My Yamaha PC-2602M is driving the JBL 2214H-1's in my system. This morning, while having some alone time, I cranked some bass heavy music and the right woofer bottomed out. That shouldn't have happened at the power level the amp was putting out, which was peaking at just over 100 watts. Also, I noticed that the clip light on the right channel occasionally flashes when the amp is below it's rated output, and the meters aren't moving uniformly when there is a mono signal.

The right woofer is is moving too much, making me think there is some DC riding the signal. Offset on the right channel, at idle and warmed up, is 6.8mV (and 6.1mV on the left). A very good reading for a 20 year-old amp, but the amp is losing control of the woofer. The left channel is fine. I did swap inputs and the speaker wires to confirm that it is in fact the amp itself and not something up the signal stream.

So what do you guys think? Possible bad cap in the signal path? I guess it's time to find a service manual.

I really wasn't expecting this, and can't really afford to pull this amp out of service and have it repaired, plus I don't know of any reputable local shops anymore. Shipping this 60 lb beast to one of the experts on this board would be expensive and it would likely get damaged.

90% of my listening is at low to medium levels, so it can stay as it is for a while unless it gets worse. I guess I will have to keep the volume low until I can get this sorted out.

Maybe a total signal path recap is in my future, once I get a manual and a parts list. Joy.:grumpy:

Does your pre have a subsonic filter or LF filter?Does the amp have AC coupling provision like your M-4..

The preamp has a subsonic filter, but it doesn't make a difference. There is no coupling switch on the amp itself. This appears to be happening in the amp, it does not follow the inputs when I swap cables, R to L.

BTW, this is a pro amp that is running unblalanced via RCA to TRS adapters.

The left channel exhibits no symptoms and has total control over the woofer, as far as I can tell.

So much for a super easy fix..

Yeah. Just getting the amp out of the rack is a PITA.

Time for me to find a service manual that is not a shitty, unreadable scan.

I finally found a service manual. It should be downloaded momentarily.

Don't test the amp with those JBL's!!!
Get a pair of dummy loads and track down the problem.

What source(s) does this happen with? Phono? Maybe a shorted shunt cap in the feedback network causing gain at DC.