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What makes a good VCA? And does Veils count as one?
MUFF WIGGLER Forum Index -> Eurorack Modules  
Author What makes a good VCA? And does Veils count as one?
jgoney
Hi!

I'm pretty new to this, so while I'm starting to understand why "you can never have too many VCAs", I'm still not so sure what to look for in one. I built the Synthrotek MST dual VCAs, and it does the job okay, but without really knowing what to look for, I can't judge if I'm missing out (I hope that makes sense).

On a related note, I was thinking of adding some more VCAs via Mutable's Veils. Can anyone vouch for Veils?
syntheticthings
Works for me.
thermionicjunky
Both designs use the SSM2164 VCA IC, which is a very good chip. The MST has a switch for linear or exponential response. Veils has a continuously variable response control, so you can experiment with the response to taste.
flashheart
Not much to look for really. Lin/log switching / variability may be useful. Sound quality or character may be be something to look for for audio VCA use. Beyond that it's just your preference for layout / features.

If you're happy with the Synthrotek fine, don't sweat it.
cyclopeatron
Veils is great. I used mine in every single patch. No bleed. Highly recommended.

I was tempted to buy a second Veils, but now I'm looking at the new Intellijel Quad VCA, which does the same and more, including bias and boost.
skeller047
If you haven't bought yet, I'd recommend the Intellijel Quad VCA, or a pair of uVCA's- precisely because of the bias control. When you are doing things other than just a straight basic synth voice patch (VCO -> VCA in, Envelope -> VCA CV in), it can be very useful.

For example, using one VCO to do amplitude modulation of another -use the bias (AKA offset) to have a base volume of the carrier, then modulate that with the output of another VCA being fed by the modulator, and controlled by an envelope or LFO. The bias control saves having to use a mixer to combine an offset and the output of VCA3 in the ASCII diagram below. Note that ENV and VCA2 below are optional, just giving discrete notes over the output of the other modules; if all you want is a drone, they aren't needed.

--- VCA1 has bias at about 50% ---

_______ENV. -----v
VCO1 ->VCA1-> VCA2
_________^
VCO2 -> VCA3
__LFO ----^

((edit spacing))
Whelm
skeller047 wrote:
If you haven't bought yet, I'd recommend the Intellijel Quad VCA, or a pair of uVCA's- precisely because of the bias control. When you are doing things other than just a straight basic synth voice patch (VCO -> VCA in, Envelope -> VCA CV in), it can be very useful.

For example, using one VCO to do amplitude modulation of another -use the bias (AKA offset) to have a base volume of the carrier, then modulate that with the output of another VCA being fed by the modulator, and controlled by an envelope or LFO. The bias control saves having to use a mixer to combine an offset and the output of VCA3 in the ASCII diagram below. Note that ENV and VCA2 below are optional, just giving discrete notes over the output of the other modules; if all you want is a drone, they aren't needed.

--- VCA1 has bias at about 50% ---

_______ENV. -----v
VCO1 ->VCA1-> VCA2
_________^
VCO2 -> VCA3
__LFO ----^

((edit spacing))

The Synthrotek MST VCA has Bleed in lieu of Bias for the same effect (I believe).
Sven
Veils has a design fail for me. When you turn the response knob from 12 o´clock to noon the signal distorts. Mutable says that this is for amplifing or distorts signals but not make sense. Why implement that in the response knob? BTW when you put the signal in the osciloscope you see well how the signal brokes. Is not a beautiful and controlled drive for creativity uses, is destruction of the signal.
pichenettes
Sven wrote:
Veils has a design fail for me. When you turn the response knob from 12 o´clock to noon the signal distorts. Mutable says that this is for amplifing or distorts signals but not make sense. Why implement that in the response knob? BTW when you put the signal in the osciloscope you see well how the signal brokes. Is not a beautiful and controlled drive for creativity uses, is destruction of the signal.


It's not a design fail, and certainly not something I purposely implemented. That's just exactly what is expected from an exponential response. Past unity gain, it grows very, very rapidly. Any VCA with an exponential response that allows gain to go past unity will exactly do that.



One could a/ trim the response so that it doesn't go past unity gain (a few diodes in the VCA CV control circuitry), or b/ add zener diodes in the final op-amp stage to provide a more gentle drive. But a/ means the VCA will be unable to boost external signals, and b/ means distortion and coloration, always, even when the signal is not at full amplitude.
oknussen
skeller047 wrote:
If you haven't bought yet, I'd recommend the Intellijel Quad VCA, or a pair of uVCA's- precisely because of the bias control. When you are doing things other than just a straight basic synth voice patch (VCO -> VCA in, Envelope -> VCA CV in), it can be very useful.




