Is the Minimoog’s VCA circuit capable of processing CV control voltages ?..does anyone have any modification info? I’m not sure if inserting a C V /DC into Q16 would work as I think this is the the audio/ac input ? Any advice on this?
An external Control Voltage input of the VCA is already provided with the jack identified : LOUDNESS EXT. on the top panel of the Minimoog on the left.
If that is what you are looking for ? Some kind of external control of the VCA ?
Hi Alien
Actually I have the Minimoog clone vca circuit by Marjan Urekar…www.synthdiy.com…minivca
I want to feed the output of a 911 EG thru this VCA and control the VCA via velocity control…but I’m not sure if this VCA can process the EG’s output..I think the Minimoog VCA is designed for ac / audio only but wonder if it can be modified? I got a suggestion to simply remove the capacitors from input and output but I am not knowledgeable enough to know if this will work.
Ah, well, that’s different. I know that capacitors in series are there to prevent DC from passing thru in audio chain, so the suggestion of removing some capacitors (C6 and C2 most probably) would make sense. But as far as the VCA design of the Minimoog being able to handle large DC voltages at the signal input, I’m not at all sure about that… Sorry.
Maybe someone with deeper knowledge than I, in electronics, could perhaps enlighten you on that ?
Hey rarecomponent.
The Urekar VCA should do exactly what you want. A Minimoog VCA (including Urekar’s version) actually has two VCAs in it, one for internal/envelope CV control, and one for external CV control. Either CV input will work fine.
In the Urekar schematic the audio basically enters the circuit at Q1, and CV1 enters at Q3 (there are a couple of other components before the transistors). Optionally, CV2 input goes into Q6. I’m pretty sure the Minimoog VCA is capable of handling 0 to +10 volts.
All VCAs have an audio input that is loudness controlled by a separate Control Voltage input. The CV is what lets you hear the audio passing through the circuit.
Several other people here can tell you more detailed info if you need it.
In re-reading your original question, note that the 911 EG output is a DC CV source (no audio) and will go into one of the two CV inputs on the VCA. You still need an audio source (oscillators, guitar, mp3, etc.) to go into the VCA audio input so that you’ll have something for the 911 to amplify.
Thanks for replies…no I don’t wish to pass audio thru the VCA I want the envelope signal to go thru instead of the audio so that I can vary the amplitude of the envelope signal via the VCA’s CV input using velocity output from a touch keyboard. I think by removing the blocking capacitors this should work as the Minimoog VCA is quite similar to the 902 VCA…but I’m not certain.
You could always use an attenuator at first, to obeserve the behavior of the VCA ? And slowly raise the level of the envelope signal, and monitor the voltage output levels of the VCA to check that they follow the input with no attenuation or modification at maximum opened VCA ?