McIntosh-C504-Owners-Manual
THE MclNTOSH C 504 STEREO PREAMPLIFIER
Reading Time: 30 Minutes
Price: $2.00
VARIOUS REGULATORY AGENCIES REQUIRE THAT WE BRING THE FOLLOWING
INFORMATION TO YOUR ATTENTION. PLEASE READ IT CAREFULLY.
WARNING: TO PREVENT FIRE OR SHOCK
HAZARD, DO NOT EXPOSE THIS UNIT TO
RAIN OR MOISTURE.
The Mcintosh you have purchased is a Model
C 504. It has a serial number located on the rear panel
of the chassis. Record that serial number here:
Serial Number
The model, serial number and purchase date are
important to you for any future service. Record the
purchase date here:
Purchase date
Upon application, Mcintosh Laboratory provides a
Three-Year Service Contract. Your Mcintosh authorized Service Agency can expedite repairs when you provide the Service Contract with the instrument for repair. To assist, record your Service Contract number
here:
Service Contract Number
Your C 504 Stereo Preamplifier
will give you many years of pleasant and
s a t i s f a c t o r y p e r f o r m a n c e . If you
have any q u e s t i o n s , please c o n t a c t :
Contents
CUSTOMER SERVICE
Mcintosh Laboratory Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-3512
INSTALLATION
HOW TO CONNECT AND
BACK PANEL INFORMATION
FRONT PANEL INFORMATION
AND USE OF CONTROLS
PERFORMANCE LIMITS
PERFORMANCE CHARTS
TECHNICAL DESCRIPTION
BLOCK DIAGRAM
Take Advantage of 3 years
of Contract ServiceFill in the Application NOW.
2, 3
4
6, 7
8
9
10
12, 13
MclNTOSH THREE YEAR SERVICE CONTRACT
An a p p l i c a t i o n for A T H R E E YEAR SERVICE C O N T R A C T is i n c l u d e d w i t h t h i s m a n u a l .
d l i n g is not covered by the SERVICE
CONTRACT.
The t e r m s of the c o n t r a c t are:
1. M c i n t o s h will
p r o v i d e all
parts,
m a t e r i a l s and labor needed to return the
m e a s u r e d p e r f o r m a n c e of the instrument to the o r i g i n a l p e r f o r m a n c e l i m i t s .
The SERVICE C O N T R A C T does not
cover any s h i p p i n g c o s t s t o and f r o m
the authorized service a g e n c y or the
factory.
4. The SERVICE C O N T R A C T is issued to
you as the o r i g i n a l purchaser. To protect you from m i s r e p r e s e n t a t i o n , this
c o n t r a c t c a n n o t be transferred to a sec o n d owner.
5. To receive the SERVICE CONTRACT,
your p u r c h a s e must be made from a
M c i n t o s h f r a n c h i s e d dealer.
2. Any M c i n t o s h authorized service agency
will repair M c i n t o s h i n s t u r m e n t s at normal service rates. To receive service
under the t e r m s of the SERVICE C O N TRACT, the SERVICE C O N T R A C T CERTIFICATE m u s t be p r e s e n t e d w h e n the
instrument is taken to the service agency.
6. Your c o m p l e t e l y f i l l e d in a p p l i c a t i o n for
the SERVICE C O N T R A C T must be
p o s t m a r k e d w i t h i n 30 days of the date
of p u r c h a s e of the i n s t r u m e n t .
7. To receive the SERVICE CONTRACT, all
i n f o r m a t i o n on the a p p l i c a t i o n must be
filled in. The SERVICE CONTRACT will
be i s s u e d w h e n the c o m p l e t e l y filled in
a p p l i c a t i o n is received by M c i n t o s h
Laboratory Incorporated in Binghamton,
New York.
3. A l w a y s have s e r v i c e d o n e by a
M c i n t o s h a u t h o r i z e d service a g e n c y . If
the i n s t r u m e n t is m o d i f i e d or d a m a g e d
as a result of u n a u t h o r i z e d repair, the
SERVICE C O N T R A C T will be c a n c e l l e d .
