Hi Tim,

thank you very much for the info. Where did you get it Service manual I
suppose. Seems there´s lots of info on the electronics and how to modify
them. Man, I´d definitely buy it if it wasn´t so expensive... so far
I´ve only got of the A-110 and A-185-part of the service manual. They
werse supplied with my A-185 prototype and a blank PCB of the VCO.

Since I am a newbie to synth-DIY it would be very cool if Doepfer could
provide us with a schematic of the "mythical expansion ´board2´". I got
to mod the A-131. Two VCAs for the price of one (plus a little of cost
for the electronics) :-)
Still begging for the DIY pages on Doepfer´s website...

Paul


Tim Stinchcombe wrote:

> Yes. Basically the 10-way connector feeds out +/-12V supplies,
> ground, and connectios to the gain, input and output pins of the
> unused vca section in the chip. Thus you would need to provide some
> circuitry to control the gain, and buffer the input and output. To
> give some idea of whats involved for the used vca, with faceplate
> held down, the left-hand TL062 provides the gain control, and one
> half of the right-hand TL062 buffers the output, the other half sums
> and buffers the inputs.
>
> 'JOUT/BOARD2' connects to the output of the vca section used on the
> board, so I'm not quite sure what Doepfer may have had in mind for
> its use on the mythical expansion 'board 2'. Notice also that
> underneath there is an unmade link 'JCV' which would allow the unused
> section to be controlled with the same gain signal as the used one.
> Also not sure what the 'AUDIOSUM/J2' was intended for, since one side
> is the summing point for the inputs, but curiously the other is just
> ground. 'CVSUM/J1' is the same for the summing point of the gain CV
> (the ground sides are marked with an upside-down 'T'.)
>
> Not a trivial task, but certainly do-able with enough commitment and
> application!
>
> Tim
>

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