Subject: Re: Help with audio o/p transformer feedback to inv OP Amp
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Date: Tue, 14 Jan 2003 07:59:40 +1300
NNTP-Posting-Date: Tue, 14 Jan 2003 07:59:43 NZDT
Turns ratio is 1:1 using modem type transformer.
Oscillation is very high freq, looking at scope. I tried a 10pF cap across
the op amp feedback resistor (thanks Win), and it did stop it, but when
using a greater ratio of transformer feedback verses op amp feedback, the
stage still oscillates. I tried a larger cap, but this introduced an
unwanted phase shift at freqs higher than 1Khz.
Im thinking I might be able to introduce the transformer feedback into the +
input instead of mixing with the (-) input.
I didnt think such a simple addition would be so difficult.
"John Woodgate" wrote in message
> Apart from the oscillation, what is the turns ratio of your transformer?
> If you have a gain of only 2 from input to primary, due to the feedback
> around the op-amp itself, and the transformer has a turns ratio of less
> than 1:2, you have insufficient open-loop gain for the overall feedback
> to do anything.
> Regards, John Woodgate, OOO - Own Opinions Only.
> Interested in professional sound reinforcement and distribution? Then go
> PLEASE do NOT copy news posts to me by E-MAIL!