Damage by improper use or m i s h a n -
Copyright 1980
by Mcintosh Laboratory Inc.
-1-
mended minimum space for installation is 15 inches
(38.1 cm) deep, 17 inches (43.2 cm) wide, and 4 ½ inches (11.4 cm) high.
To install the instrument in a Mcintosh cabinet,
follow the instructions that are enclosed with the
cabinet. For any other type of installation follow
these instructions:
1. Open the carton and remove the PANLOC
brackets, hardware package, and mounting template
from the carton. Remove the C 504 from its plastic
bag and place it upside down on the shipping pallet;
unscrew the four plastic feet from the bottom of the
chassis.
2. Mark the cabinet panel.
Place the mounting template in the position on the
cabinet panel where the instrument is to be installed,
and tape it in place. The broken lines that represent
the outline of the rectangular cutout also represent
the outside dimensions of the chassis. Make sure
these lines clear shelves, partitions, or any equipment. With the template in place, first mark the six A
and B holes and the four small holes that locate the
corners of the cutout. Then, join the four corner markings with pencil lines, using the edge of the template
as a straightedge.
The PANLOC system of installing equipment conveniently and securely is a product of Mcintosh
research. By depressing the two PANLOC buttons on
the front panel, the instrument can be locked firmly in
place or it can be unlocked so that the chassis can
slide forward, giving you easy access to the top and
rear panels.
3. Drill Holes.
Use a drill with a 3/16 inch bit held perpendicular to
the panel and drill the six A and B holes. Then, using a
drill bit slightly wider than the tip of your saw blade,
drill one hole at each of two diagonally opposite corners. The holes should barely touch the inside edge of
the penciled outline. Before taking the next step, make
sure that the six A and B holes have been drilled.
The trouble-free life of an electronic instrument is
greatly extended by providing sufficient ventilation to
prevent the buildup of high internal temperatures that
cause deterioration. Allow enough clearance so that
cool air can enter at the bottom of the cabinet and be
vented from the top. With adequate ventilation the instrument can be mounted in any position. The recom-
4. Saw the Panel Cutout.
Saw carefully on the inside of the penciled lines. First
make the two long cuts and then the two short cuts.
After the rectangular opening has been cut out, use a
file to square the corners and smooth any irregularities in the cut edges.
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5. Install the Mounting Strips.
In the hardware package you will find two mounting
strips, four 6-32 x 1-1/4 inch fillister head screws and
two 4-40 x 1-1/4 inch flat head screws. These are long
enough for any cabinet panel thickness up to one
inch.
The screws pass through the PANLOC bracket flange,
the cabinet panel, and then through the mounting
strips previously mounted.
7. Install the Instrument.
Guide the AC power cord through the panel opening
to the back of the cabinet; then, slide the instrument
into the opening carefully so that the rails on the bottom of each side of the chassis engage the tracks on
the mounting brackets. Continue to slide the instrument into the cabinet until it is stopped by the adjust
position latches. Press the latches inward, this permits the instrument to slide into the cabinet until its
front panel is flush with the cabinet panel. Depress
the PANLOC buttons at the lower left and right corners of the instrument panel to lock the unit firmly in
the cabinet. Depressing the PANLOC buttons again
will unlock the instrument so that it can slide forward
to the adjust position; if you press inward on the adjust position latches then you can remove the instrument from the cabinet.
Starting at the right-hand side of the panel, insert a
4-40 x 1-1/4 inch flat head screw into the center hole in
the panel, marked B on the template. On the back of
the panel, align a mounting strip with the holes in the
panel and tighten the screw until the screwhead is
pulled slightly into the wood.
Repeat this procedure to attach the mounting strip
to the left side of the panel.
6. Attach the PANLOC Brackets.
Using two of the 6-32 x 1-1/4 inch fillister head screws
in the A holes on each side, attach the PANLOC
brackets to the cabinet panel; the short flange is
mounted against the front (face) of the cabinet panel.
