Playmaster AM/FM stereo tuner lital

Playmaster AM/FM stereo tuner lital
KA1635
AM stereo plus synthesised tuning
Playmaster AM/FM
stereo tuner lital
Our new Playmaster synthesised AM/FM stereo
tuner will outperform anything presently available
on the market, regardless of price. As well as
including an FM tuner section which is every bit
as good as any other synthesised design, it is
the only unit featuring a genuine wideband, low
distortion AM stereo tuner. Naturally, it has a
digital readout, 1 2-station memory, automatic
seek and an optional infrared remote control.
by JOHN CLARKE
There's just one way to sum up the
performance of our new AM/FM stereo
tuner. In a word, it's superlative.
We've been hard at work on this
beauty for almost a year now and to say
that we're proud of the result would be
the understatement of the year. Our new
design includes the latest technology and
boasts such high falutin' features as
stereo AM decoding, synthesised tuning
and microprocessor control. But this is
one synthesised tuner that doesn't
sacrifice performanace at the expense of
fancy features.
In designing the new tuner, we kept
just one object in mind: we wanted the
best possible performance, regardless of
the cost. The result is this superb design
which puts most commercial units in the
shade.
As can be seen from the photograph,
most of the circuitry is accommodated
on one large printed circuit board (PCB).
Three separate, smaller boards are used
for power supply components, the front
panel LED displays and control
pushbuttons, and the FM front end. The
main board and the display board are
connected by means of several plug and
cable assemblies while the FM front end
plugs directly onto the main board.
No expensive test gear is needed to
build the tuner. A digital multimeter and
two plastic alignment tools will suffice.
Stereo AM
Despite the introduction of AM stereo
on February 1st 1985, commercial
AM/FM tuner manufacturers have done
little to cater for the Australian AM
stereo market. Only three brands are
currently on the market and the
performance of these generally leaves
something to be desired, both in terms of
audio bandwidth and distortion. We
wanted to do much better.
Our new Playmaster stereo tuner has
not been compromised with regard to
AM bandwidth, distortion or overall
performance. It utilises the, wide
frequency bandwidth available from the
AM transmitters to give the best sound
possible in AM stereo. Until you've
heard it, you won't believe that AM
stereo could sound so good. Depending
on the program material it can sound
•every bit as good as FM stereo!
But the new tuner not only produces
exceptional sound; it is also a delight to
operate. It is all pushbutton controlled
and responds instantly to your
commands. Press one of the six memory
pushbuttons and the tuner locks quickly
onto the pre-programmed station. A
highly visible 15mm high green readout
displays the received frequency.
The 10-level signal strength meter is
without doubt the most useful available
'on any tuner we have seen for a long
time. Combined with the quieting curves
The tuner is housed in a slimline rack-mounting case. This view shows the unit prior to silk-screening of the fk ont panel.
•
ELECTRONICS Australia, December, 1985
View inside the prototype. The FM front end is in the screened metal enclosure at the top left of the main board.
(to be published next month), it gives you
all the information you need to allow
you to get the best signal quality.
Slimline styling gives the tuner a neat
and up-to-the-minute appearance. The
black anodised front panel is screen
printed and is fitted with black
pushbutton switches. The switches and
memory indicating LEDs protrude
through holes in the front panel while
the green LED display is located behind
a neutral perspex sheet inserted into the
front panel.
This display includes the digif,41
frequency readout, signal strength meter
and AM/FM and stereo/mono
indicators. The AM, FM, stereo and
mono indicators each consist of a LED
light bar module which emits a diffused
green light. Covering these is a black film
negative of the indicator lettering.
When the light bar module is lit, the
light only shines through the clear
lettering - of the covering film. The
indicator word is thus displayed with a
very professional appearance.
Controls
The front panel controls are quite
straightforward. At the extreme left is a
pushbutton on/off power switch while
immediately to the right of the display
window are pushbuttons for forced
mono and station seek.
The Seek control does just as its name
suggests. When pressed, it sends the
tuner scanning up the frequency band
and automatically locks it onto the next
available station.
Station selection is by means of the
up/down Tune pushbuttons or any one
of the pre-programmed memory
pushbuttons. The two Tune pushbuttons
provide manual station selection. Press
the up button and the tuner increments
in steps of 9kHz for AM or 100kHz for
FM. Similarly, pressing the down button
causes the tuner to decrement.
If either button is held down, the tuner
will scan at a fast rate until the button is
released.
To the right of the Tune buttons are
the AM/FM switch, the six memory
pushbuttons and the Memory Enable
switch. Up to 12 stations can be preprogrammed into the memory switches,
six for the AM band and six for FM.
It's quite easy to store a station in one
of the memory locations. The tuner is
simply tuned to the desired frequency,
using the Seek or Up/Down buttons.
Then the Memory Enable switch and
appropriate station pushbutton is pushed
to store the setting. If a station button is
not pressed within the five seconds, the
ME light will extinguish.
Tuner development
As previously stated, Work first began
on the tuner circuitry about 12 months
ago. Many of the components required
for the project were specialised and we
were fortunate that manufacturers and
parts suppliers were keen to assist in
meeting our needs.
We needed ceramic filters for the AM
intermediate frequency (IF) stages and
for station detection, as well as for the
FM IF stage. A ceramic resonator was
also required for the AM stereo decoder.
IRH Components were very helpful in
this regard and supplied us with the
necessary samples, some of which were
specially imported for the project.
Similarly, we obtained various ICs and
components from Geoff Wood
Electronics, Motorola, National
Semiconductor, Philips, Plessey, Neosid,
Soanar and Watkin Wynne.
Our major problem, however, was to
find a suitable microprocessor IC, vital
for frequency synthesis and control.
Eurovox Australia (Melbourne) was able
to help out here. They use a custom
NEC microprocessor in their car radios
and car cassette players fitted as standard
equipment in GMH, BMW, Porsche and
Alfa Romeo vehicles. In particular, we
acknowledge the help and enthusiasm of
Klaus Schuhen at Eurovox who supplied us with sample microprocessors,
companion prescaler ICs and crystals, a
Eurovox car radio and service
information.
Using this information, we have
developed a completely original tuner
design, based around the NEC custom
microprocessor. To our knowledge, its
overall performance exceeds that of any
commercial AM/FM tuner, produced in
Australia or anywhere else.
ELECTRONICS Australia, December, 1985
a,
Paymaster AM/FM stereo tuner
248Z
SUP T
AM TUNER
TRANSFORMER
POWER
SWITCH
REGULATOR
LOOP ANTENNA
-
FM TUNER
REGULATOR
+ 28V
1
-12V +12V +5V
FM FRONT END
WITH RF FILTERS,
LOCAL OSCILLATOR
AND MIXER
DUAL MODULUS
PRESCALER
+18 AND +17
LOCAL OSCILLATOR
OUTPUT
d
10.7MHz
IF
RF BANDPASS
FILTERS
...A9C IN
ki
od VARICAP
BUFFER
AMPLIFIER
VARICAP TUNING
VOLTAGE
VARICAP
TUNING
VOLTAGE -
SUPER
CAPACITOR
F4
4,5M1
Hz
ERROR
OUTPUT
AM
OSCILLATOR
,, . INPUT
MICROPROCESSOR
MODULUS
CONTROL
OUTPUT
LOCAL
OSCILLATOR
BALANCED
MIXER
FM INPUT
STOP AMIFM MUTE
AGC IN
WIDE BAND
50kHz FILTERS
AGC
FM IF WITH
CERAMIC FILTERS,
LIMITER AND
QUADRATURE
DETECTOR
NARROW BAND
450kHz STATION
DETECTOR
TATION DETECT
OUTPUT
12V TO FM7
12V TO AM
FORCED
Airsommiwo,
T
SIGNAL
STRENGTH
METER
AUDIO
OUTPUT
INPUT
AMIFM
POWER SUPPLY
SWITCH
+12V 10.—
•
AMIFM
STEREO DECODER
WITH BLEND
LEFT
TO
STEREO
LED
RIGHT
CONTROL LINES TO
FREQUENCY AND
DISPLAY LEDS AND
PUSH BUTTON
SWITCHES
TO
STEREO
LED
MUTE
LEFT
19kHz NOTCH
FILTERS AND 19kHz
RIGHT
a. LOW PASS FILTERS
CQUAM
AM STEREO
DECODER
LEFT
AGC
OUT
RIGHT
9kHz NOTCH
FILTERS AND
10kHz LOW PASS
FILTERS
4 GAIN
AUDIO SIGNAL
SWITCHING
FORCED
MONO
INPUT
p
TO
SIGNAL
STRENGTH
METER
RIGHT
LEFT
AUDIO OUTPUT
FRONT PANEL DISPLAY
I• f*"
SIGNAL STRENGTH
METER
innn
u,
0
MONO
O MONO
0 SEEK
.43 TUNE AP
0 0
3
0
4
0
0 0 0 0
PUSH BUTTON SWITCHES
0
AMIFM o
1
2
0
MEMORY
b6 ENtIAE
BED'S
0
0
o
An NEC microprocessor drives the front paffel display and provides synthesised tuning of the AM and FM front ends.
Block diagram
The importance of the microprocessor'
in our new tuner is emphasised by the
block diagram. In addition to driving the
front panel display, it provides frequency
synthesised tuning of the AM and FM
tuner front- ends and controls power
supply and audio output signal
switching.
Before discussing the microprocessor
control further, let's first take a look' at
the AM and FM tuner stages.
Both the AM and FM tuners operate
on the superheterodyne principle. In
each case, a local oscillator tracks the RF
filters and is mixed with the incoming
RF signal. For AM, the oscillator
frequency is always 450kHz above the
frequency of the tuned station while for
FM it is always 10.7MHz above the
tuned frequency.
As a result of this mixing, we obtain a
constant intermediate frequency (IF) of
450kHz for the AM tuner and 10.7MHz
for the FM tuner, regardless of the tuned
frequency. These intermediate
frequencies are then filtered and
detected.
AM tuner
The AM tuner utilises a large loop
antenna which provides a virtually noise
free signal to the tuner. Since the loop
antenna is a balanced circuit, it acts to
reduce common mode interference. In
practice, there is almost a complete lack
of background noise when tuned to a
station.
Following the antenna are the RF
bandpass filters. They provide gain at the
ELECTRONICS Australia, December, 1985
tuned frequency, with sufficient
bandwidth to ensure a wide audio
frequency response.
An essential feature of the AM section
is the fully balanced mixer. It enables the
use of a wideband 450kHz ceramic filter
in the IF stage, giving a response only
6dB down at ± 12kHz, but sharply
rolled off to 35dB down at ± 20kFIz and
60dB at ± 40kHz.
Signal from the IF stage is directed to
a narrow band station detector and to a
C-QUAM AM stereo decoder stage.
The narrow band station detector
block comprises a gain stage, a narrow
band ceramic filter and a detector. The
ceramic filter has a bandwidth of about
2.5kHz and is 24dB down at 9kHz which
is the frequency separation of the AM
stations. A station detect signal thus
appears at the output only when the
tuner is set to the correct station
frequency.
At a setting 9kHz away from the
station, the attenuation from the ceramic
filter is sufficient to prevent a station
detect signal.
The AM stereo decoder is a complete
stereo decoding and pilot detection
system based on the Motorola
MC130201) C-QUAM chip. This
provides a high quality detector plus
stereo decoding.
Stereo reception is obtained when a
25Hz pilot tone is detected and there is
sufficiently low signal noise. As soon as
noise appears on the signal, the decoder
automatically switches to mono. The
decoder can also be manually switched
to mono using the forced mono input.
In addition to the left and right audio
outputs, the C-QUAlvi decoder also
provides an automatic gain control
(AGC) signal. This signal is inverted and
controls the gain of the RF banclpass.and
450kHz filter stages.
The AGC voltage is also abed to drive
the signal strength meter via another
inverter stage.
The left and right audio outputs from
the decoder are filtered using 9kHz
notch and 10kHz low pass filter stages.
The notch filter removes 9kHz whistles
caused by adjacent stations beating with
the received station while the low pass
filter cum gain t stage removes high
frequency noise from the audio.
It also boosts the output level from the
AM tuner so that it matches the audio
output from the FM tuner.
FM tuner
There's nothing radical about the
design of the FM tuner. It's a perfectly
conventional arrangement with both the
IF and stereo decoder stages based on
standard National Semiconductor 10-.1
The front end includes the RF filters,
a local oscillator and the mixer. Double
tuning is used on the first stage before
amplification using a dual gate
MOSFET device. The unbalanced mixer
is tuned to the 10.7MHz IF and its
output passed to ceramic filters in the IF
circuitry.
A National Semiconductor LM1865
advanced FM IF intergrated circuit is
used for this section of the tuner. It
includes gain, limiting and quadrature
detection of the modulated FM signal. A
feature of the IC is linearisation of the
quadrature detection to considerably
reduce distortion.
The IC also provides an AGC signal
output which is applied to the front end
and eliminates the need for local/distance
switching. It also reduces third order
intermodulation products due to strong
out of band signals overloading the front
end.
ELECTRONICS Australia, December, 1985
The Microprocessor chip is at bottom centre of the main board, the AM tuner circuit at left, and the FM tuner at right.
Playmaster AM/FM stereo tuner
Also included with the IC is a station
detect output and a signal strength
output suitable for driving the signal
strength meter.
Following the detector is a National
Semiconductor LM1870 FM stereo
decoder chip. This device incorporates a
blend feature which reduces the stereo
separation at low signal levels to improve
the signal-to-noise ratio.
The left and right audio outputs are
filtered with 19kHz notch filters and
38kHz low pass filters. The notch filters
filter the 19kHz stereo pilot tone while
the low pass filter reduces the 38kHz
residual output produced by the stereo
decoder.
