To: 'Analogue Heaven' analogue@hyperreal.org,
From: "Caloroso, Michael E" CalorosoME@corning.com,
cc:
Subject: [AH] DIY: Minimoog Power Supply and Tuning Scale/Range Calibration
Date: Fri, 22 Jan 1999 20:49:28 -0500
Man this took a long time to type up. I hope you AHers appreciate this!
************************
POWER SUPPLY CALIBRATION
************************
WARNING This procedure will expose the user to hazardous voltages. Proceed
with caution. If you are in any way uncomfortable with this procedure, then
take the unit to a qualified repair shop. I am providing this for
information only and the user assumes all risks.
Before performing any adjustments, you must first calibrate the power supply
regulators. You will need a 3-1/2 digit voltmeter with 0.1% accuracy and a
second pair of hands.
1) Turn off power to the Minimoog.
2) Remove the rear cover from the Minimoog's hinged panel assembly.
3) After you take off the cover, put one screw in the center of the bottom
of the rear panel so that you can use it as a post to prop up the panel,
just like if you were adjusting the angle of the panel.
There are two large boards as you face the rear of the Minimoog. The board
on the right is the oscillator board. The board on the left is the Filter
board.
4) On the Filter board, remove the two screws at the top. Take your
screwdriver and gently pry the board out of the socket - they're tight.
5) With the Filter board out of the way, you now have access to the Power
Supply board.
6) Apply power to the Minimoog. Allow a ten minute warmup period.
7) Observe the trimpots on the Power Supply board. Note the two on the
left; the top trimpot is (+) 10 volt trim, the bottom is (-) 10 volt trim.
8) Observe the Oscillator board connectors. There are two connectors, the A
connector is on the right, the other is B. The connector pins number 1A,
2A, 3A and so on starting from the right of the connector.
At this point, one person is to hold the voltmeter probes while the other is
to adjust the trimpot and read the voltmeter.
9) Connect the positive probe of the voltmeter to Oscillator board pin 1A
10) Connect the negative probe of the voltmeter to Oscillator board pin 2A
11) On the Power Supply board, adjust the (+) 10 volt trimpot for +10.00
volts.
12) Connect the positive probe of the voltmeter to Oscillator board pin 3A
13) On the Power Supply board, adjust the (-) 10 volt trimpot for -10.00
volts.
14) Turn off power to the Minimoog & reinstall the Filter board.
******************************
TUNING SCALE/RANGE CALIBRATION
******************************
WARNING This procedure will expose the user to hazardous voltages. Proceed
with caution. If you are in any way uncomfortable with this procedure, then
take the unit to a qualified repair shop. I am providing this for
information only and the user assumes all risks.
This procedure requires a strobe tuner or a frequency counter.
You can calibrate the oscillator with or without the rear cover intact.
There are access holes for the trimpots, but not all of them. It is also
possible that you have a older Minimoog with a newer oscillator board, and
only the access holes for the older oscillator board.
These instructions are laid out for calibration without the rear cover, so
you should keep the Minimoog in a stable environment, IE away from drafts
because abrupt changes in temperature will affect your calibration.
For instruction on removing the rear cover, refer to the Power Supply
Calibration section.
1) Apply power to the Minimoog and allow a 30 minute warmup period.
2) Connect the tuner or counter to the HIGH MAIN OUTPUT jack.
There are two large boards as you face the rear of the Minimoog. The board
on the right is the oscillator board. The board on the left is the Filter
board.
A440
====
3) Observe the Filter board. The trimpot on the bottom left hand side is
the A440 trimpot. Turn on the A440 switch on the front panel and adjust
this trimpot for 440hz.
4) Turn off the A440 switch on the front panel.
At this point, we are ready to calibrate the Oscillators. There were three
versions of the oscillator boards.
