[sdiy] mono/poly mod, electonic basics

[Synthusiast]

Hi Thom,

You did a good job finding the place for an audio input on the Mono/Poly :)
I bought my Mono/Poly with almost the same mod you described already fitted
in (mine used an extra DC filter cap right after the jack). The mod works ok
if you crank up the volume of the gear you're feeding into the Mono/Poly,
but I found that often the audio input signal level was too weak to be used
this way. After several tries of designing an amplifier circuit for the
audio input mod, I haven't found any good solution yet. Using an OTA could
be the answer, though I still have to try that one.

Cheers,
Martijn

> Hello,
>
> I just modded my Mono/Poly to accept an external input to the filter. It
> works, but I was wondering if you guys could tell me exactly why :) and
also
> if I should alter it to protect the synth and/or input.
>
> The filter uses an SSM2044. I used the datasheet, and at first thought of
> adding the input straight to the first pin, w/ a preceding pot to keep the
> signal down if needed. Lava at the Zen Mono/Poly site told me he had
already
> tried this, and it didn't work. Now, I figured it might work to put it at
> the amp which sums the 4 vco signals, and it does. I thought it would
> because I've seen it in so many schematics, but I don't really understand
> it. Why would it work before the amp but not after? At either place the
> signals are being jammed together, right? What makes that op-amp a
'mixer',
> if that is what's happening?
>
> Also, I grounded the jack, but that's it. The mod is jack-->pot-->op-amp.
Is
> there anything I should do there for further protection? It almost seems
too
> simple and good to be true.
>
> Thanks for sharing the knowledge. I'm learning slowly, and I appreciate
all
> the wit and wisdom you guys share.
>
> thom
>
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