Phase lock loop control
Varicap diodes are used to tune the
local oscillator and RF sections of both
tuners. These diodes change capacitance
in respOnse to a control voltage and are
connected in parallel with inductors to
form tuned circuits.
The varicap control voltage is derived
from the error output of the
microprocessor. This error output drives
a varicap buffer amplifier which supplies
a control voltage in the range from OV to
28V DC.
In a superheterodyne tuner, the local
oscillator frequency varies according to
the tuned station and this frequency is
read by the microprocessor controller. In
the case of the AM tuner, the local
oscillator signal is applied directly to the
input of the microprocessor.
A somewhat different arrangement is
employed for the FM local oscillator. In
this case, the oscillator output is divided
with a dual modulus prescaler chip
before being applied to the
microprocessor. The dual modulus
prescaler divides by either 16 or 17,
depending on the modulus control
output from the microprocessor.
Inside the microprocessor is a phase
lock loop (PLL) comprising three
separate components: a reference
frequency generator, a phase detector
and a programmable divider.
The reference frequency generator
produces a reference frequency by
dividing down the external crystal
reference of 4.5MHz. For AM, the
reference frequency is 9kHz and for FM,
25kHz.
The programmable divider divides the
incoming station frequency and
compares it with the reference frequency
in the phase detector. This produces the
error voltage which is fed to the local
oscillator varicaps to "lock" the tuner
onto the station.
Since. the local oscillatOr is a precise
multiple of the internally generated
reference frequency, this phase lock
control loop is called a "frequency
synthesiser".
Apart from synthesis control, the
microprocessor performs several other
functions.
To begin with, it has several control
lines which drive the frequency display,
the mono and AM/FM status indicators,
and the memory selection LEDs. With
the exception of the mono indicator
these are all multiplex driven.
The microprocessor also scans the
pushbutton control switches. When one
is pressed, the microprocessor responds
to the switch function and this response
is seen as a change in the display.
Power supply and audio signal
switching is controlled by the AM/FM
output. The mute output mutes the
audio signal whenever the
Microprocessor is changing stations.
The stop input is used during the seek
mode, when the tuner is used to
automatically scan to the next station.
When a station is located, the station
detect output from the powered tuner
goes high and the microprocessor locks
onto that station.
Finally, the microprocessor is
permanently powered up via a 5V
regulator. However, if the tuner is
disconnected from the mains supply,
either intentionally or because of a
blackout, a super capacitor (47,000pF)
maintains power to the memories so that
the tuner does not have to be reprogrammed.
So much for the block diagram. In Pt.
2 next month, we'll publish the full
circuit details.
ELECTRONICS Australia, December, 1985
"
MAST ER S ERE.° A 'MOM UN
Second article has all the circuit diagrams
Playmaster
Ptin 2
AM/FM
stereo tuner
Last month, we introduced our new
synthesised AM/FM stereo tuner and
described the block diagram. In part 2 this
month, we give the full circuit details and list
the specifications.
by JOHN CLARKE
The circuit for our new Playmaster
Stereo AM/FM Tuner is quite large
and, as a consequence, covers several
pages. This is something of a blessing,
however, since it breaks the circuit into
three manageable sections: AM tuner,
FM tuner and microprocessor control.
We will describe the operation of each
circuit section separately.
As discussed last month, microprocessor ICI performs a major roll in driving
the display, tuning the AM and FM
front ends, and switching power 'to either tuner as appropriate. Before we
discuss this further, let's first take a
look at the AM and FM tuner circuits.
AM tuner
The AM tuner circuit is a high-performance superheterodyne design employing varicap tuning, a double-balanced mixer, ceramic filters and stereo
ELECTRONICS Australia, January 1986
decoding. It is a brand new design, developed completely from scratch.
Input signals from the loop antenna
are fed to a balanced circuit consisting
of toroidal transformer Tl. As stated
last month, this acts to reduce commonmode interference so that the tuner is
provided with a noise free signal. The
unbalanced secondary of Ti is directcoupled to terminal 5 of antenna coil
1,1.
The winding across terminals 4 and 5
is a special modification to the standard
7210 coil assembly and comprises a few
hand wound turns on the L1 coil former. These provide very light coupling
to the tuned winding across terminals 1
and 2.
RF tuning of the antenna circuit is
provided by varicap diode Di in conjunction with the 3-30pF Wilmer connected across the 7210 winding. A tap-
View inside the prototype. The microprocessor chip is at the bottom centre of the photograph.
ping of the winding at terminal 6 directly couples to gate 1 of dual gate
MOSFET Ql.
01 is used as a self-biased common
source amplifier with the L2 winding
(7211) forming the drain load. Varicap
diode D2 and its associated 3-30pF trimmer are capacitively coupled to L2 to .
form the second RF tuned circuit. The
1Mii resistor across D2 discharges the
varicap when the control voltage at its
cathode is altered.
Note that self-bias for Q1 is provided •
by the 22051 source resistor while the
AGC (automatic gain control) voltage is
applied to gate G2 via the 100kfl and
471d1 resistors.
The output from the second RF stage
appears at terminal 6 of L2 and is coupled to the differential input of doublebalanced mixer stage 105 (MC1496) at
pins 1 and 4. The open collector outputs
at pins 6 and 9 are loaded with the balanced primary windings of L3 and its
parallel 560pF capacitor which form a
tuned circuit at 450kHz.
Supply decoupling is via a 560f1 resistor and 0.1gF capacitor.
04, L5, D3 and the associated 3-30pF
trimmer form the local oscillator. A
feedback tapping between Q4's emitter
and terminal 4 of L5 ensures continued
oscillation, while VR1 sets the level of
oscillation. Note that D3 is isolated
from the L5 winding via a 680pF capacitor. This reduces the maximum tuned
circuit capacitance.
To explain further, the RF stages
must be tuned from 522 to 1611kHz
which represents a capacitance ratio of
9.5:1 (which is the square of the
1611/522 ratio). The local oscillator, on
the other hand, must be tuned from
(522 + 450) kHz to (1611 + 450)kHz
which represents a 4.5:1 capacitance
ratio.
A separate winding on L5 couples the
oscillator output to the second differential input stage of the mixer (IC5) at
pins 7 and 8.
Because the mixer is a balanced type,
only the sum and difference frequencies
appear at the output. This fact is very
useful since it allows the use of a wide
band ceramic filter (SFP450D) in the IF
stage.
As stated last month, the filter
sharply rolls off the response beyond
±12kHz and is 60dB down at ±40kHz.
However, it also has secondary peaks in
its response so that the attenuation of
the filter is only 15dB down •at
±150kHz. Normally, this would render
the filter useless, since signals around
600kHz would pass through the IF filter
virtually unattenuated.
The balanced mixer neatly solves this
problem, however. It rejects both the
incoming RF and local oscillator signals,
and allows only the mixed signal
through to the IF stage. Consequently,
the rising response outside the passband
of the ceramic filter is unimportant,
The output from the ceramic filter is
coupled to gate 1 of Q2, another
BFR84 dual-gate MOSFET transistor.
L4 and the 390pF capacitor form a
tuned drain load for Q2 which provides
some gain for the IF stage.
At this point, the IF output is split
into two paths. One path is derived
from the drain of Q2, amplified by common emitter stage Q3, and applied to a
band
narrow
ceramic
filter
(SFZ450C3N). This filters a very narrow band centred on 450kHz which
means that it passes signal only when
ELECTRONICS Australia, January 1986
Playmaster AM/FM stereo tuner
the IF stage is centred on 450kHz. In
other words, an output from the filter
only occurs when the tuner is exactly on
station.
The output from the narrow-band filter is rectified by D4 and D5, filtered
and applied to the base of Q5. Whenever the signal is sufficiently strong, the
base of 05 is pulled below 0.6V. Consequently, Q5 turns off and supplies a station detect or stop output signal to pin
13 of the microprocessor.
The second signal path from the IF
stage is derived from a tapping on L4
(terminal 6) and coupled to the pin 3
input of IC4, an IVIC13020P Motorola
stereo decoder. This versatile chip performs a range of functions. It provides
low-distortion synchronous detection of
the incoming IF signal, stereo decoding,
an AGC output and automatic stereomono switching.
A forced mono input (pin 9) allows
manual switching to mono operation.
The 3.6MHz ceramic resonator sets
the frequency of an internal VCO which
therefore operates at eight times the
450kHz IF. In operation, the VCO
locks onto the IF and provides a phase
reference for stereo decoding. The
decoded left and right audio outputs appear on pins 7 and 8 respectively and
are fed to the notch and low-pass filter
circuits.
The AGC output from IC4 appears at
pin 4 and is applied to inverting amplifier IC6b. The resulting AGC output
signal appears on pin 7 and is used to
control the gain of MOSFET transistors
01 and Q2 as discussed previously? In
this way, a constant signal level is provided at the input to IC4 over a wide
range of signal conditions.
Further, IC6a inverts and level shifts
the AGC signal to drive an NSM39152
LED-bargraph signal strength meter.
This
10 LEDS and has a loga.
• features
rithmic response. It accepts a DC signal
and displays -the relative level compared
to RLO (ground) and RHI, the high
reference set by the 2.2kfl and 6.81d1
resistors.
Diode D10 isolates the output of IC6a
from the FM signal meter drive circuitry.
The left and right audio outputs from
IC4 are fed to 9kHz notch filters based
on L6. and L7. These remove any 9kHz
whistles caused by adjacent stations.
VR2 and VR3 are used to adjust the
depth and sharpness of the notch (in
each channel), while tuning is provided
by adjusting the slugs in the L6 and L7
inductors.
Following the 9kHz notch filters are
active filter stages IC7a and IC7b, each
with a gain of 1.2. These filters roll off
the response above 10kHz to remove
high frequency noise from the audio
output signals.
Finally, the left and right audio outputs are applied to 1C12, a 4052 CMOS
analog switch (shown on the FM tuner
circuit) page 37) which selects either
the AM or FM tuner outputs.
FM tuner
The FM tuner front end is designed
to accept a 75fi unbalanced antenna.
When used with a balanced 300f1 dipole
antenna, a 300f1 to 750 balun will be
necessary. The standard adaptor type
used for television antenna inputs is
quite suitable.
L8 is the 75fl input and this couples
to a double-tuned filter consisting of L9,
D19 and L10, D20. The RF ouput signal from the filter is then applied to
gate 1 of 06, a low noise dual gate
MOSFET with L11 as its drain load.
ELECTRONICS Australia, January 1986
The amplified output appears at the
drain of Q6 and is fed via a 1.5pF capacitor to another tuned stage consisting
of L12 and varicap diode D21.
AGC is applied to gate 2 of Q6 and
operates during very high signal level
conditions to prevent overload.
The local oscillator has a tuned circuit
comprising L.13 and varicap diode D22
for the collector load of 08. Feedback
via the 3.3pF capacitor from emitter to
collector ensures that the circuit oscillates. A 2.2ki1 resistor and 6.8pf capacitor provide supply decoupling.
Local oscillator injection to mixer
stage 07 is via a 4,7pF capacitor to the
base, while the output signal from L12
is also fed to the base via a 6.8pF capacitor.
Mixer stage Q7 has a 10.7MHz tuned
collector load consisting of L15 and a
47pF capacitor. The output signal is extracted from pin 3 of L15 and applied to
ceramic filter CF1 and to the wide band
AGC input (pin 20) of 1C2, an LM1865
FM 1F/detector chip from National
Semiconductor.
Quite a lot happens inside the
LM1865. It contains a buffer stage,
limiter amplifier, quadrature detector,
V
Specifications
AM Tuner
Tuning Range
Frequency Response
Harmonic Distortion
Audio Output
Stereo Separation
AGC Range
Signal-to-Noise Ratio
Usable Sensitivity
522 to 1611kHz
—3dB at 5.5kHz (see graph)
mono: 0.4% at 30% modulation
stereo: <1% at 30% modulation
450mV RMS into 4.7kti load at 100%
modulation
typically 30dB
40dB for a 6dB change in audio output
70dB with respect to full output for signal
levels of 9 and 10 on bar graph display;
better than 60dB with respect to full output for signal levels greater than 6
350/4V at —6dB audio level
FM Tuner
87.9 to 107.9MHz
—1dB at 20Hz, —0.5d8 at 15kHz
mono 0.15% (100Hz); 0.15% (1kHz);
0.2% (6kHz)
stereo: 0.4% (100Hz); 0.4% (1kHz); 0.4%
(6kHz)
Audio Output
450mV RMS into 4.7kti load at 100%
modulation
,
34dB (50Hz); 34dB (1 kHz); 36dB (10kHz)
Stereo Separation
Subcarrier Product Rejection 48dB
19kHz Rejection
62dB
see graph
Signal-to-Noise Ratio
Tuning Range
Frequency Response
Harmonic Distortion
ELECTRONICS Australia, January 1986
9
0
1 rack-mounting cabinet,44 x
254 x 430mm (Altronic*s Cat.
