[sdiy] Op-amp substitution for MC1776

[Blandon Ray]

Hi all,

I'm trying to rehabilitate a 1970s-era guitar preamp which uses the
above ICs... actually, it uses the MC3476 which is the same thing
"selected for low cost" (i.e. barely meets the worst possible specs).
It's a "micropower" opamp with a pin to set the bias current via an
external resistor - as installed it's about 4 microamps.

This design is so old they don't even list any noise specifications
for it on the datasheet. The ones in mine "might" be OK but they show
some evidence of battery acid near the pins, so I'd like to replace
them. The only current substitution I could find was the NJM4250,
which is no better, and maybe even a little worse. Analog and
TI/Burr-Brown make a few "micropower" designs, but most of them are
single-supply or low-voltage (this design uses +/-9v), or not
available. I know you can't get super-low-power and super-low-noise in
the same design, usually, so I'll settle for low power and reasonable
noise.

Any suggestions would be appreciated. Here's the schematic and parts
list if anyone's curious:

http://monkey.org/~blandoon/gfx/preamp1.jpg
http://monkey.org/~blandoon/gfx/preamp2.jpg

Thanks
Blandon