Carvin X100B

[Tiny_Daddy]

The complaint for this amp is it's just not "loud". So I check it out and sure enough even with the volume up all the way it is obvious the power amp is not being pushed. The 10K feedback resistor seemed a bit small so I disconnected it. Big change. This amp was swamped with negative feedback. The amp would self-oscillate with no speaker connected. A 100K feedback resistor seems about right.
But one channel is way quieter than the others. Anyone else know of mods for this amp?

[DummyLoad]

check and see if your x100b is prior to rev. "C" and if yes, the power resistors (R128 & R129) on the PCB are installed underneath the PBC. they run hot, and over time burn through the board taking out the low volt +/- supply for the solid state circuitry - the bias supply cooks as well...  the rev. "C" will have 3 secondaries + a bias tap on the PT, prior revisions have two secondaries + bias tap on PT.

if they are, then consider relocating the resistors on the top of the board, raising the body of the resistors about 1/4" up off the board. if any of the traces have crystallized, bypass the trace with a jumper wire. IIRC they are 5W resistors, you probably could replace them with ohmite 8W and cool things down a bit.

on the unit i have, the damage was so catastrophic (too many smaller traces cooked away) the board was deemed unrepairable.

most of the schematics online are for the rev. "C" - if you need it, i can email you a copy of the march '82 dated schematic.

[jerrydyer]

I saw a smoked one too. I have pics here somewhers.

[Tiny_Daddy]

OK got it. According to the Carvin ECO for this board's serial number, change R15 to 1.5K and change R97 (feedback resistor) to 15K.