No. H-0411)
1 screen printed front panel, 486
x 46rnm
1 negative film, 185 x 31rnm
1 sheet of neutral perspex, 179 x
24mm x 1.5-3mm
2 pieces of tinplate, 101 x 24mm
2 pieces of tinplate, 52 x 24mm
1 piece of tinplate, 52 x 20mm
1 PC board, 330 x 216mm, code
'
85tu12
1 PC board, 66 x 110mm, code
85 s12
1 double-sided PC board, 94 x
51mm, code 85fm12
1 double-sided PC board, 370 x
35mm, code 85db12
1 Ferguson PL24/20VA low profile transformer
1 mains cord and plug
1 cord grip grommet
2 bullet sockets with insulating
sleeving
4 rubber feet
10 6mm spacers
4 12mm spacers
1 Belling Lee 750 panel-mounting socket
1 stereo panel-mounting RCA
socket
1 2-way panel-mounting screw
terminal
1 DPDT mini push on/push off
switch with 10mm black cap
12 snap action black keyboard
switches (Ja ycar Cat. No. SP0721)
9 Molex 8-way 0.1-inch pin headors
8 Molex 8-way 0.1-inch cable
connector sockets
64 crimp terminals to suit above
sockets
94 Molex pin sockets
50 PC stakes
1 TO-220 heatsink, 30 x 27 x
12mm, Thermaloy 8030
1 4.5MHz parallel resonance
crystal
1 earth lug
I 11 1/
PsrList For Synthesised Stereo
Wire & cable
100mm of 8-way rainbow cable
300mm 0.8mm enamelled
-topper wire
25mm 0.6mm enamelled copper
wire
130mm 26B&S enamelled
copper wire
220mm twin shielded wire
2 metres 30B&S enamelled
copper wire
37 metres 36B&S enamelled
copper wire
3 metres hookup wire
ELECTRONICS Australia, January 1986
a
t
Integrated Circuits
1 NEC D1710G/016 or /227 MPU
1 NEC 553AC dual modulus
prescaler
1 LM1865 advanced FM IF
system (National
Semiconductor)
1 LM1870 FM stereo
demodulator (National
Semiconductor)
1 MC13020P C-QUANI AM stereo
decoder (Motorola)
1 MC1496G (metal package)
balanced modulator/
demodulator (Motorola)
2 DS75492 MOS to LED hex digit
drivers
1,40106, 74C14 hex Schmitt
trigger
1 4052 2-pole, 4-way CMOS
.
switch
2 LF353, TL072 dual op amps
1 LF347, TL074 quad op amp
3 7805, LM340T-5 3-terminal
+5V regulators
1 7812, LM340T-12 3-terminal
+12V regulator
1 7912, LM320T-12 3-terminal
—12V regulator
1 LM317T adjustable 3-terminal
regulator
Transistors and diodes
4 BB204E3 or BB204G varicap
double diodes (Philips). Note:
do not mix B and G types.
3 BB212 AM varicap double
diodes (Philips)
1 BF450 PNP HF transistor
1 BF240 NPN HF transistor
1 BF981 N-channel dual gate
MOSFET
2 BFR84 N-channel dual gate •
MOSFETs
1 BF494 NPN transistor
5 BC549 NPN transistors
8 BC327 PNP transistors
1 BC337 NPN transistor
2 BC547 NPN transistors
1 2N5485 N-channel FET
19 1N4148, 1N914 small signal
diodes
10 1N4002 1A silicon diodes
Optoelectronic
components
1 NSM39152 green bar graph
display (Geoff Wood
Electronics)
2 MU03-5201 6 x 9mm green
light bar modules (A&R
Soanar)
2 MU02-5201 14 x 14mm green
light bar modules (A&R Soanar)
4 MAGI 63 green common anode
7-segment displays (Stanley
A&R Soanar)
6 3mm
green LEDs
,
1 3mm red LED
,
Ceramic filters and
resonators
2 Murata SFE10.7MI, ceramic
filters °RH)
1 Murata SFP450C
) AMStared IF
ceramic filter
1 Murata SFZ450C3N ceramic .
filter
1 Murata CSA3.6MT7 ceramic
resonator & CSCSINKI."50pF
d' 3001K 30f*
capacitor
Inductors
2 Neosid type El adjustable
inductance assemblies
1 Neosid type E3 adjustable
inductance assembly
1 Neosid type A5 adjustable
Inductance assembly
1 Neosid 4329R/2 ferrite ring
core
1 Jabel 7210 1 st RF bandpass
coil
1 Jabel 7211 2nd RF bandpass
coil
1 Jabel 9185 IF coil
1 22p,H choke
1 l8p,H choke
1 6.8µH choke
1 F16 ferrite slug
4 Philips 4322 022 22265
potcores, PL14/8, with nut
4 Philips 4322 021 30250 coil
formers
4 Philips 4322 021 30950
inductance adjustors
4 Philips 4322 021 30440 ta9
.
plates
4 Philips 4322 021 30520 brass
containers
4 Philips 4322 021 30630 springs
•
Capacitors
&
Resistors
AM
tuner
Capacitors
1 2200p,F 25VW axial electrolytic
2 1000p#F 16VW PC electrolytic
1 470p,F 63VW axial electrolytic
2 470p,F 25VW axial electrolytic
1 100AF 25VW axial electrolytic
1 33p,F 16VW PC electrolytic
1 10µF 25VW PC electrolytic
3 10p,F 16VVV PC electrolytic
2 4.7pF 16VW PC electrolytic
0
AM/FM Tuner
plate, Philips 2222 629 09103
3.001µF (1 nF) miniature ceramic
plate, Philips 2222 629 09102
1 47pF miniature ceramic plate,
Philips 2222 652 10479
1 27pF miniature ceramic plate,
Philips 2222 652 10279
1 6.8pF miniature ceramic plate,
Philips 2222 652 09688
.pF miniature ceramic plate,
14'
Philips 2222 652 09478
13.3pF miniature ceramic plate,
Philips 2222 652 09338
1 1.5pF miniature ceramic plate,
Philips 2222 652 09158
3 4.2-20pF Murata D series
trimmers
1 3-11pF Murata D series
trimmer
Resistors (0.25W, 5%)
1x
, 1Mfl, 4 x 56k0, 1 x 33ka, 1
x 18kfl, 2x 10kfl, 1 x 3,3kfl, 1 x
2.2kil, 1 x 1.5kfl, 1 x 1kfl, 1 x
.
220n, 2 x 220
2 2.2µF 16VVV PC electrolytic
3 1µF 16VW PC electrolytic
2 0.47µF 16VW tantalum
11 0.1µF ceramic
4 .056µF metallised polyester
1 .022µF metallised polyester
10 .01µF ceramic
2 .01µF (10nF) ceramic plate,
Philips 222 629 09103
4 .0033µ,F metallised polyester
2 .0018µF metallised polyester
1 .001µF metallised polyester
1 .001µF ceramic
1 .001µF (1nF) miniature ceramic
late, Philips 222 630 09102
miniature ceramic plate,
1 68O
Philips 2222 630 09681
1 560pF ceramic
2 470pF ceramic
1 390pF ceramic
1 56pF ceramic
1 33pF ceramic
3
3 pMuraaDseres
trmmes
e
Resistors 0.25W, 5% unlesp
stated)
2 x 1Mfl, 1 x 300kf/ 2%, 1 x
270kf/, 2 x 220ka 3x 150kft 1
x 110kfl 2%, 7 x 100kfi, 1 x
82kfi, 2 x 47kfi, 1 x 33kfl 2 x
22kfi 2%, 2 x 18kfi 2%, 3 x 12kci
2%, 2 x 10kfi, 2 x 8.2k11 2%, 1 x
7.5kn 2%, 2 x 6.8kil, 3 x 5.6 kn,
1 x 4.7ka, 1 x 3.9ka 2 x 3.3kft
2 x 2.7141 2%, 3 x 2.2kfi, 2 x
1.6kfi 2%, 1 x 1.2kfi, 2 x 1kfi, 1
x 9100 2%, 1 x8200, 5 x 5600,
1 x 4300 2%, 1 x 270f1, 2 x
2200, 3 x 1000, 1 x 4.7k11,
miniature horizontal trimpot, 2 x
2kfl miniature'horizontaltrimpots
Tuner control circuit
Capacitors
1 47,000µF (.047F) 5VW super
capacitor
2 000µF 16VW PC electrolytic
4 47p,F 16VW PC electrolytic
4 10µF 25VW PC electrolytic
4 10µF 16VW PC electrolytic
2 1p,F 63VW PC electrolytic
1 1µF 35VW PC electrolytic
1 1µF 25VW PC electrolytic
1 0.33µF metallised polyester
1 0.1pc ceramic
2 .01µF ceramic
2 .01µF (10nF) miniature ceramic
plate, Philips 2222 629 09103
1 .01µF metallised polyester
1 680pF miniature ceramic plate,
Philips 2222 630 09681
1 100pF miniature ceramic plate,
Philips 2222 652 58101
2 22pF ceramic
2 4.7pF ceramic
Resistors
1 x 1M11, 1 x 220ka 1 x 150kfl,
1 x 33kft 9 x 10ka 4 x 5.6kfl, 2
x 4.7kfi, 1 x 2.7kfl, 1 x 2.24/, 1
x 1.8kfl 7 x 1kfi 6 x 8200, 1 x
680a 1 x 470ft 1 x 330f1, 1 x
220a 2 x 1200, 2 x 82f1, 2 x
56f1, 4 x 47a 7 x 2211
Capacitors
1 220µF 16VW PC electrolytic
2 47µF 16VW PC electrolytic
1 22p,F 16VW PC electrolytic
2 10µ,F 16VW PC electrolytic
16VW PC electrolytic
24
32.2p-F 16VW PCelectrolytic
3 1,uF 16VW PC electrolytic
1 0.33µF metallised polyester
1 0.22µF metallised polyester
3 0.1µF ceramic
1 .047µF metallised polyester
4 .012µF metallised polyester
5 .01µF (1 OnF) miniature ceramic
plate, Philips 2222 629 09103
2 .0056/1F metallised polyester
3 .0047µF metallised polyester
2 .0018µF metallised polyester
2 .0015µF metallised polyester
1 .001µF metallised polyester
2 150pF ceramic
FM front end
signal strength meter drive circuit and
an AGC output. In addition, it provides
a stop output which is connected directly to the stop input (pin 13) of the
microprocessor.
The output from the input buffer
stage of IC2 appears at pin 3 and is fed
to a second 10.7MHz ceramic filter
(CF2). It then passes to the limiter amplifier which ensures that the input
nal is driven well into clipping. The
limiter, in turn, drives the quadrature
FM detector associated with the tuned
circuits on pins 10 and 11.
The circuit effectively performs quadrature detection by measuring the voltage across L16 and the parallel 82pF ca-
Resistors (0.25W, 5% unless
stated)
2 x 390ka 2 x 270kf/, 3 x
100ka 1 , x 47ka 1 x 33k11, 2 x
2241, 2 x 20kfl 2%, 4 x 15kfl,
1 x 12kfl, 3 x 10kfl, 6 x 10kf/ 2%,
1 x 8.2kfi, 1 x 7.5kfl 2%, 2 x
4.7kfl, 1 x 4.3kf/ 2%, 2 x 3k,f/ 2%,
1 x 2.2ka 1 x 330f1, 1 x 22kfl
horizontal cement trimpot, 3 x
10kfl horizontal cermet trimpot, 1
x 51(0, horizontal cermet trimpot
FIand stereo
decod r,
Capacitors
1 6.8µF tantalum
7 .01µ,F (10nF) miniature ceramic
‘
1 82pF miniature ceramic plate,
Philips 2222 652 58829
*a
i
-
,
pacitor. L17 limits the voltage swing
across the quadrature coil while the
4.3kfi resistor reduces the Q of the
tuned circuit to provide more linear detection.
The AGC output is extracted from
pin 18 and applied to gate 2 of Q6 in
the front end via a lkfl/331(11 voltage
divider. It operates when a strong signal
is present or when a strong out-of-band
signal is detected at the wideband AGC
input (pin 20). In the latter case, the
AGC acts to reduce intermodulation
distortion.
Pin 8 of IC2 provides the meter output signal which is split into three separate paths. First, it drives the signal
strength meter via D23. Second, it
drives the stop threshold (pin 13) via a
voltage divider consisting of a 4.7kfl
resistor and trimpot VR4. And third, it
drives the blend input of 1C3, the
LM1870 phase locked loop FM stereo
demodulator.
VR4 sets the stop input threshold
while VR5 sets the blend threshold (ie,
the signal level below which blending
from stereo to mono begins). The idea
behind blending is to improve the
nal-to-noise ratio at very low signal
levels. It does this at the expense of
stereo separation of the upper treble
frequencies.
In addition to the blend signal, 1C3
ELECTRONICS Australia, January 1986
Playmaster AM/FM
stereo tuner
also accepts the detected audio signal
from pin 15 of 1C2. This signal is fed
via two 2.2µF capacitors to pins 2 and
19.
VR6 sets the frequency of the VCO
which forms part of the phase locked
loop. The PLL locks onto the transmitted 19kHz stereo pilot tone and drives
an electronic switch at a 38kHz rate to
decode the stereo information.
Q9 connects to the forced mono input
(pin 4). When Q9 is on, the input is
pulled low and the VCO is stopped,
thus forcing mono reception.
The 50As de-emphasis components
are at pins 14 and 15. The parallel 15k11
and 22kQ resistors set the output level.
The left and right channel audio outputs appear at pins 13 and 12 and are
AC-coupled to 19kHz notch filters
based on L18, VR7 and L19, VR8. Adjustment of the notch filter frequency in
each channel is by means of a tuning
slug in the relevant inductor, while the
associated trimpot adjusts the sharpness
and depth of the null.
Following the notch filters are two
simple third order low pass filters based
on IC8b and IC8c. These roll off the response above 19kHz to remove the
residual 38kHz switching components.
The resulting left and right channel
audio outputs appear at pins 7 and 8
and are fed to pins 11 and 4 of 1C13.
Audio switching
IC13 is a 4052 analog multiplexer/
demultiplexer used here as a 2-pole
3-position switch.
The A and B inputs control the switch
input selection. Input A selects either
the AM or FM audio inputs. When A is
high, the FM audio at inputs 3X and 3Y
are fed through to the outputs at X and
Y. When A is low, the AM inputs at
2X and 2Y are fed to X and Y.
