Re: Opamp preamplifier design question

MRW wrote:
On May 31, 10:25 pm, John Popelish <jpopel...@xxxxxxxx> wrote:
You can always roll the gain off at 20,000 Hz or some such,
if you want, with a feedback capacitor, but within the audio
band, the extra gain inside the feedback loop will improve
the accuracy of the programmed gain.

This gave me an idea. I'm thinking of using a feedback resistor &
capacitor to limit the maximum voltage amplitude out of the pre-
amplifier. I was thinking of tapping off part of the pre-ampl output
voltage and re-directing it to a comparator. I'm also going to add a
SPDT analog switch in series with the feedback resistor & capacitor
and also with just a feedback resistor.

The basis of the circuit is that if the pre-amp output voltage
surpasses a threshold value. Then the switch enables the resistor &
capacitor branch. But due to the RC time constant, the effects of this
feedback branch won't be fully realized until after the time constant
(would this be considered the attack time?). Are my thoughts correct?

Here is a sketch of what I was thinking: http://i12.tinypic.com/6gx3s7l.jpg

What is the point of having the capacitor in series with the resistor? The gain will change with just the resistor. Also, you can just use the contact to parallel additional resistance with the one that sets the highest gain. There is no need to disconnect one resistor and substitute another. 1 contact saved, and a nasty noise pulse reduced, during the moment when there is no resistor connected. But to be practical, there needs to be a lot more effort put into the switching decision than just comparator. There has to be some sort of filter that prevents switching on a single pop, and holds that decision for a reasonable period, after a loud sound, before it changes its mind during a very brief silence.
.

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