[sdiy] mono/poly mod, electonic basics

[Thom Somneevich]

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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