VCAs for Dummies (or is it just me?) - How does this work?

So VCAs are somewhat of a cornerstone of modular as far as I understood. Getting some helped me to understand some basic as to why that is the case but how do these work? As I find a lot of info on this topic still confusing I would really want to talk about my specific case:

I have 2 Doepfer 130-2 VCAs ( I thought the switch thingy could let me dodge the linear vs. exponential topic for now).

First topic: Gain
For the sake of simplicity, I have a Signal with a Value of 10 coming in so the gain gives me an output of 1 at 1, an output of 2 at 2, and so on. First of all, is that how it works, or am I making things up beginning from this point?

Second topic: CV
This is where my headache begins. What does CV exactly do? The CV knob is doing the same for the CV value as the Gain for the Input value I assume (so again at a CV Signal 10 gives me a CV of 1 at 1, a CV of 2 at 2. So how do these values get merged? Will the CV value be added to the Input (after gain) or is it a multiplication? Am I right to assume that a CV of 2 and an Input of 3 will get me to an output of 5 (or is it a multiplication and gets me an output of 6?). Is the output capped? As most stuff in modular works in a certain range it should be but where is that cap and will it "distort" or anything if pushed past?

Thanks for anyone willing to teach me.

Watch this and have your eyes opened to what your ears can hear :)

I can offer you two tips on VCA use. 1. Volume modulation 2. Pan modulation.
This video explains well, and I suggest you patch up something and try this approach. Its a good way to start learning about modulation via vca.
Also, CV is "control voltage" and is sent out in what ever way you command it to.

Also, a kind poster here has this in the tag, take it to heart: "Utility modules are the inexpensive, dull polish that makes the expensive, shiny modules actually shine!!!"

VCAs. The thing that new builders neglect...until they discover just how much their build SUUUUUUUUUUUUUUUCKS without them!

VCAs have so many uses, it's nuts. But then, you have to remember that the initial idea for modular synthesis partly came from analog COMPUTERS, which are very dependent on voltage relationships with/between op-amps. Since all the analog computer voodoo lies in how you use those, it makes perfect sense that we have a similar circuit in modular synths.

Anything that needs level control for which you don't happen to have several extra arms and hands, that's where VCAs go. Audio and CV/mod levels are the basics, though. You can also use them as amplitude modulators, by feeding an audio signal to both the signal AND CV inputs. Lots of clangers and yowls! A couple of them make up the guts of stereo autopanners. And performance mixers are usually jam-packed with VCAs to control levels, panning, AUX send/returns, and so forth. And if you want to scan/xfade through a VCO's waveforms, a quad VCA + a quadrature LFO are a must. And that list goes on...

I think some of the problem with them lies not just with the "boring factor", but the term "amplifier". People look and think "well...I've GOT an amplifier and it's hooked up to my speakers already, so I don't need all of these amplifiers...right?" Wrong. Whatever the cause of this, it's a HUGE trap and part of the "boring module" issues that people run across...which I've termed "sexy module syndrome". These modules don't come with a plethora of knobs and lights and so forth, so people load up on the "better" modules that DO have all of that...then wonder why their $7k+ box sounds like total ass, give up on modular, and yet another cab gets consigned to the closet. It's not necessary...people just need to do their homework about these instruments BEFORE grabbing the Magic Plastic and burning yet another expensive hole in it.

Plug an oscillator straight into the input of a vca,
Plug the output of a vca to your mixer or whatever you use to hear stuff
Now turn the gain to zero on your vca - you can’t hear your oscillator anymore
Now turn the cv to zero
Plug a sine wave lfo into the cv input and slowly raise the cv value from 0 -10

Can you hear what is happening to your oscillator volume ?

You can plug anything into the cv input, like envelopes, lfo, or even the outputs of other vca’s. I like plugging sequencers into them, which is why I have a lot of sequencers in my racks

There are lots of other uses but this is the most frequent use and it’s when you say that you are using the cv input of the vca to shape the amplitude of a sound or for us simpletons, we can just say volume.

Hope this helps

I often tend to chain my VCAs to "entwine" some Euclidean trigger sequences with different offsets to create a rhythmic pattern.

Wouldn't in that case a mixer be the way to go? Like a Doepfer A-138n for example which mixes 4 of those sequences at 4TE whereas the dual VCA only gives me 3 (In+CV+CV / out to second In is used for the chain). I was told VCA > Mixer but I am not so sure about that. As of my understanding right now a Mixer > VCA whenever the use case doesn't need the input gain to be 0.

Started experimenting with the "volume control" use and really like it thx for the vid, definitely brought some ideas on what could be done.

EDITED Jul 29th 2021, 11:28

but a vca that mixes > mixer or vca

Here is the non-technical explanation.

The VCA is the actual unit that does the work when it comes to controlling the amounts of anything else. Like a volume control on your phone or car's stereo, it controls the amount of whatever it is you're putting through it.

But where a VCA differs from a simple volume knob is that it has an input for automation. Instead of turning the knob by hand, you can use a CV voltage to do it. VCAs can control the amount of audio. They can control the amount of other CV signals being routed through them. They are the basic building blocks of automation aka MODULATION.

