizes the sound pressure on each side of the diaphragm, thus causing a roll-off in the low-frequency response. The air leak and the total enclosed volume
~f the cartridge combine to form a high-pass filter whose cutoff frequency is determined by the time constant of the pressure equalization. For the GR ceramic microphones, the time constant is .08 s, which results in a low-frequency cutoff (response down 3 dB) of 2
Hz. The microphone can withstand a pressure step of approximately 0.1 atmosphere
(1.5 psi, 3 in. of Hg, or 10
4
Pa). For a ramp pressure-change with time, the rate of change of pressure is 1 atmosphere/s. At sea level, this amounts to an initial rate of climb of 30,000 ft/s
3.6.1 0 Vibration Sensitivity.
It the 1-in. ceramic microphone is subjected to an acceleration of 1 gat 20 and 100
Hz with the force perpendicular to the plane of the diaphragm, the microphone will generate an equivalent sound-pressure level of 100 dB.
3.7 GR ELECTRET-CONDENSER MICROPHONES.
3.7.1 General.
The GR electret-condenser microphones are available in tour models: 1-in. and '/2-in. microphones, each with a flat random-incidence response, and 1-in _ and '12-in. microphones, each with a flat perpendicular-incidence response_ Each is supplied with an adaptor to %-in. thread and a wooden case. The accessories supplied and available are described in para. 1.2 and 1.3, respectively_
The properties of the electret-condenser microphones are noted in Section 2. A comparison of the random-incidence responses for typical electret microphones with those of other types is shown in Figure 3-2.
3-12
3.7.2 Calibration.
The electret-condenser microphones are furnished with the appropriate perpendicular-incidence or random-incidence response curve. Figures 3-12 and 3-13 give the corrections to be added algebraically to the random-incidence response to obtain the perpendicular- or grazing-incidence response or the pressure response. Similar curves in Figures 3-14 and 3-15 give the corrections to be added to obtain the random- or grazing-incidence response or the pressure response from the perpendicular-incidence response.
Figure 3-12. Corrections to be added algebraically to the random-incidence response to obtain the perpendicular/ grazing-incidence free-field response, or pressure response for the 1-in. electret microphone, Type 1961-9601.
2
0
2
4
6
8
0
200
4
2
0
8
6
4
v
A' v
/"'"'"'"'"
r-
L
--:::-r---
PR~SSUR~ l~
GRAZING
.\
~
\
20 7 10kHz 5
FREQUENCY -Hz
I
50 70 100kHz 200kHz
Figure 3-13. Corrections to be added algebraically to the random-incidence response to pbtain the perpendicularor grazing-incidence free-field response, or pressure response for the %-in. electret microphone, Type 1962-9601.
4
6
0
2
6
4
2
2
0
8
-~00
/
v'"'""''"'"
1/
/
'
--
-~::-
1""--..
"1"'"'1
'
'~-
....
GRAZING
500 700 1 H
.
'
2 5
7 10kHz
20 50
70 100kHz
FREQUENCY -Hz
\
\
"'""
Figure 3-14. Type 1961-9602 Microphone. Correction curves for random incidence response, grazing incidence free-field response and pressure response.
+4
2
0
2
6
8
0
2
4
6
-I
8
200 r""""-oo""""""'
500 700 1kHz
':-...
:\.'""""
'"~"';-.~ ~
1\
\ \
5 7 10kHz
FREQUENCY- Hz
\""'"
\
20
50 70 100kHz
3-13
4
+ z
0 z
4
·10
6
• z
-14
6
.
-I zoo
500 700 1kHz
-...
~
--~
\1\."' """""
PRESSl!~E\
\ r\.
\ \
'\
'I\
20
'""'""
I
50 10 100 kHz 200kHz 5 7 10kHz
FREQUENCY- Hz
Figure 3-15. Type 1962-9602 Microphone. Correction curves for grazing incidence free-field response and random incidence response and pressure response.
3.7.3 Directional Patterns.
Typical directional patterns for the electret-condenser microphones at various frequencies are shown in Figures3-16and 3-17. The microphonesareomni-directional within 3 dB to approximately 3 kHz for the 1-in. and 6 kHz for the 1/2-in. microphones. o· o•
90"
••
1
ZIO u~·~
~
."o
Li-to
Figure 3-16. Typical directional response patterns for the GR 1-in. electret·condenser microphones.
Figure 3-17. Typical directional response pattei for the GR Y.z-in. electret-condenser microphalli
3.7.4 Dynamic Range.
The limits of the dynamic range are set by the noise level of the microphone-andpreamplifier combination for the low limit and by the total harmonic distortion for the upper limit.
3-14
Microphone Only
Dynamic Range
*
for Microphone/
Preamplifier Combination
Microphone
Size linchesl
Upper Limit for 3% Distortion ldB SPL)
Maximum
Safe Limit
(dB SPL) re 20JJPa
(dBSPL)
y,
140
140
160
170
22- 140
30- 145
•A-weighted noise level to maximum rms sinewave signal without clipping.
3. 7.5 Temperature Effects
The temperature coefficient of sensitivity for both 1-in. andY,-in. electret-condenser microphones is less than +0.015 dB/ o
C, typically +0.01 0 dB/ o
C.
A typical temperature-sensitivity change curve, at a low frequency of 500
Hz, based on tests of a sample of five '/2-in. microphones is shown in Figure 3-18.
The temperature coefficients of sensitivity is independent of frequency at frequencies below
2kHz, and it increases slightly at higher frequencies. The frequency response changes of an electret-condenser microphone at different temperatures are shown in Figure 3-19.
SENSITIVITY
SHIFT dB
+1.0
+0.5
____ -h-
0.0
-0.5
1--------------=-------=c-:-=.------='-=-=--------
----
-1.0
-10
+10 +20 +30 +40
TEMPERATURE 'C
+50
Figure 3-18. Change in sensitivity of electret-condenser microphone relative to sensitivitY at 23 o
C.
FREQUENCY IN H:~:
Figure 3-19. Electret Microphone Frequency Response Change With Temperature.
3-15
1000
100
,.o
~
,,.
Q;-~
<><>:-
'-
A"'
I /
10
/> /
1
100 80 60
TEMPERATURE
-•c
40 25
Figure 3-20. Effect of changes of temperature and-humidity on the stability of electret-condenser microphones lsee text).
::"'t=:
_.,
0 '
Figure 3-21. Long-term sensitivity shifts of ,electret-condenser microphones.
The operating temperature range for electret-condenser microphone~
'1s now
+60°C to -40°C. Microphones should not be exposed to temperatures higher than +100°C or lower than -50°C.
3. 7.6 Thermal Shock Effects
The electret-condenser microphones are designed to withstand adverse environmental conditions, shocks and stresses. In the Table 3-2, the data on two electret microphones exposed to a thermal shock are shown. The microphones were kept as -40°C inside a temperature chamber, and then suddenly brought out to room temperature (+22°C). They were immediately covered with frost which slowly thawed and evaporated. A calibrator was used to measure the sensitivity shifts of the microphone of 250Hz. The maximal shift of sensitivity and the remaining shift, one-half hour after the thermal shock, are shown in the table.
Table 3-2
THERMAL SHOCK TEST
MICROPHONE SENSITIVITY CHANGE (dB)
AT 250Hz
TEMPERATURE°C
S/N
+22 -40 +22*
10408
0.0 +1.0 -0.1
11656
0.0 +0.6
*Thirty minutes after the thermal shock
-0.2
3-16
3. 7. 7 Humidity Effects.
A most important consideration for an electret-condenser microphone is the stability of its electrostatic charge with time under different conditions of temperature and humidity. A decrease of electrostatic charge will produce a change in sensitivity of the microphone. G R electret microphones are polarized by a unique method that, combined with carefully controlled aging, makes possible an optimal polarization of a given polymer material.
Figure 3-20 shows the stability of GR electret microphones at different temperatures and humidities. The time un.lts of the ordinate scale show the length of time the microphones can remain at a given temperature and humidity before incurring a sensitivity loss of 1 dB. The solid line gives the time under dry conditions; the dash line shows the time-temperature relation with 99% relative humidity. For example, the sensitivity of an electret microphone will shift 1 dB, if it is continuously exposed to the severe environment of 99% relative humidity and 55°C for two years.
Because of the bound nature of electret charge, voltage breakdown across the air gap cannot occur in the electret-condenser microphone. This ·,sa frequent mechanism of failure in the air-condenser microphone at high humidity. All measurement microphones, the air condenser, the electret condenser. and the ceramic are high-impedance devices. Their insulation resistance between the output terminals is subject to the effects of contamination. At high humidity, the change in the insulation resistance can produce a shift in microphone sensitivity.
In the electret microphone, a new insulating material, less susceptible to contamination, is used between the output terminals.
A sample of five microphones was exposed for two days to 95% relative humidity.
Their sensitivities at 250 Hz changed between 0.3 dB and 0.5 dB, but they recovered to 0.2 dB of the initial sensitivity within two hours when brought back to 50% relative humidity. The temperature was constant during this test.
3. 7.8 Ambient Pressure Effects
The sensitivity of the electret microphone will change less than -0.2 dB fo_r an increase of 10% in ambient pressure. The time constant of the air leak is .03, which produces a low-frequency cutoff (decrease in response of 3 dB) at 5Hz. The allowed rate of change of ambient pressure is less than 0.2 atm/s.
3.7.9 Vibration Sensitivity.
Electret-condenser microphones are less sensitive to vibrations than any other type.
When subjected to an acceleration of
1 gat 20 or 100 Hz, with the force perpendicular to the plane of the diaphragm, the 1-in. and '12-in. electret-condenser microphones will generate an equivalent sound-pressure level of 83 dB.
3.7.10 Long-Term Stability
Figure 3-21 shows the long-term stability data of a group of five electret-condenser microhones during a fifteen month period. The sensitivity shifts stayed within ±0.3 dB limits.
3-17
Type 1560-P42
Preamplifier-Section
4
4 .
1 DESCRIP T ION . . . . .
4 .
2 IN STALLA TION . . . .
4 .
3 I NPU T CONSIDERATIONS
4 .
4 USE OF LONG CABLES
4 .
5 NOISE . .
.
. .
. .
4 .
6 C IRCUIT DESCRIPTION
4 .
7 SERVICE AND MAINTENANCE .
4-0
4-0
4-8
4-9
4-15
4 19
. 4-20
14-in.
MIKE
MIKE
COiECTOR
GAIN
I
I
\
- j l -
SIAS
SWITCH
CABLE
RELEASE
I
CABLE
CONNECTOR
\-
A3
MALE
Figure 4.{). Contro l s and connectors.
4.1 DESCRIPTION .
A comple t e description of the Type 1560 P42 Pre amp lifi e r (Fig u res 1 -1 and 1-2) is given in para. 1 . 1 .3.
4 .2
1NSTALLATION.
4.2.1 Connecting the Transducer.
NOTE
Although it is no t necessary , it is good practice to turn off the power t o the 1560-P42 P reamplifier w hile the transdu c er is being connected or disconnected . (The FET is diode p rotected against surges .
)
Connec t i on of the t r ansducer to the Preampl if ier i s made by means of a 0.460-60 thr eaded c oaxial connec t or . This c onnector provides e l ectr i ca l c ontact between the mic r o pho ne shell and the Preamplifier circuit ground . The ground connec tion is electrica ll y iso l ated f rom the case at the Preamplifi e r. which serves as a shield .
4-0
1K
800
600
500
400
300
LENGTH fEET OF CABLE f@
50 pF/ft)
5K
4K
3K
PROCEDURE:
• Select length of cable used.
• Using chart I, draw a line from length through max. frequency to impedance.
• Using chart II, draw a line from impedance through peak volts to peak current.
Allow for crest factor.
IMPEDANCE f.n)
PREAMP
PEAK
CURRENT
2K
SPL dB frms)
USING 1-IN.
CERAMIC or%-IN.
ELECTRET f-40 dB re
1 V/Pa )
®
20m A lOrnA
8mA
6mA
SmA
4mA
3m A
200
2m A
100
80
60
50
1mA
8001lA
EXAMPLE:
1000 ft. cable at 10kHz= 320 Q
At 140 dB SPL peak current is 9 mA
NOTE
Leave room for crest factor of noise signals.
• (See Figure 4-11 and multiply rms volts by 1.4, assuming X 1 gain for
1560-P42.)
Figure 4-1. Nomograph to calculate current requirements in long cables.
1560-P42-9
4-1
NOTE
The circuit ground of any adaptors that are used with the Preamplifier must be insulated from the shell of the Preamplifier, to preserve the 3-wire output consideration. All GR adaptors retain this feature.
The connection between circuit ground and shield is made at the analyzing instrument for all equipment. This connection must be provided to realize the full shielding capability of the -P42 Preamplifier (refer to the schematic diagram for output-connector pin destinations, Figure 4-18).
The input terminals of the Preamplifier provide a direct connection for all 1/2-in.
GR microphones. To convert transducers of other sizes to this thread, the appropriate adaptor must be inserted between the transducer and the Preamplifier. The adaptors are described in para. 1.2.2 and 1.3.2 and are shown in Figure 1-4.
Because the depth of the center-pin contact of 1-in. microphone has not been standardized, standard 1-in. microphones, such as the WE 640AA and the
MR 103, are supplied with a small sliding center contact. This contact should be adjusted to the depth necessary to
provide
the required contact
between the center pin
of the microphone and the Preamplifier.
The GR Vibration Pickups, Types 1560-P52, -P53, and P54, can be connected to the Preamplifier by use of the 1560-9669 Adaptor. Other vibration pickups will require special adaptors for this connection.
4.2.2 Tripod Mounting.
The 1560-9590 Tripod is designed to accept the 1560-P42 Preamplifier. Complete instructions for its use are given in para. 1.3.6.
4.2.3 Output Connections.
The 1O-ft output cable supplied with the Preamplifier is terminated in 'a Switchcraft type 3A, 3-pin, male connector that mates directly with similar female connectors on the 1560-P62 Power Supply and on most GR analyzers and sound-measuring instruments. The shield is connected to the outer shell of the Preamplifier, but is
not
connected to ground except at the analyzing instrument or by the output cable of the
156Q-P62 Power Supply.
The pin connections for the Preamplifier output cable are as follows:
Pin 1 -circuit ground
Pin 2- power-supply connection (+15 to 25 Vdc)
Pin 3- output signal (from Preamplifier)
Shell - shield
NOTE
The circuit ground and the shell
(shield) ot the
Preamplifier must be connected at the analyzer.
4.2.4 Adjustments.
Adjustment of the Preamplifier consists of setting two slide-switch controls, labelled GAIN (X1, X10) and 200 V (ON, OFF). These are accessible through cutouts
4-2
in the outer shell of the -P42. A notch in the slider of each switch is used to set the controls to one position or the other. Use any small tool (such as a screwdriver or ball-point pen) to set these controls.
Gain Adjustment.
The gain of the Preamplifier can be set to either X 1 or X 10 by means of the GAl N switch. It should be set to optimize the dynamic range of the system. For low levels (such as less than 60 dB SPL for -60 dB microphone sensitivity level) and/or for long cable runs, set the GAIN switch to X10, to eliminate the influence of the analyzer noise on the measurement. With high signal levels (above 120 dB SPL for -60 dB microphone sensitivity level) set the GAIN switch to X1, so that the output signal will not be clipped because of overloading. For levels between 60 and
120 dB, either X1 or X10 can be used, the choice depending upon the reading desired on the indicating analyzer.
Polarizing Voltage.
The +200-V polarizing voltage for air-condenser microphones can be turned ON and OFF by adjustment of the slide switch marked 200 V, on the
Preamplifier. This voltage is generated in an internal blocking oscillator operating at approximately 60 kHz (refer to the schematic diagram). The voltage is applied to the center pin of the input connector through several decoupling networks. At least +15 V at the Preamplifier terminals is required to ensure stable generation of the 200 V. The
200-V supply is turned on by connecting the low-voltage supply to the oscillator through the 200 V (ON, OFF) switch. Set the switch ON for air-condenser microphones and OFF for all other transducers.
NOTE
The available current from the +200 V polarizing supply is extremely low and not hazardous. However, an increase in input noise due to leakage current may result if the polarizing voltage is left on with ceramic transducers. Left on with electret-condenser microphones, it will produce a temporary change in sensitivity and frequency response. The electret microphone will recover a few minutes after the polarizing voltage is turned off. Use the +200-V supply only with ordinary air-condenser microphones.
The power consumption oi' the Preampli-fier increases slightly when the polarizing supply is ON (the current increases about 2-3 mA above the current of the amplifier circuit of the Preamplifier).
4.2.5 Power.
The Preamplifier can be powered from a number of G R sound-level meters. and analyzers, as shown in Table 1-2. The power is applied via the input connector to the
Preamplifier. For use with instruments that do not supply power for the Preamplifier, or where insufficient current is available to power the polarizing supply, or for runs with long cables, the 1560-P62 Power Supply is available. This integrated charger and line/battery-operated supply provides the necessary current and voltage for most
4-3
applications. Refer to Table 1-2 and Figure 4-2 to determine the required current for the length of cable used. Details of the Power Supply are given in Section 5 of this manual.
I k
FREQUENCY- Hz
10 k lOOk l560-P42-4
Figure 4-2. Required de current vs cable length at
1
V, rms.
Although the 1560-P42 Preamplifier is designed to be used with G R instruments that supply the proper power, there may be instances in which the user wishes to use a different supply. This use is entirely satisfactory if certain precautions are taken:
With the class AB output stage, the power supplied to the Preamplifier must be current limited so that the output stage of the Preamplifier will
not
be damaged if the output is heavily loaded (such as with a short circuit) when a signal is applied to the load. Output currents above 30 mA at rated voltages should be avoided. G R analyzers and the 1560-P62 Power Supply provide this current limitation. Other supplies should be set to give a maximum short-circuit current of 15 mA. If this is not possible, insert a 1 00-.Q resistor in series with the supply lead (pin 2 of the -P42 output connector), to provide minimum protection (see Figure 4-18).
If the supply current is monitored with a de milliameter, the true average current
(other than the quiescent current) drawn by the 1560-P42 Preamplifier, when the load is driven by a sine wave, is actually twice the indicated current, because the current drawn from the positive lead of the power supply by the class AB output stage occurs during only the positive half of the cycle. In other words, therefore, the reading of an average-reading meter must not exceed 10 mA.
Average current to load~
(mAreadin
9
-mAquiescentl X 2.
Note that, in a system where cables in excess of 1000 ft are driven, the placement of the power supply will influence the capability of the system (the I R drop in the cable becomes significant). Placement of the supply near the preamplifier will avoid the loss of the powering voltage through the long cable.
4.2.6 Insert Voltage.
1
General.
Provision for connecting an insert calibration signal is provided by a type-274 double jack (PL2) built into the output plug. The insert voltage can be used
1. For a complete discussion of the theory of insert-voltage calibration, refer to Beranek, L. L.,
Acoustic Measurements,
John Wiley & Sons, Inc., New York, 1949, pp 601, 602.
4-4
to determine the system sensitivity if the open-circuit sensitivity of the microphone is known; it can be used to determine the absolute calibration of the system by direct comparison with a reference microphone; also, an operational check on a system can be made with the insert voltage. The equipment needed for these operations is listed in
Table 4-1. The insert terminating resistor is 10 S1 (R20) and the maximum insert voltage is 1 V rms. The signal is applied across the insert resistor, effectively putting the insert voltage in series with the transducer.
-------------------------Table4-1-------------------------------
EQUIPMENT REQUIRED FOR USE IN MEASURING SENSITIVITY
Name
Oscillator
Decade Attenuator
Voltmeter
Requirements
1 I<Hz, 1 V
0-1 00 dB in 0.1-dB steps
0-10 V ac ±5%
Recommended*
GR lype 1310 Oscillator
G R Type 1450 TB Decade
Attenuator
HP Type 400 EL Voltmeter
Analyzer
Power Supply
Cor FLAT weighf1ng,
70-100 dB
20 V, 15 mA
Resistor 590 n
±1%
Sound Source Stable repeatable source
Reference microphone
Long-term stability; with adaptor to fit input calibration traceable to -P42 Preamp! ifier to NBS
Patch Cords (2)
Adaptor
GR 274 to GR 274, 3ft
Microphone cartridge to
0460x60 thread
>1 footlong Clip Leads (2)
*Or equivalent.
GR Type 1564 Sound and
Vibration Analyzer
GR Type 1560-P62 Power
Supply
GR Type 1562 Calibrator
WE. 640AA
GR Type 274-NQ
GR 1560-2630
4-5
Determination of System Sensitivity.
The following procedure should be used to determine the sensitivity of the system when the open-circu·lt sensitiv"1ty of the microphone is known: a. Make the setup of Figure 4-3. Connect the oscillator to the 274 insert terminals
(the connector at the end of the Preamplifier output cable). Connect the voltmeter between the threaded portion of the input connector and the shell of the Preamplifier, i.e. across the insert resistor (clip leads can be used). Power for the Preamplifier is not needed. In the figure, Ri is the insert resistor (nominally 10 S1) and Rw is the internal wiring resistance (typically a few tenths of an ohm).
I N PUT
~f:TER
I
I
r- ---
SHELL--1
OUTPUT
CABLE
~~:i'Atis Dr-:'-----r-+-'WV-'
I
I
[_~
I
______ _J __ ....
-= _ _
_._---':,f;---.,
Figure 4-3. Setup for determination of system sensitivity.
1560-P42 PREAMPLIFIER
1560-45
b. Adjust the oscillator to 1 kHz. Set its output so that the voltmeter reads V
1
=
.01 V. c. Transfer the voltmeter to the insert terminals and read V
2 .