Input B is the mute input and selects
either the OX, 1X or OY, 1Y inputs
which are all connected to ground.
Thus, when B is low (ie, during tuning),
the audio inputs are tied to ground and
the outputs at X and Y are muted.
Inverting op amps IC8a and IC8d
buffer the X and Y outputs of 1C13.
These each have a gain of 1.44 and provide a nominal 450m.V RMS audio output signal.
Microprocessor control
The A and B control signals for IC13
are derived from IC1 which is the NEC
microprocessor. In the case of the A
input, the control signal is applied from
pin 29 via inverters IC9d and IC9e. The
B input is direct driven by pin 2.
IC9e also drives Q10, Q11, Q12 and
Q13 to switch the power supply rails to
the AM and FM tuners. When pin 13 of
IC9e is high, Q12 and Q11 are turned
on and power is supplied from the
+12V regulator to the FM tuner.
When pin 13 of IC9e is low, Q12 and
Q11 are off and Q13 is on. This
switches on 010 so that power is now
applied to the AM tuner.
Pin 30 of IC1 (ST) controls mono/ste-
reo switching of the AM and FM
tuners. When the tuner is switched to
mono, pin 30 goes high and the output
of IC9b goes low to switch on the mono,
LED indicator.
Assumihg that FM is selected, Q9
also switches on and pulls pin 4 of the
FM stereo demodulator (IC3) low. If
AM is selected, pin 7 of IC9b goes low
and pulls pin 9 of the AM stereo
demodulator (IC4) low via D8.
Pin 9 of 1C4 is also connected via D7
to the mute output of IC1. This forces
pin 9 low during muting, and enables
stereo reception almost immediately a
station is received. Wtthout this feature,
the decoder would detect noise during
tuning and go into a long count mode
before switching to stereo.
Control loop
The synthesised control loop for the
AM and FM tuners involves local oscillator buffer stages Q16 and 017, dual
modulus prescaler IC11, and error output buffer stage Q15 and 014.
Pin 11 of IC1 drives the error output
buffer. It controls the buffer such that,
if the local oscillator frequency is lower
than the internal reference frequency,
the error voltage is low and Q15 and
Q14 turn off.
Conversely, if the local oscillator frequency is greater than the internal
reference, the error voltage goes high
and Q15 and Q14 turn on. When both
frequencies are equal, the error output
floats (le, goes open circuit).
A high voltage supply for the error
output buffer is derived from an
LM317T 3-terminal adjustable regulator. The 2.7kfl resistor connected between the adjust terminal and ground
sets the output of the LM317 to +30V.
015 and Q14 then set the tuning volt-
The new Playmaster tuner is built into a slimline rack-mounting case fitted with a screened front panel.
ELECTRONICS Australia, January 1986
I
a,
ELECTRONICS Australia, January 1986
%3
Playmaster stereo
Multiplexing
Apart from synthesis control, IC1
also drives the multiplexed display. DlD6 are the digit driver outputs while the
segment driver outputs are from Sa and
Sg.
The D1-D6 outputs are fed to Schmitt
trigger inverters IC12a to IC12f and
these drive transistors Q18-Q23. Q19Q22 switch the display digits while Q23
switches the memory indicator LEDs.
Q18 switches the FM and AM LED indicators.
The Sa to Sg segment outputs drive
0
age applied to the varicap diodes in the
tuner front ends.
Q16 and Q17 buffer the FM and AM
local oscillator outputs. For FM, buffering is achieved using FET Q16 which
has L20 as its drain load. This stage
drives IC11 which divides by either 16
or 17, depending on the modulus control output from IC1 (pin 16).
The output of IC11 is fed to the FM
oscillator input of IC1, divided by an internal programmable divider, and compared with the reference frequency, as
discussed last month.
tuner
Power supply
'
DECIBELS
AUDIO OUTPUT AT 1080kHz
9kHz
WHISTLE
FILTER
-
100
20
1k
HERTZ
,
10k
20k
AUDIO
STEREO BEACON
METER
0,
, . . . .
to,
METER
SlElt0 WITH BLEND
--.\
STEREO
4.
k
•
I
;
I
I
o
0O'
This graph plots the bandwidth of the AM tuner. The response is 3dB down at
5.5kHz, with a deep notch at 9kHz due to the whistle filter.
DECIBELS
the display via 75492 display drivers.
Note that 101(11 resistors are connected
in series with the inputs to these
drivers. Tbese reduce the current drawn
from the segment outputs of IC1 and
thus help reduce the multiplex noise induced into the tuner circuitry.
In addition to driving the display
drivers, the Sa, Sb, Sc, Se and SI segment outputs are also connected via
diodes D28-D32 to the switch matrix.
The other side of the switch matrix is
connected to the KO to K3 inputs of
IC1. These inputs are normally held low
with the 5.6kfl resistors.
When a switch is closed, a high output from one of the segment outputs
will pull K3, K2, K1 or KO highs, depending on the particular switch
pressed.
Diodes D33-D36 select the various
programmed options in IC1. For example, D36 ensures that memory indication is by way of separate LEDs. With-.
out this diode, the memory display output would be in 7-segment format.
,
MONO
--...„........__________.
......
2
10
II
100 '
1
1k
.
2k
RF LEVEL AT 98MHz, 7511 (uV )
This graph plots the performance of the FM tuner. Ultimate signal-to-noise ratio is
75dB in mono and 70dB in stereo.
.
ELECTRONICS Australia, January 1986
The tuner circuitry requites several
rail voltages and these are derived from
a PL24/20VA transformer (shown on
the AM tuner circuit).
First, an unswitched positive supply
rail is provided by a full wave rectifier
circuit consiting of D11, D12 and a
470µ,F filter capacitor. This provides the
standby power for the 5V regulator connected to the VDD and INT-bar pins of
'Cl.
A 47,000µF (.047F) super capacitor is
also connected to these pins via a 680f1
resistor. Diode D27 isolates the super
capacitor from the regulator output.
The supercap retains the station settings
in memory when power is removed
from the circuit.
Following the power switch is a bridge
rectifier (D13-D16) which supplies
+15V and —17V rails. These unregulated DC rails drive several 3-terminal
regulators to give regulated ±12V rails
and two +5V rails.
Note that ICs 6,7,8, & 13 are supplied
with power via isolating diodes. This
has been done to provide a slow turnoff, thus preventing thumps in the audio
output when the tuner is switched off.
Diodes D17, D18 and their associated
capacitors function as a voltage doubler.
The output of the doubler appears at
the cathode of D18 and supplies a
nominal +51V rail to the LM317 30V
regulator.
That completes the circuit description.
Next month we will describe construction and alignment.
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ELECTRONICS Australia, January 1986
_STEREO
2
0
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4
PLAYMASTER STEREO AWFM TUNER
111.10 .11.111.111.111010
Third article has the construction details
aster
Ia
stereo
Pt. 3
iffier
Although the circuit of our new Pla ymaster
AM/FM Stereo Tuner is fairly complex,
construction is quite straightforward. This
month, we detail the PCB assemblies, give the
coil winding details, and present a complete
wiring diagram.
by JOHN CLARKE
Because the tuner circuit includes a
number-of specialised components, we
recommend that it be built from a complete kit. This constructional article will
assume that pre-punched metalwork has
been supplied, along with a screenprinted front panel and all other necessary parts.
A main single-sided printed circuit
board (PCB) coded 85tu12 and measuring 330 x 220mm accommodates most of
the tuner circuitry. This includes the
AM tuner, FM IF strip, filters, and
microprocessor control components.
A smaller double-sided PCB coded
85fm12 and measuring 94 x 49mm is
used for the FM front end. This board
is shielded with a tinplate box and secured to the main PCB with screws and
nuts. Electrical connections between the
two boards are via an 8-way pin header.
A second double-sided PCB accommodates the display and switch components., Coded 85db12 and measuring 370
x 35mm, it is secured to the front panel
of the tuner case. Rainbow cables connect between this PCB and the main
PCB via 8-way pin headers and match-
ELECTRONICS Australia, February 1986
ing cable connector sockets.
Finally, a single-sided PCB coded
85ps12 and measuring 65 x 100mm is
used for the power supply circuitry.
The complete tuner circuit is housed
in a slim-line rack mounting cabinet
measuring 430 x 254 x 44mm.
Commence construction by inspecting
the PCBs for shorts between tracks or
breaks in the copper pattern. Check
also that all the holes have been drilled
and that a square cutout has been made
in the main board for IC1.
If the square cutout has not been
made, proceed as follows: Position IC1
on the underside of• the PCB and line
up the IC pins with the copper tracks.
Now mark the outline of the IC body at
each corner with a pencil and drill a
large hole in the centre of the marked
area.
The cutout can then be carefully filed
to the correct size. Once completed, the
IC should sit neatly in the hole with all
pins lined up with the copper tracks.
Do not solder IC1 in position at this
stage.
Jr
Begin assembly of the PCBs by installing ,PC stakes at all external wiring
points. These points are clearly indicated on the wiring diagrams. PC stakes
are also used on the main board to terminate the connections from the loop
antenna sockets and to terminate the
leads to Ti.
Note that PC stakes 1 to 8 on both
the main and power supply PCBs are
inserted upside down (ie, with the
shorter section on the component side).
This is to allow the power supply wiring
to be run to the underside of each PCB.
The PC stake on the display PCB (at
point 11) is also inserted this way. All
other stakes are inserted conventionally,
with the longer section on the component side of the board.
Main PCB
Continue assembly on the main PCB
by installing all the low profile components. These include the wire links,
resistors, diodes, ICs and transistors.
Note that some of the resistors are 2%
tolerance types. These are marked with
a star on the parts layout diagram.
Check the orientation of the diodes,
transistors and ICs when they are being
installed. Be sure to use the correct
semiconductor type at each location.
A special technique is used for soldering IC1 into position. This is a surface-
mounting component containing 52
closely-spaced leads. As a result, normal soldering methods will cause solder
bridges between the tracks.
First, use your soldering iron to tin
each of the copper track lands where
the pins of the IC will make contact.
Use a soldering iron temperature that is
just sufficient to melt the solder and
quickly tin the copper with a thin layer
of solder.
along each of the pre-tinned leads of
IC1 to clean them. The IC can then be
installed from the copper side of the
board with the pin 1 indication (a dot in
one corner) positioned as shown in the
parts layout diagram.
To solder the IC, first clean the tip of
your soldering iron with a damp sponge
to remove any excess solder. Now heat
each corner pin of the IC along its
whole length so that it melts the solder
on the copper track below. At the same
time, use a small screwdriver to hold
the heated pin hard against the PCB
until the solder cools.
The remaining leads of IC1 are then
soldered in similar fashion.
The main PCB assembly can now be
completed according to the wiring diagram. This involves installing the
capacitors, ceramic filters, trimpots,
8-way pin headers, regulator ICs and
the crystal.
Note that the display +5V regulator
lies flat against the PCB and is fitted
with a small U-shaped heatsink. Apply
a smear of heatsink compound to the
back of the regulator tab before bolting
it down.
Six different capacitor types are used
on the main PCB: electrolytic, tantalum, supercap, metallised polyester and
two types of ceramic. The electrolytics
and tantalums are the only polarised
types. The supercap is non-polarised
and an be inserted either way round.
The Philips miniature ceramic plate
capacitors are flat-bodied types with yellow bodies and coloured tops. Do not
substitute for these capacitors otherwise
the tuner will be microphonic. They are
marked on the parts layout diagram
with a small cross.
The three trimmer capacitors in the
AM tuner section should all be oriented
so that the flat side of the trimmer body
is inserted into the ground track.
Ceramic filters
Five ceramic filters are used in the
circuit, two in the FM tuner and three
in the AM tuner. The SFE10.7ML
ceramic filters in the FM section (CF1
and CF2) have a dot on the body to indicate the output pin.
The SFP450D can only be installed
one way, while the SFZ450C3N narrow
Repeated from last month's issue, this view shows the layout inside the chassis. The FM front end is at bottom right.
ELECTRONICS Australia, February 1986
17
Playmaster stereo tuner
•
:
•• : •
Here is the parts layout for the main PC board.
ELECTRONICS Australia, February 1986
;
• :
band ceramic filter should be installed
so that the arm of the cross embossed
on top of the filter body is adjacent to
the right hand side of PCB. The
CSA3.6MT7 resonator can be installed
either way round.
Table 1
Coil
Type
Wire
Turns
Start
Finish
LI
7210
36B&S
50
jumble wound
pin 4
pin 5
L3
El
36B&S
60
36B&S
60
bifilar wound
36B&S
46
jumble wound
pin 5
pin 4
pin 4
pin 6
pin 2
pin 3
36B&S
6
36B&S
70
7
36B&S
36B&S
9
jumble wound
pin
pin
pin
pin
pin
pin
pin
pin
Coil winding
Fig.1, Fig.2 and Table 1 show the coil
winding details. To avoid confusion, we
recommend that each coil be soldered
into circuit as it is completed.
The 16-turn centre-tapped primary of
T1 is bifilar wound (see Fig.2). To do
this, cut two 550mm lengths of 30B&S
enamelled copper wire (ECW) and twist
the two wires together using a hand drill
until there is about one twist every
3mm.
Wind 16 turns on the toroid and
determine the ends of each winding
using a multimeter. The 50-turn secondary can now be wound on the opposite
side of the toroid using 36B&S ECW.
Fig.2 shows how the primary and secondary windings are connected to the
PC stakes on the main PCB. The toroid
is secured to the PCB using two wire
straps as shown in the layout diagram.