There are some fine points regarding different types of VCAs and what they can do. VCAs can be set-up in many different ways... so you might find some that respond in linear or exponential fashion. You will find some with a manual knob. You'll find others that have no manual controls and are just three little jacks. Sometimes a set of VCAs will be built to do duty as a mixer as well.

Okay played around with my VCAs a little bit more and found the Doepfer 130-2 VCAs are creating a pretty loud clicking sound when being on volume control duty. Out of plaits is connected to the VCA and CV is connected to an LFO (doesnt matter which waveform). Is that normal or am I doing something wrong ?

Okay played around with my VCAs a little bit more and found the Doepfer 130-2 VCAs are creating a pretty loud clicking sound when being on volume control duty. Out of plaits is connected to the VCA and CV is connected to an LFO (doesnt matter which waveform). Is that normal or am I doing something wrong ?
-- 9xpad

If the issue isn't limited to one waveform (and one that has a hard leading edge!), then my bet is that you could be overloading one of the inputs...and since it's a "click" on the output, my bet is that the culprit is the CV input. Try this: set up a VERY SLOW triangle LFO, then feed that to the CVs. At the same time, also connect an oscilloscope to watch the LFO cycling through the waveform. My bet is that once the LFO reaches the maximum voltage limits, the "click" appears. Also, set the scope so that you can read the voltage on the Y axis, and you'll have a good indication of what's really happening and at what voltage level it occurs.

This click could also be the result of some DC offset voltage getting into the LFO waveform and pushing it well beyond the operational limit of the CV inputs. Remember: if you have a +5/-5 volt cycle, inputting an offset will make that +whatever voltage the offset is. Jam in an offset of +10VDC, and suddenly your high value on the mod signal is peaking at a really unacceptable +15V. If the LFO has an offset control, that should be at ZERO when generating bipolar modulation signals.

Hey @9xpad, I'm pretty new to modular too but, -- what @Greenfly said, I'd second. I have the Doepfer A-135-2 Quad VCA and was also confused at first. You need to feed an audio signal to the IN, feed the OUT into your mixer that sends the audio out to whatever speakers or external sound source you have. Set the mixer level to something audible, but set both VCA knobs to zero. Plug an ADSR envelope or LFO output into the "CV" jack on the VCA module, then slowly dial up the "CV" knob until you start to hear something. Whatever envelope you're feeding in should now be modulating the audio signal -- so if it is an oscillator drone, say, with a cycling sawtooth LFO applied, it will start chopping itself up into the sawtooth shape accordingly.

If you're getting clicking, whatever you're feeding into the CV probably has zero attack/decay slope (like a rectangle wave). Use a softer wave or slew or ADSR type envelope generator to eliminate those. You might also have something dialed in too high.

It took me a while to get used to, because I was so used to audio sources that had triggers/gates built into them fundamentally -- you trigger the sound, and it already has some kind of envelope controlling the audio applied. With a lot of modular it's just the opposite. The sound is always "on" and you have to engineer backwards to mute and control it. It's super fun but takes a little getting used to, and I still have plenty more to absorb/learn, bc like Lugia mentions there's other uses for VCAs as well.

Okay played around with my VCAs a little bit more and found the Doepfer 130-2 VCAs are creating a pretty loud clicking sound when being on volume control duty. Out of plaits is connected to the VCA and CV is connected to an LFO (doesnt matter which waveform). Is that normal or am I doing something wrong ?
-- 9xpad

If the issue isn't limited to one waveform (and one that has a hard leading edge!), then my bet is that you could be overloading one of the inputs...and since it's a "click" on the output, my bet is that the culprit is the CV input. Try this: set up a VERY SLOW triangle LFO, then feed that to the CVs. At the same time, also connect an oscilloscope to watch the LFO cycling through the waveform. My bet is that once the LFO reaches the maximum voltage limits, the "click" appears. Also, set the scope so that you can read the voltage on the Y axis, and you'll have a good indication of what's really happening and at what voltage level it occurs.

This click could also be the result of some DC offset voltage getting into the LFO waveform and pushing it well beyond the operational limit of the CV inputs. Remember: if you have a +5/-5 volt cycle, inputting an offset will make that +whatever voltage the offset is. Jam in an offset of +10VDC, and suddenly your high value on the mod signal is peaking at a really unacceptable +15V. If the LFO has an offset control, that should be at ZERO when generating bipolar modulation signals.

-- Lugia

Okay investigated a bit. Unfortunately, I don't have a scope but I would really like to get one as that could help me out a lot. Any recommendations (preferably non-modules as my space already is pretty limited)? So the culprit creating static and clicks is the slop setting on my Pamelas new workout in combination with a euclidean (example 4steps 3 trigger). It gives me 3 clean Gates (beep-beep-beep-nothing) but every now and then instead of the 4th step being mute, it gives a super small Gate just a really short spike that is audible as a click. I thought slop just introduces timing errors but this is creating an extra unwanted trigger.

Plaits has an in built VCA. If you are planning on using and external VCA make sure the one built in plaits is fully open then do what @eexee and @Lugia are suggesting.

I suggested you use an lfo as this way you don't have to worry about triggering it, if you plan on using an envelope you are going to also have to also learn how to to trigger it, or send a gate signal to the envelope.

EDITED Aug 1st 2021, 03:23