[sdiy] mono/poly mod, electonic basics

[Scott Gravenhorst]

This is an example of a summing amplifier, a fancy way
to say 'mixer'.  It's a basic analog computer building
block.

http://www.play-hookey.com/analog/

Has tons of info on analog computers, most of which is
used directly in analog systhesizer technology.  You may
recognize many of the mini-schematics shown.

Enjoy.

>>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.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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