Butt Whuppin by PL 3300

[wattsabundant]

The other day the wife was watching TV and I wanted to rock out. So I pulled out the Bose headphones and plugged them in. The right channel was white noise on top of the music even with the volume at minimum. The main out to the amps was dead quiet. I pulled the preamp out and off to the basement. See attached PDF of the headphone schematic. I also attached screen shots from a scope.

The first one is the noise with no signal. The second is both channels of main unswitched output which is clean. The third is the headphone output. The frequency is around 200 Hz.

I installed 7812 (12 volt) regulators on the opamp power supplies a couple years ago. I didn't attach a screen shot of them as they are dead quiet with the scope AC coupled at 100 millivolts.

If there is anything I despise, it's throwing parts at a problem and hoping it works. Despite that I changed the opamp and the output transistors Q201 and Q202. I've heard of noisey resistors before, but never seen it.

Any ideas?

 

[mlucitt]

I would initially suspect noise from a open/broken trace on the PCB. You could try re-flowing the solder runs of the suspect channel in the area of concern and see if that helps. No parts expended in that exercise, and even if it does not cure the problem, it may prevent other problems in the future.