The indicated increase in voltage (V
2 -
V
1 ) is caused by the drop across Rw, (typ.lcally a total of -0.3 to
-0.5 dB). This is the loss that must be added to the voltage at the insert terminals to give the desired voltage across the insert resistor. Record this value for future use. d. Install the microphone on the Preamplifier. Connect the plug on the output cable from the Preamplifier to the input of the 1564 Sound and Vibration Analyzer. Power for the Preamplifier is supplied by the 1564. The oscillator should remain connected to the insert-voltage terminals, with its output still set to the value of V
2 , at 1 kHz. e. With the Preamplifier operating on X
1
gain, note the reading (V
3 ) of the analyzer
(calibrated to read voltage). The difference in voltage (V
1 -
V
3 ) is a result of the capacitive loading of the transducer by the Preamplifier and Preamplifier gain or loss. vl
The ratio of V
3 expressed in dB (20 log
10 vl
V
),
3 is the value to be subtracted from the open-circuit sensitivity level of the microphone to obtain the system sensitivity levRI.
For example, if the sensitivity level of the microphone is -40 dB re
1 V/Pa
and
V
1
/V
3
=
1.175
(=
1.4 dB), then the system sensitivity level is
R
5
=
-40- 1.4
=
-41.4 dB re
1 V /Pa.
If a more-accurate method is required, short the input with a GR
1560-2630
adaptor (with shorted terminals) and supply power to the -P42. Note the difference
4-6
between the voltage at the insert terminals and at the output of the -P42 cable. This method removes simultaneously the errors due to amplifier gain and the wiring loss.
Comparison with Reference Microphone to Obtain Open-circuit Sensitivity.
a. Make the setup shown in Figure 4-4. The 590-D resistor at the attenuator output provides the proper 600-D load for the attenuator when the 1 o-n insert resistor is driven. Power for the Preamplifier is furnished by the 1564. b. Connect the reference microphone to the -P42, and place the 1562 Calibrator, set at 1 kHz, on the microphone. (The actual level of the calibrator signal is not important, but it must be repeatable.) Set the oscillator output at zero. c. Read the voltage output from the Preamplifier on the analyzer. Record the value as Vref· Remove the sound source. d. Set the oscillator output level for maximum (approximately 10 V) at 1 kHz
Adjust the 1450-TB Attenuator to give a reading equal to Vref on the 1564. Note the setting, At, of the attenuator. e. Turn the oscillator output to zero. Replace the reference microphone with the unknown and place the sound source ( 1562) on the unknown microphone. Note the
1-kHz reading, Vunk. of the analyzer. f. Remove the sound source and connect the oscillator as before, with the output setting used in step d ( 10 V). Adjust the 1450-TB attenuator to give a level equal to
Vunk on the analyzer. Note the attenuator setting, A 2. g. The open-circuit sensitivity level of the unknown microphone is then
Sunk = Sref +(At - A2 ).
For example, if
Sref
=
-30 dB re 1 V
/Pa
At
=
4.5 dB
A 2 = 13.5 dB then
Sunk= -30 + (4.5- 13.5)
= -30-9.5
=
-39.5 dB re 1 V /Pa
PREAMPLIFIER OUTPUT CABLE
.____.__ __
I
1
I
I
I
I
I
I
....
-
-----------
274 -NO PATCH CORD
L - - - - - - - - - - '
1560-P42 PREAMPLIFIER
''''""
Figure 4-4. Setup for comparison of unknown with reference microphone.
Operational Check of System.
When a system has been set up and calibrated, a voltage can be applied to the insert terminals to serve as a reference. Note the values of the insert voltage and the analyzer reading, for future reference. (The absolute values are not important.) As an operational· check at a later date, or after system
4-7
modifications, the same voltage is applied to the insert terminals. A deviation in the analyzer reading from the original reading is an indication of a change in the system response.
4.3 INPUT CONSIDERATIONS.
The equivalent INPUT circuit of the Preamplifier is determined by the FET input stage and its associated biasing and protection networks. Protection for the transistor from surges of the polarizing voltage (with condenser microphones) is supplied by very low-leakage semiconductor diodes. These diodes produce a slight increase in the input capacitance and add some leakage resistance. The 200-V polarizing voltage is supplied through a "bootstrapped" 1 GS1 resistor, which, in effect, increases its ac resistance to well above 2 GS1. The net input resistance is approximately 2 GS1. The input capacitance is established by the F ET plus the diodes, and '1s typ'1cally 3-4 pF, with 6 pF maximum. (Use of the driven shield minimizes the input capacitance for small-diameter microphones.) As a result of this nominal input capacitance, there is some transducer insertion loss due to the resultant capacitive-divider effect. Figure 4-5 gives the insertion loss for microphones of various capacitances.
A low-frequency roll-off is encountered when the Preamplifier is driven from a capacitive source because of the equivalent input resistance. The" Lower" and "Upper
Frequency Range" columns of Table 1-1 give the frequencies at which the response is down 3 dB, for the various microphones. Input protection diodes CR 1 and CR2 uti I ize the signal-source impedance to limit the pk-pk input voltage to the power-supply value. If the 1560-P42 is driven from a 1 O-S1 or lower source impedance, such as that of a power amplifier, it is important to limit the pk-pk input voltage to the power-supply value, to avoid damaging CR 1 or CR2.
-6
5
•
3
I
2
0
GR
\
.. I
1\ t
ELECTRET i iii
10
j
20
-!Witmr
50
GR mr~L'1TRET ~
'"Till
500 1000
100 200
TRANSDUCER CAPACITANCE- pF
Figure 4-5. Insertion loss vs transducer capacitance.
4-8
4.4 USE OF LONG CABLES.
4.4.1 General.
The 1560-P42 Preamplifier is designed with the capability of delivering substantial signal current and signal voltage to the driven cable at the preamplifier output. Thus, longer cables can handle substantially higher signals at higher frequencies than were possible heretofore with other preamplifiers. However, to utilize this capability, the user must have a thorough understanding of the problems to be encountered.
In any system involving active amplification driving a load, the to\lowing ettects, with their related causes, should be considered:
1. Distortion. Insufficient current to drive the particular load at the desired signal voltage level (i.e., the signal level is too high for the load).
2. Change in frequency Response. The output characteristics of the amplifier, in conjunction with the impedance of the load, alter the frequency response of the signal.
3. Attenuation. Also brought about by the interaction of the output amplifier impedance and the load impedance, this is a moditication ot 2, above, but it is generally considered a flat loss of signal with respect to frequency.
4. Power-supply voltage drop. This item is a fourth effect, resulting indirectly from the use of an amplifier powered through a long cable. The voltage drop in the power lead of the cable is a function of the resistance of the cable and the current drawn by the driving amplifier. If the amplifier is operating class A-B or B, the current is a function of the output level, the frequency, and the impedance of the cable being driven.
These general problems can be circumvented if one has a thorough knowledge· of their causes. It is assumed, in the appraisal of the system, that the ultimate goal is the flattest possible frequency response, with minimum attenuation and minimum distortion, over the range of interest. The following paragraphs should bring about a better understanding of the problems and their solutions.
4.4.2 Definitions.
Short Cables. A short cable is one in which no appreciable change in performance of the system or in measurement results is produced in the frequency range of interest by use of the cable. Thus, for our analysis, short cables can be excluded. In general, short cables for use with the 1560-P42 Preamplifier are those that are 500ft or less in length.
Long Cables. Long cables are those that alter the signal appreciably when driven by the preamplifier. For our analysis, long cables are those whose driving wavelength is much longer than the cutoff wavelength of the cable. If the frequency of the driving signal is above the cutoff frequency, the attenuation in the cable decreases uniformly as the square root of the frequency. However, for audio frequencies, the cable is invariably being driven well below cutoff frequency. Typically, the wavelength is greater than 5000 ft at 150kHz for polyethylene dielectric cables.
4-9
4.4.3 Equivalent Circuits.
The sources of signal alteration in an amplifier/cable system can be demonstrated best by means of the equivalent circuit of the cable (see Figure 4-6) driven by the amplifier and the equivalent circuit of the output stage of the amplifier. It is the interaction of these elements that produces the alteration or degradation of the signal.
In most microphone/preamp! ifier applications, where low-level signals are involved, the cable is usually assumed to be an unterminated, unmatched line. It appears as a simple lumped capacitance at the output of the driving amplifier. The equivalent shunt capacitance at the output of the amplifier increases as the length of the cable increases.
I i
...J -
I
lr''"
RLOAO
(NEGLIGIBLE EFFECT
IF >100 kfi)
Figure 4·6. Equivalent circuits for the output stage of the Preamplifier and the cable.
-3
Figure 4·7. Typical cable loss vs frequency, due to output loading of 1560·P42 for a pure capacitance load.
Cable capacitance is 50 pF/ ft.
~
!-4
9
~ -5
CD c
<.>
-6
-7
-8
-91
0
-I
-2
b
..........
~ t'-1"'
1']\
~
~
~
\
\
500FT
(0.025J4F)
IOOOFT
(0.05J4F)
"
2000 FT
( O.IJ4F)
5000 FT
(<H'!>)"fl
100
10
FREQUENCY- kHz
Certain cables, whose resistive and inductive reactances are
small
with respect to their capacitive reactance, do behave according to the above simple assumption. Also, a flat loss is introduced at low frequencies by the capacitive divider effect between the output coupling capacitor of the amplifier and the lumped cable capacitance. The
4-10
cable loss vs frequency for various lengths of 1560-9667 cable (Belden #8771 )* is shown in Figure 4-7. For this curve, the capacitance only (50 pF/ft) is used as the effective impedance. In reality, with most audio cables whose effective impedance is approximately 50 n, the resistive and inductive reactances are not negligible. They must, therefore, be taken into account. Indeed, as the cable length increases, the effective load impedance for the amplifier never decreases to zero, but is restricted to the 50-n self termination of the cable.
4.4.4 Cable Response.
Figure 4-8 shows the results of these effects on the response, using the total effect of the same cables, with a 1560-P42 Preamplifier. Because the cable is driven from a low impedance rather than its natural impedance (as would be the case in a matched line) the cable appears as a distributed tank circuit driven from a short circuit. The result is a family of curves with resonant peaks. The frequency is determined by the
UC
constants of the cable, and the amplitude is determined by the ratio of the cable resistance to the amplifier output resistance. It should be noted that the actual equivalent circuit of the cable as used is not an unbalanced coaxial system, but rather a balanced system, because the cable braid is a shield, not a return path. It is important, when the system response is measured, that this shield be connected to the circuit ground at one end only. In a laboratory setup, this condition must be maintained.
4
I
0
-I
-2
-3
-4
-5
-6
-7
-8
I '
I
J
i\
~
I
I\
1000
1
FT
.......-::::::'
10
"\.
\
\
\
\
\
""
\
1\
\
1\
2000FT
\
\
1\
\
"'
\
5000 FT
\ 3000 FT 1\
'"
4000 FT
~
100
I
FREQUENCY- kHz
1.-
500FT _
Figure 4-8. Measured cable loss of the Preamplifier vs cable length for Belden #8771 cable. Pre·
amplifier gain is
X
1, powered from the receiver end.
*Belden Corp., P.O. Box 5070-A, Chicago, Ill.
4-11
The equivalent circuit of the cable is shown in Figure 4-9. For cables up to 5000 ft and frequencies up to 10kHz, there is little effect on the signal. For longer cables or higher frequencies, the effect must be corrected, or it must be taken into account when the results are evaluated. This can be done by using corrective equalizers or by altering the results mathematically to give a flat frequency response. In both cases, a knowledge of the cable characteristics is needed.
Figure 4-9. Equivalent circuit for long cables.
20
I I I
IIIII I I I
OPEN-CIRCUIT UPPER VOLTAGE. LIMITED!\
BY 1560-P62 (AT LOW VOLTAGE.) l
IO
8
6
en
4
1-
...J
~ 3
en
~
2
I
1-
:;:) a.
1-
6
1.0
~
:;;)
0.8
~ x
0.6
~
0.5
0.4
0.3
0.2
'
~
~
I'
~
'
'\
"
"
0
0-<'~
'·
'\;,.o_,.
~ ~A'
0
"<"
~A'
/
~A'
1:l
oo o-<'
0
'<"s-
~A'
'v
00 o-<'
'"'o
~.~
"'
/0
~.~
~-<'l"s:
00
A'~
.I
'"
r\
~.~,"
~
~
r\
~
I'
?)
~
'
"-'\
'
0.
I
2 3 4 5 6 8 10
FREQUENCY- kHz
20 40 60 80100
1560-51
Figure 4-10. Maximum rms sine-wave output voltage for various lengths of Belden #8771 cable
ISO pF/ft) at the output of the 1560-P42, using the 1560-P62 current-limited Power Supply with
1% total harmonic distortion limit.
4-12
When a long connecting cable is used between the preamplifier and the measuring instrument, the output from the preamp I ifier may have to be restricted because of the low reactance load of the cable. Figure 4-10 shows the maximum rms sine-wave voltage at the output of the 156Q-P42 versus frequency. The 1560-P62 current-! imited
Power Supply was used, and the distortion was limited to 1%. The curves are for
Belden #8771 cable (50 pF/ft). Refer to Figure 4-11 to convert voltage to SPL in dB re 1 V/Pa for a particular microphone. Divide by 10 to obtain maximum output volts with X 10 gain on the Preamplifier. With this value, use Figure 4-1 to obtain peak supply current required by the 1560-P42.
1/1,
I o.v
10,000 mV
7,000
5,000
2,000
1000 mV
700
500
200
100 mV
70
50
20
10 ..
v
7
5
~
IL
\o-
2
5
70~ mV
~
500
~
IL
:i1zoo
<.> i
100
p.V
70
50
20
0
v li
#~~ VIIIIV~~~~~~~~
~(j ~
V
ll
VII
II
V VIII V VII
'7
/ ~.
9:-9:-~<&
I
0
,tt;
4'
.::i'
1/ 1/1/1/111/ 1/1/ 1/
1/ 1/ 1/1/
,~().
llllllll~ll
t;f-
rv"
IL ILIL v v
" I l l ,
~~
VVGYD~VIIV
1/1/1/1/'
~~t~tltl
Vl tffl
,~~.o
.._o
VVVV /VV V/VV:f
t>
.,o
IL'
~ ~
vv
ll
VI
Ill! ll
,~vv
1 / /
/1/'~
7'o~I./../V
1 / / / v-~"'L
1 / 1 v
1/ I ,
" ll
~~~
,
,
II.~'>J7VI/
v v v
" v~
v v v
v~
ILIL
~~~
~~~
1/ 1/
I
.ov
O.IV
.OIV
001\1
/ I / ' I / /
1/ 1/ / / 1/ 1/ to,.
v
7
5
2
0.7
0.5
.,.
/
It/ II
v / vv
...
~~
I
I/
/ 1
~
/
/V
/ / /
I I
IV
0.2 o..t,.
v
0
vv
V/
/ /
/V
10 20 30 40
v v
I II
v
/ / /
50 80
v
70 80 90 100 110
SOUND PRESSURE LEVEL (SPL) -dB
120 130 140
·-
Figure 4-11. Open-circuit output voltage vs SPL vs microphone sensitivity.
4-13
4.4.5 Predicting tne Resulting Response.
In general, the impedance of audio cables cannot be controlled, because of the twist of the inner conductors. The impedance may vary from 40 to 100 n, depending upon the make and the basic capacitance. While the resistance and capacitance of a cable can be measured quite easily, determination of the distributed inductance is more difficult.
Also, once these parameters are known, it is tedious to calculate the response at all the required frequenc·tes ot interest. Even when this has been accomplished, it ·Is well to check the results by making an actual measurement. rather than by attempting to predict the results.
4.4.6 Measuring the Cable.
To measure the cable, a stable oscillator and a wide-band voltmeter that cover the frequencies of interest are required. As noted above, the actual cable is a balanced system (i.e., the direct and return paths for the signal have practically the same resistance and inductance). Consequently, when the cable is measured, the return path of the cable must not be short-circuited by the common returns of the oscillator/analyzer combination. With this short circuit, measurements on a coiled cable in the laboratory will not be representative of the cable stretched out, in the field.
4.4. 7 Using the Results.
The above measurements should be used to correct the results of the final analysis.
A mathematical correction can be time consuming and too slow for real-time analysis.
Corrective equalizers can be constructed and placed at the analyzer end, to return the signal to a flat frequency response.
4.4.8 Other Solutions.
Several methods are available to avoid the problem of frequency-response shift by long cables. However, they usually produce new problems:
1. Matching the Cable. This method requires matching the cable impedance at both the source and the load. There is then an automatic 6-dB loss in output level, and additional power is required by the amplifier. Most audio cables are 50 n impedance; this means that 20 mA is required to drive 1 V rms into the cable. Also, a large output coupling capacitor is needed to drive the cable at low frequencies.
2. Using 60Q-S1 Cable. This is similar to the above solution. However, the higher impedance reduces the power requirement and the size of the coupling capacitor for the matched system. With this impedance level, interference is increased. Consequently, matching transformers are used to convert the line from low-impedance unbalanced-to-ground to 600-D. balanced-to-ground. High-quality transformers must be used to affect a good solution.
3. Using Line Drivers. With this method, amplifiers are placed in the line at such
·mterva\s that the trequency alteration is above the point ot interest. This requires special feed-through amplifiers and greater power-supply capability or amplifiers with a local power-supply feed (usually an inconvenience in the field).
4-14
4.5 NOISE.
4.5.1 Input Noise.
The major source of noise in the Preamplifier is the FET input stage
1
(refer to para.
4.6). However, some additional noise is produced by the protection diodes, CR1 and
CR2. The noise spectrum is also influenced by the magnitude of the source capacitance. This capacitance, in conjunction with the real input resistance, shapes the input-noise spectrum. Bootstrapped resistor R 1 behaves like a resistor many times larger with respect to the input signal, but for noise, it appears as 1 GS1.
Figure 4-12 shows the basic 1 /3-octave noise spectra from 25 Hz to 25 kHz for several typical source capacitances. The vertical coordinates are given in equivalent sound-pressure noise levels for a microphone sensitivity level of -40 dB re 1 V /Pa.
Refer to Figure 4-11 to convert the levels to those for microphones of other sensitivities. For example, if the equivalent noise level with a -40 dB re 1 V /Pa microphone is 10 dB, a -50 dB re 1 V /Pa microphone would give an equivalent noise level of 20 dB.
Table 4-2 gives typical A- and C-weighted and flat-response noise levels for various source capacitances used on the 1560-P42 Preamplifier in the X1 gain position.
Source
Line Input
1" Ceramic
1" Electret
1" West. Elec.
1" B & K
Y:!' Electret
Y:2' B & K
Y." B & K
Y,." B & K
INPUT NOISE FOR THE
1560-P42 PREAMPLI Fl ER
Source
Impedance
600n
390 pF
125 pF
68 pF
47 pF
25 pF
18 pF
6.8 pF
4.7 pF
Noise (dB)*
A Weighting C Weighting
20.5
20.5
22.5
23.5
24.5
22.5
23.0
28.0
30.0
32.0
27.0
29.0
34.0
36.0
35
38.0
43.0
45.0
Flat
24.5
25.0
32.0
34.5
36.0
38
41.5
46.0
47.0
*Equivalent sound level for a microphone with a sensitivity level of -40 dB re 1 V /Pa uncorrected for capacitance loading.
NOTE
Although it is not necessary, it is good practice to disconnect the preamplifier power before removing or attaching the microphone.
A period of 10-20 s is required for the input capacitor to discharge through the rr1ternal circuitry after the capacitor has been charged to 200 V.
1. Johnson, J. B.,
1928.
DO
97-109.
Thermal Agitation of Electricity in Conductors,
Physical Review, Vol 32, July
VanDer Ziel, A.,
Thermal Noise in Field Effect Transistors,
Proc IRE 50, 1962 pp 1808-1812.
Sanderson and Fulks,
A Simplified Noise Theory and Its Application to the Design of Low Noise
Amplifiers,
GR Reprint A-88.
4-15
dB
40 f---1--h
1_:__1--f=f-=R
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20
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FREQUENCY IN HERTZ
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-=-::_
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40
30
1--c-1--
IN-l--t.---
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'-1--- --1---1--- _:__
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- -1---:
=f------j
-f---- --
--=---,-=--=-----:
t-==-~ ~· ~-
- - _:.::.
_c-:_
= _::
\=f-=_1-.::- -
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- ----- I _::_
18 pF
20
10
I==~
-
:-!=--'-""'-,...
l=cc::--:
- - 1 - - - - -
1= --
·.::.r-='•= ---~1-'----t=--=r=
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2 r:::J=J--CC-
I _:__ 1-t---C-
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-+-- --
-+~
1=1=1=1--
1:= c:_
~-~
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100
.:o,.::_f-=
"2:1
1--f----1---
--::-=- .----
=-=
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- I -
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FREQUENCY IN HERTZ
40
47 pF
30
20
- .j_::CI--- -1---
I '
-~_+= ~~~::t -
__:__"=.
=-~
-
1-
+---l---l---l--l_c-:_ -
-~ : 1--t--1--1--+-
- -- +-.-r=-1-=J=r-:-1=
-1-
J=l--1----+-lt--1---
1-=t---t-- - _,.____
-1-1---1--f-+=1--- =-i-=1--l---1--- -1---
1---1.--:1---
1--[;=1= '- f- -
~>-~
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-1=
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I~ _j~ ~- :_--
!=
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I_:_ 1=-
•
·~-
1--'l _.___,_
250 •• 00 Z<OO
rREQUENCY IN HERTZ
Figure 4-12. Basic 1/3-octave noise spectra for microphones of various source impedances.