Ll is a standard 7210 coil which re-
2
4
2
6
L5
El
L6,L7
PL14/8 36B&S
290
jumble wound
pin 3
pin 5
L15
E3
308&S
16
30B&S
7
jumble wound
pin 1
pin 4
pin 6
pin 3
L16
A5
pin 1
30B&S
16
single layer wound
pin 6
L18,19 PL14/8 36B&S
2,51.1
jumble wound
pin 3
4
3
1
5
pin 5
26B&S
13 turns on F16 slug
single layer wound
quires an extra winding between pins 4
and 5. To do this, first remove the
metal cover from the coil baseplate.
This done, jumble wind 50 turns of
36B&S ECW on the stem above the ferrite shield for the main coil. A few
drops of molten candle wax over the
L9,L10
6.51
coil will hold the windings in place.
Clean the ends of the wire with a
sharp knife or fine glass paper and solder them to terminals 4 and 5. Finally,
replace the metal shield. 1
r
L3 is wound 9.}r an El coil assembly.
Cut two
lengths of 36B&S ECW
and twist them together using a hand
drill so that there is about one turn
every 3mm. Wind on 60 turns and separate each winding by testing for continuity with a multimeter.
It is important that the start of one
winding be connected to pin 5 and the
start of the other to pin 4. The finish
ends of the windings go to pins 4 and 6
respectively.
The 46 turns of 36B&S wire can now
be wound on top of the bifilar winding.
This done, slip the ferrite cylinder over
the winding, install the plastic cover and
screw in the ferrite slug. Finally, replace
the metal shield.
L5 is also wound on an El coil assembly and is critical for correct oscillator
operation. Table 1 has the winding details. Be sure to wind all coils in the
same direction and seal the windings
with wax after they have all been
completed.
L12
7.51
L8
1T
L14
1.5T
L13
4.5T
a
EARTH
PIN
•
• •
1 2 3
L6,L7,L18,L19
VIEWED FROM ABOVE
2 Lir-- 8
L1,L3,L4,L16
VIEWED FROM ABOVE
WIRE : 0.8 EC
4 ID
WIRE : 0.8 EC
4 ID
WIRE : 0.6 EC
4 ID
Fig. 1
DIMENSIONS IN MILLIMETRES
STAKES ON PCB
4392R'2
TOROID
EARTH
LOOP
ANTENNA
501, 36 BBS ECW
161, 30 B&S ECW
Fig. 2
TO L1
WINDINGS
9 22
95
A = 7 DIA
B = 3.2 DIA
MATERIAL: 0.3 TINPLATE
Fig. 3
DIMENSIONS OF MILLIMETRES
This diagram shows the dimensions of the metal
shield for the FM front end.
•
Parts layout for the FM front end. Theparts are
mounted on the track (blue) side of the PCB.
ELECTRONICS Australia, February 1986
9
Playmaster stereo tuner
••,•••••
•
Above: view of the FM front end. The coils are waxed after alignment to prevent microphonics. At right are the parts layout diagrams for the display PCB.
L6, L7, L18 and L19 each require 20
turns of 36B&S ECW wound on PL14/8
formers. These coils are best wound
using a hand drill. The coil former can
be held between two washers with a
bolt and nut to secure the assembly.
The bolt is then held in the drill chuck.
A small amount of molten wax can be
used to keep the winding in position.
Alternatively, insulation tape can be
used.
Note that there are two halves to the
PL14/8 potcores: the basecore which includes an integral nut, and the top half
from which the inductance adjustor enters to screw into the nut. The two
halves go together and enclose the coil
former.
This assembly is housed within the
brass container with the spring located
between the top of the container and
the top half potcore.
Be sure to solder the leads of the
windings to pins 3 and 5 as shown on
the baseplate diagram. The baseplate
then inserts into the brass container and
is aligned so that the rectangular cutout
in the side of the container coincides
with the slot on the baseplate. Tabs on
the container bend over to hold the
completed coil assembly together.
L16 and 121 are relatively straight-
forward and consist of single layer windings on their respective formers (see
Table 1). Seal the L16 winding with wax
after it has been completed.
FM front end
The first thing to note here is that the
parts are installed on the track side of
the 85fm12 double-sided PCB. This
means that the component leads must
be soldered on the component side of
the PCB and, in some cases, on the
groundplane side as well.
The procedure is quite simple: just
remember to solder each component
lead wherever it passes through a copper pad.
Begin by installing the six PC stakes
(two for the antenna input and four to
support part of the metal shield). The
resistors, capacitors, transistors and
varicap diodes can then be installed, together with inductor L11.
Keep all component leads as short as
possible. That is mandatory if it is to
perform well.
es •
The 8-way pin header is shown dotted
on the parts layout diagram. It is
mounted on the underside of the board.
Note that several through-board links
must be installed adjacent to the pin
header.
The trimmer capacitors should be ori-
0.g
Playmaster stereo
tuner
The assembled display PCB. Note that many of the parts are mounted using Molex pins (see text).
ented so that the pin on the flat side of
the trimmer moulding connects to
ground.
Coils
Diagrams for the air wound coils are
shown in Fig.2. These should all be
tightly wound on a 4mm mandrel (eg, a
5/32-inch drill bit) to agree with the
dimensions shown on the diagram.
Be sure to wind each coil in the direction indicated in Fig.2 so that it will correctly fit the PCB. Remove the enamel
from the ends of the windings before
soldering.
L15 is wound according to the data in
Table 1 but note that the metal cover is
not used with this coil. Note also that
the coil must be waxed to prevent microphonic effects. The pins of L15 are
soldered to the underside of the PCB
only.
Metal shield
A tinplate metal shield surrounds the
FM front end and the diagram for this
is shown in Fig. 3.
Cut the tinplate to size with tinsnips
and bend up the pieces with flat nose
pliers. This done, drill holes for the 75ohm panel socket and attach it to the
panel using machine screws and nuts.
The side pieces can then be soldered to
the ground plane of the PCB and the
corners soldered together.
The inner shield piece is soldered at
either end to the side pieces and also to
the four PC stakes located in-line across
the PCB.
Connections between the 75-ohm
socket and the PCB are made using
short lengths of tinned copper wire.
The FM front end module is secured
to the main board using screws and
nuts. First, insert the screws from the
top of the FM front end PCB and screw
on the nuts. The nuts are then soldered
to the PCB groundplane and the screws
removed.
Finally, mount the module in posi-
tion, secure it by inserting the four
screws from beneath the main PCB, and
solder the 8-way pin header.
That completes the FM front end.
Display PCB
The display . PCB (85db12) involves
several unusual construction methods,
so it would be wise to read the following procedure carefully.
There are two overlay diagrams, one
showing the components on the top of
the PCB and the other showing the
components mounted on the underside.
Begin assembly by installing the resistors, diodes, transistor and IC10 on the
top of the board. Note that some of the
resistors are mounted end-on. As before, component leads must be soldered
to both sides of the PCB.
Those pads that do not hold component leads are used for through-board
links. There are nine of these throughboard links in all.
LED 4, LED 5, the pushbutton
switches and the 7-segment displays are
all mounted using Molex pins. Take
care not to get solder inside the pins
when soldering them to the top of the
board. You can avoid this by soldering
on the flat side of the pin only.
Once the Molex pins have been
mounted, the displays and switches can
be installed. Orient the switches so that
the flat of each switch body faces the
right hand side of the PCB.
The 7-segment displays and switches
are pushed all the way into the Molex
pins, while the LED 4 and LED 5 bar
modules are only partially inserted.
Line them up with the tops of the 7segment displays, then solder the bar
modules to the Molex pins to secure
them.
LEDs 2 and 3 are installed by
standing them off the' PCB as far as
possible.
The NSM39152 bar display module is
mounted proud of the PCB using
0.7mm tinned copper wire. You will
ELECTRONICS Australia, February 1986
need 12, 15mm lengths. Solder these
into the edge connector bus, then
mount the module on the PCB so that it
lines up with the 7-segment displays.
The rear side of the display board
carries the 8-way pin headers and a
1O LF electrolytic capacitor. Solder these
in position, then return to the top of the
board and install LED 1 and LEDs 6-11
in position (but don't solder them yet).
Next, mount the display PCB on the
sub-front panel using 12min standoffs
and countersunk screws and nuts. The
front panel can then be bolted to the
case using the Allen screws supplied,
and the LEDs pushed into the front
panel holes. Check that the LEDs are
all correctly aligned before soldering
their leads.
At this stage, you should check that
all switches operate without sticking before removing the display board from
the front panel assembly. Any switches
that catch in the front panel holes can
be adjusted by carefully bending the
supporting Molex pins.
Construction of the display PCB can
now be completed by soldering the
LEDs to the pads on the top side of the
board.
Power supply PCB
Assembly of the power supply PCB
(85ps12) is straightforward. The main
point to watch here is that one of the
470µF capacitors must be rated at
63VW (to allow for variations in mains
voltage). The other two 470µ,F capacitors are rated at 25VW.
Check the orientation of each component before soldering. The diodes are
all 1N4002 types.
Chassis assembly
Now that all the PCBs have been
completed, wiring can proceed between
the power supply PCB and the main
PCB. This wiring is run beneath the two
PCBs and must be installed before the
boards are mounted in the case.
Playmaster stereo tuner
The display board wiring can now be
completed by running a short length of
hookup wire from point 11 back to the
corresponding point on the main board.
Rear panel wiring
The rear panel carries the antenna terminals and a pair of RCA audio output sockets.
With this job completed, the various
items of hardware can be mounted.
Begin by fitting the four rubber feet to
the corners of the baseplate, then
mount the antenna terminals, RCA
sockets and power transformer. The
wiring diagram shows the general layout
inside the chassis.
The main PCB is mounted on 6mm
spacers and should be located so that
the 75-ohm antenna socket passes
through a matching hole in the rear
panel. We secured each of the untapped
spacers with a nut before installing the
PCB. A second set of nuts is then used
to secure the board to the stand-offs.
The power supply PCB is mounted on
12mm spacers directly in front of the
transformer.
The method of securing the power
on/off switch will differ according to the
brand of switch. It must be mounted so
that the pushbutton knob protrudes the
correct disance through the front panel.
In some cases, the switch can be
mounted directly on the sub-front
panel. In other cases, a mounting
bracket may be required to move the
switch away from the front sub-panel.
We used a mounting bracket made
from fibreglass board material. This was
stood-off the sub-front panel using 6mm
spacers.
The next step is to mount the display
PCB on the sub-front panel using the
12mm standoffs. • Note that it may be
necessary to use insulating washers between the PCB and standoffs to avoid
shorting out the PC tracks. Check this
point carefully or you'll strike trouble
later on.
The wiring between the display and
main PCBs is run using four 8-way
cable assemblies. Cut four lengths of
8-way cable — two at 260mm, one at
330mm, and one at 100mm. Separate
the ends for 25mm and strip 2mm of insulation from each wire.
The cables can now be connected to
the sockets. Insert the cable through the
connector socket shell and crimp and
solder each wire to the crimp terminals.
This done, pull the terminals back into
the connector socket.
When the cable assemblies are completed, they can be plugged into the
PCB headers. Connect the long cable
between the A headers, the two
medium length cables between the B
and D headers, and the short cable between the C headers.
Check that pin 1 of each header on
the main PCB matches up with its corresponding pin 1 on the display PCB.
Parts layout for the power supply PCB. Note the 470µF 63VW electrolytic capacitor.
ELECTRONICS Australia, February 1986
A dual screened cable connects the
left and right audio outputs on the main
PCB to the output RCA terminals.
Note that the cable screen is soldered
directly to a PCB stake on the PCB adjacent to the output sockets. From
there, a short length of hookup wire
also runs to the outer contacts on the
RCA sockets (see wiring diagram).
The AM antenna terminals are connected to the main board using short
lengths of hookup wire.
Mains wiring
The mains cord passes through the
rear panel and is clamped with an inline cord clamp grommet. The earth
wire (green/yellow) is terminated to an
earth lug while the active (brown) and
neutral (blue) leads are terminated on
the transformer pins using bullet connectors. These connectors should be insulated using plastic sleeving.
Scrape away the anodising from
around the mounting hole before bolting the earth lug to chassis. This is essential to ensure a good earth contact.
Make the earth lead slightly longer than
the active and neutral leads so that it
will be the last to break if strain is
placed on the cord.
The transformer secondary is connected to the power supply PCB using
the four leads supplied. Connections to
the on/off switch should be run using
mains-rated hook-up wire.
Final assembly
A negative film artwork will be supplied with each kit and this should be
affixed to the sub-front panel using
double-sided adhesive tape. Position the
artwork so that the 7-segment displays
and the signal strength meter are all
visible.
Finally, the plastic sheet can be fitted
to the front panel cutout and the panel
bolted to the case. In the prototype, the
plastic sheet was held in position by virtue of being a force fit into the panel
cutout.
Alternatively, the plastic can be secured by applying a thin film of adhesive to several points along the edges.
That's all we have space for this
month. Next month, we will continue
with the alignment details. In the meantime, do not be tempted to switch the
unit on as there are a few important
points to follow.
AM LOOP
ANTENNA
INPUT
1•
•
•
•
••
••
••
•
••
•
••
•
•
0
••
•
•••
DISPLAY PCB
7• •8
RCA AUDIO
TERMINALS
RIGHT
D.
