It is possible to exchange one of the input cv jacks with a potentiometer for both the upper and the lower VCA.
This modification is possible to make for version 1.2 of the Dual VCA pcb.
First desolder the CV1-jack, and then follow these instructions.
The potentiometer must be a 9mm linear potentiometer with a resistance of 100k ohm. It should have a long knurled shaft. See the images below.
Make sure to mount and solder it nice and straight in a 90 degree angle so that it appears like the image above. It is difficult to adjust after you have soldered, so make sure you get it right before you solder anything.
The first, left leg (1) on the potentiometer should be soldered to the pad on the bottom side of the PCB. You must bend the leg to get a good placement of the potentiometer.
Then you have to bend down the wing into the drilled hole. Use a sharp knife to scratch the pcb near the wing to reveal the copper so that you can solder the wing to the pcb copper. Make sure the potentiometer is aligned correct before you make any soldering.
On the top side, you have to bend down the wing, but no soldering of the wing here. Then you have to bend the MIDDLE LEG (2) of the potentiometer so according to the image above. The leg shall touch only one pad on the pcb, see above. Solder the middle leg.
Finally you have to solder a VCC cable to the right leg (3) of the potentiometer. The cable should be soldered to the positive side of the C16 capacitor. It is good practice to use heat shrink tubing to protect soldered metal parts. See images above.
It is the same procedure to mount a potentiometer also on the lower VCA. The VCC cable should be soldered to the SAME pad for both potentiometers. So if you mount two potentiometers, there will be two cables sharing the same pad on the C16 capacitor.
Now when you are finished, you can use the potentiometer to manually adjust the bias of the VCA. The cv2-jack is used as a modulation source as usual.