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What to look for in a VCA?
MUFF WIGGLER Forum Index -> Eurorack Modules Goto page 1, 2  Next [all]
Author What to look for in a VCA?
honeyb
Ok, so beyond the obvious ("it amplifies the signal based on a control voltage!!")--

I'm thinking some kind of mixing for input signals might be good, for creating polyphonic voices -- even if just 2-4 channels, could be useful

Erica Synths has some other additionally interesting ideas:
Two CVs with separate attenuators (initially suggested as one for ASDR, one for LFO)
Fade between linear/logarithmic response
Bias control
Feedback
honeyb
How to balance out all the potential additions (it could include a filter!!) to get a minimal feature set which makes the core purpose (allow voltage control of input(s)) more useful/interesting.

i.e. "modular" means each module does one thing, really well.
chysn
honeyb wrote:
i.e. "modular" means each module does one thing, really well.


Not necessarily. It gets a bit tedious when each module does one thing, and sometimes the interplay between different features can make modules more interesting, while not making them harder to use.

Examples in the VCA realm include Optomix (mixing, filtering, dynamic control (VCA)), Veils (mixing, and/or individual VCAs), The Bends (voltage-controlled mixing, polarization, offset, VCA-like things).

There's a nice sweet spot between modules that do everything and modules that do exactly one thing.
Joe.
An LED indicator for each CV input thumbs up
honeyb
Joe. wrote:
An LED indicator for each CV input thumbs up

Yes, stupid of me to forget the blinky lights. smile
honeyb
chysn wrote:

Examples in the VCA realm include Optomix (mixing, filtering, dynamic control (VCA)), Veils (mixing, and/or individual VCAs), The Bends (voltage-controlled mixing, polarization, offset, VCA-like things).


Thanks!

The reason I'm asking is because I'm planning on building my own. My wife says I can get carried away-- trying to limit this build to features others have found useful. I'm still new at this, want to temper my judgement.
pieter
Having a bit of gain in your VCA can be very useful, especially when you have modules from different manufacturers with slightly different standards.
Shledge
Bias knob, having 2x initial max gain and linear/exp control to increase it further, even if it's just to amplify line level signals. If it's a bipolar VCA, have a "dead zone" or a center detent.

Also if there are multiple VCAs on a module, the ability to have a summed output. Looking at you, 2hp.... meh
honeyb
Shledge wrote:
Bias knob, having 2x initial max gain and linear/exp control to increase it further:


So I get this right: the Bias knob controls the base level amplification the module provides. Any CV inputs add to this bias amount (thus negative CV subtracts...)
Shledge
Pretty much, but it also sets the level of audio going through without CV, so it can be used for drones.
luketeaford
I like make noise vcas because they are also mixers. The way the knobs are normalled to offset voltage but become an attenuators for an external signal is awesome to me because you can patch what you need. Sometimes you want bias, sometimes you want an offset. You can use the vcas in series or in parallel, there's a sum out and an aux in. Great designs for a lot of flexibility.

the only thing I can think to improve would be to add an additional aux input and remove the individual channels from the sum if they are patched out. I sometimes have to mix externally... I wouldn't mind trading a little added complexity for a little more flexibility.

Also it is essential for me to have DC coupled vcas so they can be used with control voltage.
starthief
honeyb wrote:
Shledge wrote:
Bias knob, having 2x initial max gain and linear/exp control to increase it further:


So I get this right: the Bias knob controls the base level amplification the module provides. Any CV inputs add to this bias amount (thus negative CV subtracts...)


That's it exactly.

My personal requirements for a VCA if I were going to replace mine would be:

- either linear, or knob control over response curve
- bias knob
- CV amount knob
- extra gain (I wouldn't want this without a CV amount knob)
- compact-ish but not tiny

Mix outputs (normalled if it's a quad VCA) are nice but not essential to me.

