View Full Version : Low hum is power supply capacitor issue?

07-28-2013, 08:13 PM
I have a Phase Linear DRS900 (Power amp) which has a low level, low frequency (60Hz?) hum. How likely is this a power supply cap issue?

07-28-2013, 08:19 PM
I would say, most likely if evenly on both channels. Don't rule out a bad ground either. be sure to un-hook all inputs and test that way to rule out other gear and bad cables. Man bad cables often cause quite alot of un-needed servicing.

07-29-2013, 03:33 PM
+1, Hum in both channels usually refers to a bad capacitor, or bad ground connection (it could be a bad solder at the PCB).

You can visually check for a bad cap, and then, press or push the PCB with some plastic tool (it could be an screwdriver handle), to bend it a bit, and listen to the hum. If it changes, or goes away, there is some bad solder somewhere.

You can check continuity between the chassis and different "ground" points, like the heat-sink, or the negative lead of some capacitors too.

It happened to me this week: hum in one channel, and I had no continuity between the chassis and the heat-sink. Pressing with my finger on the heat-sink solved the problem. I re-soldered some points at the power amp board, the hum went away.