Princeton 65 DSP is noisy

[rockman627]

I'm fixing this for a friend. The amp is fairly quiet with nothing plugged in but becomes fairly noisy with a guitar plugged in. The noise is like when you hit the cranked distortion pedal. I plugged a guitar in and ran a cable from pre-amp out to my Roland micro cube. I didn't hear the noise at the micro cube. I plugged into the power amp in and got the noise. I'm thinking it doesn't need filter caps because it's quiet with nothing in and I should concentrate on the power amp section. Does that make sense?

[The Dude]

Based on what you've done so far, I agree with your assessment.

[Jon Snell]

Sounds like the power amplifier stage has a noisy component.

[rockman627]

I left my multimeter at work so I'm just getting around to this. I don't have an o scope so I start checking resistors and continuity. Sometimes I get lucky. So I start right where the power amp in goes, around P8b and P7b. R63 is ok, R64 is OK. I check from R63 to P7b: one side of R63 reads 108.2K ohms the other side 107.2 ohms. I should read open with C42 in between R63 and P7b correct? Or are there some exceptions to this rule? C42 is one of those capacitors that looks like half a domino. What type are they called?

[g1]

You have parallel paths going on so you won't read an open across C42. One side has R63 and R64 to ground, one side has R60 to ground thru the switch in J4.

[rockman627]

Thanks. I'm glad I asked.