Peavey Series 400 Bass head speaker input getting hot!

[byacey]

I've seen high frequency oscillation
In the preamp caused by a dirty shorting contact on the input jack, which allows the input to float unterminated.

 

[Merlin Magic]

Well I have both, a high frecuency pitch in the first channel and an oscilation about 60 Hz in the second channel. I have not thought of the input part... I´ll check it out and let you know. Thanks again

 

[agedhorse]

I don't think it's even possible for the amp to oscillate at 60Hz. Perhaps there is noise due to an intermittent ground.

Does the amp make these noises with nothing connected to the input?

Is your scope analog, and not some cheap PC based scope? Often, cheap digital scope type objects cause more issues than the solve, either by being noise, or adding artifacts to an otherwise correct trace.

 

[Merlin Magic]

I have not checked the frecuency of the second channel, but the first channel turned out to be just as you sugested, a floating input. The osciloscope is cheap, but it does it´s job. It is not cpu based.

 

[agedhorse]

Ok, I have seen techs waste hours chasing artifacts that do not really exist.
If the low frequency noise is on one channel, it's almost certainly an intermittent or poor ground of a critical node. Rarely is it a bad cap, even if the internet assumes it's ALWAYS a bad cap.

 

[Merlin Magic]

Thanks again, I´ll check that out. It actually makes more sense that way. Thanks.

 

[Merlin Magic]

Thanks to all of you I got rid of the oscillation. Thanks guys!!!!

 

[agedhorse]

What was the LF noise traced to?

 

[Merlin Magic]

A reaaaaaaaaaaaaaaaaaaaaaaaaaaaaaally bad solder on the Low Mid, Low Bass Low treble pots and Yes you´ve guessed it.... a bad capacitor. A 100V .03 M en the board... and also a bad diode on the PS. I really apreciate all the help guys.... If I can be of any help just let me know.