"[...] the pre-amp was rated at 25 watts, and can drive speakers all on
its own..."
A preamp is an audio hub center, that accepts all types of micro/milli
volt signals from various input devices, adjusting and outputing them
to an industry standard signal known as line level. Power stage inputs
are designed to accept and amplify such designated signals. Line level
is a relative small signal.
Normally, output from a preamp is never expressed in watts, but as
voltage gain in a db ratio. Wattage ratings listed on the
back of the preamp, refer to its' max. draw from the wall outlet.
If you say you have a JVC PREamp that drives speakers, than who am I
to question it. It does however, conflict with my understanding of the
amplification process, which takes place in stages. Your device is
acting like an int./amp, and devices are defined by their in/out
characteristics. You know; if it walks like a duck, and quacks like a
duck, then it's a duck. By that logic, your device is an Integrated
amplifier, apparently putting out anywhere from 25-100W, per your
assessment.
My approach is never replace anything big, like the plate amp, until all
the usual suspects are cleared of guilt.
So where are we? Does the system work in the original configuration? If
you can play it that way all night long, then the problem isn't in the
plate amp, or at least in the high level input. Remember, there are two
sub inputs. Something could be wrong with the line in circuit. Run the
plate amp off another line out device for two hours or so. Don't use
questionable cables!! If no hum, the plate amp is off the hook, and the
problem points to the HT receiver's mono-out circuit. You could
experiment, and run L/R (no splitter) out from, say, the tape-out or
what ever signal out jacks you have available. It's not ideal, but I've
done it. The adjustable gain on the sub can compensate for the slight
variation from line level. Anything to allow the sub to play in the line-in
mode for an extended period of time.
Replacing the plate amp is a piece of cake, should it come to that.
IMHO, your not there yet.
Keep us posted!
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