OK, I have an old Tenma 72-630, 1-15VDC, 30A peak, 24A continuous, output power supply that I've been using to power an automotive audio power amplifier for my home theater subwoofer. I've been experiencing a hum from the beginning, but I just turned the amps gain down until it was negligible. The Power supply has a dedicated ground on it's 110V AC power connector, while the rest of the audio equipment doesn't. I would really like to dispense with the hum. Recently I downloaded the Power Supply's manual, because years ago I misplaced the one that came with it, and saw this:

"When using the 72-630 power supply with RF equipment, a .01uf capacitor should be connected across the output terminals." RFI? Hum?

However it doesn't say what type/voltage, i.e., electrolytic, polarized, ceramic, polypropylene, etc? And since I'm not really an electronics technician per se, I have no clue. I know just about enough to get me in serious trouble.

Anyone familiar with the cap application and/or the hum?

Thanks in advance for any help you might provide.

P.S. I'm a 61yo but I think I'll be able to understand your explanation; ThreeQuarterHeimers and all, you know... ;-)

 

Welcome to AAC!

I'd try a ceramic cap (X7R, X5R, or Y5V, or even Z5U) before resorting to anything "better".

 

The cap probably won;t get you anything.

The basic idea with the capacitor is to "bypass" RFI. That will disturb the regulation of the power supply and the power supply might oscillate.

HUM could have a number of causes:

#1. 60 Hz shielding
#2 Ground loops (grounds at different potentials)
#3. The power supply itself

Remember:

A shield reduces RFI
Twisting reduces EMI

Power supply wires carrying AC too close to signal wires can be an issue. Parallel is worse than crossing.

Connecting the minus side of the supply to earth ground can help. It can also hurt.

You might want to short the amp's input with a resistor and turn up the gain to see if you have hum.