LEFT
11
6•
50
11
•
•
•
•
•
•
•
FM FRONT END PCB
FM 750
INPUT
••
•
•••
•
A
EARTH GREEN YELLOW
CORD
CLAMP
GROMMET
6•
7•
2•
8•
MAINS
CORD
POWER SUPPLY PCB
•
•••
•
•
•
5•
3•
Si
POWER
SWITCH
4• 9•
ELECTRONICS Australia, February 1986
Step-by-step alignment details
PlaYntaSter
AM/FM
stereo tuner
Alignment of the Playmaster AM/FM Stereo
Tuner is quite straightforward and requires
only a few simple tools. The procedure mainly
involves adjusting the various tuned circuits in
the RF, IF and local oscillator stages on a
step-by-step basis.
by JOHN CLARKE
While most readers will be unfamiliar
with the alignment of superheterodyne
tuner circuits, the procedure is really
very simple. You don't need a lot of
fancy tools and instruments either. The
only tools required are a small screwdriver, a plastic alignment tool, a tuning
wand and a multimeter.
An audio signal generator and a digital frequency meter would also be
handy for adjusting the 9kHz and
19kHz notch filter circuits, but are by
no means essential.
An unusual but necessary tool is the
coil tuning wand, which you will have to
make yourself. It consists simply of a
short length of plastic tubing with a
piece of brass (a brass nut or screw) in
one end and a piece of ferrite (coil
slug) in the other. You can use the F16
slug from coil L16 to make a temporary
wand.
The tuning wand is used when making adjustments to the FM front end.
The plastic alignment tool is used for
adjusting the coil cores and trimmer capacitors and can be purchased from
your kit supplier. Do not use a screwdriver or other metallic object, as these
will affect the circuit operation and give
incorrect results.
ELECTRONICS Australia, March 1986
Switch on
Initially, the tuner power switch must
be switched on before mains power is
applied. This is to ensure correct resetting of IC1. After that, the tuner may be
switched on and off using the power
switch in the conventional manner.
Note: this switch-on procedure should
also be adopted if the tuner is disconnected from the mains for more than a
few days.
Check that the power switch is on
(confirm this with your multimeter),
then plug in the power cord and switch
on the mains. Now check the supply
voltages: there should be +5V at the
output of each of the three 5V regulators, +12V and —12V on the 7812 and
7912 regulators respectively, and about
+30V on the output of the LM317.
If any of these voltages is incorrect,
check the input voltage to the regulator.
If all is correct so far, check the
operation of the front panel switches
and the display. There should be a frequency reading on the :display and either the AM or FM indicator should be
lit. Pressing the AM/FM switch should
change both the indicator and the frequency reading.
Next, check that the +12V rail is
switched to the AM circuit when AM is
selected, and to the FM circuit when
FM is selected. For AM, check for
+12V on pin 6 of IC4, for FM, check
for +12V at pin 17 of IC2.
Assuming all is well, operate the
TUNE buttons and check that the AM
display ranges from 522 to 1611kHz in
9kHz steps. Similarly, check that the
FM display ranges from 87.9 to 107.9
MHz in 100kHz (0.1MHz) steps.
Each memory LED should light when
its respective switch is pressed. Initially,
all the memories will probably be set to
the same frequency. To program each
memory, select the required frequency
using the TUNE buttons, then press the
ME switch and the required memory
switch.
The ME LED should extinguish as
soon as a memory switch is pressed, or
if the ME switch is re-pressed. If no
switch is pressed it should automatically
extinguish after five seconds.
Next, check that the SEEK control
sends the tuner scanning up the frequency band. Don't expect it to lock
onto a station at this stage though. That
won't happen until after alignment.
The tuner should stop seeking as
soon as another button (other than
MONO) is pressed.
Finally, check that the programmed
memories remain intact when the tuner
is switched off and on at both the power
switch and mains.
FM alignment
To align the FM front end you will
need the tuning wand, alignment tool
and multimeter.
The first step is to set the local oscillator range which must be from (87.9 +
10,7)MHz to (107.9 + 10.7)MHz. This
is easily achieved by measuring the varicap voltage. The procedure is as follows:
(1) Select FM by pressing the
AM/FM switch, then adjust the white
3-11pF trimmer capacitor associated
with L13 to about half-setting. Note
that the trimmer is at minimum capacitance when the pointer faces the flat
side of the trimmer, and at maximum
setting when it faces away from the flat
side.
(2) Measure the output voltage from
the LM317 regulator (between ground
and the metal tab of the regulator) and
write it down.
(3) Connect your multimeter between
the link marked "varicap voltage" and
ground (use the tinplate shield for
ground), and set the display on FM to
read 87.9MHz. Adjust the spacing between the L13 coil windings for a reading of about 3V.
Note that opening the coil decreases
both the inductance and varicap voltage. Conversely, closing the coil increases the inductance and the varicap
voltage.
Note also that the above conditions
are only valid when the local oscillator
is locked at the frequency indicated by
the display plus the 107,9MHz offset. If
the oscillator is not locked, the varicap
voltage normally stays at around 28V.
(4) Once the varicap voltage at
87.9MHz has been set, set the display
to 107.9MHz by pressing the TUNE
down button. This done, adjust the
3-11pF trimmer capacitor (white) for a
reading that is 2.5V less than the
LM317 output voltage. Normally, this
will be about 27V.
Note that the alignment tool may affect the FM local oscillator, so always
read the voltage with the alignment tool
out of the trimmer.
(5) Check that the varicap voltage at
107.8MHz is lower than at 107.9MHz.
If not, readjust the trimmer for a
slightly lower varicap voltage reading at
107.9MHz and check again.
(6) The new trimmer capacitor setting
will have altered the voltage at
87.9MHz. This means that L13 will require further adjustment. Set the display to read 87.9MHz and readjust L13
for a reading of about 3V.
(7) Return to 107.9MHz and readjust
the trimmer as in steps 4 and 5. Repeat
the above process until both voltages
are correct.
RF filters
The next step is to align the RF filters
so that they track with the local oscillator. This requires two good off-air signals, one near 90MHz and the other
around 106MHz. (A complete list of
station frequencies appears elsewhere in
this issue.)
Note that if there are no local stations near these frequencies or if there
is only one FM station, then alignment
accuracy will suffer. Where there is
more than one station, choose two that
are widely separated.
If only one station is available, alignment can only be achieved for that station. When another station begins transmission, the RF stage will require further adjustment.
Alignment of the RF filters requires
use of the tuning wand. Here's how it
works:
When the ferrite end of the wand is
inserted into the coil, it increases the inductance. If the signal level increases,
the coil needs to be made more inductive and this is achieved by compressing
the coil.
Baal
411, 1 I 41, ift
ilf I I 1
411
* *
et
0111111111111111111111
Similarly, when the brass end is inserted into the coil, the inductance is
decreased. If the signal level increases,
the coil should be made less inductive
by opening up the coil windings.
When the coil is adjusted so that the
signal level goes down or, does not
change when the ferrite and brass ends
are independently inserted, the coil is
correctly tuned. Here's what to do:
(1) Connect an FM, antenna to the
75-ohm input. This can be a dipole, an
FM Yagi or log periodic (wide band)
TV antenna. If the antenna is for a
300(1 termination, a 300-75(1 balun
transformer will be required.
(2) Adjust each of the 4.2-20pF trimmers (red) associated with L9, L10 and
L12 to about half setting.
(3) Connect a multimeter between
ground and test point TP1, and select
the station near 90MHz. Program this
station into memory 1 (press ME and
memory 1).
(4) Using the tuning wand (see
above), adjust L9 and L10 for maximum signal reading on the multimeter.
Note that the signal from L9 couples inductively to L10. Do not attempt to
alter the 4mm edge to edge spacing between them as set by the PCB hole
positions.
During this entire procedure, make
frequent checks of the AGC voltage at
pin 18 of 1C2. If it drops below +5V,
temporarily short the AGC line to
ground until the adjustment is complete.
(5) Tune L12 for maximum reading
with the multimeter connected to TP1.
Don't forget to check the AGC. (Note:
it would be nice to have two multimeters, one to monitor TP1 and the other
to monitor the AGC).
(6) Select the station near 106MHz
and program this into memory 2. Ad-
* 111 IIIL 111
Ili 11 II
Ilk Ilk 110. 111k
111011 111
PLAY TE STEREO AMfFM TUNER
41../...40411040.
Our new Playmaster tuner offers stereo AM performance matching that of professional studio monitors.
ELECTRONICS Australia, March 1986
as
Playmaster stereo tuner
just the 4.2-20pF trimmer capacitors
(red) with the alignment tool for a maximum reading (meter on TP1). Note: always check the reading after the tool
has been removed from the trimmer.
(7) Return to the memory 1 frequency
and re-align the coils again using the
tuning wand. Re-adjust the trimmers at
the memory 2 frequency. Repeat this
procedure until the coils and trimmers
both peak without further adjustment.
(8) Adjust L15 for a maximum signal
when receiving either the memory 1 or
memory 2 frequency.
(9) Impregnate the coils in the FM
front end with wax. This is to prevent
the coils from vibrating and producing
microphonics in the resulting audio.
Quadrature coil
(1) Remove the F16 slug from the
tuning wand and screw it into the L16
IF coil.
(2) Tune to a station that, gives at
least a level six reading on the signal
level meter. Connect the multimeter
across TP2 and TP3 and adjust L16 for
OV.
Seek adjustment
By now the FM tuner should operate
on Seek. The level of signal at which
the tuner stops is set by trimpot VR4.
Rotate the trimpot until the tuner only
stops at stations that give more than
level 5 on the signal level display.
This setting stops the tuner at stations
that will produce a noise free signal in
stereo. You can of course set this control so that the tuner stops at any level
of signal desired.
Blend adjustment
The blend adjustment at VR5 sets the
The Balanced
Loop Antenna
ANTENNA LOOP OF
INSULATED COPPER WIRE
TWIST
FEED-WIRES
TOGETHER
DIRECTION OF
TRANSMITTER
Fig. 1
ELECTRONICS Australia, March 1986
signal level below which blending occurs. We opted to keep the stereo signal-to-noise ratio above 40dB. This is
shown in the quieting curves published
in January 1986.
(1) Connect your multimeter between
the wiper of VR5 and ground. Tune to
a station that gives level 5 on the signal
strength meter.
(2) Adjust VR5 for a reading of 0.8V.
If you cannot find a station that provides a level 5 signal, try adjusting the
antenna until the correct signal level is
indicated (eg, try using a short length of
wire).
Stereo decoder
VR6 must be adjusted so that stereo
decoder IC3 can lock onto the 19kHz
stereo pilot tone. This can be achieved
in one of two ways:
(1) Set the mono/stereo switch to
stereo mode.
(2) If a frequency meter is available,
temporarily connect a 15kil resistor between the 19kHz output at TP4 and the
positive supply. Note that there are two
PC stakes provided for this. Connect
the meter to TP4.
(3) Disconnect the antenna, tune to a
vacant spot on the band and adjust VR6
for a reading of 19kHz on the frequency
meter. Remove the 15kil resistor.
Note that the circuit diagram shows
TP4 at ground potential. This is an
error — TP4 should go direct to pin 16
of IC3.
(4) If no frequency meter is available,
tune to a station and adjust VR6 for
stereo indication on the front panel.
Rotate the trimpot clockwise and find
the position where the stereo switches
off. Now rotate the trimpot anti-clockwise and find the position where stereo
ceases.
The correct position for VR6 is midway between these two locations.
19kHz filters
The 19kHz notch filters are tuned by
adjusting coils L18 and L19 and trimpots VR7 and VR8. This requires an
audio signal generator. If no audio signal generator is available, ignore this
step.
(1) If a frequency meter is available,
set the output frequency of the audio
generator to exactly 19kHz.
(2) If no frequency meter is available,
the following method will allow the
audio generator to be set to give a
highly accurate 19kHz signal. It requires
an audio amplifier and a loudspeaker.
Switch off the tuner and solder a 15k0
resistor between TP4 and the adjacent
PC stake for the positive supply of the
FM tuner. This done, connect a 22kfl
resistor between TP4 and the input to the
amplifier. SE.4
Finally, connect a 100kfl resistor between the audio generator output and
the same input of the amplifier.
Switch on the tuner and tune into a
station broadcasting in stereo. The
19kHz output from TP4 will now beat
with the audio oscillator output and this
can be heard via the loudspeaker. Adjust the frequency of the audio generator until no beat note is heard.
The audio generator frequency will
now be within about 20Hz of 19kHz.
(3) Alternatively, if a dual trace oscilloscope is available, compare the 19kHz
output at TP4 with the audio generator
frequency. Use the XY position on the
timebase control to display a Lissajous
figure. Both frequencies are the same
when the trace does not rotate.
(4) Now cut the input link to IC3 (as
marked on the overlay diagram) and
apply the 19kHz signal from the audio
generator to the IC3 side of the link.
In order to obtain a noise-free signal, the AM tuner circuit is designed
for use with a balanced loop antenna. Because the loop antenna is a
balanced circuit, it acts to reduce common mode interference.
The loop antenna should be made from a suitable length of insulated copper wire arranged as an upright rectangular loop. Ideally, it
should be oriented so that the plane of the loop points towards the transmitting antenna. It should also be located as close to the tuner as
possible to avoid long feedwires.
The pickoff point should be half way up one vertical side of the loop,
preferably the side furthest away from the transmitter. The two feedwires
should be twisted together and run to the antenna inputs of the tuner as
shown in Fig.1.
In strong signal areas, a small loop which surrounds a window may
be satisfactory. In most cases though, a much larger loop or a multiple
loop antenna will be necessary to give adequate signal strength.
Playmaster stereo tuner
Note that the signal level from the generator should not exceed 3V RMS. If
the generator cannot supply this amount
of signal, set the level to maximum.
Use your multimeter to monitor the
resulting 19kHz left and right audio outputs. This should be set to AC millivolts. Note that most digital multimeters
will not measure at 19kHz, so it will be
necessary to resort to a standard moving
coil meter. Alternatively, use an oscilloscope.
(5) Adjust the tuning slug L18 for a
null in the left channel. This done, adjust VR7 for best null. Similarly, adjust
L19 and VR8 for the right channel.
