Erica Synths DIY Polivoks VCO kit - Manual (Page 11)

TUNING THE OSCILLATOR
Ensure all components are placed correctly and soldered well. Check for
possible short circuits that may be leſt aſter soldering.
Ensure power supply voltages are as exactly +12.00V and -12.00V as possible.
Allow some minutes for the VCO to warm up.
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Connect a precise voltmeter with range at least +/-15V to the Test Point 1
(TP1).
Apply 5.00V to CV input.
Set panel FREQUENCY pot to 12 ‘o’clock. When tuning VCO2, set DETUNE pot
to 12 ‘o’clock. Set CV level pots to zero.
Switch around various octave settings. Check the voltage change on the
voltmeter between octaves. Ideally it should be 1.00V per octave.
Tune tirm pot TP1 so that octave steps are as close to 1.00V as possible.
Mostly you can just switch between two center settings, and adjust the trim
pot, only occasionally checking voltages on other settings.
If voltage change step between octave switch steps is wider than necessary
(more than 1.00V), turn the trim pot clockwise. If voltage change step
between octave switch steps is narrower than necessary (less than 1.00V),
turn the trim pot counterclockwise.
If 1.00V steps can only be acquired on certain octave switch settings, and on
others it significantly differs, there is likely a component value mismatch in
octave divder resistor array.
Aſter successful tuning, voltages on the output of octave selector should be
like, for example, -9.62V at "32" (or lowest octave setting), -8.62V at "16",
-7.62V at "8", -6.62V at "4" and -5.62V at "2" (or highest octave). Common
offset to all these voltages will vary between oscillators, what is important, is
the exact 1.00V relation between steps.
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Connect a voltmeter to GND and pin5 of OP5.
Tune trim pot TP4 so that voltage reads about -0.82V.
Select SAW waveform.
Ensure panel FREQUENCY pot is 12 ‘o’clock, and both modulation pots are set
to zero. When tuning VCO2, set DETUNE pot to 12 ‘o’clock.
Set the octave switch to some middle-low setting, "16" (-1 oct) for example.
Connect a precise frequency meter to the VCO module output.
Apply 5.00V to CV input. You can use a voltage divider made up of two
resistors, connected to the same +12V supply and GND, providing the middle
point of about 5.00V
Set internal tune offset trim pot TP2 approximately to the middle. It can be
done by exploring the whole range and then setting to the medium value.
Set internal trim pots TP3 and TP5 (TP5 has so little impact on the trimming
of the VCO, that we will leave it in this position) to approximately the middle.
It can be done by exploring the whole range and then setting to the medium
value.
Note the frequency on the frequency meter. Switch around various octave
settings. Check the ratio of frequency relative to the previous one. Ideally it
should change twofold for every octave when going higher, and should half per
every octave step when going lower.
For example: Say, you have written down the frequency X Hz at the setting "8"
(0 oct). When setting octave switch to “4”, output frequency should read 2*X.
Tune trim pot TP3 so that octave steps in measured frequency are as close to
the shown above as possible. Mostly you can just switch between two center
settings, and adjust the TP3, only occasionally checking frequencies on other
octave settings.
Turning the trim pot TP3 clockwise with make octave steps narrower, while
turning counterclockwise - wider. Overall tuning will also change at the same
time - this is not a malfunction. So, if the octave frequency step is too wide,
turn the TP3 clockwise a bit, and check the octave step again. If it is too
narrow, turn the TP3 counterclockwise.
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Select SAW waveform.
Ensure panel FREQUENCY pot is 12 ‘o’clock, and both modulation pots are set
to zero. When tuning VCO2, set DETUNE pot to 12 ‘o’clock.
Set the octave switch to some mid setting, "8" (0 oct) for example.
Connect a precise frequency meter to the VCO module output.
Apply 5.00V to CV input.
Adjust Offset trim pot TP2 as you fit necessary to your application. Obtaining
440Hz at the panel tune knob center position may be desirable. However it
depends on CV source and tuning needs of your particular setup.
Usually, round integer (x.00V) voltages are tuned to 27.5Hz multiplied by any
powers of two; for example: 5.00V may be tuned to 880Hz (note A5) for classic