[sdiy] How does the JX3P VCA work?

Andrew Simper andy at cytomic.com
Mon Jan 20 03:08:32 CET 2014

Be careful talking about "the" MS20, there are two of them. The
schematic shown looks like it is based on the MS-20 rev2 OTA based
daughter board ( KLM-307
), including the 6 dB one pole bass boost shelf post amp. The MS20
rev1 and JX3P both use a single biased transistor.

All the best,


On 20 January 2014 00:04, Justin Owen <juzowen at gmail.com> wrote:
> -----Original Message-----
> From:  [rburnett at richieburnett.co.uk]
>>The VCA in the JX-3P only uses a single pass transistor between the
> attenuated source and the op-amp.  I've never seen the other arrangement
> with two matched transistors before.
> So if the JX3P only uses a single transistor (?) and the MS20 definitely only uses a single transistor - what's with the second transistor in the schematic from the OP?
> - Justin
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