wrote:
Hi,

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

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

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

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

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

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

Any help would be very much appreciated.

Cheers,

Kev.


It is normal to hear noise in a mixer with all the gains full up and
nothing connected to the input.
Obvioulsy you will turn down the inputs that are not being used.

Before you redesign this thing, I suggest you connect a real mic to the
input and try it in your application. If you are using it for any
typical application it will probably be fine. If you are using for
some real quiet chamber music etc, it might be a bit noisy, in which
case you could try more sensitive mic i.e. condenser mics with built in
preamps.

Ordinary op amps are fine for line level applications abd it sounds
like the unit has discrete transistros for the mic preamps which are
the most critical parts.

Try it out before you tear it apart.

Mark