Hey guys,
Bought one of these little amplifiers to play around with about a year ago, while building and tweaking it I accidentally shorted some of the contacts on a metal plate and it bit the dust. I recently pulled it back out to repair it, I got it back up and running and have signal flowing through it again. Only problem is now i have a nasty 120hz hum coming from the output.
Below are the schematics and data sheet. I have tested past the Op-amp. It seems like everything is clean all the way up to the STA540. The inputs to the 540 show a clean wave but when I hook up to any of the outputs I see the noise. The noise is very dominant and is not altered by the volume pots in any way.
One thing im not sure is correct is I have a 7.5 volt reading on the signal out. Im thinking there is a short between output and vs. I've worked with the diagnostics pin and it seems to come back clean.
Any ideas on what to check or look out for?
540 Data Sheet
https://www.sparkfun.com/datasheets/Components/General/STA540.pdf
Schematic
https://www.sparkfun.com/datasheets/Kits/STA540 Audio Amp v11.pdf
Bought one of these little amplifiers to play around with about a year ago, while building and tweaking it I accidentally shorted some of the contacts on a metal plate and it bit the dust. I recently pulled it back out to repair it, I got it back up and running and have signal flowing through it again. Only problem is now i have a nasty 120hz hum coming from the output.
Below are the schematics and data sheet. I have tested past the Op-amp. It seems like everything is clean all the way up to the STA540. The inputs to the 540 show a clean wave but when I hook up to any of the outputs I see the noise. The noise is very dominant and is not altered by the volume pots in any way.
One thing im not sure is correct is I have a 7.5 volt reading on the signal out. Im thinking there is a short between output and vs. I've worked with the diagnostics pin and it seems to come back clean.
Any ideas on what to check or look out for?
540 Data Sheet
https://www.sparkfun.com/datasheets/Components/General/STA540.pdf
Schematic
https://www.sparkfun.com/datasheets/Kits/STA540 Audio Amp v11.pdf