((edit spacing))


agreed - i have the uVCA and love the feature (also have Veils and love the 20db of gain it offers)
Armstrb
I have Veils and love it. Very clean. Unity mix feature is very useful.
Varthdader
Love my Veils.
Love my Blinds to attenuvert too.
Sven
pichenettes wrote:
Sven wrote:
Veils has a design fail for me. When you turn the response knob from 12 o´clock to noon the signal distorts. Mutable says that this is for amplifing or distorts signals but not make sense. Why implement that in the response knob? BTW when you put the signal in the osciloscope you see well how the signal brokes. Is not a beautiful and controlled drive for creativity uses, is destruction of the signal.


It's not a design fail, and certainly not something I purposely implemented. That's just exactly what is expected from an exponential response. Past unity gain, it grows very, very rapidly. Any VCA with an exponential response that allows gain to go past unity will exactly do that.



One could a/ trim the response so that it doesn't go past unity gain (a few diodes in the VCA CV control circuitry), or b/ add zener diodes in the final op-amp stage to provide a more gentle drive. But a/ means the VCA will be unable to boost external signals, and b/ means distortion and coloration, always, even when the signal is not at full amplitude.


Many thanks for this explanation, everything is clear for me now.
hinterlands303
Sven wrote:
Veils has a design fail for me. When you turn the response knob from 12 o´clock to noon the signal distorts. Mutable says that this is for amplifing or distorts signals but not make sense. Why implement that in the response knob? BTW when you put the signal in the osciloscope you see well how the signal brokes. Is not a beautiful and controlled drive for creativity uses, is destruction of the signal.


Piggybacking on Olivier's response (which is clearly more knowledgeable than mine) the other vca's I have with an exponential response behave the same way. With the uVCA you have to be careful when adjusting the linear/expo knob - I tend to simultaneously adjust the cv knob as to avoid distortion/eardrum explosion. Once you get the hang of it this is really useful though.
Faastwalker
Looking at my first VCA module. Have x2 VCAs on my Kilpatrick Phenol. But they are quite basic. As you can never have too many, and with more features than the ones I have, I'm looking at the Mutable Veils. Either that or the Intellijel Quad VCA, which is about $100 more expensive over here in Aus. Trying to work out if it's worth the extra or if there are any other options to consider. I love the idea of having the 4 inputs that can be summed to one output. So the two options I've identified look like good ones.
Josef_K
Faastwalker wrote:
Looking at my first VCA module. Have x2 VCAs on my Kilpatrick Phenol. But they are quite basic. As you can never have too many, and with more features than the ones I have, I'm looking at the Mutable Veils. Either that or the Intellijel Quad VCA, which is about $100 more expensive over here in Aus. Trying to work out if it's worth the extra or if there are any other options to consider. I love the idea of having the 4 inputs that can be summed to one output. So the two options I've identified look like good ones.


I have a Veils and like it a lot, imo a touch of the overdrive (or a lot on sinewaves) can often sound quite pleasing. However for tremolo or when modulating the amount of a modulator I often use a different VCA rather than mix in a CV offset. So if you think you'll be doing that a lot then the extra $100 for the Intellijel is absolutely worth it imo.
starthief
I think if I were starting over, I'd go with the Intellijel quad. Having bias controls as well as CV attenuators is really convenient, as I've found with a couple of my LPGs that have VCA modes.

I'd add to that at least one bipolar VCA and maybe something with interesting character; ModDemix is both. And I'd rather have no VCAs than no LPGs smile
Bignorthumbrian
Veils is great.
Superaction80
Varthdader wrote:
Love my Veils.
Love my Blinds to attenuvert too.


If you’re already happy with your current unipolar vcas and you don’t need more to manage additional voices, Blinds might be worth a look. You can get Blinds to act as a unipolar vca as well, though getting it to settle on zero is fiddly by nature. That said, it’s an insanely useful module. You lose the boost switch on the intellijel quad, but you gain the attenuversion Varth mentioned, as well as crossfading and ring modulation. I love mine.

Again, if you need classic voice dynamics, the intellijel quad/veils would probably be a better choice.
jeninboy
Veils works for me but I think Blinds would provide more (albeit different) functionality, worth considering Blinds perhaps?
pieter
I have an Intellijel quad VCA and a Blinds. The offset on the VCA is great for playing with the responses of bipolar CV signals, among other things, and I love the shape fine tune (boost is a bonus). When I want tremolo on top of my ADSR I use Blinds, because that module is literally perfect for mixing modulation. Both modules will never leave my rack.
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