POLK RT3000P humming after service

tpoppa

I just had a pair of POLK RT3000P amps recapped. There both making a low humming sound, even when disconnected from the rest of my system.

I thought maybe it was a ground loop issue and have tried to hook it up a few different ways. I am using a decent line conditioner.

I've never had any noise issues with any other components. Any ideas on how to trouble shoot this?

WLDock

Plug into different outlets/room, etc. Also, put a ground lifter on it to see what that does.

Gatecrasher

Where did you have them "serviced" at?

A lot of times simply replacing capacitors doesn't fix issues with the amps.

I would definitely try what WLDock suggested first though. The fact that both of them are acting the same tends to point to a ground loop issue or something.

tpoppa

They were serviced by Polk.

I've tried a ground lifter. I've tried different outlets. I've tried different surge protectors. I've unplugged every other component in my system. I still have this low electrical humming coming from the woofers.

[Deleted User]

Hello,
Sorry you're having a problem. Have you tried them directly plugged into a wall outlet without the surge protector? Also, do you happen to have a dimmer switch on any of the lights in that room? This might seem unusual, but do you know if there is a radio station close to where you live?
Also, does the green LED stay on when the unit is standby or does it go off?
Regards, Ken

tpoppa

Ken,

I've tried plugging them directly into the wall, both with and without a ground lifter.

There is no dimmer in that room and no radio stations anywhere near here.

When in standby the green light is off. I can still hear a very slight hum when the speakers are in the off position or on standby. It not as loud as when they are turned on but you can still hear it.

[Deleted User]

Thanks for the information. Since the service work was done by Polk it comes with a 1 year warranty. If it were me I'd give them a call at 1-800-377-7655 and let them know that there's still a problem.

Gatecrasher

If you disconnect the speaker wires from the speakers do they still hum?

When you adjust the volume level on the subwoofer with no signal present in standby does the hum change any?

I think the amps with the power indicator that turns off when no signal is present were the 1st design and they were more susceptible to the RF interference but they shouldn't hum.

Here's a story I had with one of my Polks that took me months to finally correct

I had a hum with a CS1000p center speaker. It's part of the RT5000 package and has some design similarities to the RT3000p subs. I tried everything and couldn't figure out what was causing it so I removed the amp and sent it in to Polk for service. They sent it back and said they re-flowed some solder but couldn't really find anything wrong with it when they tested it. So I reassembled it in the cabinet and when I tried it out it still had the exact same hum.

I called Polk back and they said to ship it back to them a 2nd time so I took it back out of the cabinet and shipped it back. About a week later I got an email from Polk saying they tested the crap out of it and couldn't find anything wrong with it. No hum what-so-ever!

So I had them ship it back and I re-installed it in the cabinet and it still had the freakin' hum! On mine I think the hum went away when I disconnected the speaker wires but as long as they were connected it had the hum. At least I think that was the way it was.

I started playing around with it some more and disconnected the volume control. It plugs into the circuit board and is the same potentiometer used on the RT3000p. As soon as I unplugged it, the hum went away. When I shipped the amp to Polk I didn't remove the volume control and send it with the amp. They told me I didn't have to.

To make a long story short, I ordered a new volume control from Polk and when it arrived I installed it in the CS1000p and the hum was gone. Here the problem I was having the entire time was caused by the volume control potentiometer. It was bad.

So as a last thing to try you might want to disconnect one of the volume control connectors from an amp and see if that affects the hum any.

It seems unlikely that both potentiometers would go bad but it's something easy to try as a sanity check. Polk tests the amps pretty-thoroughly before they ship them back so there is a good chance it's something on your end that they don't have in the equation when they test them that is causing the hum.

tpoppa

Gatecrasher wrote: »

If you disconnect the speaker wires from the speakers do they still hum?

Yes.

Gatecrasher wrote: »

When you adjust the volume level on the subwoofer with no signal present in standby does the hum change any?

No.

Thanks for your insight. I am willing to try anything.

villian

Are you running the line level input, or speaker level, or both (With either the OEM straps or third party jumper wires?

I've accidently left the jumpers on before when using the line level input, and that'll definitely cause some noise.

Secondly, how audible is the hum? How close to the speaker do you have to be to hear it? Turn your AVR on and make sure the subs are on, turn the sound up to trigger the plate amps, now turn the sound to the lowest setting on the AVR. Next go up ONE click on the volume dial of the AVR. Do you hear any difference between "On - Zero Volume" and "On - 1 click of volume"?

Every amplifier will make some noise, so if it's something you only hear with your ear within 3" of the subwoofer, then it's perfectly normal.




Lastly, does Polk still do repairs on the RT3000 amps? I was under the impression that they didn't? I have 4 RT3k plate amps and one CS1k needing repairs!