> The input amp has a hi frequency osc.

I don't know any details of your circuit, so this is only a general answer.
Some amps are unstable without compensation, especially a low gains.  Try
adding a "compenstation capacitor".  Some amps have explicit pins for this,
otherwise put it directly from output to the negative input.  Of course this
assumes your circuit doesn't drive the negative input with a low impedance
at high frequencies.  Start with the smallest capacitor you can find and
work up slowly.  Usually only a few 10s of pF will do it.  Too much
compenstation will cut into the desired bandwidth.

Of course this assumes you have good clean and well bypassed power supplies
at the amp.  All else is irrelevant until this is taken care of.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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