4-16
dB
40
30
-f-::-'
·r-
-r--r--
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r-·
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==: _ __:_
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=-+-
I= r- -
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68 pF
20
I--
10
FREQUENCY IN HERTZ
40
30
390 pF
20
10
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FIGURE 4-12 (contl
1\JUU Zl
In addition to providing protection for the FET, diodes CR 1 and CR2 limit the peak-to-peak input signal to the power-supply voltage. Also, the recovery time for large overloads is greatly enhanced by these diodes; i.e., the amplifier will stabilize in a very short time after overloads.
The effect of the protection diodes, CR 1 and CR2, and resistor R 1 is to increase the C-weighted noise for 390-pF sources by 1.5 to 2.5 dB and for 18·pF sources by 5 to
7 dB.
4.5.2 Oscillator Noise.
The source of the polarizing-voltage for condenser microphones is a de-to-de converter consisting of a blocking oscillator and doubler-rectifier-filter circuit. The
4-17
oscillator frequency is typically 60kHz. Residual oscillator noise is filtered out by the weighting networks or by the filters in the subsequent analyzer.
An analysis using a 1 /4-in. or 1 /8-in. microphone may require measurements within the 'frequency range oi the oscillator operation. The user should be aware ot the magnitude of the oscillator spurs in any analysis. Equivalent input-signal peaks of approximately 6 J,J.V on X1 gain or 18 J,J.V on X10 gain at the fundamental oscillator frequency are typical. Upper harmonic spurs are 3-4 dB lower in magnitude. The size of the spur is relatively independent of the microphone capacitance. Refer to Figure
4-11 to relate this undesired signal level to the equivalent input sound-pressure level for the particular microphone being used.
4.5.3 Low-Supply-Voltage Noise (Oscillator Motorboating).
If the power-supply voltage drops below
+
15 V de, the 200-V polarizing supply will not regulate properly. The result is a low-frequency noise produced by changes in the polarizing voltage. To verify this cause, switch off the 200-V polarizing voltage
(the switch on the 1560-P42). If, after the amplifier stabilizes, the noise disappears, a low power-supply voltage should be suspected. Note that condenser-microphone operation requires 2-3 mA more supply current than operation with ceramic microphones. With long cables, the power-supply voltage will drop as a result of quiescent and signal currents. Refer to Table 1-2 to determine whether or not the power supply is operating out of '1ts range.
4.5.4 Power-Supply-Noise Rejection.
If the 1560-P42 Preamplifier is driven from a noisy power source (such as a de-de converter regulator), it is often useful to know the degree with which power-supply noise will interfere with the signal. A measure of power-supply noise attenuation vs frequency for a typical microphone/preamplifier combination is given in Table 4-3.
Attenuation of power-supply noise*
Frequency
(Hz)
2
10
100
1,000
10,000
100,000
Rejection (dB)
X1 Gain X10 Gain
-29
-40
-46
-46
-46
-44
-11
-20
-25
-25
-25
-17
*Measured at the output of the 1560-P42 Preamplifier. Source capacitance of microphone is 390 pF.
4-18
4.6 CIRCUIT DESCRIPTION.
4.6.1 Amplifier Section.
The 1560-P42 Preamplifier consists of two main sections: an amplifier, to provide the gain, and an oscillator, to furnish the polarizing voltage for condenser microphones. To provide the high impedance required for use with either ceramic or condenser microphones, the 3-stage amplifier section incorporates a low-noise F ET
(01) in the input (refertotheschematicdiagram, Figure4-18).
The incoming signal is ac coupled to the gate of 01. The gate potential is established by the voltage divider, R2 and R3. Approximately half of the de power-supply voltage is introduced at the gate of 01. For maximum gain and minimum noise, 01 should operate near its lOSS value (the value of the current through the drain when the source is shorted to the gate). Resistors R5 and RB are factory selected, to establish a bias for 01 such that it will operate near its lOSS value.
Protection against input surges is provided by diodes CR 1 and CR2.
A complete de feedback loop gives increased stability. The 2-position GAIN switch
(SW1) is located in the feedback path.
The class AB output stage (03, 04) provides up to 10 mA peak and greater than 1
V rms, to feed long lengths of cable. Crossover distortion is reduced by slight bias via double diode CR3 and resistors R12 and R13. The loading of voltage amplifier 02 is kept to a minimum by use of high-gain transistors, 03 and 04.
A slight roll-off at high frequencies is produced by C3 and R9, to eliminate oscillations at unity gain.
Because of the capacitive nature of the microphones, loading of the capacitive element should be minimized. This is accomplished by placing a driven shield around the input lead. The shield is driven from the source of 01. Thus, effectively, no potential difference exists between the shield and the input lead, and, during measurements, loading is kept to a minimum.
The output impedance of the Preamplifier is very tow ( 15 n in series with 3.3 J.lF ).
Normally, it should feed a 100 kQ (or higher) impedance such as that of a sound-level meter or analyzer. Resistor R 15 is inserted in series with the load and provides additional phase margin for capacitive toads. It also prevents damage to the
Preamplifier it the output is inadvertently shorted. To give additional short-circuit protection the current from any power supply used with the Preamplifier must
be limited to 15-20 mA,
as is the case with most G R analyzers and the 1560-P62 Power
Supply.
4.6.2 Oscillator Section.
The oscillator section of the Preamplitier supplies the 200 V required by condenser microphones for polarization. This voltage is derived from the pulse transformer T1 and transistor 05. The oscillator operates at approximately 60kHz, well above the usual audio spectrum.
Capacitor C6 is charged through resistor R 16, turning on transistor 05. The feedback winding of oscillator transformer, T1, turns off 05. The turn-on pulse is
4-19
transformed by T1 to> +100 V output pulse. Diodes CR5, 6, and 7 serve as a voltage doubler and CAB is a low-noise rectifier with a breakdown of 200 V.
4.7 SERVICE AND MAINTENANCE.
4.7.1
GR Field Service.
The 1560-P42 Preamplifier is covered by the warranty given at the front of this manual.
The warranty attests the quality of materials and workmanship in our products.
When difficulties do occur, our service engineers will assist in any way possible. If the difficulty cannot be eliminated by use of the following service instructions, please write or phone our Service Department giving full information of the trouble and of steps taken to remedy it. Be sure to mention the serial, 10, and type numbers of the instrument.
4.7.2
Instrument Return.
Before returning an instrument to General Radio for service, please contact our
Service Department or nearest District Office requesting a "Returned Material" number. Use of this number will ensure proper handling and identification. For instruments not covered by the warranty, a purchase order should be forwarded to avoid unnecessary delay.
4.7.3 Minimum- Performance Standards.
The equ1pment listed in Table 4-4 is required for incoming inspection, periodic operational checks, or trouble analysis of the Preamplifier. The procedures are given in the following paragraphs.
The special dummy microphone used for the noise test consists of a Switchcraft
390P1 adaptor with a 390-pF capacitor inserted between terminals 1 and 3, on one end.
GR 1933 PRECISION
SOUND-LEVEL METER
AND ANALYZER
SWITCHCRAFT
387 P1 ADAPTOR
CABLE ATTACHED
TO PREAMPLIF'IER
GR 776 -A ADAPTOR CABL-E
GR 776-A
ADAPTOR
CABLE
PATCH CORD
7
GR274-NQ
HP 334A
DISTORTION t.IE1'"-11
(FOR D11lffTION)
Figure 4-13. Test setup for minimum-performance checks.
4-20
Name
Oscillator
Decade Attenuator
Precision Sound-
Level Meter and
Analyzer
Distortion Analyzer
TEST EQUIPMENT
Minimum Requirements
3Hz-500kHz
100 mV- 1 V open circuit
0-40 dB in 10-dB steps
40-140 dB C Weighting
To measure <0.25% distortion
Recommended*
GR Type 1310
GR Type 1309
GR Type 1450-TB
GR Type 1933
Ac Voltmeter
Voltmeter
Power Supply
Resistor
Patch cord
(2 needed)
Adaptor cable
(2 needed)
Shielded cable
100 mV- 1 V
0.2 -- 2 v
3-20Hz
20 V de, 15 mA
600 n
±1% (termination)
GR274 to GR274, 3ft
GR274 to BNC plug (male)
Hewlett Packard Distortion Meter, Model
334A
HP Type 400 EL
Ballantine 316
GR Type 1560-P62
GR Type 274-NO
GR Type 776-A
Adaptor
Adaptor
3-pin microphone connector (male) GR Type 1560-9665 to 3-pin microphone connector
(female)
GR274 to phone jack
Phone plug to 3-pin female microphone connector
3-pin microphone connector
GR 777-02
Switchcraft 3B7P1
GR 1560-9669 Adaptor
Adaptor 3-pin female microphone connector Switchcraft 386P1 to BNC plug
Dummy Microphone 390 pF
DVM
Oscilloscope
Range 0-200 V de, accuracy ±2%
Bandwidth- 50 MHz
RiseTime-1 ns
Data Prec. 2540
Tektronix Model 547 with 1A1 plug-in unit
•or
equ\va~ent.
4-21
Gain Check (X1).
Make the setup shown in Figure 4-13. The 400 EL Voltmeter is to be connected alternately at the output of the 1450-TB Decade Attenuator (connection
A in the diagram) and the output of the 1560-P62 Power Supply (connection B).
Use the following procedure:
Set
1450-TB
131 0-B
Attenuation ~ 0 dB
FREQUENCY-1kHz
1560-P42
OUTPUT -
"'='
1 V rms
200 V switch- OFF
1560-P62
GAl N switch- X
1
Switch- LINE ON
400 EL
METER RANGE~ 1 V a. Adjust the 1310 output for a reading of 0 dB on the meter at the output of the
1450 attenuator (connection A). b. Change to connection B. The 400 E L must now read 0 ±0.3 dB.
Gain Check (X10).
Change the above settings of Figure 4-13 as follows
1450-TB
1560-P42
Attenuation- 20 dB
GAIN switch- X10
The 400 E L must read 0 ±0.3 dB.
Frequency Check.
Using either the HP 400 EL Voltmeter or the Ballantine 316 Voltmeter in the setup of Figure 4-13, make the frequency measurements indicated in
Table 4-5. In each case, perform step A with the voltmeter at Point A, then step B, voltmeter at point B.
- - - - - - - - - - - - - - T a b l e 4 - 5 - - - - - - - - - - - - - -
FREQUENCY CHECKS
Step B
1310
Frequency
1560-P42
Gain
Voltmeter
Used
1450-TB
Attenuation
(dB)
Step A
Reference
On Voltmeter
Range dB
Setting c
0 m·;;
...
~
c.,
Ln ...
'<1' ...
..-<(
1560-P42
Output
(dB)
3Hz
5Hz
20Hz
3Hz
5Hz
20Hz
X1
X1
Xl
X10
X10
X10
100Hz
10kHz
100kHz
500 kHx
X1
X1
X1
X1
100Hz X10
10kHz X10
100kHz XlO
300kHz X10
316
400 EL
20
20
20
20
20
20
20
20
20
20
20
20
20
20
0
0
0
0
0
0
0
0
10
10
10
10
10
10
2V
2V
2V
2V
2V
2V
1
v
1
v
1
v
1
v
1
v
1
v
1 v
1
v
20
20
7 to 13
9 to
11
20 9.75 to 10.25
40 7 to 13
40 8.5 to 11.5
40 9.7 to 10.3
20 0 ± 0.25
20 0 ± 0.25
20 0 ± 0.25
20 0 ± 1.0
40
0 ± 0.3
40
0± 0.3
40
0 ± 0.3
40
0 ± 2.0
4-22
Noise Check. In the setup ot Figure 4-13, connect the 400 EL Voltmeter to point A and the 1933 Sound-Level Meter to point B (the output from the 1560-P62 Power
Supply). The procedure is given below. a. Set:
1450. TB
400 EL
131 D-B
156D-P42
156D-P62
Attenuation - 20 dB
METER RANGE- 100 mV
FREQUENCY- 1 kHz
OUTPUT- 100 mV (read on 400 EL)
GAIN- X10
200 V- OFF
Switch- BAT ON (no power cord connected)
1933
RANGE- 130 dB Full Scale
WEIGHTING- C
METER- SLOW b. Adjust theCAL control on the 1933 so that its meter reads 130 dB. c. Remove the input to the 1560-P42 at the output of the 387-P1 adaptor. Install the 156D-P9 Dummy Microphone, with shorting cap, on the
1560-P4~ input. d. Change the 1933 attenuation to 50 dB Full Scale
The 1933 must now read less than 41 dB.
Distortion Check. Make the setup ot Figure 4-13. Connect the 334A Distortion Meter to point B. Replace 1310 with 1309 oscillator. a. Set:
1450. TB
1309
156D-P42
1560-P62
Attenuation - 0 dB
FREQUENCY- 1 kHz
OUTPUT- 1 V rms
GAIN-X1
200 V- OFF
Switch - BAT ON
334A FUNCTION- DISTORTION b. Measure the distortion on the 334A to be less than 0.25%. c. Change the output trom the 1309 to 0.1 V rms (at the input to the 1560-P42) and set the GAl N switch on the 1560-P42 at X 10. Again the distortion must be less than 0.25%. If the distortion is higher, check the oscillator distortion (at point B).
4.7.4 Trouble Analysis.
The following details should be helpful in locating the faulty component, if trouble develops in the Preamplifier: When components are disconnected or replaced, use good soldering technique. Use a small tip on the iron and fine-gauge solder. Keep the heat to a minimum.
Amplifier Section. Terminate the input of 600 Q and turn the 200 V switch off. Table
4-6 gives the transistor voltages with a power-supply voltaqe of 20 V. Use the 400 E L
Voltmeter (or equivalent) for the measurements. Connect the negative terminal to the ground of the power supply (not to the Preamplifier shield). Be sure pin #1 is connected to ground.
Also, check the
+ terminal of capacitor C4. With the GAl N switch on X 10, this should be approximately 10 V ( 1/2 of the power-supply voltage). If C4 is at B+, 02 is
4-23
probably shorted, and should be replaced (see base connections on the schematic diagram). A short circuit between the drain and source of 01 will cause 02 to conduct tQO heavily, in which case, replace 01.
Current 01 Configuration.
The device used
in
current production units for 01 is a type 2N3958, a selected dual F ET that can bP. most easily identified by observation that 3 of the ·6 leads coming out of the base have been snipped off. In this circuit, the bias resistors, R5 and R8 are 3K and 36K, respectively; no selection is required.
Early
Q
1 Configuration.
In early production units, 01 was a type 2N3457 that required careful selection of bias resistors for proper operation. If it is replaced, resistors R5 and R8 must be selected according to the IDSS value of 01, the value of the current through the drain when the source is shorted to the gate.
Determine the IDSS value by using the circuit of Figure 4-14. Then select Allen
Bradley 1/8-W, 5% resistors as shown by Table 4-7.
CAUTION
When changing 01, use a small soldering-iron tip and fine-gauge solder, with only enough heat to produce good connections. Overheating diode
CR 1 or CR2 may produce noise, requiring its replacement.
01
02
03
04
Table 4-6
TRANSISTOR VOLTAGES
Location Volts gate source drain emitter base collector emitter base collector emitter base collector
11.5
+19.4
20.0
19.4
12.0
11.4
12.0
20.0
11.4
10.8 gnd
Table 4-7
SELECTION OF BIAS
RESISTORS FOR 01. lOSS Value of 01 l~tAI
R5 tknl
R8
(kn)
50-100
100-175
175-250
12
6.2
3.3
150
75
43
Figure 4-14. Circuit for the determination of the lOSS value of 01.
8+ LESS
AVERAGE CURRENT
(2-4mA)THROUGH
COLLECTOR
;--'\_h.["""'--
+13V
Rl~
__
'l ___ l __
- - - -
1
- -
GNO
- - - -
I
'
BASE
I
I
+0.6V
-s v
Figure 4·15. Waveforms at transistor 05.
Oscillator Section.
Check the waveforms at 05, using the fast-rise-time pulse oscilloscope. The waveforms are shown in Figure 4-15.
4-24
A de che c k for continuity can be made on the transformer windings.
Observation of the output pulse at transformer T1, pin 1, will yield an e rr o n eo us am p litude measure m ent be c ause of s c ope prob e loading.
To check for 100 Vat the jun c tion of CR5 and CR6, use the 1806 Volt m eter on
OPEN GRID. There should be 200 Vat the anode of CR7. Diodes CR5, 6. and 7 are very fast rise- and re c overy time diodes , rated at 225 V . Repla c ements should be made only with type 1N661 diodes, from Texas Instruments In c orpora t ed (Dallas, Texas ).
(HIDDEN) (HIDDEN)
Figure 4 · 16. Interior views of the 1560 · P42 Preamplifier; (to p ) c i r cu it s i de of etched-circuit boa r d;
(bottom) component side.
:efOt." DMeription
C l
C2
C3
C4
C5
C6
C7
C8
C9
CIU
Cl l
C l 2
C A PAC I TORS
Ce r a m ic , .
001 pF , 10
' 200 v
E l ec 1 l y1 t c , 80
I'
, 20 · , 1 5 V
Ceram i c, .
001 IJF, 1 0 '\ , 200 V
E l ec Jmlytic , 10 vr ,
20 • 30 v
Elect ro l y ti c , J O pF ,
20'~ ,
30 V
Ceram i c , 330 pF , 10 ': , 200 V
E lecrr o lyJ i c , 1 IJF ,
20'~ .
35 V
Ceram i c, .
OO i fJF, Ill':' , 200 V
Ceramic . 1 JJF ,
1 0~ .
2 00 V
Ceramic .• 1 <1P . 10 '-> . 200 V
C.C
r a mic • • 022 JJF ,
±.
.U~ .
200 V
Ceram i c, .
!lln pF ,
1() '{' ,
200 V
CONNECTO R S
P LI
OIOOES
CR I
CR2
CR3
C R4
C RS
C R b
CR7
CR8
4 Pin C o nnector on Board
Type DHD707
Type DHD707
M I' D200
Type DHD707
Type 1 N66l/TI-UK I -G Package
Type 1N661/ TIUK J -G P.
acl<oge
Type l N66 J / TI -UN I -G Pac k age
Type
CSR -1 7580
R ESISTORS
Rl
R 2
Cv rnp
Comp .
.,
,
1
1 c;n
00
, kll t2~
, 5 li'
,
, I
1 /8 W
/8 W
1 560 1'42 PR EIIMI' Li l' I EJ\
ELECTRICAL PARTS LIST
F ed
GR PaortNo . Mig Code
MfgPo~~rt
No.
44{) 0-644{) 72982 8 12I 026 X5RO-I02K
44 50-6300 37942 MTP, 80 pi?
, 20 ' .
'
4 400-0 4 40
72982
R l2 1 -Q26-X5R0 102K
4451H >J20 17<1 42 \: · 1 P , 1111;1 ,
lll
4450-0320 37942 MTP , 10 !JF
, 20"'
4400-644 1 72982
8 !
!1-{J26-X5R 0 -311 K
4 450-0400 56289 1 62 ·0 , I pf, 2 0~
4400-044 0 72982 8l2 l -Q26·X5RO-I02K
4400-0 4 4 0 72982 8121-o26-X5R0-IIJ2K
4400-(14 4 0 72982 8 l 2 l -o26 X5RO-I02K
4400-()44~ 7 2 !>1{ 2
· M2U0-65 1 ·221M
4 400-6 4 4 0
72982 8 1 2 l -026-X5R0lU2K
1 5 6 0 2 3'10 2 4 655 1560 2370
60821 009
079 1 0 0110707
6082· 1( )()9
07910 0 11 0707
6082 -1 036 06751 MP0-200
60821 009
07910 OH0707
6082 1032
06751 1 1\'66 1
6082-1032
0675 1
11\'661
6082-1032 11675 1 I N66 1
6083·1079 079 1 0
CSR1 7 58 D
6096-6108 0 I I:! I llll , I
(;{!
,
~209(
6098-4105 0 1 12 1 llO, 100 HI,
5~
F td Stock No .
