700/1 “Tim” WOPL driver board

Hmmm fired Tim up today and the right channel getting hot. Pops borrowed my multimeter so I shut things down waiting for him to stop in I’ll check the bias... sounded great, just hot. I’ve pushed it pretty hard at times though too. Also, and I don’t have the schematics or the amp in front of me rn, but I’d like to make the meters more sensitive. They don’t hardly move until you’re really driving the amp hard near clipping. It’s just a resistor value change if I remember right no?
 
AngrySailor said:
Hmmm fired Tim up today and the right channel getting hot. Pops borrowed my multimeter so I shut things down waiting for him to stop in I’ll check the bias... sounded great, just hot. I’ve pushed it pretty hard at times though too. Also, and I don’t have the schematics or the amp in front of me rn, but I’d like to make the meters more sensitive. They don’t hardly move until you’re really driving the amp hard near clipping. It’s just a resistor value change if I remember right no?
Click to expand...
Turn your bias pots full CCW (all the way down) until you can retrieve your meter to measure it.
 
Gepetto said:
Turn your bias pots full CCW (all the way down) until you can retrieve your meter to measure it.
Click to expand...
Amp is off till then. Refresh my memory, bias is checked from the test point on the board to the emmiter at the DCP right?
 
AngrySailor said:
Amp is off till then. Refresh my memory, bias is checked from the test point on the board to the emmiter at the DCP right?
Click to expand...
There are also two testpoints on the backplanes for bias+ and bias - in addition to the one on the driver board, which is positive. If you use the TPs on the backplanes, you should get the same values but opposite polarity.

It’s measured against the speaker/meter outputs OR the “output” TP on the backplane.

Given that there are bias +/- on the backplanes, does this mean that the NPN/PNP banks could “mis- bias” due to an emitter resistor or transistor fault independently and cause a thermal runaway in one column only?
 
AngrySailor said:
Amp is off till then. Refresh my memory, bias is checked from the test point on the board to the emmiter at the DCP right?
Click to expand...

If your output offset is zero, then you can check from the bias test point on the board to the ground terminal anywhere in the amp.
 
MarkWComer said:
There are also two testpoints on the backplanes for bias+ and bias - in addition to the one on the driver board, which is positive. If you use the TPs on the backplanes, you should get the same values but opposite polarity.

It’s measured against the speaker/meter outputs OR the “output” TP on the backplane.

Given that there are bias +/- on the backplanes, does this mean that the NPN/PNP banks could “mis- bias” due to an emitter resistor or transistor fault independently and cause a thermal runaway in one column only?
Click to expand...

It means that I put them on there so the inquisitive folks on this forum could check the top to bottom symmetry on their full comp amps :-)
 
Bias 350mV left, 580mV right with the pot full CCW. rises to 680mV full CW. DC offset 0v
 
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