[sdiy] How does the JX3P VCA work?

Justin Owen juzowen at gmail.com
Tue Jan 21 10:58:51 CET 2014

Interesting - I'd never actually looked at the rev2 schematic.



-----Original Message-----
From: Andrew Simper [andy at cytomic.com]
Received: 20.01.2014 02:08:36
To: Justin Owen
Cc: SDIY List
Subject: Re: [sdiy] How does the JX3P VCA work?

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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