[sdiy] stupid non-inverting opamp

[Ken Stone]

The pot varies gain by either shunting the "gain cell" output to ground
(less over all output), or increases gain by shunting the inverting input of
the "gain cell" to ground (more over all output).

There is only one feedback loop. The other is merely a voltage divider.

Ken


>So, I'm debugging the last of my EFM modules and of all things the simplist
>part of the module isnt working.
>
>Specifically :
>http://www.themusic.net/rmp1-preamp.jpg
>
>The always struck me as "I've got an opamp left over, I'll add a preamp" and
>I almost just left it off the panel, but now I have a knob for it and jacks
>so I hate to not make it work.
>
>In short, it doesnt work.  Looking at the circuit I dont understand it.  I
>see the feedback I'd expect ( R3 ) but then theres the outside feedback loop
>of the pot, C4, and R2.  I just dont grok what was being done here, it
>almost looks like a tone control vs a plain preamp.
>
>I'm about to just rip out R2/C4 and move the pot to R3 with a resistor in
>series, and bump R1 up to pot+new resistor and be done with it, but it'd be
>nifty to know possibly what was intended with the circuit before I go
>hacking on it.
>
>Any ideas?
>
>-- 
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> - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
> - SynthGeek        -
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_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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