M-Audio AV32.1 speaker hums and it won't go away

Desolator69

Estimable
Oct 23, 2014
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4,560
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Hey everyone,

I recently bought a new 2.1 speaker setup, the M-Audio AV 32.1, however since plugging it in it seems to have a quiet but annoyingly noticeable hum. I got them off of eBay for £99.95 as they are a refurbished model (might be important?).

The product page of the speakers:
http://m-audio.com/products/view/av32.11

Before explaining it I'll describe my chain:

PC -> Behringer U-Phoria UMC 22 (USB audio interface) -> Behringer HD400 Hum Destroyer -> M-Audio AV32.1 Speakers

After a quick spectrometer test with my phone it seems that the hum is at 150 Hz, with other smaller peaks at 50, 100, 120, 150 and 250 Hz. I'm in the UK so power is at 50 Hz so it seems it's caused by a ground loop and its harmonics or something, so I bought a Behringer HD400 "Hum Destroyer" after reading reviews of this thing getting rid of ground loops.

Still humming... Even if I unplug the speakers from the mixer coming from my PC they still hum. Any idea what would cause this? Is it an internal thing of the speakers, and if so should they be returned?

Note: I'm using balanced 1/4" TRS cables all the way from the audio interface -> hum destroyer -> speakers for both the left and right channels. The sub (which contains the power and amplification stuff) is quite close to a plug socket and extension cord, however moving it from them doesn't seem to help at all, nor does plugging it into its own extension cord with nothing else plugged into it... Also the back of the sub gets really hot, the kind of hot where I can hold my fingers onto it for 2-3 seconds but any more and it hurts.

Any ideas for what I can try! Or should I return it?
 

Desolator69

Estimable
Oct 23, 2014
12
0
4,560
0
Just an after thought. My old speakers (Trust Tytan 2.1) didn't hum and I have just noticed now that it uses an "electric razor" style, ungrounded EU plug that fits to a UK power plug adapter and has no metal ground pin. The M-Audio speakers have a metal ground pin. Could this have been the cause of the hum?

Why do one of these speaker sets have a ground pin and the other not? Mainly just curious now.
 
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