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How to Connect and
Back Panel Information
Refer to the d r a w i n g on page 5.
Rear panel input j a c k s are provided for a stereo
high level source (AUX), 2 stereo t u r n t a b l e s (PH 1 and
PH 2), 2 stereo tape recorders (TAPE 1 and TAPE 2),
and a stereo tuner.
Rear panel o u t p u t j a c k s are provided to feed 2
stereo tape recorders (TAPE 1 and TAPE 2), and a
stereo power a m p l i f i e r (MAIN).
C O N N E C T I N G TO POWER AMPLIFIERS
C o n n e c t the j a c k s labeled "OUTPUTS M A I N " to the
input of a stereo power amplifier. The Left MAIN jack
is c o n n e c t e d to the left a m p l i f i e r input jack. The Right
M A I N j a c k is c o n n e c t e d to the right a m p l i f i e r input
jack.
A Front panel h e a d p h o n e j a c k is provided w h i c h is
fed by an a m p l i f i e r in the C 504.
C O N N E C T I N G TURNTABLES
C o n n e c t the cable f r o m the left c h a n n e l of the turntable into the INPUT PHono 1 Left j a c k . C o n n e c t the
cable f r o m the right c h a n n e l of the t u r n t a b l e into the
INPUT PHono 1 Right j a c k . The C 504 has s h o r t i n g
plugs in the P h o n o 2 i n p u t s to prevent u n w a n t e d
noise. Remove the s h o r t i n g plugs f r o m the input j a c k s
only w h e n they are to be used. For a s e c o n d t u r n t a b l e ,
c o n n e c t PHono 2 in the same way, after r e m o v i n g the
s h o r t i n g plugs.
C O N N E C T I N G PROGRAM SOURCE GROUNDS
A single G R O U N D post is provided to w h i c h
g r o u n d s for t u r n t a b l e s , record changers, tape decks,
etc. are c o n n e c t e d . To prevent h u m p i c k u p , the left
and right program cables and the ground wire from
that source s h o u l d be w o u n d or t w i s t e d together.
Make sure the g r o u n d wire does not make any conn e c t i o n to the s h i e l d s of the left and right program
cables b e t w e e n the source and the input of the C 504.
C O N N E C T I N G TAPE RECORDERS
To Record:
C o n n e c t a cable from the OUTPUT TAPE 1 Left j a c k
to the left high level input of the tape recorder. Connect a cable from the OUTPUT TAPE 1 Right j a c k to
the right high level input of the tape recorder. Connect a s e c o n d recorder in the s a m e manner to the
OUTPUT TAPE 2 j a c k s .
AC POWER OUTLETS
There are 4 black AC power o u t l e t s , and 2 red AC
power o u t l e t s . The AC power to the black outlets is
c o n t r o l l e d by the front panel s w i t c h . Use these
o u t l e t s for a power a m p l i f i e r , tuner, tape recorders,
etc. The red r e c e p t a c l e s are on at all t i m e s . Use the
red o u t l e t s for t u r n t a b l e s or record changers. Turnt a b l e s are p r o t e c t e d by this arrangement. It is
necessary to turn off a t u r n t a b l e or record changer
w i t h its o w n A C power s w i t c h .
To P l a y b a c k / M o n i t o r :
C o n n e c t a cable f r o m the left c h a n n e l o u t p u t of a
tape recorder to the TAPE INPUT 1 Left jack. C o n n e c t
a cable from the right c h a n n e l o u t p u t of a tape
recorder to the TAPE INPUT 1 Right jack. C o n n e c t a
s e c o n d recorder in the s a m e manner to the TAPE INPUT 2 j a c k s .
C O N N E C T I N G A STEREO TUNER
C o n n e c t a c a b l e f r o m the left tuner o u t p u t to the L
TUNER INPUT jack. C o n n e c t a cable f r o m the right
tuner o u t p u t to the R TUNER INPUT jack.
