[sdiy] What is wrong with this circuit?

[mike ruberto]

On Jan 30, 2008 6:03 AM, Mike <profpep at hotmail.com> wrote:
>
>
>
> > Something is bugging me about this circuit. It just looks wrong to me.
> > I think it's the feedback section around M1...
> >
> http://s108.photobucket.com/albums/n13/somnium7/gear/?action=view&current=RX-7_Mic_Input.jpg
> >
> > Shouldn't R12 be connected directly to the negative input?
> > Does this look normal?
> >
> I think that R12 is connected via the capacitor to avoid getting DC on the
> pot, and thus avoiding scratchy noises when it's moved.

Ok this makes sense but it seems that the pot is in the wrong place.
Wouldn't it be a more elegant solution to use a lower resistance pot
in series with R10 with the cap between the pot and negative input?
R11 would then be uneccessary with a proper value for R12.

I take it M1 is a
> discrete component op-amp. I guess R11 is to provide a max gain limit and to
> DC bias the imput, along with R9, which also defines input impedence - some
> discrete op amps are said to work badly at very high input impedences. I am
> not an audio expert however - perhaps a post on the Prodgy Pro forum might
> be an idea.

Yes the part is a discreet opamp. I do have plenty of questions for
folks at Prodigy Pro but I think the forum admin went permanently AFK
because new accounts never get activated now.


>
> Mike
>
>
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