" bravely wrote to "All" (19 Mar 05 04:44:50)
--- on the heady topic of "Reducing hiss by changing op-amps ?"

Yes, 4558's are pretty bad for noise. You will certainly get better
noise performance with newer pin compatible drop-in replacements. If
they are socketed the job will be even easier. Something like an
NE5532 has the same pinout but because of its greater bandwidth it may
require a small cap between output and inverting input.

BTW if you are listening to the mic inputs unshorted at maximum gain
then they will indeed seem noisy, this is normal. If the mixer was
intended for a DJ environment then a little noise in the mic isn't
bad. If it is a recording console then the least noise would be best.


pc From:
pc Xref: aeinews sci.electronics.design:4297 sci.electronics.repair:43412

pc Hi,

pc I have an audio mixing desk from the 80's that is a bit 'hissy' (i.e.
pc background noise with no inputs). Would I be able to reduce this by
pc replacing the op-amp ICs with lower noise versions ? ...or is this
pc sort of noise nothing to do with the op-amps ?

pc I have obtained and scanned the schematics, in case anyone fancies a
pc quick look. It's only a 1Mb PDF file, located he-

pc http://homepage.ntlworld.com/anengin..._Schematic.pdf

pc The vast majority of the op-amps are physically labelled:-
pc '4558 DD'
pc ' JRC '
pc ' 1266B '

pc I'm presuming these were made by the Japan Radio Company. (The
pc schematic refers to them as 'TA4558NB')

pc The desk incidentally, is an 'INKEL MX-1410' made in Korea.

pc Any help would be very much appreciated.

pc Cheers,

pc Kev.

.... Which sparks some mnemonic circuitry.