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Single transistor VCA circuit
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gasboss775



Joined: Jan 02, 2016
Posts: 210
Location: Scotland

PostPosted: Thu Jan 26, 2017 4:10 pm    Post subject: MOSFET VCA Reply with quote  Mark this post and the followings unread

It is possible to make a MOSFET based VCA too. Here is a possible circuit:

I haven't breadboarded this so it's possible that some of the component values might need tweaked. The opamps can be TL071/72/74 or TL081/82/84


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danja



Joined: Nov 29, 2017
Posts: 1
Location: Italy

PostPosted: Wed Nov 29, 2017 5:06 am    Post subject: Capacitor values Reply with quote  Mark this post and the followings unread

Thanks for the circuit. I'm going to play on the breadboard later, but my guess is that the input cap C1 should be at least 100nF, will depend a bit on the value of R1 so as not to block bass. C2, C3, I imagine should both be pretty small, maybe 1nF - 10nf, so as not to block the treble.
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gasboss775



Joined: Jan 02, 2016
Posts: 210
Location: Scotland

PostPosted: Sat Dec 02, 2017 8:12 am    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Yes, but I've seen the same basic idea used with other op amps. The scrap below, using a TLO72, is from the TR909 clone rim shot. I've also seen an LM324 used.


I like this type of VCA for percussion circuits as the distortion and control signal breakthrough tends to accentuate the attack portion of the sound, which is generally desirable in a percussion sound.


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