596 1 -929-9967
596 1 -929-9967
596 1 -929 · 9967
4-25
4-26
Ref Des Description
RESISTORS (Cont)
R3
R4
R5
R6
R7
RH
R9
R10
R11
R12
R13
R14
R1!J
R16
R17
Rl8
R19
R20
R21
R22
Comp., 100 k!2, 5o/c, l/H W
Comp., 2.2 GU ±20'1•, 1/H W
Comp., 3 k£2 ±5%, l
/~
W
Comp., 3.0 k\2, 5%,
1
/H W
Film, 1.06kl2±1%, 1/10W
Comp., 36 k\2 ±5%, l/H W
Comp., 10012, 5%, 1/H W
Film, 10.2U2±1'fr, 1/lOW
Comp., 10 Hl, 5%, 1/8 W
Comp., 27 n, 5%, 1/8 W
Comp., 27 n, 5%, 1/8 W
Comp., 100 kfl, 5%, 1/8 W
Comp.,1012±57c,l/HW
Comp., 240 kfl, ±5%, 1/8 W
Comp.,
220
n~
±5%
Comp., 10
Mn,
±5%, 1/8 W
Comp., 100 Mil, 10%, 1/8 W
Comp.,
10 fl, 5%, 1/8 W
Comp., 3 kfl, 5%, 1/8 W
Comp., 100 Mfl, 10%, 1/8 W
SWJTCHES
SWl
SW2
Switch (Actuator)
(Contact)
Switch (Actuator)
(Contact)
TRANSFORMERS
Tl Transformer Asm,
TRANSISTORS
Ql
Q2
Q3
Q4
Q5
Special
Type D30A3
Type 2N4124
Type 2N3906
Type D26E1
ELECTRICAL PARTS LIST
(cont)
fod
GR Part No. Mfg Code
609H-41 05
609H-822H
6098-2305
6098-2305
6619-:1102
6098-3365
609H-11 05
6619-3101
6098-3105
6098-0275
6098-0275
6098-4105
609H-01 05
6098-4245
609S-1225
60%-6105
6098-7109
6098-G105
6098-2305
6098-7109
1560-7620
1560-8700
1560-7b20
1560-8700
1560-4141
H21 0-1260
8210-1204
8210-1154
8210-1112
8210-1205
01121
01121
01121
01121
91637
01121
01121
91637
Ol121
01121
Ol121
01121
01121
00912
01121
00912
01121
01121
01121
01121
BB, 1 00 k!2, :>C,<
BB 2 2 GIL +2o";
BB: 3. kll
±:)~
BB, 3.0 k!2, 5'il
MF-50, 1.06 U2
±1'-~. l/10
W
BB, 36 kll E,,;
BB, l 00 rl,
S<Jr-
MF-50, 10.21.12 ±1'/, 1/10 W
BB, 10 kfl, 5%
BB, 27 n, 5%
BB, 27 n, 5%
BB, 100 kfl, 5%
BB, 1012 ±5'//
BB, 240 kfl, ±5%
BB, 220 n, ±5%
BB, 10 Mn. ±5%
BB, 100 Mfl, 5%
BB, 10 n, 5%
BB, 3 kfl, 5%
BB, 100 Mfl, 10%
24655
24b55
24655
24655
24655
24655
24454
04713
.04713
24454
Mfg Part No.
1560-7620
1560-8700
1560-7620
1560-8700
1560-4141
8210-1260
D30A3
2N4124
2N3906
D2GE1
Front
End
ASM 1560-2613
Contact ASM 1560-2550
PIN 4
~1P~~:~w,:t(:~:;~~·
AT5
AT4
CR4
CR2
AT7
R16
Figure 4-17. Etched circuit board (P/N 1560-2791) for the 1560-P42 Preamplifier. Top 3 views are from etched side of board, bottom 2 views from component side. Preamplifier pinout functions are shown in bottom-right corner.
S I D G N D
40 3
2 1
B+
INSERTV
~
,;.,
CIO
"' +
lOOK
"~
THREROE01
_ H_fi.,_L _ llR\~EK
SHitlt> I
------y
I
I
IAT7
Cl
,OOI.u
~~~~-~
I
T
I(-AT6
I
.J
I
Rl
IG
<,
3"
I
1-001"1
I
R20
10
'
ATI
~l
IAT4
I
CRI
I I
lOOK
'--;;]
/
,
,0~
-Tc'!
1"'1\U
~
80A.I
Aq
100 r ...
I
~"
7
I AI I rT-,
t•
=r··
; '9';
CR"3
I
I
Ot.>K
I
~
KI_O
>
(l)Q4
"
I AT2
RD
I
BASE DIAGRAMS
(BOTTOM VIEWS)
TRANSISTORS
~ lOOK
+_L
l
C7 l.u
...
AT3
BK
IIJH
QF\RN&t
COLOR
WHITE
COLOR
INDEX
W
D~~
Gi?N
BANDS
Y[L
BANDS
INDEX
GYrrn~
R D r u
OR OR
B
c
E
D~~
BCE BCE
B
c
E
~
L__j L__j
02 05
E B C
~
03,4
B+ y
I zoo vi swc:
{
__.
GATE I
~o
DRAIN I 0
SOURCE I
0 DRAIN 2
0
0
GATE 2
01
Rl"l
220
BL
ATS
RESISTANCE IS IN OHMS K'103 M'10
6
, CO •lOot
CAPACITANCE IS IN FARADS.J!·I·0·6,p•IO l2
'IOLTAGES [l(PLAINED IN INSTRUCTION 600K SHI'iiCE NO\ES
CONTROL ~~;:_-_:_-; •REAR CONTROL
Q•SCREWORIVER CONTROL wT-WtRE TIE TP•TEST POINT
COMPLETE REFERENCE DESIGNATION I,..CLUOES SUBASSEMBLY
LETTER C-RI.B Rl ETC
I.
II c
R
4
Figure 4-18. Schematic diagram for the 1560-P42 Preamplifier. cs
IO..u..
TRANSFORMER Tl
~®{
BOTTOM VIEW
PRI~I
5 6
3
I
(c5)
4
~
2
SEC-I
PRI·/ REO
PRI-2. GOLD
SEC-I GREeN
TERMINAL ARRANGEMENT
AND NUMBERS
Type 1560-P62 Power Supply
Section5
5 .
1 DESCRIPTION . . . . . . . • . . . . .
5.2 CONTROLS, CONNECTORS, AND IN DICATORS .
5.3 ACCESSORIES SUPP LIED.
5 .
4 IN STALLA TION • .
5.5 OPERAT I ON
5 .6 REMOTE OPERAT ION
5 .
7 BATTERY TE ST . •
5 .8 CHARG I NG THE BATTERY
5 .9 THEORY . . . . .
. .
5 .
10 SERV IC E AND MA INTEN ANCE
5 · 1
5
·
2
5-3
5-4
5 ·6
5-6
5-6
57
5-7
5 B
5.1 DESCRIPTION .
The 1
56Q.P62 Power Supply (Figure 5-
1)
is intended
to
supply power to the
1560-P42
Prearnplifi~r
when
the
latter is used with instruments that do no
t
include the necessary source of power (refer
to
Tab
l
e 1
-
2)
.
The Power Supp
l
y can a
l
so be used
when l
ong cables are
t
o
be
d
ri
ven
at
high leve
l
s
. I
t can serve as a charger for rechargeable batteries
in
other instruments, such as
the 1561
Sound
-
Leve
l
Meter and the
1952
Universal Fi
l
ter.
~
Y
1
GFNERAl R ADIO
Figure 5-1.
Type
1 560.P62 Power
Suppy .
DS1
5-1
Included in the Power Supply are two nickel-cadmium rechargeable batteries, a battery-charging circuit, and a battery-checking circuit. The batteries are held in a slide-out clip, for easy removal.
Specifications for the 1560-P62 Power Supply are given at the front of this manual.
5.2 CONTROLS, CONNECTORS, AND INDICATORS.
5.2.1 Front-panel Controls and Indicators.
The front panel contains one selector switch (S1) and a battery-test light (OS1).
The switch turns off the power to the unit in the ALL POWER OFF (ccw) position.
In the CHARGE ONLY position, with the line connected to the power line, the batteries accept current only from the line. In this mode, a full 22-mA charging current is applied to the batteries.
In the LINE ON position, the batteries are again charged with 22 mA, but battery voltage is also applied to the output connector from the preamplifier. (Some increase in ripple will be noted in this position.) The batteries act as a filter to the line, and any loading from the preamplifier reduces the charging current to the batteries (the current is limited to 22 mA).
In the BATtery ON mode, the line is disconnected from the unit; there is no line current in the transformer and the batteries are connected to the load.
With the switch in the ON, REMOTE position, the batteries are connected to the load when the instrument to which ·,t ·,s connected has at least 1 mA at 15 V on pin 2 of its input connector. In this mode, the on-off switch of the analyzing instrument becomes the on-off switch for the Power Supply.
The BAT CHECK position gives a spring-loaded momentary test of the battery. The front-panel pilot lamp (DS1) will light if the battery is charged sufficiently for operation. The light is used as a measure of the state of charge of the battery. It will not light if the battery voltage drops below 17 V. Since the change of illumination with voltage is rather sharp, the relative intensity of the light can be used as a measure of the state of charge of the batteries. For the test, the switch is held in the BAT
CHECK position for several seconds. If the light intensitY gradually diminishes somewhat during that time, the battery should be charged.
5.2.2 Rear-panel Controls.
The CHARGE switch (AS2) on the rear panel permits connection of the charging circuitry to either the INTernal BATtery (normal operation) or an EXTernal BATtery.
In the EXTernal BATtery position, charging voltage is applied to the TO EXTERNAL
BATTERY connector, AJ4 (see Figure 5-2). Connection from AJ4 to instruments such as the GR 1561 Sound-Level Meter is made by the cable (P/N 1560-0491) supplied with the -P62 Power Supply.
Slide switch AS1 (50-60Hz, 100
V- 125 V, 200 V- 250 V) is used to select the proper line voltage, either 100-125 or 200-250 V.
Connection for the INPUT (FROM PREAMP) is made at connector AJ2, a
3-contact female Switchcraft type A3 connector, and connection for the OUTPUT
5-2
(TO ANALYZER) is made at AJ3. a 3-contact male type A3 connector . The signal passes directly from pin 3 of the INPUT to pin 3 of the OUTPUT. Note that the shield of the connectors is not connected to the circuit ground. but is connected to the case of the -P62 Power Supply. Ultimate connection of the ground
to the connectors must be made at the final analyzing instrument.
Connector AJ5 is a subminiature phone jack, $witchcraft, Type TR-2A in parallel with AJ3.
5.3 ACCESSORIES SUPPLIED.
The accessories supplied with the Power Supply are listed in Table 5-1 .
Figure 5-2. Conttoh and connectors on the rear panel of the Power Supply .
Table 5-1
ACCESSORIES SUPPLIED
Quantity
Supplied Item
Use
Adaptor cable
Connects OUTPUT socl<et to an analyzer
(3ft) or recorder with type 274 double-plug input connector.
GR
Part No.
Charging cable
Connects TO EXTERNAL BATTERY
(20 in) socket to 1561 charging terminals.
1560-0491
Extension cable Connects OUTPUT socket to an analyzer
1560-9665
(4ft) with female Switchcraft type A3 input connector .
1560-9677
5-3
5.41NSTALLATION.
5.4.1
Power.
The power cable (P/N 4200-9622, supplied) connects to AJ 1, a polarized male plug.
Line-power protection is afforded by a 1/16-A slow-blow fuse in an extraction-post fuse holder, AF1.
5.4.2 Dimensions.
The dimensions of the 1560-P62 are shown in Figure 5-3.
5.4.3 Mounting.
The 1560-P62 Power Supply may be ordered completely assembled in a metal cabinet, ready for bench use (P/N 1560-9575). The instrument is locked in the cabinet by two captive 10/32 screws in the rear panel.
To mount the -P62 in an EIA standard 19-inch relay rack, order a rack-adaptor set
(P/N 0480-9742), consisting of the parts listed in Table 5-2. The method of mounting is shown in Figure 5-4 and the procedure is as follows: a. Loosen the two captive 10/32 screws in the rear of the cabinet until the instrument is free; slide the instrument forward, out of the cabinet. b. Remove the four rubber feet from the cabinet. Be sure to save all parts as they are removed, for possible reconversion of the instrument to bench mounting. c. Pierce and push out the plugs from the four bosses (C) in the sides of the cabinet, near the front. The blank panel can be attached to either side of the cabinet, as desired.
Use the holes in the side toward the blank panel. Do not damage the threads in the holes. d. Press the subpanel (D) into the blank panel (E). to form a liner for the latter. e. Place the blank panel so that the short flange of the subpanel is toward the cabinet. Attach the blank panel (E) and subpanel (D) to the cabinet, using two 5/16-in. screws (F) as shown. Note that the screws enter in opposite directions- one from inside the cabinet and one from the flange side, as shown. f. Attach one Rack Adaptor Assembly (handle) to the side of the cabinet opposite the blank panel, us·mg two 5/16-inch screws (l}. Again, note that the screws enter in opposite directions one from inside the cabinet and one from outside. Use the upper and lower holes in the Assembly. g. Attach the other Rack Adaptor Assembly (handle) to the wide flange on liner
(D) and the flange on the blank panel (E). Use two 5/16-in. screws (M) through the two holes in the flange that are nearest the panel and through the upper and lower holes in the Assembly. Again, the screws enter in opposite directions. h. Install the instrument in the cabinet and lock it in place with the two captive screws through the rear panel that were loosened in step a. i. Slide the entire assembly into the relay rack and lock it in place with the four
9/16-in. screws (N) with captive nylon cup washers. Use two screws on each side and tighten them by inserting a screwdriver through the holes (P) in the handles.
To reconvert the instrument for bench use, reverse the above procedures, first re-
19
- - - - - - - - - - - - l
RACK ADAPTOR SET""
0480-9742
____j,
=
RACK MOUNT
f - - - - - - -
8.500 _ _ _ _
@o
BENCH
NOTE: DIMENSIONS IN INCHES
1560-57
Figure 5-3. Dimensions of the Power Supply.
- - - - - - - - - - - - - - T a b l e 5 - 2 - - - - - - - - - - - - - -
PARTS INCLUDED IN THE RACK ADAPTOR SET
P/N 0480-9742
(see
Figure 5-4)
Fig.
5-4
Ref. No. Used GR Part No.
E
D
H
F ,J,K,L,M,
N
1
2
Blank Panel
Sub-Panel
Rack Adaptor Assembly
Support Bracket
Hardware Set
Includes
8 Screws, BH 10-32, 5/16"
4 Screws, BH 10-32, 9/16" w. nylon cup washers
0480-8932
0480-8952
0480-4902
0480-8523
0480-3080
Note: Discontinued
Figure
5-4.
Method of mounting the Power Supply and a blank panel in a relay rack.
5-5
moving the entire assembly ·Of instrument, cabinet, and blank panel from the rack.
Next remove:
1. The instrument from its cabinet.
2. The blank panel (E) (with handle attached) from one side of the cabinet;
3. The Rack Adaptor Set (handle) from the other side of the cabinet.
Push the four rubber feet into the cabinet. Install the instrument in its cabinet and lock it in place with the two captive screws through the rear panel.
5.5
OPERATION.
Set the external charging switch to INTERNAL BATTERY and the front panel control to LINE ON. The instrument will now provide sufficient current and voltage to the INPUT (FROM PREAMP) connector to operate a 1560-P42, 1972-9600 (or
1560-P40) Preamplifier for upwards of 100 hours of continuous operation. The actual time will vary, depending upon the amount of signal current that the preamplifier presents to the load, and whether or not the -P42 is used for ceramic or condenser microphones. If the Power Supply is not plugged into the ac line, the LINE ON and·
BATTERY ON modes are identical. In the LINE ON position and if the Supply is plugged into the ac line, however, depending upon the state of charge of the batteries, some small ripple component may be seen as de output that drives the Preamplifier. If there is a hum problem, setting the front-panel control to BATTERY ON will remove any connection to the ac line.
5.6
REMOTE OPERATION.
Set the front-panel switch to REMOTE. Connect the output of the -P62 Power
Supply to any instrument that normally supplies at least 1 mA and at least 15 Vat pin
2 of the connector to which the output of the -P62 is connected. Turning the analyzing instrument on and off will now turn the 1560-P62 on and off. No remote charging is provided by this remote connection.
5.7
BATTERY TEST.
Without connecting the power supply to 11 0-V (220-Y} source, check that the batteries are inserted in the power supply and the battery switch on the rear panel is set to INTernal BATtery. Rotate front panel switch to BATtery CHECK position. The front panel lamp (DS1) should light. If not, the batteries need charging.
5.8
CHARGING THE BATTERY.
Before connecting the Power Supply to the line, be sure to set the power-voltage switch to the proper position. Connect the line voltage to the input-power connector.
Set the front-panel switch to either CHARGE ONLY or LINE ON, depending on how
5-6
the instrument will be used. If the batteries have been fully discharged, they should be recharged for approximately 12 to 14 hours (overnight is usually satisfactory). If the
-P62 is going to be used in the Ll NE ON position to recharge the batteries, some allowance must be made for the nominal load.
CAUTION
DO NOT overcharge the batteries by leaving the instrument in the charge mode for more than several days. Long-term (weeks) charges should be strictly avoided. Also, the batteries should be fully discharged occasionally so that they will maintain their capacity.
Charging an External Battery.
To charge an external battery, connect the cable supplied (P/N 1560-0491) to battery terminal AJ4, EXTERNAL BATTERY. Connect the other end to the instrument whose batteries are being charged, such as the 1561.
Set the 1561 to CHARGE. Set the rear-panel charge switch on the Power Supply to
EXT BAT and the front-panel switch to CHARGE ONLY. The charging current will now be applied to the 1561 batteries. The 1561 batteries can be used in the
OPERATE or LINE ON modes in the -P62.
5.9
THEORY.
The schematic diagram of the Power Supply is given at the end of this Section, in
Figure 5-7.
The 1560-P62 Power Supply consists of two nickel-cadmium rechargeable batteries and related charging, testing, and overload-protection circuitry. The charging circuitry consists of power transformer T1, rectifiers CR 1 through CR4, and either R 1 or R2.
These elements compose a constant-current charging circuit for the batteries. The
.current-limiting resistor is R 1 or R2, which is connected to the line voltage (R 1 or R2 depending on whether line switch S1 is connected to 110 or 220 V). This resistor, in conjunction with the winding resistance of the T1 primary winding, provides the constant-current charging for the batteries.
The open-circuit voltage at the secondary of T1 is approximately 60 V. However, when loaded with the batteries, a constant current of approximately 22 mA is fed into the batteries. In the event that the batteries are removed, diodes VR 1 and VR2 behave as voltage-limiting devices so that, in the charge-operate mode, 25 V maximum will appear at the de output terminals of the Power Supply. It should be noted that, because there is constant current in the batteries, the batteries should not be left in the charge mode constantly, as damage will probably result.
Transistor 01, in conjunction with R3, R4 and VR3, behaves as a sensing device to denote whether or not the battery is adequately charged. It does this by loading the batteries with a modest discharge and sensing the voltage at the battery terminals. If the voltage is sufficiently high, pilot light DS1 will be illuminated.
The load current of the Power Supply is limited to 20-mA peak as a result of the current limiting action of 01 and 02 in conjunction with R39, CR5 and CR6. The
5-7
nominal maximum current limit is 15 mA. The true nominal is in the vicinity of 20 mA to allow for normal tolerances in semiconductor elements and temperature variations. 02 is turned on via transistors 03 and 04. This circuitry provides the additional feature that a short-circuit continuously applied to the output of the Power
Supply will not drain the batteries to the point where they will become dead. This is done by sensing the voltage at the battery terminals. If the voltage drops below 16 V, then the current supplied to 02 to turn it on is removed. This is done via Zener diode
VR4 and transistor 03. This feature lengthens the life of the batteries many times over, because excessive discharge may reverse-polarize one of the batteries and thus damage it. The de output of the Supply is applied to pin 2 of AJ2, which is the jack into which the preamplifier is connected. No voltage is applied to the output connector AJ3 of the Power Supply. However, AJ3 is used so that, for remote applications, where it is desirable to utilize a second instrument to turn on and off the Power
Supply, pin 2 of AJ3 provides the sensing terminal. Such instruments as the 1564,
1921, 1558 and many other G R instruments, have nominal 1 or 2 mA at 16 V available at pin 2 of their connections. This small current and voltage is used to turn on 04 of the -P62 Power Supply and affords a remote turn-on and turn-off feature: It must be noted, however, that in the remote mode the battery-low sensing circuitry is not operative.
5.10SERVICE AND MAINTENANCE.
5.10.1 GR Field Service.
The 1560-P62 Power Supply is covered by the warranty given at the front of this manual.
The warranty attests the quality of materials and workmanship in our products.
When difficulties do occur, our service engineers will assist in any way possible. If the difficulty cannot be eliminated by use of the following service instructions, please write or phone our Service Department giving full information of the trouble and of steps taken to remedy it. Be sure to mention the serial, ID, and type numbers of the instrument.
5.10.2 Instrument Return.
Before returning an instrument to General Radio for service, please contact our
Service Department or nearest District Office requesting a "Returned Material" number. Use of this number will ensure proper handling and identification. For instruments not covered by the warranty, a purchase order should be forwarded to avoid unnecessary delay.
5.10.3 Trouble Analysis.
Table 5-3 shows the de voltages at various points in the circuitry. The cabinet on the instrument is removed by unscrewing the two captive Phillips-head screws through the back panel.
Two general problems that might arise are no charging of the batteries, or no output voltage. The transformer and rectifier diodes are seldom at fault, but the
5-8
batteries may be dead. Either remove the batteries or set the battery switch to EXT
BAT. With the line connected and the switch at CHARGE ONLY, +20 to +26.5 V should appear from wire tie 5 (WT5) to WT2. If this voltage is incorrect, determine and replace the faulty component in the charging network. If the voltage is correct re-install the batteries and again observe the voltage at WT5 in the CHARGE mode. If the voltage drops to zero, the batteries are probably shorted and should be replaced. If the voltage at the output of AJ2 (pin 2) is less than 18 V with good batteries, check that the turn-on circuitry is operating. Check the voltages on 03 and 04 according to
Table 5-3. If they are correct, the trouble is probably a faulty 02; if they are not check 03 or 04 or Zener diode VR4. As a final check, short pin 2 of AJ3 to ground.
The voltage across R9 should be approximately 0.6 V. This assures proper current limiting through 02.
DC VOLTAGES* c
B E
Ot
02 t
03
04
6.9
20.8
6.9
7.2
7.2
20.4
7.2
7.8
6.8
21.0
6.8
7.2
*Measured between point noted and WT2. t Depends on battery voltage. Table based on fullv charged battery of 21 V and no load.