C O N N E C T I N G AUX
C o n n e c t the left c h a n n e l cable f r o m any high level
source (tuner, TV set, tape recorder, etc.) to the INPUT
AUX left jack. C o n n e c t the right c h a n n e l cable to the
INPUT AUX Right jack.
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LEFT
SPEAKER
RIGHT
SPEAKER
TAPE RECORDER
#1
POWER
AMPLIFIER
AC POWER TO
TUNER, TAPE RECORDERS,
POWER AMP, ETC.
AC POWER
TO TURNTABLE
FM ANTENNA
TURNTABLE #1
TUNER
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TURNTABLE #2
TAPE RECORDER
#2
Front Panel Information and
Use of Controls
INPUT SELECTOR
The four p o s i t i o n
INPUT
SELECTOR
c h o o s e s the i n p u t
program selected.
The INPUT SELECTOR is t u r n e d t o :
AUX:
output
high level program source requiring flat
c o n n e c t e d to the Aux input j a c k s to the
put stage. Such a source c o u l d be
recorder, a t e l e v i s i o n set. etc.
The C 504 is d e s i g n e d so it may be used w i t h t w o
tape recorders. The four center p u s h b u t t o n s on the
front panel c o n t r o l the signal to and from these
recorders.
They
permit
playback of either
recorder, m o n i t o r of either recorder as recordings are
being made, or c o p y i n g of tapes from one recorder to
a n o t h e r w h i l e l i s t e n i n g to a separate program.
C o n n e c t s the
from
any
amplification
h i g h level ina n o t h e r tape
MONITOR TAPE 1 p u s h b u t t o n out: The program
source as s e l e c t e d by the INPUT SELECTOR is fed to
the power a m p l i f i e r s and heard through the loudspeakers. P u s h b u t t o n in: Signal from a tape recorder
p l u g g e d into TAPE 1 IN is fed to the power amplifiers
and heard t h r o u g h the loudspeakers.
TUNER: C o n n e c t s the o u t p u t f r o m an AM or FM
tuner to the high level input stage. In this p o s i t i o n the
C 504 has flat a m p l i f i c a t i o n .
MONITOR TAPE 2 p u s h b u t t o n : F u n c t i o n s similarly
to MONITOR TAPE 1 for a s e c o n d tape recorder.
IMPORTANT: W h e n the C 504 is operated with
either MONITOR p u s h b u t t o n at the in p o s i t i o n , the
p r o g r a m heard w i l l be that f r o m the tape recorders only. Signal f r o m any other source will not be heard. To
hear any other source, make sure the MONITOR
p u s h b u t t o n s are OUT.
PHono 1: C o n n e c t s the o u t p u t of a m a g n e t i c p h o n o
c a r t r i d g e p l u g g e d i n t o P H o n o 1 to the p h o n o a m p l i f y ing stages. The response of these s t a g e s has been
shaped to precisely c o n f o r m to RIAA s t a n d a r d s .
PHono 2: Same as P H o n o 1 for a s e c o n d t u r n t a b l e .
The MONITOR s w i t c h e s are m e c h a n i c a l l y int e r l o c k e d to prevent s i m u l t a n e o u s m o n i t o r i n g from
t w o tape recorders. If one b u t t o n is at the in position,
it must be p u s h e d again to release it to the out posit i o n before the other b u t t o n can be pushed.
PUSHBUTTONS
TAPE COPY T1
T2 p u s h b u t t o n out: The program
source s e l e c t e d by the INPUT SELECTOR is fed to the
input of tape recorder 2. P u s h b u t t o n in: C o n n e c t s the
o u t p u t from tape recorder 1 to the input of tape
recorder 2 w i t h o u t a f f e c t i n g the program being heard
f r o m the speakers. In this p o s i t i o n a copy of the prog r a m on tape recorder 1 can be made on tape recorder
2. To m o n i t o r the original use MONITOR TAPE 1
POWER O N : The POWER ON p u s h b u t t o n energizes
the C 504 c i r c u i t s and c o n n e c t s power to the b l a c k AC
power o u t l e t s on the rear panel.
