Re: Opamp preamplifier design question

MRW wrote:
On May 31, 8:17 pm, John Popelish <jpopel...@xxxxxxxx> wrote:
If you cascade two amplifier stages made with similar
opamps, the one with a gain of 400 will have a bandwidth of
1/16th of the one with a gain of 25. If you make each stage
have an equal gain (100 in this case) you will get the
highest overall bandwidth out of the pair.

Thanks, John! Is that 1/16th of the gain-bandwidth of the opamp with a
gain of 25? Or is that 1/16th after (gain-bandwidth)/25 ?
How did you get 1/16th by the way?

400 is 16 times 25. lets say you have 7 MHz GBW opamps. the one programmed to have a gain of 400 will have a bandwidth of 7,000,000/400= 17,500 Hz. The one programmed to have a gain of 25 will have a bandwidth of 7,000,000/25=280,000 (16 times higher than the gain 400 unit). If each of those stages were programmed to have a gain of 100, each would have a bandwidth of 7,000,000/100=70 kHz.

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.
.

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