[sdiy] stupid non-inverting opamp

[Gene Stopp]

It takes a little while for it to sink in - it's kinda clever. That ground
on the pot wiper is pulling double duty. The non-inverting gain is variable
all the way down to zero, unlike the normal non-inverting amp with a pot in
the feedback loop. It may be prone to distortion since there's a potential
initial gain of 101 cut down by a 10K/100K divider. It would be interesting
to plot the gains at various pot settings to see what kind of pot rotation
versus gain curve it has.

- Gene



-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Don Tillman
Sent: Wednesday, January 25, 2006 5:17 PM
To: xyzzy at sysabend.org
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] stupid non-inverting opamp


   > Date: Wed, 25 Jan 2006 14:22:36 -0800
   > From: Tom Arnold <xyzzy at sysabend.org>
   > 
   > http://www.themusic.net/rmp1-preamp.jpg
   > 
   > 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.

This is a preamp circuit that a., does not invert, b., provides
variable gain, c., allows for gain less than unity, and d., doesn't
introduce noise by cutting the signal level and then applying gain
again.

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com