(6) Switch off, remove the 15kfl and
22kfi resistors, and remake the link to
IC3.
AM tuner local oscillator
As with the FM tuner, alignment of
the AM tuner begins with adjustments
to the local oscillator.
(1) Select AM by pressing the
AM/FM switch.
(2) Connect a multimeter between
ground and the emitter of Q4 and adjust trimpot VR1 for a reading of 1.6V.
This sets the output level of the local
oscillator.
(3) The next step is to set the local
oscillator range which must be from
(522 + 450kHz) to (1611 + 450kHz).
As for the FM tuner, this is achieved by
measuring the varicap voltage.
Rotate the green 3-30pF trimmer capacitor associated with L5 to about halfsetting.
(4) Connect a multimeter between
ground and the link marked "varicap
voltage". Set the AM display to read
522kHz and adjust the slug in L5 for a
voltage reading of 1.2V.
(5) Press the TUNE down switch to
select 1611kHz on the display. Adjust
the trimmer capacitor for a reading of
about 27V.
Note that the alignment tool may affect the oscillator, so always check the
voltage after the alignment tool has
been removed.
(6) Tune to 1602kHz and check that
the varicap voltage is lower than at
1611kHz. If not, readjust the trimmer
for a slightly lower varicap voltage at
1611kHz and check again.
(7) Repeat steps 4 and 5 and continue
until the voltages at each frequency are
correct.
Note that if you cannot arrive at the
correct voltages, the oscillator level
ELECTRONICS Australia, March 1986
should be slightly re-adjusted and the
procedure repeated.
RF filters & IF stage
The RF filters must now be aligned
so that they track with the local oscillator. Two strong off-air signals will be
required, one near 603kHz and the
other near 1395kHz.
If local stations are not near these frequencies, choose the two that are furthest apart. The low frequency station
can be as low as 531kHz, while the
high frequency station can be anywhere above 1206kHz.
To receive these, you will need to
construct a balanced loop antenna. This
should be connected as shown in Fig.1.
(1) Adjust the two trimmers associated with Ll and L2 to about half setting. Also, adjust the slugs in L1 and
L2 so that they protrude slightly from
the metal can. This will very roughly
align the front end.
(2) Connect the multimeter between
ground and the AGC point at the 10Old2
resistor (near D8) as indicated on the
overlay diagram.
(3) Select the station near 603kHz
and program this into memory 1. Adjust the slugs in L1 and L2 for a minimum reading on the meter.
(4) Tune the station near 1395kHz
and program this in memory 2. Adjust
the trimmers associated with Ll and L2
for a minimum reading on the meter.
(5) Repeat steps 3 and 4 and continue
until the coils and trimmers require no
further adjustment.
(6) Tune in any station that provides
good signal strength. Adjust the slugs in
L3 and L4 for a minimum reading on
the meter.
Checking tracking
performance
The AM section is now aligned at
two frequencies; ie, those programmed
into memories 1 and 2. At other frequencies, however, the alignment may
not be satisfactory. This can be checked
by selecting six stations which are
spread evenly from the low frequency
end of the band to the high frequency
end.
(1) Program the six selected stations
into memory.
(2) Select each station in turn and rotate VR1 slightly in either direction
from its set position. Check that the AGC
level is close to a minimum for each station — ie, within about 0.25V. Return
VR1 to its original setting after each station has been checked.
If tracking is good across the band,
you can skip the next section and proceed straight to the stereo decoder. On
the other hand, if the alignment is out
for sotne stations, the oscillator and RF
stages will require further adjustment.
This will involve adjusting the varicap
voltage range for the local oscillator
and retuning the RF stages.
The main tracking problem is likely
to be at the low frequency end of the
AM band. To cure this, the maximum
capacitance of the varicaps should be
reduced by increasing the varicap voltage at the low frequency end of the
band.
(3) Disconnect the multimeter from
the AGC and reconnect it between
ground and the link marked "varicap
voltage". Now select 522kHz and increase the voltage from 1.2V to 1.7V by
adjusting the slug in L5.
(4) Repeat steps 5, 6 and 7 in the section' "AM tuner local oscillator". Note
that VR1 may require further adjustment to accommodate the new range of
varicap voltage.
(5) Retune the RF coils as described
above under the heading "RF filters
and IF stage". Check again for correct
tracking and repeat this process until
tracking performance is satisfactory.
Note, however, that it is impossible to
obtain perfect tracking right across the
band.
Seek control
(1) Press the SEEK control and
check that the tuner stops on the next
local station higher up the frequency
band.
(2) In most cases, the sensitivity of the
SEEK control will be satisfactory for
local stations. To increase the sensitivity,
increase the 33pF capacitor at the base of
Q3 and vice versa.
An alternative here is to replace the
33pF capacitor with a yellow 6.8-48pF
Murata trimmer capactor. The trimmer
can then be adjusted to provide optimum sensitivity for the SEEK control.
Stereo decoder
(1) Tune in a station (either stereo or
mono) and measure the voltages at pins
10 and 19 of IC4 (MC13020P). These
should both be about 4V with respect
to ground.
9kHz notch filters
The left and right channel notch filters comprise L6 and VR2 for the left
channel and L7 and VR3 for the right
channel. These require adjustment to
null out the 9kHz tone generated by adjacent stations.
(1) If a frequency meter is available,
set the output frequency of the signal
generator to 9kHz.
(2) De-solder the positive ends of the
1µF capacitors at pins 7 and 8 of IC4.
Connect the signal generator output to
each filter input in turn and monitor the
corresponding audio output with a moving coil multimeter set to AC volts.
Note that up to 3V RMS can be supplied to the filter inputs. If the generator cannot supply this level, then set it
for maximum output.
(3) Adjust L6 for a null in the left
channel, then adjust VR2 for maximum
null. Repeat these adjustments, then
adjust L7 and VR3 for the right channel.
(4) If no frequency meter is available,
the filters will have to be adjusted by
ear. This should be attempted at night
when distant stations 9kHz away from
the local stations will cause loud 9kHz
whistles.
Connect the left output of the tuner
td your stereo amplifier, tune to a station with a loud 9kHz whistle and adjust the slug in L6 for minimum whistle.
This done, adjust VR2 to eliminate the
whistle completely.
(5) Connect the right output of the
tuner to the amplifier, disconnect the
left, and adjust L7 and VR3 to null out
the whistle.
That completes the alignment of the
Playmaster Stereo AM/FM Tuner.
AM bandwidth
Some readers may be keen to experiment with a wider AM tuner bandwidth. This can be obtained by altering
the response of the audio output filters,
IC7a and IC7b.
For example, if the .0018F capacitors are changed to .0082µF, the 18k11
resistors to 5.8kil, the 22kfl resistors to
8.2kfl and the 12kfl resistors to 3.3kfl,
an overall response that is only 2dB
down at 8kHz and 6dB down at 10kHz
can be obtained.
Be warned, however, that the wider
frequency response will result in high
frequency monkey chatter becoming
quite noticeable at night, particularly in
poor signal areas. In most cases, the
original values will provide the best
overall compromise.
That's all on the new Playmaster
tuner for now. We'll take a break for a
few months before describing the infrared remote control. In the meantime,
settle back and enjoy the results of your
efforts thus far.
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at 1kHz This performance is very closely matched in the right channel.
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This graph shows the frequency response (upper trace) and residual noise (lower trate)
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These graphs by courtesy of Radio Manufacturing Engineers Pty Ltd.
ELECTRONICS Australia, March 1986 a..g
NOTES & ERRATA'
PLAYMASTER STEREO AM/FM TUNER (December 1985 , 2/TU/55): The four
Philips PL14/8 potcores used for the 9kHz no tch filters (L6 and
L7) and 19kHz notch filters (L18. and L19) wi 11 be suppl ied with a
different ferrite material from the original part speci fied. The
new type number is 4322 022 22265. Coil wind ing details for these
four coils are now 303 turns each using 36B& S enamelled copper wire.
Please alter these details in Table 1 of the February 1986 issue.
In the alignment article of March 1986 the adjustment of the
19kHz notch filters in step 4, page 80, should be made with the
FM tuner set in Mono.
The CSC500K7 50pF capacitor used with IC4, the MC13020P
AM stereo decoder, will be replaced with a 30pF type in
subsequent kits.
Some of the Philips miniature ceramic plate capacitor type
numbers have been changed due to supply availability. The
capacitance values, however, remain the same.
Notes and Errata
PLAYMASTER STEREO AM/FM
TUNER (December 1985-February
1986, File 2/TU/55-57): the following
points should be noted in addition to
notes and errata previously published:
(1) Diodes D7 and D8 are shown incorrectly oriented on the parts layout
diagram. The circuit diagram is correct.
(2) The 1µF capacitor on the collectors of 014 and 015 is shown with incorrect polarity on both the circuit and
layout diagrams.
(3) The 2.2kQ resistor shown connected to pin 9 of 1C4 on the parts layout diagram is incorrect. The correct
value is 1001d1 as shown on' the circuit
diagram.
(4) The anode of D9 should connect.
to the output of the +12V regulator,
not to the AM +12V as shown on the
circuit diagram for the AM Stereo
Tuner. The parts layout diagram is
correct.
In addition to the above, we recently
had an opportunity to inspect a tuner
which had been assembled from a Jaycar kit. Here's what we found:
(5) The four 5.61a1 resistors con
nected from KO, KI, K2 and K3 of IC1
to ground may need to be increased to
15kfl to increase, the contact, bounce
time for the switches. Note that this
modification is only necessary if the
memory LEDs do not light or only light
momentarily.
The resistors may need to be reduced
again to prevent false triggering (station
jumping) if the infrared remote control
circuit is subsequently installed.
(6) The 560pF capacitor across L3 at
pins 6 and 9 of 105 may have to be reduced to 470pF to enable tuning of the
coil.
(7) The 5.6kQ resistors in series with
VR2 and VR3 in the 9kHz notch filters
may need to be reduced in order to obtain maximum null.
(8) For correct operation of the Seek
control with FM, pin 12 of IC2 should
be connected to ground (pin 7) via a
221di resistor (any value between 101di
and 1 00kci will do). This resistor can he
installed on the copper, side of the PCB.
(9) The 220kfl resistor at the base of
05 may have to be reduced to as far as
47kfl to provide correct sensitivity of
the AM Seek control.
(10) Some readers may encounter
problems with the AM local oscillator at
the low frequency end of the band. This
is due to excessive output from the oscillator forward biasing the varicap
diode. The problem can be cured by
reducing the nine turns of the feedback
winding at terminals 5 and 6 of L5. Remove only a portion of a turn at a time
and allow the pin 5 lead to exit from
beneath the cylindrical ferrite ring
covering the coil.
The best procedure is to determine
how much of the winding needs to he
removed to stop the oscillator altogether (ie, when the varicap voltage
suddenly jumps to maximum) and then
to wind about 0.2 of a turn extra on the
coil. This done, check that the oscillator
operates reliably over the entire frequency range and when the' power is
switched off and on again. If not, increase the winding on the feedback coil.
Notes & Errata
PLAYMASTER STEREO AM/FM
TUNER (February 1986, File 2/TU/57):
several electrolytic capacitors are shown
with reversed polarity on the parts layout diagram on page 60. These are the
1000µ,F capacitor located at the bottom
right hand coiner of the PCB and the
two l0/.LF electrolytics immediately to
the right of the 7805 regulator (the one
with the heatsink) near the centre of the
board.
Notes & Errata
PLAYMASTER STEREO AM/FM
TUNER (December 1985, File 2/TU/5557): the 30pF compensation capacitor
which replaces the CSCSOOK7 50pF capacitor in the AM stereo decoder section has three terminal pins instead of
two. It should be installed with the centre pin connected to ground and the
outer pins both connected to pin 17 of
IC4.
Readers should also note that a
1-metre length of wire is required to
wind the 60 turns on coil L3, rather
than the 755mm length specified in the
article (page 61, Feb. 1986).
Finally, readers should note that L21
in the coil winding table (page 61, Feb.)
should have been listed as L20. L21 is a
standard off-the-shelf 22p,H choke.
Remote contr
for the
Playmaster tuner
For the final touch of luxury on your
Playmaster Stereo AM/FM Tuner you need
the Infrared Remote Control. With this you can
sit back and select any of the 12
programmed stations at will or tune to any FM
or AM station with the up and down tuning
buttons.
.
Are you an impatient radio listener,
dodging from one station to another
trying to find the music to suit your
mood? Are you a lazy listener, not
wanting to shift from your chair when
the station you have selected started
putting out the wrong notes? If so, you
by JOHN CLARKE
need this remote control accessory if
you are to obtain full enjoyment from
the Playmaster stereo AM/FM tuner.
You can be far more selective with.
the remote control. If a particular piece
of music or advertisement is not to your
liking, then you can zap onto another
station with a flick of
button-pushing digit. S'wonderful, S',narvellous!
Although the remote :.:Jntrol does not
mimic all the control functions available
on the tuner, it does allow remote tuning to any station. There are two ways
to do this.
'Firstly, each of the six AM and six
FM stations in memory can be selected.
This is done using the six memory.
switches in conjunction with the
AM/FM switch on the remote control.
Secondly, to access unprogrammed AM,
or FM stations, use the Tune up or
Tune down switches.
The functions not available on the remote control are Seek, Mono, ME
(memory enable) and Power on/off.
The remote control transmitter unit
consists of a small plastic case incorporating nine pushbutton switches. Two
infrared (IR) transmitting diodes located behind a small re-(' window at the
front of the case emit coded infrared
light. Power for the unit is supplied
from a small nine volt battery.
