* The issue 1.1 Discrete VCA boards connect the normally unused pin 6 of the MU connector
to socket ground. With the link on PSU not fitted, and using an Oakley MU Dizzy distribution
board with a five way power cable, will allow the socket ground to be kept separate from
module ground to prevent ground loops.
Trimmers
Although you can use a simple fine bladed screwdriver for this adjusting the trimmers you
should really use a proper trimmer tool. Vishay, Bourns and others make trimmer adjusters for
less than a pound.
You should make sure your modular has been powered up for at least ten minutes prior to
calibration. Also, it is a good idea to have the room temperature close to what it would
normally be when playing your modular.
OFFSET:
Turn the GAIN pot to its maximum level. Ensure all other pots are at their
minimum settings. Measure the output voltage from the output socket with a good digital
voltmeter. Adjust OFFSET with a jeweller's screwdriver or equivalent until the output voltage
is 0.000V +/- 5mV.
LIN:
Insert a 5V peak triangle wave signal at roughly 440Hz to the IN1 (DC) input. Turn the
CV1/GAIN pot to the maximum and the IN1 (DC) and CV 2 pots to their middle positions.
Listen to the output of OUT B on your monitoring system. You should hear a slight
bleedthrough of the triangle wave input. Now adjust LIN until the signal level decreases to its
minimum. You may have to turn up the gain of your monitoring system to fine tune the null
point.
EXP:
Insert a 5V peak triangle wave signal at roughly 440Hz to the IN1 (DC) input. Turn the
IN1 (DC) and CV2 pots to their maximum. All other pots should be at their minimum settings.
Connect a 5V source to the CV2 input. This could be a fixed voltage source, a triggered
envelope generator or midi-CV convertor – anything that will give you a +5V output signal.
Now with a scope measure the output voltage at OUT A and adjust EXP until the signal level
in EXP mode is the same as in LIN mode. It doesn't have to be that accurate – within 250mV
will be fine.
If you do not have a scope just simply listen to the OUT A signal and flip the switch from LIN
to EXP and adjust the EXP trimmer until there is no change in volume when you flip the
switch. It doesn't have to be that accurate, just try to get the two signals sounding roughly the
same.
If you can't get the levels equal then double check the voltage going into CV2. The EXP mode
is very sensitive to changes in level around 5V. If you can't get OUT A loud enough then the
voltage going into CV2 may well be lower than 5V. If it's too loud then the CV may well be
significantly over 5V.
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