The first version was originally installed in Minimoogs up to approximately
serial #1300 and were entirely discrete, but is mentioned nowhere in the
service manual. I do not have schematics for it, and I do not know what it
looks like. I cannot verify if this calibration will apply to this
oscillator board version. It is pretty likely that most of these boards may
have already been upgraded to newer versions. If you have a Minimoog that
is under #1300 and you are not sure which board you have, you will need
schematics and a qualified repair shop to tell you which board it is.
The second version is more common and was installed in Minimoogs below
serial #10175, beyond that the third version (the temperature stabilized
board) was installed in Minimoogs serial #10175 and up. Older Minimoogs may
have their original boards replaced with the third version.
5) With the cover off, observe the Oscillator board. On the right side of
the board, there will be a matrix of trimpots. If you see two columns of
three trimpots, you have the second version. If you see four columns of
three trimpots, you have the third version.
TUNING PROCEDURE, SECOND VERSION
================================
This is the board that is in my Minimoog. I modified the procedure slightly
because it tunes it better.
The arrangement of the trimpots is as follows: each row pertains to each
oscillator, the top is OSC1, middle is OSC2, bottom is OSC3. The trimpot on
the right is RANGE, the one on the left is SCALE. Near the bottom is a lone
trimpot, this is the OCTAVE trimpot.
Only the RANGE and SCALE trimpots are accessable through the access holes on
the rear cover.
6) Set the front panel controls as follows:
TUNE=0
GLIDE=0
PITCH WHEEL=CENTER (detent)
MOD WHEEL=OFF
OSCILLATORS
-----------
OSCILLATOR MOD=OFF
OSC 3 CONTROL=ON
ALL OSC RANGE SWITCHES=2
ALL OSC WAVEFORMS=RAMP
OSC 2 RANGE=0
OSC 3 RANGE=0
MIXER
-----
ALL OSC MIXER VOLUME=5
NOISE/EXT IN=OFF
FILTER
------
FILTER MODULATION=OFF
KEYBOARD CONTROL 1=OFF
KEYBOARD CONTROL 2=OFF
CUTOFF FREQUENCY=(+)5
EMPHASIS=0
AMOUNT OF CONTOUR=0
CONTOURS
--------
ATTACK=1M
DECAY=1M
SUSTAIN=10
MAIN OUTPUT VOLUME=5
MAIN OUTPUT=ON
OSC1
====
7) Turn on OSC1 in the mixer on the front panel. All other switches in the
mixer should be OFF.
8) Hold down the HIGH A key and adjust OSC1 RANGE trimpot for 3520hz.
9) Hold down the LOW A key and adjust OSC1 SCALE trimpot for 440hz.
10) Repeat steps 8 and 9 until no further adjustment is necessary.
The remaining adjustments can be done without the tuner or counter. You can
monitor the Minimoog with headphones or an amp.
OCTAVE
======
11) Hold down the LOW A key.
12) Turn on A440 on the front panel.
13) Adjust the front panel TUNE for unison.
14) Change the OSC1 RANGE switch on the front panel to 16.
15) Press the HIGH A key.
16) Adjust the OCTAVE trimpot for unison.
17) Set the OSC1 RANGE switch back to 2 and turn off A440.
OSC2
====
18) Turn on OSC1 and OSC2 in the mixer on the front panel. All other
switches in the mixer should be OFF.
19) Hold down the HIGH A key and adjust OSC2 RANGE trimpot for unison.
20) Hold down the LOW A key and adjust OSC2 SCALE trimpot for unison.
21) Repeat steps 19 and 20 until no further adjustment is necessary.
OSC3
====
22) Turn on OSC1 and OSC3 in the mixer on the front panel. All other
switches in the mixer should be OFF.
23) Hold down the HIGH A key and adjust OSC3 RANGE trimpot for unison.
24) Hold down the LOW A key and adjust OSC3 SCALE trimpot for unison.
25) Repeat steps 23 and 24 until no further adjustment is necessary.
