Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

February 08, 2023, 09:23:41 PM

Login with username, password and session length

Recent Posts


SWR Workingman's 12 combo- Hummmmmm

Started by mikebarg, January 05, 2022, 05:04:32 PM

Previous topic - Next topic


Well this has been sitting on the bench waiting for me to get to it. It has a moderately loud hum. I have recorded it. I thought 60hz hum but, i checked the full wave bridge and the 2 main power capacitors. They all checked good. Any ideas where to go from here. See the video here https://youtu.be/mNbTI2KNZyI


How did you check the caps?  Just because the value is close doesn't mean it i well connected.  Sounds like DC on the speaker to me.  If so TURN IT OFF or the speaker will be destroyed.

Does the speaker cone move one direction and stay when you power up?  Take the wires off the speaker and measure for DC voltage between them.

Otherwise check the solder on the main filter caps.  Check the main power rails for ripple.


I pulled the caps and tested them. The value and ESR both looked good. I re-installed them on the board. I also removed the full wave bridge and checked it out of circuit. It's good too.


I don't see any DC on the speaker output.


OK, then the ripple?  You have a positive and a negative supply in there.  Are both up to about the same voltage and free of ripple?


Ok. one of the caps has no measurable ripple, but the other has .45 vAC.


Can you check if C7 (2.2 mF) in poweramp is OK?