CV Mixer Prob. Solved

[wbf at aloft.lucent.com]

> Date: Fri, 20 Sep 1996 11:56:37 -0700 (PDT)
> Orig-From: "A.S.P." <ms20 at itchy.serv.net>
> To: synth-diy <synth-diy at horus.sara.nl>
> Subject: CV Mixer Prob. Solved
> Sender: owner-synth-diy at horus.sara.nl
>
> First of all, thanks to all for responses to my query.
>
> I tried replacing the 30pF cap across the output buffer with larger
> values, but this did nothing.
>
> As a last ditch effort, I replaced the buffer IC (LF411) with a 741 and
> the problem went away.  I don't know why and I do find it surprising, but
> the circuit works now.  (Any ideas why?)
>
> ROmeo

Sometimes circuits will oscillate as yours did when replacing older op
amps with newer models that have improved slew rate or different
internal compensation.  Try comparing spec sheets on the 741 and LF411;
maybe you can spot such parameter changes.  Then you'll be able to
modify your schematic to use the "better" part.  Or just leave the 741
in there and make music now!  How well is the amp's power supply pins
bypassed?

Bill Fox	wbf at aloft.lucent.com