> Yeah, I know, but all I have on hand are some 741's, 748's,
> and 393's. Would one of the others be a better choice?
> Operating on a shoestring here.  ;-)

A 393 will go down to 2V. It's designed as a comparator but
you may be able to use some feedback to get it acting more
like an op amp. If the signal is big and clean enough though
you could use it as a comparator to square up and amplify
the 40kHz

As an exercise in frivolity, how about using one of the 741s
you've got lying around to make a charge pump (oscillator +
diode-capacitor doubler) to give you 9V for the input stage
741 ?

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