You're done! Reinstall the rear cover and enjoy!
TUNING PROCEDURE, THIRD VERSION
===============================
I have never owned a Minimoog with this board, so I am just copying the
procedure from the manual.
The arrangement of the trimpots is as follows: each row pertains to each
oscillator, the top is OSC1, middle is OSC2, bottom is OSC3. From the
right, the 1st trimpot is SHIFT (also known as RANGE), the next is OCTAVE,
the next is SCALE, and the fourth is HI END.
Only the SHIFT, OCTAVE, and SCALE trimpots are accessable through the access
holes on the rear cover. If the Minimoog is below serial #10175 and you
have the third version board, there may or may not be new access holes
drilled out for OCTAVE.
26) Set the front panel controls as follows:
TUNE=0
GLIDE=0
PITCH WHEEL=CENTER (detent)
MOD WHEEL=OFF
OSCILLATORS
-----------
OSCILLATOR MOD=OFF
OSC 3 CONTROL=ON
ALL OSC RANGE SWITCHES=16
ALL OSC WAVEFORMS=RAMP
OSC 2 RANGE=0
OSC 3 RANGE=0
MIXER
-----
ALL OSC MIXER VOLUME=7
NOISE/EXT IN=OFF
FILTER
------
FILTER MODULATION=OFF
KEYBOARD CONTROL 1=OFF
KEYBOARD CONTROL 2=OFF
CUTOFF FREQUENCY=(+)5
EMPHASIS=0
AMOUNT OF CONTOUR=0
CONTOURS
--------
ATTACK=1M
DECAY=1M
SUSTAIN=10
MAIN OUTPUT VOLUME=10
MAIN OUTPUT=ON
SCALE
=====
OSCx=OSC1, OSC2, or OSC3
27) Turn on OSCx in the mixer on the front panel. All other switches in the
mixer should be OFF.
28) Change OSCx RANGE switch on the front panel to 16.
29) Hold down the LOW A key and adjust OSCx SHIFT trimpot for 55hz.
30) Hold down the HIGH A key and adjust OSCx SCALE trimpot for 440hz.
31) Repeat steps 29 and 30 until no further adjustment is necessary.
repeat for each oscillator
HI END
======
OSCx=OSC1, OSC2, or OSC3
32) Turn on OSCx in the mixer on the front panel. All other switches in the
mixer should be OFF.
33) Change OSCx RANGE switch on the front panel to 2.
34) Hold down the LOW A key and adjust OSCx SHIFT trimpot for 440hz.
35) Hold down the HIGH A key and adjust OSCx HI END trimpot for 3520hz.
36) Repeat steps 34 and 35 until no further adjustment is necessary.
repeat for each oscillator
37) Repeat SCALE (steps 27-31) and HI END sections (steps 32-36) until no
further adjustment is necessary.
OCTAVE
======
OSCx=OSC1, OSC2, or OSC3
38) Turn on OSCx in the mixer on the front panel. All other switches in the
mixer should be OFF.
39) Change OSCx RANGE switch on the front panel to 32.
40) Hold down the HIGH A key and adjust OSCx SHIFT trimpot for 220hz.
41) Change OSCx RANGE switch on the front panel to 2.
42) Hold down the HIGH A key and adjust OSCx OCTAVE trimpot for 3520hz.
43) Repeat steps 39 through 42 until no further adjustment is necessary.
repeat for each oscillator
SHIFT
=====
OSCx=OSC1, OSC2, or OSC3
44) Turn on OSCx in the mixer on the front panel. All other switches in the
mixer should be OFF.
45) Change OSCx RANGE switch on the front panel to 16.
46) Hold down the HIGH A key and adjust OSCx SHIFT trimpot for 440hz.
repeat for each oscillator
You're done! Reinstall the rear cover and enjoy!
WHEW!!!!!
MC
Opinions (and mistakes) expressed herein are my own and not those of my
employer.