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pushbutton and to monitor the copy use MONITOR
TAPE 2 pushbutton.
left...turning the c o n t r o l to the left a c c e n t s the left
c h a n n e l by r e d u c i n g the right channel o u t p u t .
TAPE COPY T2
T1 pushbutton out: The program
source selected by the INPUT SELECTOR is fed to the
input of tape recorder 1. Pushbutton in: Connects the
output from tape recorder 2 to the input of tape
recorder 1 without affecting the program being heard
from the speakers. In this position a copy of the program on recorder 2 can be made on recorder 1. To
monitor the original use MONITOR TAPE 2 pushbutton and to monitor the copy use MONITOR TAPE 1
pushbutton.
right...turning the c o n t r o l to the right a c c e n t s the
right c h a n n e l by r e d u c i n g the left channel output.
The LOUDness c o n t r o l (small center knob) increases both bass and treble f r e q u e n c i e s of both
c h a n n e l s as it is t u r n e d c l o c k w i s e . A d j u s t m e n t of the
LOUDness c o n t r o l a l l o w s life-like frequency balance
w h e n playing m u s i c s o f t l y . Its c o n t o u r is the same,
regardless of the p o s i t i o n of the v o l u m e c o n t r o l . This
c o n t o u r is a c c u r a t e l y m o d e l e d after the family of
" E q u a l L o u d n e s s " curves i d e n t i f i e d by Fletcher and
M u n s o n . The flat response p o s i t i o n of the c o n t r o l has
a detent for easy reference.
MONO: The MONO pushbutton switches the audio
circuits from stereo mode to MONO. The program
heard will be monophonic. The TAPE OUT jacks are
not affected by the MONO pushbutton.
The l o u d n e s s c i r c u i t r y is c o m p l e t e l y independent
of the v o l u m e c o n t r o l . Therefore, any desired amount
of c o m p e n s a t i o n can be introduced regardless of
volume control position.
EQUALIZER FREQUENCY CONTROLS
Each of three EQUALIZER FREQUENCY controls
modifies upward or downward the tone balance of a
band of frequencies centered on the frequency marked above the control. The flat position of the control
has a detent for easy reference. Each control provides
12 dB boost or cut at the specified center frequency.
V O L U M E CONTROL
The V O L U M E control is a p r e c i s i o n step
control manufactured
for M c i n t o s h Laboratory. It has 32 steps
w i t h a 70 dB range,
plus v o l u m e off. Left
and
right
channel
t r a c k i n g are w i t h i n
1 dB. This e x t r e m e accuracy is obtained through
s p e c i a l e l e c t r o n i c a l l y c o n t r o l l e d resistance element
t r i m m i n g . T r a c k i n g accuracy is permanently maintained and o p e r a t i o n is noise free.
Use the EQUALIZER FREQUENCY c o n t r o l s to
modify the s o u n d and tone b a l a n c e of p r o g r a m
material. Here are s o m e s u g g e s t i o n s f r o m w h i c h to
start:
Problem
Equalizer Correction
Bass t o o weak
Raise 30
Male vocalist needs r e i n f o r c i n g
Raise 30
H u m on p r o g r a m
Reduce 30
Female v o c a l i s t r e i n f o r c i n g
Raise 750
V i o l i n s , t r u m p e t s dull
Raise 750
Drum " b r u s h e s " not a u d i b l e
Raise 10 K
Hiss and/or noise on p r o g r a m
Reduce 10 K
H E A D P H O N E JACK
A H E A D P H O N E jack is provided to drive low impedance d y n a m i c h e a d p h o n e s from an internal power
amplifier.
BALANCE and
LOUDness
The
B A L A N C E and
LOUDness c o n t r o l s are
c o n c e n t r i c . The BALANCE control
(large
outer knob) a d j u s t s for
equal v o l u m e of either
the left or right channels. The v o l u m e of the c h a n n e l s can be varied
relative to each other w i t h o u t a f f e c t i n g their c o m b i n ed v o l u m e .