Fig Ref
5·5/5·6 Ont
81 Position
BAT CHECK
BATON
BATON
BATON
1560-P62 POWER SUPPLY
MECHANICAL PARTS LIST
Description GR Part No.
Fed
Mfg Code Mfg Part No.
FRONT PANEL
1.
2,
1
1
4
1
Cabinet, convertible bench:
Cabinet gasket
Foot
5260-2060 24655
Knob asm. ALL POWER OFF /CHARGE 5500-5321
24655
ONLY /LINE ON/BAT ON/BAT ON
4181-2911
24655
5331-3086
24655
REMOTE/BAT CHECK, including retainer 5220-5402
4181-2911
5331-3086
5260-2060
5500-5321
REAR PANEL
1.
2,
3.
2
1
2
4.
6.
7.
8.
9.
1 s.
1
1
1
Nuts for battery cover asm,
Battery cover asm,
Slide switch, A-S1, LINE VOLTAGE
SELECTOR;A-S2,CHARGE
Fuse mounting device
Power plug, A-J1
Plug asm.,
A-]4,
TO EXTERNAL
BATTERY
Multiple plug, A-}3, OUTPUT (TO
ANALYZER)
Subminiature phone jack AJ5
Multiple socket, A-J2, INPUT (FROM)
PREAMP)
1521-6610 24655
1560-1350
24655
7910-0832
82389
5650-0100
71400
42-40-0210
24655
1561-2040
24655
4220-3100
71468
4260-1110
82389.
4230-2600
82389
1521-6610
1560-1350
11A-1118
HKP-H
4240-0210
1561-2040
XLR-3-32
TR-2A
D3F
5-9
1
5-10
F tgUre
1
S-6 . ll/ledlani 1
6 c:a parts rear view .
L
~v
•
4 1 sso-
8~ l
II
11
••
J
J
J
REFDES
BT
BT
1
2
ELECTRICAL PARTS LIST
l560-P62 POWER SUPPLY
PIN
1560-4200
DESCRIPTION
BATTERY 9.6V NICAO
BATTERY 9.6V NICAD
PART NO.
FMC
B410-l040 24655
8410-1040 24655
MFGR PART
8410-l 040
841 0-l 040
313 .062 s s l
2
3
4
5
1
2
FUSE SLO-BLOW lll6A 250V
SWITCH SLIDE 2 PDS DPOT STEADY
SWITCH SLIDE 2 POS DPDT STEADY
5330-0300 75915
RECEPTACLE POWER IEC STO 6A 250V
RECPT AUDIO 3 CONT FEMALE
RECPT AUDIO 3 CONT MALE
PLUG ASM
M!NATURE PHONE 2 CKT SW
424D-0210
4230-2600
42 20-3100
1561-2040
42b0-l110
24655
82389
823 89
24655
82389
791D-0832 82389
7910-0832 82389
4240-0210
D3F
03M
1561-2 040
11<-2~ llA-1266 llA-1266
NUMBER
CR
CR
CR
CR
CR
CR
OS
REFDES c
PIJWER SUPPLY PC SOARD " V "
DE SC R I P TI 0 N PART
PIN
NO. t 56Q-4185
FMC
MFGR
CAP ALUM 660 UF 25V 4450-6125 56289 l OinOE RECTIFIER 1N4003
2 DIODE RECTIFIER lN4003
3 DIODE RECTIFIER lN4003
4 DIODE RECTIFIER lN4003
5 DIODE DHD-707 30PIV JR.OOlUA
51
6 DIODE OHD-707 30PIV IR.OOLUA SJ
6081-1001
6081-1001
6081-1001
6081-1001
6082-1009
6 082-l 009
14433
14433
14433
14433
07910
07910
LAMP FLANGE BASE lOV .Ol5A 10000 5600-0314 71744
PART
300667G025
l N4003 lN4003 lN4003 l N4003
CD8ll72
CD8l!72
CM- 344
Q
Q
Q
Q
~
R
R
R
R
R
R
R
R
R
R
R
VR
VR
VR
VR l TRANSISTOR 2N3414
2 TRANSISTOR 2N3638
3 TRANSISTOR 2N3414
4 TRA~SISTOR 2N3414
8210-1290
8210-1278
8210-1290
82LD-l290
562 B9
07263
56289
56289
l
RES COMP 2.7 K 5PCT 2W
2 RES
WW
AX LEAD 6.8K OHM 5 PCT 5W
3 RES FLM 7.68K l PC1 t/8\1
4 RES FLM 7.15K l PC T l/8\1
5 RES COMP 300 OHM
6 RES COMP 30 K OHM
5PCT l/4W
5PCT l/4W
7 RES COMP 39 K 5PCT l/4W
8 RES COMP 100 K 5PCT l/4W
9 RES COMP 33 OHM 5PCT l/4W
10 RES CO~P 30 K OHM 5PCT l/4W
11
RES COMP 100 K '>PCT 1!4W
12 RES COMP 22 K 5PCT l/4W
SWITCH ROTARY ASM
6120-2275
666Q-2685
62 50-l7b8
6250-1715
6099-1305
6099-3305
6 099-339 5
6099-4105
6099-0335 b099--3305
6099-4105
6 099-3225
81349
75042
81349
81349
81349
B1349
81349
81349
81349
81349
81349
81349
789Q-534l 24655
l
2
3
4
TRANSFORMER POWER
ZENER 1N758A
ZENER lN965B
ZENER l N957B
ZENER l N957B lOV l5V
6.8V
6. 8V
0748-4000 24655
5PCT
5PC
T
5PCT
5PCT
.4W 6083-1012
.4w 6083-1015
.4W 6083-1009
.4w 6DB3-l 009
14433
14433
07910
07910
NUMBER
2 N3414
PN 3638
2N3414
2N3414
RCR42G272J
AS-5 6.8K 5PCT
RN5507681F
RN550715l F
KCR07G30l J
RCR07G303J
RCR07G3 93 J
RCR07Gl 04J
RCR07G330J
RCR01G303 J
RCR 07G L04J
RCR07G223J
7890-5341
0748-4000
IN758A
IN965B
IN95 7B
IN95 7B
5·11
0
0
"-...T.wl-l
IZOo~v, l_?_2Q_v_j w.Y.'f-
0
0
0
S/
wcsc
~
~TJ
3
1?3
?.t.BJ<
Y£
;£~~~
A-SZ wri-Ro
ALL
POWER
OFF
CHARGE
ONLY uNE
ON
BAT
ON
BAT
ON
REMOTE
BAT CHECK
G(f,
3,
4
TR!lNSISTOR
!3t~S£S
t.ASJ'COMPO/V£N7' /Vt1M8C:I2 US£0 .' d/YBOARO;
Cl,CR6.~051"((4 1 RI2_
51
1
I.,A·FI.~
A-115
Tl.~
VR4
A-S2
Figure 5-7. Schematic circuit diagram of the 1560-P62 Power Supply.
8R w;r.BK
BK
11-J~
'Lr_o_LxT£Rtjf!LJjAI_r¥!lj
Type 1972-9600 Preamplifier/Adaptor
Section 6
6.
1
GENERAL .
.
6.2
I
NSTALLAT
I
ON
6.3 NOISE . . . .
6.4 SERV
I
CE AND MA
INT
ENANCE .
61
6-1
6-3
6-4
6
.
1 GEN
E
RAL
.
An inexpensive interface between a GR ceramic or electret mic
r
ophone and the measu r ing instrument is the 1972
-9600
Preamp
l
ifier/Adaptor ( Fi gure 6
-
1). This s i mple, easy-to-use preamp lif ier is designed to satisy
l ess~emanding r
equ ir ements than those met by the 1 560-P42 Prea mplifie r :
I
t has reduced output vo
l
tage and
c
urrent capabi lit
i
es, offers on ly unity gain, and does not supp ly the pola
ri
zing vo
l
tage required to ope
r
ate condenser mic rophones. In effect, the 19 72-9600 serves as an impedance conve rter for ceramic microphones and vibration pickups.
I
t provides a nominal input impedance of 2.2 Gn in parallel with
l
ess than 3 pF
.
It has an output impedance of approximate l y
1
0 n. The schematic diagram
is
g iv
e
n in Fi gu
r
e 6-4.
PIN
Figure 61 .
Type
1 972-9600
Preamplifier/ Adlptor.
IIJHIII
6
.
21NSTALLATION
.
6.2.1 Power.
T he Preamplifier is powered through the 3-wi re (plus shie
l
d) output
cable
f
r
om the analyzing instrument or power supply. Table
1 -2 l
ists the
~R
instruments that can provi
de
the necessary power for
the
Preamplifie
r
. The 1560-P62 Power Supp
l
y is a
l
so avai
l
able to supp
l
y this power (ref er to Section 5)
.
With the
1
972
-9
600 Preamplifier, the current i s
l
imited to 4 mA. The output stage is operating c
l
ass A, so that
the
average supply current drawn is the measu r ed de supply current. regard
l
ess of the
l
oad.
The measured (indicated) etc supply current is the ave
r
age current drawn.
6
.
2.2 Mounting.
The 1560
-9
590 Tripod is recomme nded for moun
t
ing the 1972
-
9600 Preamplifier .
Refer t o para.
1.
3.5 for a discussion o f the use of this Tripod.
6.2.3 Connections.
The Preamplifier is terminated in a .460-60 male screw thread at the input and a male Switchcraft type A3 connector at the output. Thus, it mates directly with the
GR ceramic microphones. The 1" ceramic cartridge can be adapted to the Preamplifier by using a 1560-2630 adaptor. Vibration pickups require a 1560-9669 adaptor.
When the Preamplifier is used with a microphone, its output can be connected directly to the input of the analyzing instrument. However, to reduce acoustical reflections from and diffractions around the body of the analyzer, a short length of cable should be used between preamplifier and analyzer. As much as 50 ft. of cable can be used before signal loss or distortion occurs. Refer to Figure 4-2 for permissible frequency limits of available current versus cable length.
If the Preamplifier/Adaptor is to be used as an adaptor (i.e., the prongs not used) with a sound-level meter that uses the microphone-plus-cable capacitance as part of the weighting network (e.g., the GR 1565), the use oi an extension cable will change the weighting characteristics. To compensate for this, a capacitor, C, Figure 6-3, must be added from high to ground (WT2 to pin 3) of the Preamplifier. Also, cable losses will cause the meter to read low by an amount that varies with the cable length. Figure 6-2 shows the value of the compensating capacitor for cable capacitances between 150 and
1500 pF and the loss to be added to the reading of the sound-level meter. This is often a convenient means of extending the upper sound-pressure measuring range of the sound-level meter.
1400
I 4
,.
I 2
.....
Q.
C3
<(1000
~
0 w
..... a: w
(J)
BOO
~
600 w
<D
0
: 400
(.)
z
..... u
200
~
(.)
1\
1/
"
"-
~
1"-
CABLE LOSS
I
CAPACITANCE
10
<D
8~
(J)
(J) g
6w
..J
<(
..
(.)
2
200 400 600 800 1000
CAPACITANCE OF CABLE (p F)
0
1200 1400 1600
Figure 6·2. Compensation required for the capacitance of various extension cables and the corresponding cable loss.
6-2
6.2.4 I nternal Bypass.
To use the Preamp li fier/Adaptor as an adaptor on l y, the output lead can be connected directly to the input by means of a jumper . This will also allow the operator to realize fu ll y the high-level capab ilities of the c~ramic microphones without distortion . No change in frequency respons e is encounte r ed. but a flat loss occurs due to the capacitance l oading of the cab l e. The procedure for bypassing is as fo ll ows: a. Remove the circuitry (on board P/N 1933-4795) from the housing . To do this. push out the pin thro ug h the housing
(see
Figure 6-1) and slide the circuitry out the
INP UT end. The output connector (P/N 1 972-2000) will remain in the housing . b . Carefu ll y unso l der and r emove the coup li ng capacito r s, C1 and C2
(see
Figure
6-3). c. Disconnect the power w ire
(B+) at pin 2. d. Solder an in su l ated wi r e from the input terminal (WT 1 , Figure 6-3) to the output terminal (pin 4). e. S li de the circuitry into the housing unti l the four leads are proper l y in serted in the output connector. The circuitry is keyed to prevent incorrect insertion . Replace the pin removed in step a. f . Place the microphone on the Preamplifie r/Adap tor and use the 1 562 Calibrator and the 15 5 1 , 1561 . or 1933 Sound-Leve l Meter to check the a lt erat i ons. Use a short connecting cab l e to the soundl evel meter.
GROUND
01 R1 TP1 02 R3 R2 (PIN 3)
( a
I
OUTPUT
IN P UT
6-3 . Interior views of the1972-
9600 Preamplifier/Adaptor,
(a) com· ponent side, and
(b) ci r cuit side.
Complete board is
PIN 1933-4796 .
WT2
R7
R5
R4 C2 R6
OUTPUT
(PIN 4) c
C1
C3
8+
(PIN21
INPUT
OUTPUT
6.3
NOISE.
WT1
01
S HIELD
(PIN 11
The in put noise of the 1 972-9600 i s s i mi l a r to that of the 1 560P42 , except that. with the fo r me r , the low-frequency noise is r educed because the protection diodes and
"bootstrapp in g" circuit h ave been om itt ed. For high-capacitance mic r ophones, the
6-3
1/3-octave noise curves for the 1560-P42 (Figure 4-12) are representative of the noise curves for the 1972-9600, except in the 20-100 Hz region, where the latter are several dB lower.
6.4 SERVICE AND MAINTENANCE.
6.4.1
G R Field Service.
The 1972-9600 Preamp\ ifier
I
Adaptor is covered by the warranty stated at the front of this manual.
The warranty attests the quality of materials and workmanship in our products.
When difficulties do occur, our service engineers will assist in any way possible. If the difficulty cannot be eliminated by use of the following service instructions, please write or phone our Serivce Department giving full information of the trouble and of steps taken to remedy it. Be sure to mention the serial, I D, and type numbers of the instrument.
6.4.2 Instrument Return.
Before returning an instrument to General Radio for service, please contact our
Service Department or nearest District Office requesting a "Returned Material" number. Use of this number will ensure proper handling and identification. For instruments not covered by the warranty, a purchase order should be forwarded to avoid unnecessary delay.
6.4.3 Operational Test.
To remove the Preamplifier/Adaptor from its housing, follow the procedure given under "Internal Bypass," para. 6.2.4, above. Re-install the circuitry by reversing this procedure.
A simple de test will indicate whether or not the Preamplifier is operating: a. With the circuitry removed from its housing, resolder the output connection. b. Apply power ( 15
V de) to pin 2 of the output connector. c. The voltage at the FET (01) source should be half the supply voltage plus a few tenths of a volt, as shown in Table 6-1. If it is not, the F ET or 02 or a related component is probably defective. Do not measure the gate voltage on 01 (high impedance). The voltage at TP1, Figure 6-4, should be half of the supply voltage.
- - - - T a b l e 6 - 1 - - - - -
TRANSISTOR VOLTAGES
(With 15-V Supply)
01
D
s
G
14.4
7.8
02
E
B c
15.0
14.4
7.8
6·4
1972-9600 PREAMPLIFIER/ ADAPTOR
ELECTRICAL PARTS LIST
ADAPT OR ASM
DESCRIPTION
REF DES p CONNECTOR ASM
PIN 1972-3100
PART NO. FMC
1972-2000 24655
MFGR PART
1972-2000
NUMBER
R
R
R
R
R
~
R
R
REFDES
1
2
3
PREAMPLIFIER PC BOARD ASM "D "
DESCRIPTION
PIN 1933-4795
PART NO. FMC MFGR
CAP CER SQ
CAP TANT 10
.OOlUF 10PCT 200V
CAP TANT 6.8UF 20PCT 15V EPOXY
UF 20PCT 30V WET
4400-6440
729B2
4450-6401 56289
4450-6320 9J201
PART
NUMBER
B121-A200-X5R-102K
1620 6B5X0015BA 2
MTP 10UF 20PCT 30V
FRONT END AS M
1560-26BO 24655 1560-2680
Q
Q
1
2
TRANSISTOR DN1330
TRANS IS TOR
8210-1260
8210-1204
17856
24655
DN1330
8210-1204
'•
6
7
RES
RES
RES
RES
RES
RES
RES
RES
COMP 2.2
CDMP 10J
COMP
75
COMP 3
.o
G 20PC T 1/8W
K 5PCT l/8W
K OHM
5PCT
K OHM
11
8W
5PC T 118W
CDMP 4.7
COMP 100
CDMP 3.0
CDMP 22
K 5PCT li8W
K 5PC T l/8W
K OHM
5PCT 1/8W
OHM 5PCT 1/8W
6098-822 8
6098-4105
81349
81349
6 098-3 755 81349
6098-2305 81349
6098-2475 81349
6098-4105 81349
6 098-2305 81349
6098-022 5
81349
RCR05G2 28
RCROSG 104J
RCR05G753J
RCR05G302 J
RCR 05G4 7ZJ
RCR05 G104J
RCR05G3 02 J
RCR05G220J
6-5
WT'S USED: 1,2.
LAST
COI'JIPONE.NTS USED ·. C3. R8 Q2.
I
- - - -
I
R"2
100 I<
R4
3K
PI
I
I
WT2.
C:l
•OOI...M.F
WTI
G
Ql
Rt
3K
R~
7oK
RS
4."]1'(
I
L
- - -
- -
- -
-
_2!.1_
TE.
!.2_
HE
0o_
+
<:"2.
,;,.s,u...f'
Rt. lOCK
RB
2.l
B+
(,ND
Figure 6-4. Schematic circuit diagram for the 1972-9600 Preamplifier/Adaptor.
Sr\IIOLD
Type 1560-P40 Preamplifier
Section 7
7.1 INTRODUCTION • . • • . . • • • • .
7.2 SUPPLYING POWER FOR THE PREAMPLIFIER
7.3 OPERATING PROCEDURES
7 .
4 SERVICE AND MAINTENANCE • • • • • .
7 1
7-2
7 3
7-9
Figure 7 1 .
Type
1560-P40 Preamplifier .
7 .
1 INTRODUCTION .
7 .
1 .
1
~r~se .
T he T ype 1 560-P40 Prea mp lifi er (Figure 7-1) is a l ow-no i se amplifier designed to cou ple a micr ophone to a coaxial cab l e without l oss or with a vo lta ge gain of 10 to 1 .
It is also u se ful as a calibrated preamp lifier of signals to analyzers, voltmeters, r eco rders, soundl eve l meters. and o ther such instrum e nt s. With the adaptors su pplied an d availctlle, n ea rly a ll types of connecto rs can be connect ed to the input o f the preamp( ifier .
7 .
1 .
2 Mechanical Description .
The preamplifier is ho used in a 1 in.-diamet e r t u b e that is finished in brushed chrome. A l in c h he xago nal section on one end prev e nts th e preamplifier fr om rolling when it i s p l aced o n a flat surface . When a micr o ph o n e i s mounted direct l y on the input end of th e preamplifier. diffraction and r ef l ec ti o n of acoustic e n ergy are minimized by the sma ll diameter o f the tube. ·
The cartridge o f th e Genera l Radi o 1971-9605 Microphone can be attached directly t o the inp ut end of th e preamplifier.
7.1.3 Electrical Description.
Two pin s of a 3-termina l microphone connecto r a t th e ou tput end of th e preampl i · tier connect to the preamplifier o utp u t ; th e third pin is used to feed
power
t o the circuit.
The active e l emen t s of th e preamplifie r are: one N -<:hanne l , fie ld -effect transistor and two conventiona l transistors. Th e field-effect transistor, spec ially se l ec ted for low noise, is connected as a source fo ll ower and feed s th e two conventiona l transistors, which are connected as a negativ efeedb ac k pair. Th e feedback is switched t o provide a vo lta ge gain of e ith e r 1 or 1 0 .
7-1
7.2SUPPLYING POWER FOR THE PREAMPLIFIER.
7.2.1 General.
The power required by the preamplifier is 15 to 25 volts at 1 or 2 milliamperes.
Types 1558-A, -AP, and -BP Octave-Band Noise Analyzers, and the Type 1564-A
Sound and Vibration Analyzers of current manufacture are designed to provide the power necessary for the Type 1560-P40 Preamplifier from their three-terminal input connectors. The preamplifier can be plugged directly into the connector, or a two-conductor shielded cable, such as those of the Type 1560-P72 series, can
be
used.
Older instruments of the above types, and the Type 1551-C Sound-Level Meter and the Type 1553-A Vibration Meter do not ordinarily supply the required povver, but they can be modified as described below (refer to paragraphs 7.2.2 through 7.2.4).
7.2.2 Power Supplied By Type 1551-C Sound-level Meter or Type 1553-A Vibration Meter.
The Type 1551-C Sound- Level Meter and the Type 1553-A Vibration Meter are not normally provided with this power capability. However, it can be added if required, preferably by a General Radio service facility. For more detailed information about this modification, write or phone the nearest General Radio sales-engineering office.
7.2.3 Power Supplied by Type 1558 Octave-Band Noise Analyzer.
Type 1558-A or -AP Octave-Band Noise Analyzers supplied prior to August, 1964, are not wired to provide power for the preamplifier. These instruments can be modified at any General Radio sales office that includes a service facility, to provide the required power at the input connector. The modification can be made by connecting a lead from the positive end of capacitor C501 to terminal
#2.
of the
Ml KE socket {refer to the Operating Instructions for the Type 1558 Octave-Band
Noise Analyzers, Figure 4-3 and 4-7).