The remote control receiver circuitry
is part of the main printed circuit board
for the tuner. For receiving the IR
transmission an IR detector diode is located directly behind the neutral density
plastic screen used for the tuner display.
The transmit .and receive circuitry is
based on the Plessey range of remote
control ICs. There is one transmitter
and one preamplifier IC in this range,
and ten different receiver ICs. These
are suitable for TV remote control,
models, computers and other general
applications.
We used the SL49OB transmitter,
SL486 preamplifier and :he ML926 receiver.
Transmitter circuitry
The transmitter circuit comprises the
SL490B, IC14, two transistors and two
IR LEDs plus a few capacitors and
resistors. The IR LEDs transmit a pulse
position modulation (PPM) 5-bit code
whenever one of the switches is pressed.
68
ELECTRONICS Australia, July 1986
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VIEWED FROM
BELOW
[email protected] TUNER REMOTE CONTROL RECEIVER
BEND LEADS
2/TUR
7.1010111111M111111.1111111111,
The remote control receiver circuit is based on the Plessey SL486 and ML926 preamplifier and decoder ICs.
Up to 32 separate code commands are
available with the SL490B. This is possible with 32 switches in an 8-row by
4-column switch matrix. Our remote
control needs less than this and uses
nine switches in a 4-column by 3-ro.w
matrix.
Switches for memories 1,2,3 and 4
have transmit codes from 01000 to
01011. The' tune down, tune up and
memories 5 and 6 have transmit codes
from 01100 to 01111 and finally, the
AM/FM switch sets transmission of
00100.
Transmit code output is at pin 2 of
IC14. It is AC-coupled via the .068p,F
capacitor to the base of transistor 025
which produce, a 1-5p,s current pulse,
each time pin 2 goes low. Thus Q26,
which is driven by Q25, directly drives
two IR LEDs with these very short current pulses.
The pulse position modulation frequency of transmission is set by the
33k[1 resistor and 0.22p,F capacitor.
Filtering for the internal 4.5V regulator of the SL490B is provided by the
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VIEWED- FROM
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TUNER REMOTE CONTROL TRANSMITTER
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The transmitter uses a Plessey SL490 IC to pulse code modulate two infrared LEDs.
ELECTRONICS Australia, July 1986
Remote control
4.7AF capacitor connected between pin
17 and the OV line.
The 9V battery powers the transmitter
while a 220AF capacitor across the supply provides the high current surges required when the. IR LEDs are pulsed
on. Standby current of the circuit is less
than 10AA.
Receiver circuitry
The remote control receiver comprises fOur ICs. Two of these are the
above-mentioned SL486 preamplifier
and the ML926 decoder. The remaining
ICs are tile 4052 and 4053 CMOS analog switches.
An IR photodiode, the BPW50, is the
detector for the transmitted IR signal. It
is connected across the differential inputs to the preamplifier, 1C15, at pins 1
and 16. The differential input stage provides rejection of common mode noise
from the diode and connecting leads.
Following this is a gyrator and four
gain stages. Each of these has a low frequency roll-off below 2kHz, effectively
rejecting any 100Hz signals (radiated by
mains powered lights) picked up by the
receiver diode. To provide these rolloffs, the 6.8AF, 47p,F, .015AF, .033AF
,
and finally the .0947AF capacitors (pins
2,3,15,5 and 6) respectively are used for
decoupling.
An automatic gain decoupling 0.15µF
capacitor at pin 8 filters the output from
an internal peak detector which measures the final output at pin 9. The resulting signal controls the gain of the
first three amplifier stages.
An internal regulator stabilises supply
to the amplifiers and theinput to this is
at pin 12. Filtering for the supply input
is with a 22AF capacitor while the 220a
'cresistor reduces the overall supply voltage to the regulator. Supply decoupling
between the sensitive input circuitry and
the output circuit is via the 47.1 resistor
and 0.33p,F capacitor.
After amplification in IC15, the received signal is sent to decoder 1C16.
This demodulates the transmitted pulse
position modulation code and waits for
two consecutive and identical codes before providing a 4-bit binary output. •
A reference oscillator input at pin 2
of 1C16 sets the operating frequency
with an RC network. In our case a
.022AF capacitor and a 221d1 resistor in
series with a 50k11 trimpot are used.
Only when the transmission rate is cor-
,
AM/FM
,
Cli El
Fig.!: how the 1C17 and 1C18 CMOS switches are arranged on the 1C1 switch matrix.
ELECTRONICS Australia, July 1986
The receiver circuitry is accommodated on the main tuner PCB.
red will 1C16 provide a decoded output
from the received signal.
Outputs at A,B,C and D are normally
pulled low with lOkfl resistors. When a
correct code is received, outputs will go
high. Note that the ML926 is designed
only to receive 5-bit transmitter codes
that have the most significant bit low,
ie. it really only decodes 4-bit signals.
(Another version of this IC is the Plessey ML927. This type responds to codes
with the most significant bit high.)
ELECTRONICS Australia, July 1986
•
Close-up view of the receiver circuitry on the main tuner PCB. The BPWSO photodiode is mounted behind the perspex front panel.
Remote control
The most significant (D) output from
1C16 is inverted by transistor 024. This
D-complement plus the A, B and C signals are applied to IC17 and 1C18.
These two ICs are CMOS binary
decoders with analog switches, 1C17 can
be considered as a three-pole two-way
switch responding to binary input codes
fed to pins -9, 10 and 11. The binary inputs are the A, B and C pins (9, 10 and
11) which have independent control
over their respective "a", "b" and "c"
switch poles. For example, when A is
high, the Y position of the "a" switch
pole is selected (AY). When A is low,
the X position is selected (AX).
The AX, AY and CY switch output
(pins 12, 13 and 3) positions connect via
diodes D37, D38 and D39 to the b, c
and f segment outputs of IC1 in the
Playmaster stereo AM/FM tuner. The
BY pole connects to the K3 switch matrix input of IC1.
For its part, 1C18 can be considered
as a two-pole four-way switch also responding to binary control codes except
that we are using it only as a single-pole
four-position switch, with the common
(wiper) being pin 13.
Note that the INHibit input at pin 6 is
normally held high by virtue of the inversion of the D output from 1C16.
When pin 6 is low. 1C18 is selected.
This means that when no signal codes
ELECTRONICS Australia, July 1986
are being transmitted, IC17 and IC18
are effectively disabled and do not affect the tuner functions.
The "OX" switch is selected when A
and B are both low. When A is high
and B low, the "1X" switch is selected.
To select the "2X" switch, A is low and
B high and finally the "3X" switch is selected with a high on both the A and B
inputs.
The OX, 1X, 2X and 3X switches connect to the K3, K2, K1 and KO lines respectively. These are the switch matrix
columns of IC1.
Fig.1 shows how the 1C17 and 1C18
switches are arranged on the ICI switch
matrix on the main tuner board. To select memory 1, we close both the OX
and AX switches simultaneously. For
the UP selection we need OX closed but
AY is closed instead of AX. Similarly,
for the 2, 3 and 4 memory selections,
we need AX closed and 1X, 2X and 3X
closed respectively. For the DOWN and
the 5 and 6 memory, the AY switch is
closed along with the respective 1X, 2X
and 3X switches.
AM/FM switching occurs when both
the BY and CY switches are closed.
Construction
The Tuner Remote Control transmitter is housed in a small platic case measuring 112 x 62 x 31 mm. All compo-
nents are mounted on a PCB coded
85rc12 and measuring 56 x 74mm. A
front panel label measuring 114 x 64mm
indicates the switch functions as well as
providing the finishing touch.
The Tuner Remote Control receiver
circuitry is mounted on the main 85tu12
PCB used in the Playmaster stereo
AM/FM tuner. Receiver diode BPW50
is secured to thy-sub--fent panel of the
tuner behind the neutral density filter
screen-on the front panel.
Construction of the remote receiver is
straightforward. Firstly, the main tuner
PCB (85tu12) will need to be removed
from the tuner case. Disconnect the
audio and AM antenna leads and remove the rear panel. Unclip the 8-way
leads between the main PCB and display PCB as well as the short stereo
lead. Now undo the screws securing the
main PCB. It should be possible to have
the PCB sitting up on edge to give sufficient room for inserting the remote control components without removing the
power supply wires.
The front panel and display PCB will
also require removal to fit the IR diode.
Drill a 4mm hole thror4gh the display
PCB directly opposite It15 on the main
PCB. This position is clearly marked
with a copper pad just next to the "t"
in the, word "top" on the display side of
the PCB.
Directly in front of this hole on the
sub-front panel, drill another hole to expose the IR detector diode. The leads
are bent back on the IR diode as shown
on the circuit diagram. Note that the infrared active• area is the flat face side of
the diode.
Use epoxy resin to secure the IR
diode to the sub-front panel. Note that
it is important not to allow the leads to
make contact with the metal panel and
avoid placing glue on the active area of
the diode.
Solder short leads to the diode and
feed them through the hole in the display PCB. The front panel, sub-front
panel and display PCB can now be reassembled.
When assembling components onto
the main tuner PCB, follow the overlay
diagram and do not forget the links.
Note that the ICs, electrolytic capacitors
and diodes must be oriented as shown.
After this PCB is completely assembled, it can be bolted back into the
case. Replace the rear panel and resolder the audio plus AM antenna wiring.
Reconnect the 8-way cables.
With the receiver complete, work can
begin on the transmitter.
Insert the resistors, BC327 (Q25), and
IC14 in position first. The capacitors
and the B1)681 (Q26) unconventionally
lie sideways on the PCB. This is to
leave sufficient room for the switches to
protrude through the front panel.
Lying flat on the PCB are the 4.7p,F
and 220AF capacitors. The 0.22;LF capacitor lies across the IC, while the
.068p,F sits on top of the 10011 resistor.
Transistor Q26 straddles the .068µF capacitor.
All switches are mounted with the
same orientation, ie, with the flat side
to the right side of the PCB. Both IR
LEDs are mounted close to the edge of
the PCB and are bent over so that they
point along the plane of the PCB. Wires
for the 9V battery clip can also be soldered in place.
The PCB can be held within the box
using one of two methods. We used
screws, 12mm spacers and nuts to support the PCB at the four corners from
the front panel. If you prefer not to see
securing screws on the front panel, then
the plastic clips that are supplied with
the box can be used. These are designed to clip into the corrugations in
the side of the box and hold the PCB at
the correct heil„ht. Cut the clips to
length so that the switch tops will just
protude through the front panel.
Place the Scotchcal label on the lid of
the box making sure it is lined up correctly before sticking it down. Drill
holes for each switch and the PCB corner mountings if used.
Make a rectangular cut-out at the
View showing the completed transmitter PCB, ready for assembly into the case.
4
The transmitter PCB is mounted on the lid of the case using four 6mm standoffs.
ELECTRONICS Australia, July 1986
Re
te control
Above: parts layout for the transmitter
PCB.
front end of the box in a position so
that the two IR LEDs will be central to
the hole. We made our hole 24mm x
12.5mm and fitted a circularly polarised
red filter into this.
Now the transmitter construction is
complete apart from assembly. The 9V
battery squeezes between the bottom
end of the case and the edge of the
PCB. In some cases, the lower corner
pillars within the case may need shaving
with a knife so that the battery will fit
correctly.
If screws are used to secure the PCB
to the front panel, place a plastic
washer under the nut at the top right
mounting hole. This will insulate the
PCB track from the electrically connected screws on the aluminium Scotchcal front panel. The remaining three
corner mounting holes have adjacent
PC tracks that are of the same ground
potential and do not require insulating.
Assemble the transmitter into the box
and it is ready for testing.
Above: actual size artwork for the trans- The two infrared diodes "look" through a
red perspex window.
mitter PCB.
Actual-size front panel artwork for the transmitter.
ELECTRONICS Australia, July 1986
Testing
Switch on the Playmaster stereo
AM/FM tuner and aim the transmitter
at the tuner. Push either the tune down
or tune up remote control switches and
adjust the VR9 trimpot in the receiver
until the tuner responds correctly to the
transmitter commands. Now check the
remaining remote control functions and
you are finally in business.
PARTS
1 PC
5r board, 56 x 74mm, code
1 Scotchcal front panel, 114 x
64mm
1 plastic case, 112 x 62 x 31mm
1 red perspex sheet approx 24 x
12.5mm x 1-2mm
9 snap action keyboard
switches, 6 green, 2 white, 1
black
1 216 9V battery
1 9V battery clip
4 6mm standoffs and screws
and nuts
Semiconductors
1 SL490 remote control
transmitter (Plessey)
1 SL486 IR remote control
preamplifier (Plessey)
1 ML926 remote control receiver
(Plessey)
1 4052 CMOS switch'
1 4053 CMOS switch
1 BD681 NPN Darlinctlton
transistor •
1 BC327 PNP transistor
1 BC547 NPN transistor
2 LD271 IR LEDs
1 BPW50 IR detector diode
3 1N4148, 1N914 small signal
diodes
Capacitors
1 220p,F 16VW PC electrolytic
1 47µ,F 16VW PC electrolytic
2 22p,F 16VW PC electrolytics
1 6.8p.Fi6VW PC electrolytic
1 4.7p.F 16VW PC electrolytic
1 0.33/LF metallised polyester
1 0.22p,F metallised polyester
1 .068µF metallised polyester
1 .033pC metallised polyester
1 .022p,F metallised polyester
A .015µ,F metallised polyester
1 .0047,aF metallised polyester
• 5 Alitc.M.,,,A t
Resist rs
(0.25W, 5% unless stated)
1 )c 33k0, 1 x 22ka 6 x 10kfl,
1 x 2.2kn, 1 x 220t2 1/2W, 1 x
100f1, 1 x 47f/, 1 x 50k1), horizontal cermet trimpot.
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