I have been trying to build quad VCA using AS2164.
I found few schematics online but they all give me inverted output. Not that I mind especially but I was wondering if there was something I was missing from this chip as nobody seems to mention that the output is inverted.
Has anybody used this chip as a quad VCA ?
on your “note” link it’s the Mixer not the VCA
and @HAGIWO is on this forum, maybe he can help you
in the notes:
“V2164 can be replaced with SSI2164, SSM2164, AS2164. (I think, unverified)”
This schem should not need another opamp to re inverted the signal out ? (I suck, but it’s a question for specialists in theory)
Ho sorry for posting the wrong link. And thanks for posting the correct one.
His videos are really nice. I have built the clock multipler-divider that he has designed and it works great.
@HAGIWO if you get a chance any comment/advice would be greatly appreciated.
The VCAs are current devices - that’s why you see resistors directly connected to the input jacks - it turns your audio voltage signal into a current, which is then passed through the AS2164 depending on the CV.
To turn your current back into a voltage you have the op-amp stage configured as an I-V converter. This configuration is inherently inverting. You could change it with a another inverting amplifier stage with unity gain. If it’s for audio it shouldn’t matter, but if you want to use it for control voltages I could see why you’d want the output in phase.
Ok, I see. I will probably add an inverting op amp after that. Thanks.
Ok. Makes sense. Glad to see I didn’t messed up.
Would a resistor to gnd (directly following the 2164) not suffice to convert the current to a voltage? You could then follow that up with a non inverting opamp to buffer that voltage. This would get rid of the inversion effect.
You probably could! I’ve seen some LM13700 CVA circuits that do just that.
There are some reasons you may not want to though - https://www.allaboutcircuits.com/video-tutorials/op-amp-applications-current-to-voltage-converter/
why not just use the op-amp’s non-inverting input?
Doesn’t work that way — the current has to go through the feedback resistor (and the feedback has to be to the inverting input for feedback to work).
Looks like it is now doing what I want.
I added an inverting op amp with 2x100k resistors followed by buffer. I am only looking at DC at the moment.
I will try to use the chip for a 3 VCA module along with 2 tl074 so have a couple free op-amps to use as a mixer/buffer.
Hopefully, I’ll post back soon with a working module.
I think mutable instruments Veils is a quad VCA that uses a couple of 2164s, the scematics should be available.