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Performance Limits
Performance Limits
P e r f o r m a n c e l i m i t s are the m a x i m u m d e v i a t i o n f r o m
perfection p e r m i t t e d for a M c i n t o s h i n s t r u m e n t . We
promise you that w h e n you p u r c h a s e a new C 504
from a M c i n t o s h F r a n c h i s e d dealer it will be c a p a b l e
of p e r f o r m a n c e at or e x c e e d i n g t h e s e l i m i t s or you
can return the unit and get your money back.
M c i n t o s h is the only m a n u f a c t u r e r that makes t h i s
statement.
OUTPUT I M P E D A N C E
Main Out
Headphone
Tape Out
POWER REQUIREMENT
120 V o l t s 50/60 Hz, 25 W a t t s
SEMI
15
14
11
11
DISTORTION
0.02% m a x i m u m at 2.5V o u t p u t f r o m
20 Hz to 20 kHz
INPUT SENSITIVITY AND GAIN
Input to Main Out
Phono 1 and 2
2.2mV in for 2.5V out
(61.1 dB gain at 1 kHz)
Tuner, Tape 1 and 2,
250mV in for 2.5V out
Aux
(20 dB gain at 1 kHz)
Input to Headphone Out
2.2mV in for 750mV out
Phono 1 and 2
(50.7 dB gain at 1 kHz)
Tuner, Tape 1 and 2,
250mV in for 750mV out
Aux
(9.5 dB gain at 1 kHz)
Input to Tape Out
2.2mV in for 250mV out
Phono 1 and 2
(41.1 dB gain at 1 kHz)
Tuner, Tape 1 and 2,
250mV in for 250mV out
Aux
(0 dB gain at 1 kHz)
INPUT I M P E D A N C E
Phono 1 and 2
Tuner, Tape 1 and 2,
Aux
than 200W (to operate
5kW or greater)
GENERAL I N F O R M A T I O N
RATED OUTPUT LEVELS
M a i n Out
2.5V
Headphone
750mV
Tape Out
250mV
Tuner, Tape 1 and 2,
Aux
than 100W (to operate
5kW or greater)
EQUALIZER C O N T R O L RESPONSE
Center Frequencies
30, 750, and 10 kHz
Boost and Cut
± 12 dB
FREQUENCY RESPONSE
+ 0 - 0 . 5 db f r o m 20
Hz to 20 kHz
SIGNAL TO NOISE
Phono 1 and 2
less
into
8W
less
into
CONDUCTOR C O M P L E M E N T
Transistors
Field Effect T r a n s i s t o r s
S i l i c o n Diodes
Integrated C i r c u i t s
M E C H A N I C A L INFORMATION
SIZE
SIZE: Front panel measures 16 inches wide (40.6
cm) by 3 5/8 i n c h e s high (9.2 cm). Chassis
measures 14 3/4 inches w i d e (37.5 cm) by 2 3/8
i n c h e s high (6.0 cm) by 14 1/2 inches deep (36.8
cm), i n c l u d i n g c o n n e c t o r s . Knob clearance req u i r e d is 1 1/4 inches (3.2 cm) in front of mounting panel.
FINISH:
Front panel is anodized gold and black w i t h
s p e c i a l gold/teal n o m e n c l a t u r e i l l u m i n a t i o n .
C h a s s i s is black.
MOUNTING:
Exclusive M c i n t o s h developed professional
PANLOC
WEIGHT:
14 p o u n d s (6.4 kg) net, 25 pounds (11.3 kg) in
shipping carton.
