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I have an annoying little noise that is constantly emanating from my speakers. At first upon Googling I thought it was the usual hum, hiss, or whatever sounds that is the by-product of a normal audio configuration. Although the sound persists even with no inputs connected to my amp (my configuration is just 4 speakers connected to one amp, nothing else), and all of the speakers connected are unpowered, so I don't know if that eliminates the possibility of a ground loop? Also, interestingly the amp only has a two-prong plug and therefore does not have a ground.

However, while trying to figure out whether this was hiss or hum I measured the frequency (admittedly, using an old iPhone app, but the app is pretty darn sure the frequency stable at 240 Hz).

Upon Googling this it seems that possibly, this is indicative of an issue with the power supply (or something related to power) because 240 is a multiple of 60, and that is the frequency of the power here.

The sound is definitely coming out of the speakers, not the amp. And as I turn up the treble/bass the noise increases, and vice versa.

That's all I've got, if anyone can help me confirm what the problem is (and whether it is repairable or if I should buy a new amp) it would be much appreciated.

Sebastian King
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    Please provide a link or model number for the amp. – uint128_t Jun 25 '16 at 20:43
  • This question seems to be relating to consumer audio, which is off-topic. I'll consider objections though. – n00dles Jun 26 '16 at 01:57
  • @uint128_t, it is a Pyle Home PTU45 amp, here is the product website http://www.pyleaudio.com/sku/PTAU45/Stereo-Power-Amplifier---2-x-120-Watt-with-USB,-AUX,-CD-and-Mic-Inputs – Sebastian King Jun 26 '16 at 08:43
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    @MarcW, the fundamental question "is a 240 Hz system noise indicative of power issues?" is pertinent to all audio systems. – Sebastian King Jun 26 '16 at 08:46
  • Usualy, only the first two harmonics from the 60 Hz mains becomes aparent in audio systems. How loud is this hum? Because you get hum in most consumer systems. – n00dles Jun 28 '16 at 17:36
  • @MarcW, if I use my iPhone again and a decibel meter, it registers 45 dB normally (away from the speaker) and 55 when near the speaker. Although when all 4 speakers are plugged in, the sound is 4x louder. – Sebastian King Jun 28 '16 at 22:24
  • Firstly, dB is a relative measurement, and I'm not sure which reference value the iPhone app uses. Secondly, if it is at a noticeable level while a source device is plugged into the amp and the volume adjustment level is quite low, then I'd say there is a fault with the unit. You should contact the manufacturer for support or get a replacement from the retailer. – n00dles Jun 30 '16 at 18:03

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The issue was a grounding loop.

There was noise when there was nothing plugged into the amp, this was noise from the cheap and poorly made Pyle amp. Once I replaced it with a better (but still relatively cheap) amp the noise only occurred when there was an input plugged in. I bought an $8 grounding loop isolator and that eliminated 100% of the extraneous noise. One of the pre-amps was plugged into a different power socket than the main amp, which resulted in the grounding loop.

Whether or not the 240Hz hum being a multiple of the 60Hz power frequency is a coincidence or not, I still do not know.

Sebastian King
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