Acoustasonic 30 DSP

[lowell]

This amp came in with lots of intermittent hiss. I would bang on it and it would stop, then bang again and it'd come back. So, naturally I took it apart and poked around w/ my chopstick. Nothing proved to be loose. Some of the shielding foil inside the cab was coming loose and hangin' inside a bit... I don't see how that would cause such noise problems, but in any case the amp was working fine outside the cab. So I tore the loose foil off and reassembled and now the thing doesn't have noise. BUT, it seems farty and distorted when turned up and the guitar play with lots of attack. So took it apart again, checked voltages... highV and lowV supplies look good and symmetrical. I connected a resistive load of 4ohms and ran 1khz in at 200mvRMS. I managed to squeeze a mere 20watts outa the thing before my scope showed signs of clipping. The more Bass and Mid I add the more distorted it gets.

So my question is does this sound normal or not? And if not, what might be causing a lack of wattage? Fyi this amp has an LM3876 output IC.

http://support.fender.com/schematics..._schematic.pdf

[soundguruman]

If you bang upon it and the hiss comes and goes, just resolder the whole board.
Another thing is clean the controls and jacks...the jacks have internal contacts switches that oxidize.
The low voltage supply comes from big sand block resistors, and zener diodes, the tracks burn up and the parts crack loose.
It can be intermittent from heat stress cracks in the solder.
I mean if you can drive it from power amp in, and see what it does, or spray the components / board one at a time w / freeze spray.
But I usually just resolder it.

[Randall]

This is an acoustic guitar amp, and is not meant to handle the output and attack of an electric guitar.