I found this VCA design based on the V2164 by @HAGIWO(thanks for posting it!) here. I thought I’d have a go at building it as I have an AS2164 lying around and, as far as I can tell from the datasheet, they are replacement ICs. I’ve put this together on a breadboard and it’s working! I can hear it shaping the sound as expected. However when I come to calibrate it things are going wrong.
With the 100k trim pot (semi-fix pot) it’s used to ensure that 0V CV results in 0V output. To do this you close the offset pot, ensure 0V is coming in on the CV and then use the trim to set the output to 0V.
The 10k trim pot is supposed to ensure that at 5V CV the output == input. Again you set the offset to closed then note the input V, set the CV to 5V and then use the trim to adjust the output V to match the input V.
However, what actually happens on my bread board is:
The 100k has zero effect, (although the output is already close to 0V at 0V CV), I can turn it through it’s full range and nothing happens.
With the 10k the output never comes close to the input. If I have a 7V input the output peaks at 1V when I’m some where in the middle of the 10k trims range although it is having some effect.
If any wiser heads than mine can spot anything obvious or can recommend some tests to help diagnose what’s up I’d be grateful for the assist? I’ve traced the connections a few times now and it looks correct, especially as I can hear it working!
I would check the voltages on the input control pins of the AS2164. 0v is fully open and +2v is closed. Can you see any variation on these pins when making adjustments
After much probing and attempting to simulate this on Falstad (I could only do this in parts in the end) I discovered some things that finally made it work! I did try the pots and they are producing input which I could trace through the system although when I got to the output I discovered the output dropped from -11.3V down to almost 0V after the final 470R resistor. I was breadboarding this on an EDU Labor test board and it looks like the jacks without a plug are grounded, as soon as I connected the OUT jack (even to nothing) I could see the output! This let me set the 0V calibration.
The next issue was the input from the on board EDU Labor source was at -0.143V which I could not get to calibrate correctly on the CV at -5V calibration. However, when I swapped out the input to use my own VCO I had an input level of 4.6V so I recalibrated for the 0V then I calibrated the CV at 5V level, but I had to set the output to -4.6V. It looks like the AS2164 is inverting the signal, although I guess that’s ok for my mono output.
Now that I’ve got this working I have a reference so I can try building a module for this ! Thanks for all of the suggestions it really encouraged me to keep digging at this
