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"Cleanliness" of VCA
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author "Cleanliness" of VCA
rishin
I've seen this phrasing used in VCA discussions on MW, so I'm curious as to what exactly it means. What could cause a VCA to be "unclean" or prone to distortion and what are important specs to keep in mind when buying one to make sure it suits what you're looking for?

Thanks!
abelovesfun
It's circuit and component choices. I am designing a VCA currently using THAT chips at the moment and am doing A/B testing for the op-amp phase between standard TL0 op amps vs ore expensive, lower noise applications.
Other VCAs designs I've played with use common OTA chips, which are fairly good, but a bit noisier and with higher distortion.

Since we are dealing with really loud signals in modular, even noisier designs aren't readily apparent to the human ear.
cptnal
I think it's more overdriven than unclean as such. That is, it's intentional and part of the VCA's character, just like you would expect character in a Marshall amp for instance.

On the other hand, sometimes you just want things to be higher or lower, in which case you'd want something "clean".

From what I've seen there'll generally be some reference to character or tone in the manufacturer's description of a VCA that has them. But then again it's all in the ear of the beholder. One wiggler's clean might be another's character.

Probably your best bet is if you have one in mind do a search on it and see what others are saying. If you can't find what you're looking for ask the question yourself. thumbs up
Rex Coil 7
"character" and "tone" .. "cleanliness" ... et al.

These are all attempts by folks to express what it is they hear. It's a lot like attempting to explain what the color ~blue~ looks like to someone that was born blind.

So best of luck in your attempts to decipher what other people describe, since there's little to associate with. This is a communication problem that is as old as the ages. You're just going to have to research the shit out of it to determine what you want. Videos/Audio Demos help. A lot.
rishin
Rex Coil 7 wrote:
"character" and "tone" .. "cleanliness" ... et al.

These are all attempts by folks to express what it is they hear. It's a lot like attempting to explain what the color ~blue~ looks like to someone that was born blind.

So best of luck in your attempts to decipher what other people describe, since there's little to associate with. This is a communication problem that is as old as the ages. You're just going to have to research the shit out of it to determine what you want. Videos/Audio Demos help. A lot.


Fair enough. Thanks!
MrsWedge
I recently got to hear my DIY synth on a PA system for the first time. With the volume all the way up and the homemade vactrol vcas all the down, it makes no audible sound at all. Is that cleanliness or lack of uncleanliness?
Navs
It depends on what you want out of a VCA, transparency or distortion. You may want both. e.g., VCAs that turn sines into squares (bad?) can be good for rounding/'warming' overly bright saws (good?).

You can hunt for SSM or THAT-based VCA modules for transparency or CA3080 OTA VCAs for VintajTone, but TBH depending on the circuit design and the levels you feed them, both can sound clean or cack.
MrsWedge
Maybe I'm old-fashioned or weird or something, but it seems to me that a vca that turns a sine into a square is not a vca at all. I designed mine to have unity gain when fully open, so hopefully there little to no distortion or clipping.
pugix
A clean VCA would be a low-distortion (high fidelity), low-noise unit. WMD has a Digital VCA that eliminates the pop caused by fast attack envelopes that can impart a sharp edge to the controlled signal.

Linear VCAs tend toward low-distortion, while Exponential VCAs can easily distort, due to their high gain. If you want distortion/overdrive, there are plenty of choices.
Navs
MrsWedge wrote:
Maybe I'm old-fashioned or weird or something, but it seems to me that a vca that turns a sine into a square is not a vca at all. I designed mine to have unity gain when fully open, so hopefully there little to no distortion or clipping.


Many old-fashioned VCAs were designed around the CA3080 OTA which, when driven, results in a sort distortion that can be desirable, either because it sounds 'tube-like' or because it is good at rounding triangles into sines. If you stick a sine into this transfer function, you get a 'squared up' sound.
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