A bipolar/unipolar switch would be pretty great. It seems most VCAs are one or the other.
pieter
Essentially what I look for in a VCA is covered by the Intellijel quad VCA. I use all it's features, and there is nothing that I think it is missing. Basically, it's a perfect module.
naturligfunktion
chysn wrote:
Not necessarily. It gets a bit tedious when each module does one thing, and sometimes the interplay between different features can make modules more interesting, while not making them harder to use.

Examples in the VCA realm include Optomix (mixing, filtering, dynamic control (VCA)), Veils (mixing, and/or individual VCAs), The Bends (voltage-controlled mixing, polarization, offset, VCA-like things).

There's a nice sweet spot between modules that do everything and modules that do exactly one thing.


Agree. For the record I think that the Optomix is a absolutely brilliant VCA. Anyone had checked out the Dynamix?

Secondly I also like the VCA from Intelljejl. Its very basic, but I like it. It do have a little blinking LED, which is essential almost.
honeyb
pieter wrote:
Essentially what I look for in a VCA is covered by the Intellijel quad VCA. I use all it's features, and there is nothing that I think it is missing. Basically, it's a perfect module.


Funny thing is I just found this old post:
http://www.muffwiggler.com/forum/viewtopic.php?p=36686&sid=f8fc8ee42fb 1a6cebac4b5795bc45efe

which seems to be where Intellijel got his start smile
honeyb
Roman Sowa gets credit for building one based on transistors
http://www.sowa.synth.net/modular/xvca.html

Seems a lot of people like to start with the CoolAudio V2164 quad VCA chip (it's in the Mutable Instruments Veils among others)

http://www.muffwiggler.com/forum/viewtopic.php?t=96486&sid=4628a6e70a1 bf663bafd6efaf16a0716
pieter
honeyb wrote:
pieter wrote:
Essentially what I look for in a VCA is covered by the Intellijel quad VCA. I use all it's features, and there is nothing that I think it is missing. Basically, it's a perfect module.


Funny thing is I just found this old post:
http://www.muffwiggler.com/forum/viewtopic.php?p=36686&sid=f8fc8ee42fb 1a6cebac4b5795bc45efe

which seems to be where Intellijel got his start smile


Well... he nailed it!
anselmi
mute button/switch with LED
Pighood


Got a pair of these

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fap fap fap... fap fap fap... fap fap fap... fap fap fap...

fap fap fap... fap fap fap... fap fap fap... fap fap fap...

fap fap fap... fap fap fap... fap fap fap... fap fap fap...
pricklyrobot
For a multi-channel VCA, some normalling on the CV inputs can be handy. So you could, for example, use one envelope to control multiple channels (if nothing is patched to their individual CV ins).

Easily done with switching jacks.
Nagasaki45
Probably not the most popular opinions but:

- I think VCAs for modulation require a bit different features than VCAs that are primarily for the main audio path. Note that I'm not talking about slow voltage changes vs. audio range signals. FM / AM and other variants of audio range modulations are still modulation. For modulation VCAs blinds is really nice, with the attenuverters on both bias and CV level. For VCAs on the main audio path I will never want attenuverters as it make it hard to mute things properly. Also, bias is probably less important. If it's a dual / quad VCA the layout should also be different. For modulation VCA input / CV / output should be next to each other, again, like in blinds. For main audio path mixing VCA a layout like tangle quartet or the intellijel quad VCA is better.

- DC coupled.

- I personally don't see a lot of value in the linear / exponential knob. I prefer that on the modulation side (maths / zadar for example).
starthief
I work with drones a lot and manual control over levels, so I find bias knobs on VCAs are good for audio smile

But yeah, I should have had "DC coupled" on my list too. I just take it for granted.
cptnal
My God! This VCA's gonna be HUGE. screaming goo yo
Shledge
I like the idea of including an AC/DC switch. Sometimes it's needed and can be used for creative effect eg. turning gates into triggers or basic envelopes. It would also be hugely beneficial to VCOs which output... in unipolar (looking at you, Verbos).
lisa
I want them to be small and few. meh Nice distortion is also a plus.
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