Set the CV2 scale pot to 10 on the Poly Midi-CV Unit and the toggle switch to 0.32V/Oct
range.
Set the lower toggle switch to the CV2 setting and the gate setting to G2. Plug in a Midi
Keyboard or software sequencer play a sequence of keys/notes at different octaves. This
time to trigger G2 and midi note 2 pitch CV (which is CV2) you need to hit 2 keys at the same
time.
In poly2 mode, the unit is duophonic so that when 2 keys are struck at once it assigns lower
note to CV1/Gate1 and upper note to CV2/Gate 2. We want to trim the CV2 0.32V/Oct so
you need to hit 2 keys (e.g. 2 keys next to each other on the midi keyboard is easiest) to
trigger gate G2 and CV2. If you hit just one key you will only trigger G1 and only CV1 will
change as you play different single notes.
Now whilst playing these two keys, transpose the midi keyboard up an octave or down an
octave. If the notes heard through the VCS3 sound flat/sharp...make small adjustments to
the
second
of the rear trimmers with a small screwdriver. You should hear the pitches of the
notes played change. Doing this you can trim the 0.32V/Oct setting of CV2 to match precisely
the scaling of your VCS3 Osc2 so it tracks chromatically over several octaves.
The fine-tuning of CV3 scaling is less critical unless you intend on using CV3 to act as pitch CV
for controlling Osc3 in the audio range. You will need to put the unit in
Poly4
play mode if
you want to use this option because in this mode, CV1-CV4 corresponds to pitches of Midi
notes 1-4. For changing play modes on the unit see later on in this guide. Note Osc3 in the
Synthi is not (by design) tracking at 0.32V/Oct but at 0.26V/Oct (!) so you will need to adjust
the
third
trimmer on the rear of the unit rather more than for CV1 and CV2 to get the scaling
down to 0.26V/Oct. Other than this the procedure is as above but the patch should now take
Osc3 to Output Ch1 and CV3 to Osc3 freq. control, which is achieved by inserting a red
precision pin to connect row 16 (stick vertical CV) to Osc3 freq. control input and also making
sure you have rotated and ‘clicked’ off the stick vertical scaling pot on the Synthi. This turns
row 16 into the third input channel, where CV3 emerges.
Switch the gate selection control to G3 and then hit 3 simultaneous keys on your midi
keyboard. This will generate CV1-CV3 pitch CV’s and trigger G1-G3 (only G1 and G2 have
Led’s that light). Apply transpose to the 3 keys you are simultaneously hitting to test
chromatic scaling of Osc3 and adjust the third trimmer as necessary.
Finally, You will have to have the inverter toggle switch in the on ‘invert’ position. Otherwise
you will find Osc3 plays ‘backwards’ i.e., playing a higher key on the keyboard (hence a larger
positive CV3 voltage) generates a lower note (and visa-versa). The reason is a bit technical
but it’s to do with the fact that all 3 VCS3 Oscillators actually track using a –ve CV (NOT
Positive CV which is the norm for most other synths). Since Input Ch1/2 invert voltages fed
into them (they are inverting amplifiers) positive midi-generated CV1 and CV2 get inverted
to –ve CV by them. But row 16 (the third Input channel) does not invert, hence the reason
why I designed the unit to allow inverting of CV3.