7.2.4 Power Supplied by Type 1564-A Sound and Vibration Analyzer.
Type 1564-A Sound and Vibration Analyzers supplied prior to February, 1965, are not wired to supply power for the preamplifier. It is recommended that these instruments be returned to a General Radio sales-engineering office that includes a service facility, for modification to provide the required povver. However, a modification kit consisting of a lead, a resistor (240 ohms ±5%, 1/2 watt), and a transistor
(Type 2N697) will be supplied without charge by any General Radio sales-engineering office.
Figure 7-2 shows the placement of the resistor and lead. Solder one end of the resistor to terminal
#2.
of the IN PUT socket. Connect the lead from the other end of the resistor to the etched-board lead that connects to the emitter of transistor 0505.
Replace this transistor with the Type 2N697 transistor supplied in the modification kit.
7.2.5 Power Supplied by Type 1568 Wave Analyzer.
The de power to operate the Preamplifier can be obtained directly from the Type
1568 Wave Analyzer. Does not apply to 1568-9000.
7-2
0505 TERMINALS
Figure 7·2. Modification of
Type
1564-A Sound and Vibration Analyzer for use with the preamplifier.
CAUTION
Terminal
#2
is connected to ground (terminal
#1)
on the connectors of some microphones, accelerometers, control boxes, and cables supplied by General Radio prior to January, 1962. If necessary, remove the connection between pins #1 and
#2
before the above connectors are plugged into any other connector that supplies power through pin
#2.
7.3 OPERATING PROCEDURE.
7.3.1
Microphone or Adaptor Attachment.
The cartridge of the Type 1971
-
9p01 lt1icrophone and the 1560-9696 Adaptor can
be
locked to the preamplifier by backing out two shouldered screws against the cartridge or the adaptor
.
Use the following procedure: a. Turn in the two screws (A, Figure 7
-
3). using the hexagonal wrench provided. b. Plug the microphone or adaptor onto the preamplifier so that the red dots
(engraved on the sides of each) are aligned. c. Back out the two screws so that their tips extend through the holes in the microphone or adaptor and their shoulders press firmly against the shell to hold the microphone fi
r
mly and to ground the shell.
7-3
GROUND
LUG
B s
50101
Figure 7-3. Interior view of the preamplifier.
7.3.2 Microphone-Sensitivity Correction.
When a microphone and preamplifier are used in conjunction with a Type 1551-C
Sound-Level Meter, a Type 1558 Octave-Band Noise Analyzer, or a Type 1564-A
Sound and Vibration Analyzer, the effective sensitivity of the microphone is increased.
This increase is brought about because the voltage loss caused by the preamplifier input-capacitance load on the microphone is less than that caused by the inputcapacitance load of the above instruments. Also, when a cartridge from a Type
1971-9606 Microphone Assembly is used, the loss caused by the capacitance of the flexible arm is not present. (The sensitivity given for a 1971-9606 Microphone
Assembly is for the combined microphone cartridge and flexible arm.)
To calibrate a system of microphone, preamplifier, and one of the above-named instruments, a Type 1562 Sound-Level Calibrator is recommended. Alternatively, the correction data given in Table 7-1 can be used to correct the sensitivity value given for the particular microphone being used. Add the correction algebraically to the specified microphone sensitivity value to obtain the effective sensitivity value. This corrected value can then be used to calibrate the measuring instrument, as directed in the
Operating Instructions for the latter. If a Type 1562 Sound-Level Calibrator is used to calibrate the system, the gain of the preamplifier should be set at X1, to prevent its possible overload (see Figure 7-4).
7.3.3 Electrical-Signal Measurements.
Connect the preamplifier to its source of power (refer to para. 7.2) and connect the input signal to the preamplifier by means of the correct adaptor. Set the gain
Microphone
Type 1971-9605
Type 1971-9606
M I CROPHON E-SENSITI VITY
CORRECTION IN DECIBELS
Type 1551-C
Measuring Instrument
Type1558
Type 1564-A
0.9 1.0
1.6
1.4
2.1
7-4
140
X
_j w
>
'j
130
1 -
~-f--r==::
~-
--f-w a:
:0
(f)
:0
::;>
~ w a..
120
g::t
• 0
ON
;
~
&;
..c
110
-o
::;> r--- -
I
L-
\----
!--,...
----t-
- -
..__
100
I
-44 -42
-
- - -
- -
-40
-~
-
-...:.YPE 1560-P40
GAIN~x
I
~ t;rr t--
- - r--r---
-
I-TYPE 1560-P40
-....._
GAIN~xiO
-38
c-=t
~
_- _·
1--
\ - -
I-
- - - -
--
1----1
-36 r--
-34
-
--
-32
t--
-30
---
MICROPHONE SENSITIVITY-dB reI VOLT/ N/m2
I
Figure 7·4. Maximum sound-pressure level that can be measured with a Type 1560-P40 Preampli· tier-and-microphone combination. The sensitivities of Types 1971-9605 and -9606 Microphones will fall between the dotted lines. Allowance is made for a peak-to-rms ratio of 14 dB. For a sine-wave acoustic signal, the maximum level can be increased by 11 dB.
switch (see Figure 7-3) to the desired gain. either X1 or X10, as engraved on the switch.
NOTE
When power is applied to the preamplifier, about one-half minute is required for the input stage to stabilize and for the preamplifier to operate.
With a high-impedance load on the preamp\ ifier, audio-frequency voltage up to 0.5 volt peak-to-peak at X10 gain or 5 volts peak-to-peak at X1 gain can be applied to the preamplifier input.
Because of the low output impedance of the preamplifier, a long cable can be used between the preamplifier and the measuring instrument. At X 10 gain; up to one-half mile of cable can be used; at X1 gain, up to one mile is satisfactory. Figure 7-5 shows the attenuation versus frequency for three different lengths of cable. The fixed loss for each length is caused by the divider formed by the preamplifier output coupling
I
I
0
..
I
I
I
I
0: g
CD
100()-FT CABLE, )(I PREAMPLIFIER GAifll
~
-3 t--
CURVE® IOOO·FT CABLE,
><10
PREAMPLIFIER GAIN
....
I-
I-
-2
-4
r-
CURVE
CURVE
CURVE
@
0
250trFT CABLE, Xi PREAMPLIFIER GAIN
2500-FT CABLE. XIO PREAMPLIFIER GAIN
-5
\-
CURVE® 5000-FT CABLE. XI PREAMPLIFIER GAIN
CURVE® 5000-FTCABLE, XIO PREAMPLIFIER GAifll
0.1
':-..
FREQUENCY-
kHz
1'-
10
IC5J
®
"
....
~
,....,
~
"'
-~
~fz p
I
50
156G.P.tG.3
Figure 7-5. Attenuation of the preamplifier output signal caused by the capacitance of the cable between the preamplifier and the measuring instrument.
7-5
Figure 7-6. Curves showing the maximum output for a maximum distortion of one percent when a long ceble terminated in a high-impedance load is driven. Allowance is made on the maximum sound-pressure level scale for an acoustic waveform having a peak-to-rms ratio of 14 dB. With a sine-wave signal, the maximum sound-pressure level can be increased by 11 dB.
C:
Q>
-150
-130
\.
\.
\.
'\..
-160
10
'
'-...
100 in
I>
~
I""-
1000
--
FREQUENCY c/1
~.l1
I
10,000
F19Ure 7-7. Typicel frequency spectre of internal noise.
/
-
290
-260
-280
~
..,
C: capacitor and the cable capacitance. When a long connecting cable is used, output from the preamplifier may have to be restricted because of the low reactance load of the cable. Figure 7-6 shows cable length versus maximum voltage output at three different frequencies, for a maximum distortion of 1%. The maximum sound-pressure level that should be measured is also shown.
A restricting factor in the use of long cables is the fact that as the length of a cable terminated in a high impedance approaches 1/4 wavelength of the electrical-signal
7-6
10
9 a it
7l1
I w
-'
"' w
VI
<(
6 \
5
J: ll.
4
3
2
';-LOW FREQUENCY
DEGREES LEAD
\
\
1\.
"'
'r--.
....
0
1Hz
).....-
1---"
...... l~k~zz
FREQUENCY IN HERTZ 100kHz
~~~~~Rl~~~~
v
IJ
j
v
)
/
500kHz
l560-P4G.2
Figure 7-8. Phase shift in the 1560·P40 Preamplifier at 0-dB gain. High-i mpedanc:e load.
~ w
VI
~30 ll.
10
0
I Hz
I kHz
7
6
0~
\
\
1\
[\
LOW FREQUENCY
DEGREES LEAD
1\.
~I'
HIGH FREQUENCY
DEGREES LAG-
~
/ lOHz
-
-
-~""'
~I-'
/
10kHz FREQUENCY IN Hz
100Hz
100kHz
500Hz
500kHz
156G.P40.1
Figure 7-9. Phase shift in the 1560·P40 Preamplifier at 20-dB gain. High-impedance load.
frequency, the amplitude and transient response at the output end will be considerably distorted.
Figure 7-7 gives the noise level of the preamplifier in the form of curves of typical values for the en and in generators versus frequency.
Figures 7-8 and 7-9 give the phase shift in the amplifier as a function of frequency.
Normally, the low side of the preamplifier circuit is connected to the shell, which may be grounded by the ground of the measuring system. Occasionally, however, problems arise from multiple ground loops caused by grounds at different points in a system. As an aid in solving such special problems, the grounding connection from the preamplifier circuit to the shell can be disconnected easily. Remove the cylindrical
7-7
tube from the preamplifier (refer to paragraph 7.4.2). Then remove the screw holding the ground lug at the end of the gain switch (see Figure 7-3). Bend the connecting lead so that the lug can not contact the shell or any part of the circuit. Then replace the screw. Also, be sure that the circuit is not grounde9 to the shell by the input or output connector. If cable connections are used, a two-conductor shielded cable for the input and a three-conductor shielded cable for the output are required. The shields must connect to the shell. The low side of the preamplifier circuit connects to terminal #1 of the three-terminal output plug.
7.3.4 Acoustic Measurements.
In acoustic measurements, the preamplifier can be used to increase by 20 dB the sensitivity of the Types 1558-A, 1558-AP, -BP, and 1564 Analyzers. In conjunction with the preamplifier, these instruments can be used for measurements down to a sound-pressure level of 24 dB re .0002 J.Lbar.
The preamplifier is also useful with the Type 1551-C Sound-Level Meter, as well as with the above instruments, when a long cable must be used. The preamplifier eliminates the loss caused by a long cable used directly after a microphone (refer to paragraph 7.3.3).
The 1569 Automatic Level Regulator can also be used with the preamplifier.
Attach the microphone to the preamplifier as described in paragraph 7 .3.1. Connect the preamplifier to its power source and to the measuring instrument (which may also be the power source; refer to paragraphs 7.2.2 through 7.2.5). Slide the gain switch
(see Figure 7-3) to the desired gain, X 1 or X 10, as engraved on the switch. When the gain is X 10, subtract 20 dB from the decibel reading of the measuring instrument to obtain the noise level at the microphone.
When a cable is used to connect them to the measuring instrument, the preamplifier and microphone can be mounted on the Type 1560-9590 Tripod. The measuring instrument and the observer can then be located at the other end of the cable, far enough removed from the acoustic field to have I ittle or no effect on the accuracy of the measurement.
When a short connecting cable, or none at all, is used, the maximum noise level that can be measured without the possibility of overloading the amplifier is given in Figure
7-4. Allowance is made for a peak-to-rms ratio of 14 dB, which is adequate for normal noise.
When a long connecting cable is used, the maximum noise level that should be measured is given in Figure 7-6. The maximum value obtained from the figure will usually be pessimistic for broadband noise measurements, since the high-frequency components of such noise usually are of lower level than the low-frequency components.
NOTE
When the preamplifier-and-microphone assembly is used, particularly when low sound levels are measured, the assembly should be protected from mechanical vibration, such as that caused by rubbing against another object. The vibration is transmitted through the mechanical structure to the microphone, and the resulting electrical signal from the microphone may cause a large error in the measurement.
7-8
For a complete discussion of the techniques of noise measurement, refer to the
General Radio
Handbook of Noise Measurement.
7.3.5 Vibration Measurements.
The preamplifier can be used to advantage with the Type 1553 Vibration Meter and the Type 1564-A Sound and Vibration Analyzer for vibration measurement and analysis. It permits the use of long cables without loss and increases the sensitivity of the measuring instrument by 20 dB.
Attach the Type 1560-9696 Adaptor co the preamplifier as described in paragraph
7.3.1. Plug the vibration-pickup cable into the adaptor. Connect the preamplifier to its power source and to the measuring instrument (refer to paragraphs 7.2.2 through
7.2.5). Slide the gain switch to the desired gain (X1 or X10). If the preamplifier is used at X 10 gain, divide the readings of the measuring instrument by 10. If readings are taken in decibels, subtract 20 dB. Allowance is made for a peak-to-rms ratio of approximately 15 dB. For a sine-wave vibration signal, the maximum g values given can be multiplied by 4.
Table 7-2 lists the maximum vibration acceleration that should be measured when
General Radio vibration pickups are used with the Type 1560-P40 Preamplifier.
The Type 1557-A Vibration Calibrator can be used to calibrate the Types 1560-P52 and -P53 Pickups with either X 1 or X 10 preamplifier gain. The Type 1560-P54 Pickup should be calibrated only with X 1 gain.
7.4 SERVICE AND MAINTENANCE.
7.4.1
Service.
The warranty stated at the front of this book attests the quality of materials and workmanship in our products. When difficulties do occur, our service engineers will assist in any way possible. If the difficulty cannot be eliminated by use of the following service instructions, please write or phone our Service Department, giving full information of the trouble and of steps taken to remedy it. Be sure to mention the serial and type numbers of the instrument.
Before returning an instrument to General Radio for service, please write to our
Service Department or nearest sales-engineering office, requesting a Returned Material
Tag. Use of this tag will ensure proper handling and identification. For instruments not covered by the warranty, a purchase order should be forwarded to avoid unnecessary delay.
- - - - - - - - - - - - - - : T a b l e
7-2--------------
MAXIMUM VIBRATION ACCELERATION
TO BE MEASURED WITH VARIOUS PICKUPS
Pickup
Type 1560-P52
Type 1560-P53
Type 1560.P54
X1 Preamplifier Gain
5.5 g
5.5 g
0.7 g
X10 Preamplifier Gain
0.55 g
0.55 g
0.070 g
7-9
7.4.2 Servicing.
Using the hexagonal wrench provided, screw in the three shouldered screws (B,
Figure 7-3) until the cylindrical tube can be removed from the preamplifier. Figures
7-3 and 7-10 show the locations of the components.
Table 7-3 lists normal voltages from each transistor to ground. Measure the voltages with a vacuum-tube voltmeter and with a battery voltage of 21 volts. A
1
0-percent deviation from the listed values is allowable.
Before making measurements, short-circuit the preamplifier input terminals. Install a resistor of about 1 0 megohms across resistor R
1
01 (see Figures 7-1 0 and 7 -11). If such a resistor is not available, momentarily short-circuit R 101 before any voltages are measured. Do not attempt to measure the voltage from the gate of 0101 to ground without a shunt across resistor R 101.
PREAMPLIFIER
TRANSISTOR VOLTAGES
Transistor
0101
0102
0103
Terminal
DRAIN
SOURCE
GATE
COLLECTOR
BASE
EMITTER
COLLECTOR
BASE
EMITTER
De Volts to Ground
21.0
8.0
8.1
16.6
8.0
7.5
11.5
7.9
7,3
7-10
Figun17-10. Etched-board layout for the Type 1560.P40 PYearnplifiet'.
NOTE
The number shown on the foil side of the board is not the port number for the complete assembly. The assembly number is 1560-2741.
TYPE 1S60-P40 PREAMPLIFIER PARTS LIST
REFOES
1560-P.r.O
ELECTRICAL PARTS LIST
PRE.\MPLIFIE'l ASM
PIN 1560-HOO
DES til IPT ION PART NO.
F~t
!IFGR
PL I 01 INSERT AUDIO 3 CONT MALE
.r.22D-5306 82389
PART
3tl086
Q 101
Q
102
Q 103
TRlNSISTOR 2N3.r.57
TRlNSISJOR PN3391A
TRANSISTOR 2N6008
8210-1082
8210-1292
821D-1291
17856
56289
56289
2N3"o57
PN3391 A
2N60D8
R ll"o liES tOHP 15 OHM SPt T 1 /loW
RCR07Gl SOJ 6099-0155 Bl31o9
791D-0830 2 ... 655 S 101 SWITCH SLIDE 2POS DPOT STEADY
SO 101 SOCKET ASM
156D-1"o00 2'-655
791D-0830
1560-UOO
NUMBER
PC
BOARD
ASM
OESCRJ PT ION REFOES
. t c; c c c c
101 tAP MYLAR .0022UF 2 PCT 200V
102 tAP TANT 22 UF 20PCT 15V
103 CAP TANT 120 Lf' 20PCT lOY
10• ClP TANT 120 Uf 20PCT lOY
105 tAP TANT 120 UF 20PCT lOY
106 ClP
Tl~T
3.3 UF 20PCT 15V
R
R
II
II
II
II
R
II
II
R
R
R ll
101 RES tOMP 1.0 G 20PCT 1/2
102 FACTORY SELECT
103 RES tOIIP 20 K OHM 5PtT 1/ W lO.r. RES COMP 56 K SPCT 1//oll
105 RES COHP 51 K OHM
106 RES tOMP 3.0 K OHH
SPCT 1/"oW
5PCT l /
107 FlCTORY SELECT
108 RES COIIP 150 k 5PtT 1/"oW
109 RES FLM 9.531t
110 FlC TORY SELECT
1 PCT l/811
111 RES COIIP 8.2 k 5PtT lHII
112 RES COHP 6.2 k OHM SPCT l/loll
113 RES CO!IP .r.70
It
5PtT 1/loW
P/N l56D-271ol
PART NO •
FMC
.r.86D--7326
.r..r.SD-5300
/oloS0-5616
•~oSD-5616
...... 50-5616
.... so-.r.60o
....
_.
...
6099-3205
6099-3565
6099-3515
6099-2305
····-····
6099-"olSS
6099-2625
6099-1"o75
56289
56289
56289
56289
56289
56289
8111o9
8l31o9
8l3"o9
813"o9
813"o9
813"o9
MFGR
PART
RCR20Gl08
RCR07G203J
RCR07G56~
RCR07G513J
RCR07C302J
RCR07Gl51oJ
RN550953lf
RCR07G822J
RCR07G622J
RCR07Git7•J
NUMBER
... 1 OP • 0022 UF 2 PCT
1500l27X0010R2
150012 7X001 ORZ
1500127X0010R2
1500H5X001SA2
•value determined by GeDenl Ra41o Laborarory.
7-11
....
N
NOTE UNLESS SPECIFIED
I POSITION OF ROTARY SWITCHES
SHOWN COUN I ERCLOCKWISE
CONTACT NUMBERING OF SWITCHES
EXPLAINED ON SEPARATE SHEET
SUPPLIED 1N INSTRUCTION BOOK
3 REFER TO SERVICE NOTES IN INSTRUC liON ROOI< F'OR VOLTAGES
APPEARING ON DIAGRAM
I
RESISTANCE IN OHMS
K 1000 OHMS M 1 MEGOHM
G •I &IGOHM • 1000 MEGOHMS
6 CAI-'I'.LIII-II>oLt_ vAl Ut_.::> UNI:_ AND
OVER IN PICOFARADS LESS
THAN ONE IN MICROFARADS
0
KNOB CONTROL
0
SCREWDRIVER CONTROL
9 AT ANCHOR TERMINAL
4 RfSISTORS 1t4 WATT
10 TP TEST POINT
ANCHOR TCR/11/NALS 1/SEC A.
T. t-9
Ill
VALVE' OE'T£RM!NE'D
BY
LAh
SO/Of
INPUT
EM§d-BASE
\
COl
-""
'
IU02,Q!03
ORA/N~VRC£
V
eAr£
Q/0/
TRANSISTORS
BOTTOM VIEW
RO
R/03
20/(
R/04
56K
RIOS
511(
A.T.
Rtf!
8.2K
()/0/
C/02
22JIF
+
RIO!
JGfl
I/2W
0!02
R/02 R/09
21'K-!SOK
AJ.8
RIOB
A.T.3
R/06
3K
3
VT
9,53K //BW
*
R/10
39-21'0
!50K
R/07
GY
5
AI.7._-v~--.-----~~------~~---
A.T.2 XJO
C/03 ll'OpF
•
.!11'6K·/,07K
//811'
I
Xi
S/0/
Y£
A.T.5
+
C/04
120)1F
C/06
3.JJJF
Rill
6.2K
R/13
41'0K
R/14
IS
*
Value determined by General Radio Laboratory.
Figure 7-11. Schematic diagram for the Type 1560-P40 Preamplifier.
