Sorry Lads, really dumb opamp question

[Martin Czech]

Now, 1 Ohm feedback resistance will kill the resisor paralell capacitance.
10k Ohm should make it more apearent. Perhaps, if it is really way up
in the tens of MHz it is really parasitic paralell capacitance
of the feedback resistor. Metal film with trim spiral (air gap)?
I guess so!

m.c.


:::X-Originating-IP: [207.206.127.34]
:::From: "Happy Harry" <paia2720 at hotmail.com>
:::To: czech at Micronas.Com, harrybissell at prodigy.net
:::Cc: synth-diy at node12b53.a2000.nl
:::Subject: Re: Sorry Lads, really dumb opamp question
:::Date: Mon, 15 Jan 2001 16:47:52 -0000
:::X-OriginalArrivalTime: 15 Jan 2001 16:47:52.0376 (UTC) 
FILETIME=[E6BE8B80:01C07F12]
:::
:::Ok... like I said here's my "theory" of what might be
:::happening... maybe the mechanism is different.
:::
:::I was driving cables (slightly capacitive load...) and
:::of course, my first take at fixing the instability was
:::to put a resistor in series with the output as you suggested.
:::
:::Even a value as low as 10 ohms was effective. There was some
:::loss.
:::
:::But I also noticed that a "feedback" resistor was equally
:::effective. Here the loss in nearly non-existant because the
:::opamp is approaching unity gain... (feedback resistor is
:::small and input resistor is almost infinite.
:::
:::Why... I don't know.  I'll entertain any better suggestion.
:::Possibly I just changed the resonant point of the circuit to where
:::it no longer hurt me.... and it is waiting to bite me in the @ss
:::somewhere else ???
:::