- 9 0 d B IHF A - w e i g h t e d ,
below 10mV input
- 8 0 d B unweighted,
b e l o w 10mV input
- 100 dB IHF A - w e i g h t e d ,
b e l o w 250mV input
- 9 0 dB unweighted,
below 250mV input
47kW and 50pF
47kW
-8-
Performance
Charts
EQUALIZER FREQUENCY RESPONSE:
CONTROLS SET AT MAXIMUM
AND MINIMUM
LOUDNESS CONTROL RESPONSE:
FOR VARIOUS CONTROL
POSITIONS
HARMONIC DISTORTION:
IN: AUX; OUT: MAIN
INTERMODULATION DISTORTION:
IN: AUX; OUT: MAIN
INPUT FREQUENCY: 60 Hz & 7 kHz:
RATIO: 4:1
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Technical Description
The C 504 is c o m p r i s e d of six basic s e c t i o n s . They
are: phono amplifier, high level a m p l i f i e r , equalizer
amplifier, o u t p u t / h e a d p h o n e a m p l i f i e r , input selector
s w i t c h i n g , and power supply. Their c i r c u i t descriptions follow.
100 m i l l i v o l t s w i t h o u t o v e r l o a d , a voltage far greater
than the o u t p u t of any current m a g n e t i c phono cartridge. Phono input overload therefore is virtually imp o s s i b l e . A signal level of 10 m i l l i v o l t s at the phono
input at 1000 Hz will p r o d u c e 1.13 volts at the tape
o u t p u t . The tape o u t p u t has a source i m p e d a n c e of
200 o h m s and is d e s i g n e d to operate into a load imp e d a n c e of 5,000 o h m s or greater.
PHONO AMPLIFIER
The phono a m p l i f i e r uses a high t e c h n o l o g y integrated c i r c u i t o p e r a t i o n a l amplifier. Its d i f f e r e n t i a l
input stage has been o p t i m i z e d for low noise and low
d i s t o r t i o n p e r f o r m a n c e . Open loop gain of this integrated c i r c u i t is 100,000. W i t h high open loop gain a
large a m o u n t of negative f e e d b a c k can be used
around the p h o n o a m p l i f i e r to further reduce noise
and d i s t o r t i o n . The f e e d b a c k network also provides
precision RIAA frequency c o m p e n s a t i o n . The network uses 1 % metal f i l m resistors and 5 % poly f i l m
c a p a c i t o r s . To achieve low noise p e r f o r m a n c e it is
essential that the f e e d b a c k network have very low impedance. As a c o n s e q u e n c e , the p r e a m p l i f i e r must be
capable of o p e r a t i n g as a power a m p l i f i e r to drive this
i m p e d a n c e . The a c t u a l power o u t p u t c a p a b i l i t y of this
p r e a m p l i f i e r s t a g e is more t h a n 100 m i l l i w a t t s , a great
margin beyond that w h i c h is required.
HIGH LEVEL AMPLIFIER
At the input to the high level or loudness amplifier
the signal passes t h r o u g h the MONO/stereo s w i t c h ,
then t h r o u g h the v o l u m e c o n t r o l , and into the
amplifier. In the past, l o u d n e s s c o n t r o l s have typically used s i m p l e passive c i r c u i t s c o n n e c t e d to a tap on
the v o l u m e c o n t r o l . As a c o n s e q u e n c e , c o m p e n s a t i o n
a c c u r a c y was d e p e n d e n t on many variables such as
v o l u m e c o n t r o l p o s i t i o n and d i f f e r e n c e s in the input
level. The C 504 uses active circuitry. The same type
of integrated c i r c u i t o p e r a t i o n a l a m p l i f i e r that is used
in the phono a m p l i f i e r is used here. It has t w o feedback loops. One feedback loop is flat. The other feedback loop c o n f o r m s to the F l e t c h e r - M u n s o n equal
l o u d n e s s c o m p e n s a t i o n . A p o t e n t i o m e t e r is placed
b e t w e e n these t w o f e e d b a c k loops m a k i n g it possible
to select any c o m b i n a t i o n of the t w o from a flat
r e s p o n s e to full l o u d n e s s c o m p e n s a t i o n . The overall
gain of the s t a g e is 20 dB at mid-frequencies and is
Input s e n s i t i v i t y of the p h o n o a m p l i f i e r is 2.2
m i l l i v o l t s . The gain of the a m p l i f i e r is 41.1 dB at 1000
Hz. The phono a m p l i f i e r has a very w i d e d y n a m i c
range. At 1000 Hz the p h o n o input c i r c u i t w i l l a c c e p t
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not a f f e c t e d by the p o s i t i o n of the l o u d n e s s c o n t r o l .
