LSI25 Hum

silenttiger

So my LSI25s are humming. This occurs with the integrated plate amp being plugged in, but no audio cables connected. The hum does not change when audio cables are connected. The hum does not change when put on a separate power circuit in the house.

There are actually two hums. On one of the LSI25's the hum is coming from the amp. This hum is audible from 6+ feet when there is no audio playing. The other LSI25 also has an amp hum, but also a low hum coming from vibrations of the subwoofer driver itself.

The hum sounds like it's at 60htz.
I've tightened the plates on the amp transformers without any positive or negative effects.

Are the transformers faulty?
I'm assuming the sound coming from the subwoofer is being transmitted through the wiring from the amp. Is there any chance it's magnetic interference and shielding would be a solution?

Thanks for any advice!

silenttiger

A few more nuggets of information:

The buzz coming through the subwoofer diminishes when the volume on the plate amp is turned down

The subwoofer and amp noise goes away when the power switch on the amp is turned to off, but the speaker power is still plugged in.

The cooling fins on the plate amp that also has the buzzing sub is almost 2X as hot as the other amp. It's too hot to keep a hand on.

[Deleted User]

Hello,
Welcome to Polk's forum. In all likelihood there's a problem with both of the bass amplifiers and one (the hotter of the two) is probably biased too high. In both situations contact Polk's CS department at either 1-800-377-7655 or via email to: polkcs@polkaudio.com
Regards, Ken