Hi Tim,
I was looking for 'datasheet 4558' when Yahoo steered me to here, and
now I'm a member 1 minute old!
I'm currently fixing a channel of a mic/line mixer which uses the
opamp 4558. This is a dual opamp IC, an improved 741 type opamp.
This IC has been used in guitar and bass amps.
Your power amp, PA, does it use the 4558 as an integral part of the
PA circuit, or does it comes before the PA itself? You see, some designs
do use an IC opamp as 1st stage of the PA. If your 4558 has a capacitor
connecting to the PA then it's not the 1st stage of your PA and this is
much easier to debug.
Efren
. channel