EQUALIZER AMPLIFIER
The equalizer a m p l i f i e r is c o n s t r u c t e d w i t h a n o t h e r
of the s a m e type low noise o p e r a t i o n a l a m p l i f i e r as
used in the p h o n o a m p l i f i e r . Three other o p e r a t i o n a l
a m p l i f i e r s are a r r a n a g e d in c i r c u i t c o n f i g u r a t i o n s that
are the e q u i v a l e n t of three series t u n e d c i r c u i t s . One
is resonant at e a c h of the three equalizer c e n t e r frequencies. These series t u n e d c i r c u i t s are inserted via
the c o n t r o l p o t e n t i o m e t e r s in either the input c i r c u i t
or f e e d b a c k c i r c u i t of the equalizer a m p l i f i e r thereby
providing a b o o s t and cut c a p a b i l i t y of 12 dB for e a c h
band of f r e q u e n c i e s . The equalizer a m p l i f i e r has a flat
response gain of 0 dB.
O U T P U T / H E A D P H O N E AMPLIFIER
The o u t p u t a m p l i f i e r is a push-pull c o m p l e m e n t a r y
class AB a m p l i f i e r u s i n g a s i g n a l inverting d i f f e r e n t i a l
stage at its input. This a m p l i f i e r drives the m a i n outputs and the h e a d p h o n e jack. More than 10 volts RMS
o u t p u t can be p r o d u c e d w i t h t y p i c a l l y no more than
0.003% h a r m o n i c d i s t o r t i o n .
A turn-on delay c i r c u i t is l o c a t e d ahead of the output amplifier. T h i s c i r c u i t uses a light e m i t t i n g
diode/light d e p e n d e n t resistor n e t w o r k that f u n c t i o n s
to t r a n s m i t no s i g n a l until t w o s e c o n d s after the
power s w i t c h is t u r n e d on and to remove the o u t p u t
s i g n a l a l m o s t i n s t a n t l y u p o n power turn-off. T h u s the
turn-on and turn-off is t r a n s i e n t and noise free.
INPUT SELECTOR S W I T C H I N G
Low level, noise c r i t i c a l input s e l e c t o r s w i t c h i n g is
done e l e c t r o n i c a l l y u s i n g field effect t r a n s i s t o r
a n a l o g s w i t c h e s . The front panel s e l e c t o r s i m p l y switches s m a l l a m o u n t s of c o n t r o l DC w h i c h turn the FET
analog s w i t c h e s off or on. This d e s i g n e l i m i n a t e s
d e g r a d a t i o n of f r e q u e n c y r e s p o n s e and noise p i c k u p
from long signal p a t h s necessary w i t h c o n v e n t i o n a l
switching.
POWER SUPPLY
To m i n i m i z e m a g n e t i c h u m r a d i a t i o n and t h u s improve s i g n a l to noise ratio the C 504 power
t r a n s f o r m e r is triple s h i e l d e d . S h i e l d i n g i n c l u d e s a
copper strap, a s i l i c o n steel strap, and finally a steel
outer shell. The t r a n s f o r m e r o u t p u t voltage is fed to a
full wave bridge rectifier and 3,300 m i c r o f a r a d filter
c a p a c i t o r s to provide the + 2 4 volts for p o w e r i n g the
plus regulator and - 2 4 volts for the m i n u s regulator.
Integrated c i r c u i t voltage regulators supply the ± 1 8
volts needed for low level a m p l i f i e r stages.
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Block Diagram
MclNTOSH C 504
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STEREO PREAMPLIFIER
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MclNTOSH LABORATORY INC.
2 CHAMBERS ST., BINGHAMTON, N.Y. 13903
607-723-3512
The continuous improvement of its products is the policy of
Mcintosh Laboratory Incorporated who reserve the right to
improve design and price without notice.
Printed in U.S.A.
039243
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