PL 101
OUTPUT
FEDERAL SUPPLY CODE
FOR MANUFACTURERS
From Defense Logist1cs Agency Microf1che
H4-2 SB 708-42 GSA-FSS H4-2
Ref FMC Column in Parts Lists
McCoy E:lctrns Mt HollvSonnos,P'A 17065
00136
JonesMtg.ChlcdgO,IL 60181
00192
Walsco Elctrns.LosAngeles.CA90018
00194
Welwyn tntntl ,West13ke,Of-i 44145
""'
SchweberEictrns,Westbulg.NY 11590
Aerovox New8edford.MA0274b
00779 AMP lnc,Hdrr~sb~;rg_PA 17105
OHl09
Alden Produ~ts .Brocl,to,'.MA 02413
01121
Allen Bradley ,M,Iwaukee,WI53204
01255
LITton tnds .. 8everly H•lls,CA90211
0128t
01295
01526
TRW,Lawndate,CA90260
Tt .Dall~s.TX
75222
GE .Waynesboro. VA <'2980
01930
Amerock.Rocklord.IL61101
01963 Chcr,.-y Etctr.:.,Waukegan.IL6008!:>
IJ6383
"""'
06743
IJ6795
IJ6915
06928
06978
"'"'
07127
07233
07261
07263
02111
02114
02606
02639
Spectral Elqrns,C•IYoltndusny.CA91745
Ferroxcube,SaugCrtles,NY 12477
Fenwatl Lab,Morton Gro"e,IL60053
GE .Schenectady,NY 12307
02660
02735
Amphenol,8roadv•ew,tL60153
RCA._Somervdle,NJ03876
02768 Fastex ,De,plams,IL60016
03042 Cartertnk,Cambr~dge,MA02142
03508
GE .. Syracuse,NY 13201
03550 VangC~ard E1ctrns .. lngte"'ood.CA90302
03636 GraYburne,Yonkers.NY 10701
03877
Transttron Elctrns ,Wdk~f•eld,MA 01880
03888
KDI Pyrot,tm.Whlppdnv.NJ07981
03911
Clo~rex.,NewYurk.NY 10001
0<009 ArrowHa•l Harttorr:t.CT06106
"'"
05245
05276
05402
05~74
11507
Motorola.,Phoen 1x.AZ85008
Com]Jonent Mig .W Bndgewater,MA 02379
Tansistor Elctrns,Benn,ngton,VT05201
Corcom.,ChlcagO,IL60639
ITT Elctrns .. Pomona,CA91166
ControlsCo.o1Amer,Mel•osePk,tL60160
V1klngtnds.,Cha"worth.CA91311
M624
05748
05820
07387
07595
07699
8arberColm•m.,Rocklurd tL6i101
8arnesMfg,Mansfleld.OH44901
Wakef•eld E:ng.,Wakefletd,MA01880
Pandu•t,TI!lley Pk,IL60477
Truelove & Madean .Waterbu1y CT 06706
Precision Monolith .S~nta Clara,CA 95050
Ctevim.,CievetcndOH44110
WLSStamo,Cievcland,OH 44104
RICh~o Plstc .. Ch,ca(IO,\L 60646
Teledyne Kntcs ,Soland
B~h.CA92075
Aladdin EtC!InS,Ndshville,TN 37210
RossMFiton.,Southanwton,PA 18966
Drg•tran Pasadena.CA91105
EagleS,gnai .. Saraboo.WI!:>3913
Cinch GrdJ.Ih•~ ,CITY ol Industry CA 91744
Avnet.,CulverC•tv,CA90230
Fairchild.,Mountajn View.CA94040
8"tche• ,N.Lo• Ang~tes.CA 90032
AmerSem•cond,ArllngtOn Htt,IL60004
Magnetic Co1e ,Newllurgh,NY 12550
07707
07828
07829
07910
07983
USM Fas 1ener .Sheltun,CT06484
Bod,ne,Bndgeport.CT06605
8odmeEictrc .• ChlcagotL60618
ContDev.ce ,Hawthorno,CA90250
State Labs.NewYork,NY 10003
"'"'
08556
Borg lnst,Delavan,Wt S31t5
Deutsch Fastener ,LosAngales.CA9004FJ
Bell Elctrc.,Ch,~ago,IL 60632
08730
09213
VemalineProd ,Frankt,n Lakes,NJ07417
GE ,Suffalo,NY 14220
09353
C&K Comoonenu.,Wa,enown,MA 02172
09«J8 Star-lron,cs.Georgetown.MA01830
09823
09856
BurgessBattery.,Freepoct.IL61032
Fenwal Etctrn, .Fram1ngham,MA 01701
09922
'""
8urndy.,Norwalk,CT06852
Gtasseal Prod.,Lmden,NJ 07036
ChicagoSwltch .. Chicago,IL60647
11236 CTSot 8erne.,Berne.tN46711
11599
ChandlerEvans.WHartfJrd,CT08101
J1983 Nortron•cs.,Mmneapqlis.MN 55427 t2040 Nationai,SantaCiara.CA90051
12045 ElctrcTranSistor> .. Fiu•h 1nq,NY 11354
12498 Tetedyne.,Mou~ta•n V1ew,CA 94043
12617 Hamt,n,l.dkeM•ti1S.WI53551
12672 RCA .Woodbr~dge.NJ07095
12697 Clarostat.Dov.er,NH03820
""' M•crome,als .• C,tyof Jndust,.-y,CA91744
DicksonEtctrns.Scottsdate.A285252
"'"
13103
Unitrode,Watertown,MA02172
Electrocraft .. Hopkms,MN 55343
TharmalloY .. Oallas,TX 75234
13148
13150
13327
13715
13919
14010
Vogue lmt.Richmond H1II.NY 11418
Vernltron .. Lacon,d,NH03246
Sot1tron D""'ces,TapPan.NY 10983
Fairchitd.,SanRataei,CA94903
Burr Brown ,Tu~son,AZ85706
Andde~ tn<t.,Van Nuys,CA 91406
14195
14196
14332
14433
ElctrcControts.W•Iton,CT06897
American Labs,Fulle<ton.CA92634
Retton ,Arcad•a.CA91006 tTT.,WPalmBeach,FL33402
14482 Watk1ns&Johnson .PatoAtto,CA94304
14608 Corbm.,Berlrn,CT08037
14655
Cornall Oub1lie, ,Newak,NJ 07101
14674 Corn,ngGiass .• Corning,NY 14630
14749 Acop1an ,Easton,PA 18042
14752 Etectrocube,SanGab"ei.CA91776
""' R&G Stoan .. Sun Valtey.CA 91352
Elctrctnst&Spclty ,S 1onaham,MA02180
14936 Genarallllst .. Hicksv 1tle,NY 11802
15238 ITT.,Lawrence,MA 08142
15476 D19ital Equip.Maynard.MA01754
JANUARY 1978
"""
36462
37942
38443
39317
40931
42190
42498
43334
43991
48671
49956
50088
50101
50507
50522
50721
51167
22753
23338
23342
23936
24351
24355
24444
24446
24454
24455
24602
24655
24759
25008
25289
26601
28605
26806
27014
27545
28460
28520
288/5
28959
30043
30646
30874
""'"
31514
31814
31951
32001
33095
33173
34141
34156
34333
34335
34649
18736
18795
18911
19178
19209
19373
19396
18617
'""'
20093
20754
21335
21688
21759
22526
22589
15605
15782
15801
15819
16037
16068
16179
16301
16352
16485
16636
16758
16950
16952
17117
17540
17745
17771
17850
17856
18324
18542
18677
51553
51642
52548
52676
52763
53021
53184
53421
"""
54715
Cutler Hdtntn~r .M•Iwaukee,WI53202
Houston lmt ,Setla1re.TX 77401
. Fellwal flctms
,Fr~m•nghdm,MA
01701
S1ncl~1r& Rush ,St LoU1s.M063111
Spruce P•neM•ca.SpruceP:ne,NC28777 lntntl Dlode .• JerseyC•W.NJ07304
Omm1 Spectra .. Farm,ngton.MI 48024
Astrolab Linden,NJ07036
Codi.Fa,rlawn,NJ07410
Stet ling tnst ,New Hyde PMk,NY i 1040 lnd•JnaG~neraL,Oolesby,IL61348
Delw .. Kokomo,IN46901
PreciSion Dynamics ,Burbank,CA91504
Amer M•cro Devices ,Summerv•lie.SC 29483
ElctrcMuld•ng.,Woonsocket,Ri02895
MohdwkSpnng,SchlllerPark,IL60176
Angstrohm Precsn.,Hagerstown.MD 21740
Smge, ,Somervitte,NJ 08876
Zehex.,Concord.CA94520
SIIICOOFX ,SdntaCiara,CA95054
Slgnetlcs.Sunnyvale,CA94086
New Prod Eng Wabash,IN46992
ScanLe .. EtMonte.CA91731
GomputerD,ode.,S.Fairlawn,NJ07936
Cycon.Sunflyvate.CA94086
Duran 1 .Watertown,WI 53094
Zero,Monson,MAOJ057
GE ,Ga 1nesville,FL32601
Eastron.,llaverhiii,MA01830
Paktron ,VIenna.VA 22180
Cabtron .. Ch•cago,IL60822
LRC Elctrns .. Horseheads,NY 14845
Electrd,lndependence,KS67301
Electlnds .. Murray Hiii,NJ07974
KMC.,LongValley,NJ07853
Fafnir 8e~r,ng .• New 8dt1an,CT 06050
Ray 1heon ,Norwood,MA02062
Lenox Fugle .Watchung.NJ 07060
!Wrg Elctrc>.NewCumberland,PA 17070
Electro Space Fabrctrs,Topton,PA 19562
UID ~lc 1 rcs ,Hollywood,FL 33022
Wavetek,San D•"!Jo,CA92112
Avnet Etctrcs,FranktmPark.IL60131
Pamotor ,6ullng,,am,CA94010 lnd•~na Gnrl Elctrc .Keilsby,NJ 08832
Andtog Dev•e<~• .. Cambndge,MA 02142
General Sem.conq .. Tempe AZ 85281
GE .Schenectady,NY 12305
GE.Syracuse,NY 13201
GE.,Cieveland,OH44112
EMCTechntgy ,Cherry Hiii.NJ08034
Gen Rad. Concord.MA 01 742
Lenox Fugle,SPia•nhetd,NJ07080
Vac111e ,8erkeley,CA94710
EG&G.,Bedford.MA 01730
TnCounty Tube .. Nunda,NY 14517
Omnt Spec[fa.,Waltham,MA 02154
Amencan Zettler ,Costa Mesa,CA 92626
Natlonai,SantaCiara.CA95051
Hartford Universal Bali.,Rocky Hlit.CT06067
HP,PcloAito,CA94304
Heyman Mlg,Ken•lworth,NJ07033
IMC M~gnetics ,Rochester,NH 03867
Hoffman Elctrcs,Et Monte,CA91734
Solrd.Stote Dev.ces,LaM•rada.CA90638
Beckmdn lnst .CedarGrove.NJ07009 tBM.Armonk,NY 10504
Per~nagMagnet•cs,Toledo,OH43609
Sot,dStateScntlc,Montgomef\l•lte.PA t8936
StandfordApptd Engs,CoS!a Mesa.CA92626
AnJtog•c,Wakelleld,MA01880
Tmrdge,PI\tsburgh,PA 15231
Jensen .. Ch•cago,IL60638
SpectrumCnntrol ,Fa1rv1ew,PA 16415
GE .. Owensboro.K¥42301
Koehter.,Marlboro.MA 01752
Sem.ooa .. CostaMesa,CA92626
S•hconGenrl ,Westmlnster,CA92683
AdvancedM1cro Dev,ces ,Sunnyvate,CA94086 lntet .. SantaCiara,CA95051
SollltonDPv•ces.,Jupiter.FL 33458
Con"anta .. Montreat.OUE,CAN
Natoonat Ltd .r...,ontreai,OUE,CAN
Mallory ,lnd•anapol•s,IN46206
Marlm Hockwell.,Jamestown,NY 14701
McG•II Mig .ValpariSo.IN 46383
Honeywell ,Minneapolis,MN55408
Mute •. Ch•cago,tL60638
Nationai.,Melrose.MA02176
New Departure·Hyatt ,Sandusky ,OH 44870
Norma Hoftman.,Stanford,CT06904
RCA .. NeW York, NY 10020
Raytheon .Waltham,MA 02154
Mostek ,Carroltton,TX75006
GHZ Dev1ces.,S.Che1mstord,MA 01824
Micro Networks.,Worcester,MA 01606
Monsanto ,PatoAtto,CA94304
Date1Syslems,Canton,MA02021
Ar,es Elctrcs,Frenchtown,NJ08825
D•abiOSystems.Hayward,CA94545
CentreEng.,StateCollege,:>A 16801
Plessev SantaAna,CA92705
SKF tnds .. Philadelphra,PA 19132
Stet1nerTrush ,Cazenovia, NY 13035
SangamoEI,trc,Spr~nqtield,IL62705
Xc11on ,Latham,NY 12110
Tyton.Mdwaukee,WI53209
Shallcross,Selma,NC 27576
AswcPrecProd,HuntsV•tle,AL35805
Shure Bro• .Ev~ns,un,tL 60202
74199
74445
74545
74861
74868
74970
75042
75376
75362
75491
75608
75915
76005
76149
76241
7638t
76385
76487
76545
78684
76854
77132
77147
Sprague ,North Adams,MA 01241
57771
58553
Stimpson .. Baypc,rt,NY 11705
Supenor Valve
.W~shmgton.PA
15301
59730 Thomas& 8et,s .. E11Zabeth,NJ07207
59875 TRW.Cteveland,0H44117
60399 Tornngton Tomngton,CT06790
61007 Towmen<1.8ra•ntree.MA02184
61637
Un10~ Cdrbide .New York.NY 10017
61864 Un11edCarr Fdst,Boston.MA
63060 V•ctoreen.,Cievetand,OH 44104
63743
Wa~<l
Leondrd ,M!
Vemon
NY 10550
65083 We"'''ghouse.,Btoomt.eld,NJ07003
65092 Wes,on.Newa•k NJ07114
70106 AcushnetCap,Nav, Bedford,MA02742
70109 AdJrns& We<!ldke,Eikhart,tN46514
70417 Chry<ler.,Oe•ro•t,MI 48231
70485 AttdntiC tnd1a RuUber ,Ch1cago,1L60607
70563 Amper~te.,Un unCqy,NJ07087
70611 Ark- I es Sw.tch .Wotertown,MA 02172
70692
70903
71126
71279
71294
71400
71450
8eadCham.,BndgePolt,CT06605
Belden ,Ch•~ago,l L 60644
Bronoun 8ea~on
C~mbndge Therm1onic ,Cambndge,MA 02138
Canf1eld .. CI•hon
Faii;.CT06403
~orge.VA
CTS ,l=lkhart,IN 46514
24422
Bussmann ,St.LouiS,MOb3107
71468
71482
71590
71866
Cannon,LosAngetes,CA 90031
CJare .. th•caqo,IL60645
Centralab,Milwaukee.WI !:>3212
Continental Carbon.,New York,NY
Coto C,),l
.Prov•den~e.RI
02905 71707
71729
71744
71785
Crescent Bux .Phltadel;.>hi3.PA 19134
Ch,Lagu M1n Ldmp.,Chjcago,IL 60640
Cmch.Ch 1cago.tl 60624
Darnell ,Downey,CA90241 71823
72136
72228
EtectromOt!Oe ,W•II•mant•c,CT06226
Con11 1 1ent~l Screw ,New 8edlord.MA 02742
Nytronl<;< ,Berkele~ Hts,NJ 07922
72259
72619
72699
D1al1ght ,Brnoklyn,NY 11237
Genrrallnst ,Ncwark.NJ07104
Dra~e ,Ch•Cd(IO,IL tl0631
72765
72794
72825
Dzus Fastener,WIMtp,NY 11795
Eby ,Phit~d~lph1~.PA 19144
Elastic Stop Nut.,Unlon.NJ01083
72962
72982
73445
Er1e ,E11e,PA 16512
Amp~•ex ElctrCS.Hicksv.Jie.NY 11801
73559
73690
73803
73899
73957
74193
Cad 1ngEtctrc .. Haltfo•d.CTOb110
EICo ReSIStOr,NewYork,NY
Tl ,AttlebOr<>MA01703
JF[) Elcncs.,Brooklyn,NY 11219
Groov·Pin .. R•dgefleld.NJ07657
Heinemann ,Trenton,r<J06602
Ooam N•chots.,Chlcaqo,IL 606l7
Hoto Krom~ .Hartford,CT 06110
Hubbell.Strattor<J,CT08497 lndus~r~al Cndmr,Chi~ago.tL60618
Amphenot ,Danbury.CT06810
Johnson,W3sar.o,MN56093
IRCITRWI ,8urhngton,IA 52601
Kurz Kasch ,Dayton OH 45401
Kuka.Mt Vernun.NY 10551
Lafay~tte
,Syosset NY 11791
Linden ,Prov11ience.RI 02905
Llltelfuse .. DesPia,ns.tl 60016
LordMtg ,Efle PA 16512
Mallory Elctrc.,Deuoit.Mt48204
Maurey ,Chlcago_IL60618
3M Co,St.Paui.MN55101
M•norRubber.81oomt•etd,NJ07003
Millen ,Malden,MA02148
Mueller Elctr.Cieveland.OH 44114
Nat•onatTube.,P,nsburg,PA
Oak lnds ,Crystal Lake,JL60014
Dot Fastener.,Waterbury,CT00/20
Patton MacGuyer.,Provldence,Rt 02905
77166
77263
77315
77339
77342
77542
77630 pass Seymour ,Syracuse NY 13209
P1erce RobertsRubOer ,Trenton,NJ08638
Pt3tt8ros .. Waterbury.CT06720
PoSitive Lockwasher,Newerk,NJ
.. P.,nceton.IN 47570
Ray·o·Vac.,Mad .. on.WI 53703
TRW.,Camden,NJ 08103
77638
78189
78277
Ge~eraltnst ,Bruoklvn.NY 11211
Shakeproof.Eigln.IL60120
Slgmatnst. Bralntree,MA02184
78429 AlrCOSpeer,StMarvs,PA 15867
78488
Stdckpole.,StMdrys.PA 15967
78553
78711
Tmnerman .Ctevetand,OH
Te 1eohontcs .. Huntlngton,N'r 11743
79089 RCA,Harrilon,Nj07029
79136 Waldes Koh,noor .New York,NY 11101
79497
79725
Western Rubber.Gmhen,tN 46526
Wlfemold .. Hartlord,CT06110
79727 Connnental W~rt.Philadetphia,PA 19101
79840 Mallory Con 1rols.,Frankfort,IN46041
79963 Z1er1ck,Mt K1Sco.NY 10549
80009 Tektronlx,8eaverton,OR97005
80030 Prestole Fastener ,Totedo.OH 43605
Vickers.,S 1 Lou1S.M063186
'"""'
80183
Lambda,Metvlile,NY 11746
Spraque ,N.Adams,MA 01247
90211
80251
MntorOta .. Frankl•n Pk,tL60131
Forrn•cd ,Cinc•nnat1,DH 45232
80258 Standard Oii..Laleyette,IN 47902
80294 8oums Labs.,Rivers•de.CA92506
80368 Sylvan•a.,New York,Ny 10017
80431 A•r F•ITer.,MIIwaukee,\\11 !;3218
80563
80740
80756
Hammarlu 1•d.,New York,NY 10010
Beckman lnlt.,f-ullerton.CA92634
TRW Ramsey St lu111S.M0 63166
80694
81030
81073
81143
81312
81349
81350
81483
81741
81831
81840
81860
Pure Carbon ,StMarys.PA 15857 lnt'llnst,Orange.CT06477
Grayhiii.,LdGrange,tL60525 lsolant,te .• s 1,rling.NJ07960
Winchester.,Oakville,CT06779
MF111arySpec 1f•catlom
JomtArmy-NavySpC'Cificat•ons tnt"! Aect•f•er .• EI S"!jundo.CA90245
Ch•cago Lock._Ch•cago,IL60641
F,llror~ ,FIUShlng,NY 11354
Ledex ,Dayton,OH45402
B""Y Wr~ght.,Watertown,MA 02172
82219
82227
82213
Sylv~n•a ,Empor~um.PA 15834
NoAmerPhd,ps,Cheshire,CT06410
IN PaTTern &Model ,LaPort.IN 46350
82389 S>'VI!Chcraft.Ch,cago,tL60630
82567 Reeves Hoffman ,Carl~<le,PA 17013
82647
Metnls & Controls .. Attleboro,MA 02703
82807 M•lwaukee ResiStor ,M,lwaukee,WI 53204
82877
82901
83003
83014
83033
Rotron .. Woodstock,NY 12498 tN General Magne1 ,ValparaiSo,IN 46383
Varo.Garland,TX 75040
Hdltwetl ,Piocenua,CA 92610
MeiS>ner,MtCarmet,IL62863
83056 C~rr Fastener .. Cambr~dge.MA 02142
83186
83259
Victory Eng .. Spr~ngfleld.NJ07081
Parker Seal ,CulverC•tY,CA90231
83330
83361
83587
83594
83740
H HSmlth.,Brooklyn.Ny 11207
BeanngSpclty ,San Franc•sco,CA
SoiJrEictrc,Warren.PA16365
Burroughs,Pia•nfletd.NJ07061
83786
83781
84411
Un•on Carblde.,New York, NY 10017
Mass Engrg.,Qulncy,MA02171
Nat•onat Elctrc•.,Geneva,IL60134
TRW .Ogallala,NB 69153
84835
849/0
84971
85604
86420
86577
86684
86687
Lehigh Metals,C3mbridge,MA 02140
SarkesTarzian ,Btoomington.IN47401
TA Mfg .Los An9e1es,CA 90039
Kepco ,Ftush 1ng,NY 11352
P~yson Callers ,Gurnee,IL 60031
PrecMetal Prod ,Stoneham.MA02180
RCA ,H 8rnson.NJ07029
REC ,New Rochelte,NY 10801
ContEictrcs.Brooklyn,NY 11222
86800
88140
88204
88219
86419
86627
89265
89482
89665
CutlerHamme,.,Lincotn,IL62686
GTE Svlvan•a .. lpsw•tch,MA01938
Gout<l Nat Battery .Trenton NJ06607
Cornell Dub!11er
,Fuqu~y
K&G Mtr ,New York,NY
Vanna,NC 27526
Potter & Brumt,etd.,Prmce,on,tN47671
Hot,zerCabot.,Boston,MA02119
89870
90201
90303
90634
90750
90952
9t032
91146
Un.tedTransformer.Ch•cago,tL
BerkshHeTran•former.Kent,CT06757
Mallory Cap.lnd•anapoh•.IN46206
Mallory Bat ,Tarrytown.NY 10591
Gulton tnds ,Metuchen,NJ08840
Westinghouse .Boston,MA02118
Hardware Prod ,Read1ng,PA t9602
Continental Wire ,York.PA 17405
Cannon.,Salem,MA01970
91210
91293
~\~U
Gerber ,Mishawaka,IN 46544
Johanson .Boonwn,NJ07005
Harm,Melbourne,FL 32901
Augat Bros,Attteboro,MA02703
91596
91637
Chandler,Wethersfield.CT06109
Dale Etctrcs.Columbus.J\IE68601
91862
91719
Etco,WiltowGrove,PA 19090
Generallnst .• Dallas.TX 75220
91836
91916
K•ngs Etctrcs,Tuckahoe,NY 11223
MephrStoToOI.,Hudson.NY 12534
91929
92519
Honeywell ,Freepon.IL 61032
Elactratnsut.,Woodside,Ny 11377
92678
92702
Edgerton Germeshuasen ,Boston,MA02115 tMC Magnet•c•.,Westbury.NY 11591
92739 Ampex ,Redwood C1ty.CA 94063
92966
93332
93346
93618
93916
,.,,.
Hudson Lamo .. Kearny,NJ07032
Sylvan,~
,Woburn,MA01801
Amer Etctrcs Labs,Lansdale,PA 19446
R&C Mfg ,Ramsey,PA 16671
Cramer ,New York. NY 10013
Raytheon .Oumcy,MA02169
WagnerEictrc .. L•vjnqston,NJ07039
Weston ,Art:h•bald,PA 18403
94271
Tel Labs,Manchester,NH 03102
94322
D>ckson .. Ch,cago,IL60619
"""
Magne~ralt .Ch1cago,1L 60630
94800
Atlaslnd .. Brookllne,NH03033
95076
Garde .Cumt>erland.RI 02884
95121
Ouality Comp .St Marys.PA 15857
95146
Alco Elctrcs.Lawlilnce,MA01843
95238
Cont•nental Conn.Woods,de,NY 11377
95275
Vitramon ,8ndgeport,CT06E>01
95348
Gordos.Btoomfleld,NJ07003
95354
Methode,RolllngMe<>dow.JL60008
95794
Amer 8rass.Tomng1on,CT06790
95967 Wocke•ser .. Ch,cago,IL60646
'"'"'
"""
98291
Aerovox H1 O .. Oiean.NY 14760
Microwave Assoc.,Burt,ng,on,MA 01601
M•l11aryStandards
L1nema"er Switch .. Wood•tock,CT 06261
Seatectro.,Mamaroneck,NY 10544
96474
96821
Compar .. Burltngame.CA940t0
North Hills.GienCove.NV 11542
99017 Protect•veCtosures,Bullato,NY 14207
99117 Metavac,Fiush•ng,NY 11386
99313
Var~an,PaloAito,CA94303
99378 Atlee.,Winche>ter.MA 01890
88600 Delevan,E Aurora,NY14052
99934 Renbrandt.,8oston.MA02118
99942 cantraJab.,MIIwaukee,WI53201
7-13
Weatherproof Microphone-Section 8
8.1 PURPOSE. . . . . .
8.2 GENERAL DESCRIPTION
8.3 ACCESSOR I ES . . . .
8.4 PREPARATION FOR USE
8.5 OPERATION
8.6 ROUTINE MAINTENANCE
8.7 SERVICE NOTES AND PARTS LIST
8-1
8-1
8-4
8-6
8-7
. 8-10
. 8-11
8.1 PURPOSE.
The 1945-9730 Weatherproof Microphone System provides uniform performance characteristics, combined with rugged dependab i I ity, under adverse weather conditions.
For instance, operating this system under conditions of 50°C and 99% RH for a period of two weeks will not affect performance.
This Weatherproof Microphone System is particularly well suited for use with GR
1945 Community Noise Analyzer Systems. It performs equally well in high humidity and under very dry conditions.
8.2 GENERAL DESCRIPTION.
The 1945-9730 as shown in Figure 8-1, is a complete weatherproof microphone system for outdoor noise monitoring. It is designed to protect its integral 1560-P42 Preamplifier and.a microphone (not included) in an outdoor environment. The windscreen system protects the microphone from damage and reduces the effect of wind on the noise measurement.
Each operating 1945-9730 system consists of two functional units, the microphone/ preamplifier assembly (See Figure 8-2) with its weatherproof housing and the mast
(See Figure 8-3) with mounting hardware. All components are listed in Table 8-1.
The microphone is not supplied but may be selected from those listed in Table 8-2.
8.2.1 Microphone/Preamplifier and Weatherproof Housing.
Refer to Figure 8-2 for a cutaway drawing that shoyvs all of the components. The outer cover is a boot made of vinyl material. It is held in place by a reusable plastic fastener which is easily removed and reattached.
The protective metal shield (perforated) is threaded and fits securely on the housing assembly. The spike is inserted into the threaded spike holder atop this shield.
0-rings are used at both ends of the adaptor to ensure a waterproof seal. The microphone selected determines the particular adaptor to be used. Only the 1-in. (23.81 mm) microphones require adaptors.
The preamplifier and desiccant cartridge can be easily removed for inspection.
Step-by-step procedures for assembly and disassembly appear in Para. 8.4.5.
8-1
8 2
Figure 8-1. Weatherpt'oof Miaophone 1945 9730 .
NOiSE CONE CAP
~.
I
I
I
MICRDPHDN~'
SPIKE HOLDER-.
'
\
\
r--·
SHIELD
I
BOOT
WIND SCREEN
I
/
(
,:T"""
ADAPTOR
HOUSING ASM.
CLAMP
(
SEAL NUT ASM
,......,..
DESICCANT CARTRIDGE
CABLE
NOTES
1.
P42 PREAMPLIFIER SWITCHES TO BE IN "X I" and
OFF
WITH THE 1945 COMMUNITY NOISE ANALYZER SYSTEM
POSITIONS WHEN USED
2. MAST CLAMPS WILL ACCOMODATE TUBING FROM 1 IN. TO 2 IN. DIA.
(MAST CLAMPS NOT SHOWN)
Figure 8-2. Microphone and Weatherproof Housing Assembly.
8-3
8.2.2 Mast with Mounting Hardware
Figure 8-1 illustrates the mast, with mounting hardware in position to hold the microphone assembly atop the supporting mast. Two cap screws (See Figure 8-3) are used to secure the assembly to the mast (supplied). Two longer cap screws are supplied for use with a 2-in. (50 mm) mast (not supplied).
The system is shipped with a 1 1/4-in. (32 mm) mast. For other needs it is recommended that the user obtain standard TV-type masts and associated hardware.
The shorter screvvs will accommodate 1-1 5/8-in. (25-42 mm) diameter masts and the longer screws 1 1/2-2-in. (40-50 mm) diameter masts.
The microphone can be operated in any oi three fixed positions·. perpendicular to the horizon, parallel to the horizon, and at a 45° angle. A free standing tripod is available (P/N 1560-9590).
Vertical is normally the operating mode for the randomly incident sound field to be expected in the community environment. A random incidence microphone is recommended.
The output cable can be attached to the supporting bracket by the cable clamp.
The bracket assembly is made of heavy-duty cast aluminum that should withstand any climatic conditions likely to be encountered. The 5-ft. mast (supplied) is constructed of heavy-gauge galvanized steel with a resin coating.
8.3 ACCESSORIES.
The following tables I ist the accessories supplied and the accessories available.
Table 8-1
ACCESSORIES SUPPLIED
Description
Adaptor (short), to 1-in. (23.81 mm) Ceramic Microphone
Adaptor (long), to 1-in. (23.81 mm) Electret Microphone
Adaptor, to Tripod Mount
Boot (2 supplied)
Desiccant Cartridge
Instruction Manual
Mast Assembly
0-rings
Windscreen, for 1-in. (23.81 mm) microphone
Windscreen, for 1/2-in. (12.70 mm) microphone
Cap screws, 2, for up to 2-in. (50 mm) mast
G R Catalog No.
1945-6210
1945-6340
1945-6280
1945-7210
1945-9600
1961-0100
1945-1540
5855-6750
1560-7552
1560-7553
7110-0300
Table 8-2.
ACCESSORIES AVAILABLE
Description
Microphones:
Electret-condenser, 1 in., (23.81 mm) random incidence
Electret-condenser, 1 in., (23.81 mm) perpendicular incidence
Electret-condenser, 1/2 in. ( 12.70 mm) random incidence
Electret-condenser, 1/2 in. ( 12.70 mm) perpendicular incidence
Ceramic, 1 in. (23.81 mm)
Windscreen Replacement Kit
Desiccant Kit
Extension cable, 60ft 118.5 m) •
• Extension cables of various lengths are available to fit several types of connectors.
G R Catalog No.
1961-9601
1961-9602
1962-9601
1962-9602
1971-9601
1945-9650
1945-9600
1933-9601
8-4
17 \....
19
18
------1
- - - - 3 g - - - -
1 2 - -
8
11
/
Figure 8-3. Syst e m Components.
8-5
8.4 PREPARATION FOR USE.
8.4.1 Inspection.
Although your 1945-9730 was carefully tested, inspected and· packed for shipping, it is a good practice to examine the outside of the container for any signs of damage.
Notify your carrier of any damage.
8.4.2 Unpecking.
Carefully remove your 1945-9730 from its shipping container. If any component appears to have suffered mechanical damage, notify the car•ier immediately so that a proper claim can be made. Be certain to save all packing material so that the claim adjuster can inspect it as well. As soon as the carrier has completed the inspection, notify your G R Representative.
If the system must be returned, repack it carefully in the original container if possible and return it prepaid to the factory for necessary adjustments.
8.4.3 Equipment Supplied.
Check that all equipment and accessories ordered were received in good condition.
If any accessories are missing, your G R Representative or the factory should be notified immediately.
8.4.4 System Components.
All items are illustrated in Figure 8-3. The numbers refer to the identifiers in the f1gure.
1 Spike- To discourage birds
2 Spike Holder- Threaded to accept spike
3 Boot - External windscreen
4 Boot Clamp - Secures boot to Housing Assembly
5 Shield- Protects microphone and preamplifier
6 Mast Clamp -attaches to mast ( 1 1 /4-in. mast shown)
7 Mast.- mast 1 1/4 inches, 5 feet long
8 Connector- Keyed preamplifier connector
9 Cap Screws- Used with 2-in. mast
10 Output Cable- Connects preamplifier output to analyzer
11 Tripod adaptor - Permits use of the system with the G R Tripod ( 1560-9590).
12 Seal Nut Assembly- Keeps desiccant cartridge and output cable properly positioned
13 Desiccant- Cartridge and insulating pad
14 Preamplifier- Connects to cable ( 10) and indirectly to microplione (17). described in Section 4
15 Microphone Extender - Houses the preamplifier and connects to microphone
16 Microphone- ( 1 /2-in. 12.70 mm) threads to microphone extender
17 Nose Cone Cap - Protective cap used only when microphone is not attached
18 Adaptors- Used with 1-in. (23.81 mm) ceramic and electret microphones
(not identical). Use short adaptor for ceramic and long adaptor for electret.
19 Windscreen- One each for 1-in. (23.81 mm) and 1/2-in. (12.70 mm) microphones
20 Housing Assembly - Encloses the desiccant cartridge and attaches to microphone extender
8-6
8.4.5 System Assembly.
a. Identify all components of the system before beginning the assembly procedure.
Arrange parts in somewhat the same order as that shown in Figure 8-3. Refer also to
Figures 8-1 and 8-2. The numbers in parentheses refer to the identifiers in Figure 8-3. b. Select the output cable (10). Insert the smaller cable connector through the seal nut assembly ( 12). the desiccant cartridge and insulating pad ( 13). Attach connector
(8) to preamplifier ( 14); observe positioning key on connector and preamplifier.
On some models the insulating pad is attached to the housing assembly. c. Set the 1560-P42 Preamplifier gain and polarizing voltage as required. Set 200 V switch OFF tor all G R microphones. Set to ON position when used with air-condenser microphones. Unity gain (X 1) is used with the 1945 system. d. Hold housing assembly (20) in one hand and insert the preamplifier (14) into the large end of the housing. e. Turn the microphone extender upside down to let the center pin drop down. Push the preamplifier (14) forward and thread into microphone extender (15). Thread other end of extender into housing assembly (20). The center pin should protrude about 1/8-in. (3 mm) from the extender. f. Fit insulating pad (if not attached) and desiccant cartridge (13) into the housing assembly (20) and secure with the threaded seal-nut assembly ( 12). g. At the base of the housing (20) pull the cable gently to make a good seal. h. Thread the protective cap ( 17) or a
1
/2-in. microphone ( 16) to the connector on the microphone extender ( 15\. The 1 (2-in. ( 12.70 mm) microphone does not require an adaptor. i. If a 1-in. (23.81 mm) microphone is to be used, install the appropriate adaptor
(18) with 0-rings before installing microphone. (Refer to para. 8.8) j.
Install proper size windscreen (19). k. Thread shield (5) to housing assembly (20). Pull on boot (3) and secure with boot clamp (4). Thread spike (1) into spike holder (2).
I. Secure output cable (
1
0) to bracket (6) with cable clamp as shown.
8.4.6 Disassembly.
This procedure is primarily the reverse of"the assembly procedure. Refer to Figures
8-2 and 8-3 and para. 13.4.5.
CAUTION
Routine maintenance procedures must be performed before the system can be used effectively.
8.5 OPERATION.
8.5.1 Microphone Placement and Orientation.
The placement and orientation of microphones is entirely dependent upon the task to be performed. The directional patterns shown should make this task somewhat less complicated.
8.5.2 Typical Directional Patterns.
Typical directional patterns for the electret-condenser microphones at various frequencies are shown in Figures 8-4 through 8-7. The 1-in. microphones are essentially omnidirectional within about 3 dB to 2kHz and within
4
dB to 6kHz tor the 1/2-in.
(12.70 mm) microphone.
8-7
o• o•
GULAR
0
~90
GRAZING
INCIDENCE
180°
Figure 8-4. Typical directional response patterns for the weatherproof microphone assembly with 1-in. microphone (lower frequencies). o•
8-8 o•
GULAR
0
~90
GRAZING
INCIDENCE
Figure 8-5. Typical directional response patterns for the weatherproof microphone assembly with 1-in. microphone (higher frequencies).
o·
+---
90
0
GRAZlNG
INCIDENCE lBO"
Figure 8-6. Typical directional response patterns for the weatherproof microphone assembly with %-in. microphone (lower frequencies). o• o•
GULAR
+---
90
.
GRAZING
INCIDENCE lBO"
Figure 8-7. Typical directional response patterns for the weatherproof microphone assembly with %-in. microphone (higher frequencies).
8-9
8.6 ROUTINE MAINTENANCE.
This weatherproof Microphone System requires virtually no routine maintenance except the occasional inspection of the desiccant cartridge and system calibration.
8.6.1 Desiccant.
The desiccant cartridge helps to keep the system dry by absorbing moisture. This cartridge should be inspected periodically, as dictated by weather conditions. In dry climates an inspection need not be made more frequently than twice a year, however, in a humid climate, an inspection may be required as often as once each month.
A blue color in the cartridge window indicates a satisfactory condition. When the desiccant color turns pink, it has absorbed a maximum amount of moisture and must be removed.
The desiccant can be rejuvinated by baking the cartridge in an oven at 50°C (122°F) until it turns blue. This process can take as long as 48 hours.
CAUTION
Oven temperatures of 75°C (167°F) and above can cause softening and deformation of desiccant cartridge.
8.6.2 Inspection of Desiccant Cartridge.
a. Simply grasp the housing assembly (near boot clamp) with one hand and unscrew the base. This exposes the cartridge. b. Observe that the desiccant, which can be seen through the clear plastic inspection window, is basically blue in color. A pink color indicates that the desiccant is saturated with moisture and is no longer effective. This should be replaced or rejuvinated as detailed in para. 8.6.1.
8.6.3 Calibration Procedures.
This procedure should be performed during initial installation and whenever it is suspected that the system may not be operating at peak efficiency.
Many us.ers, however, routinely calibrate before and after every measurement. a. This system should be calibrated to a sound-level meter or analyzer, using accepted acoustic calibration procedures and a sound-level calibrator (GR Type 1562 or equivalent). b. Before the 1562 calibrator can be placed on the system microphone, the boot, the perforated shield, and the windscreen must be removed. The selected microphone must be attached to the preamp! ifier and the preamp I ifier GAIN and polarizing voltage switches must be set to accommodate the levels being measured. Refer to para. 4.2.4 for a detailed description of preamplifier adjustments. c. Adjust the microphone sensitivity of the analyzer (to which the microphone is connected) for an indication which corresponds to the output level from the calibrators
·(114dBforGR 1562). d. Acoustic calibration should be performed to verify that the system is operating properly. Refer to analyzer instructions for additional details.
8.6.4 Typical System Calibration Procedure.
A typical analyzer-microphone combination (GR 1945 Community Noise Analyzer) calibration procedure is presented here for reference purposes only.
8-10
Turn on the 1945 Analyzer and proceed: a. Set the MIC/AUX switch to MIC and WEIGHTING to FLAT. b. Press the DISPLAY LEVEL button. c. Using a GR 1562 or 1567 Sound-Level Calibrator, supply the microphone with
1-kHz sound as described in the calibrator instruction manual. d. Determine whether the calibrating level should be nominal (114 dB) or, perhaps, a small correction is required for temperature or atmospheric pressure. (Refer to the calibrator instruction manual.) e. Set the 1945 CAL adjustment, using the screwdriver supplied, for the corresponding DISPLAY reading. f. Remove the calibrator and press DISPLAY OFF.
The complete 1945 Community Noise Analyzer System is described in G R publication 1945-0100.
8.7 SERVICE NOTES AND PARTS LIST.
Whenever trouble is suspected with an analyzer system using the weatherproof microphone, an operation check should be performed to ensure that the analyzer is operating properly. Reference to the analyzer instruction manual should provide th~ information needed to verify performance.
After it has been determined that the microphone system is at fault, reference should be made to Section 4. This section deals with the 1560-P42 preamp! ifier, the heart of the Weatherproof Microphone System.
When the trouble is with the microphone itself, an instrument calibration check should be performed with another microphone (preferably one known to be operating properly).
If replacement or repair of the microphone is indicated, contact your nearest G R repair facility.
This section (front) also provides a complete parts list of replaceable components of the microphone system.
8.8 WEATHER SEAL
If the 1-in. microphone is a ceramic unit, a seal is needed to exclude moisture from the interior of the microphone-extender/preamplifier assembly.
Check to see if the base adaptor has a .040-in. dia. hole drilled through it near the center terminal. If not, then this hole must be drilled before proceeding with the next step. (Remove microphone from adaptor before drilling).
To seal interface between the microphone and adaptor, free the lock-screws and separate the units, without disconnecting the leads. Apply a continuous bead of silicone sealant (Silastic 731 RTV or equivalent) around the adaptor flange as shown. Reassemble adaptor to microphone and secure lock-screws. Wipe off sealant that has squeezed out of joint. Apply sealant over lock screws and let cure per instructions for sealant.
8-11
1945-9730 Weatherproof Microphone System
PARTS LIST
Weatherproof Housing Assembly 1945-3210
Item
Shield Assembly
Clamp, Housing Assembly
Seal Nut Asm
Microphone Extender A:m
Housing Asm
Clamp, Mast
Clamp, Mast (w/cable clamp holes)
Nose Cone Cap
Pad, Foam
Cable Clamp
Spike
Clamp, Insulated
Screw Cap 0.190-32, 0.500 SS (2 required)
Screw Cap 0.250-28,0.750
Screw Cap 0.250-28, 1.000
Screw Cap 0.250-28, 2.000 (2 required)
Assembly, Mast
Adaptor 1-in. Cer.
Adaptor Tripod
Adaptor 1-in. Elect.
"0" Rings, 0.875 x 0. 750 x .062 (4 required)
Preamplifier, Complete (Detailed parts information can be found elsewhere in the publication.)
BEAD HERE..,..,.,_
Part No.
1945-1560
1945-1500
1945-1220
1945-2000
1945-2010
1945-5011
1945-5021
1981-6060
1945-7220
1945-8560
1945-6290
4320-1200
7110-1899
7110-0175
7110-0210
7110-0300
1945-1540
1945-6210
1945-6280
1945-6340
5855-6750
1560-9642
HOLE
'
--
Figure 8-8. Weather Seal Adaptor detail.
-------
GenRad
300 BAKER AVENUE, CONCORD, MASSACHUSETTS 01742
ATLANTA 404 394-5380 • BOSTON 617 646-0550
CHICAGO 312 992-0800 • DALLAS 214 234-3357
DAYTON 513 294-1500 • LOS ANGELES 714 540-9830
NEW YORK <N. Y.l 212 964-2722, <N.J.) 201 791-8990
SAN FRANCISCO 408 985-0662 • WASHINGTON, DC 301 948-7071
TORONTO 416 252-3395 • ZURICH <Oll
55
24 20
Printed <n
U.S.A.
300 Baker Avenue, Concord, MA 01742
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