Nasty high pitches tone

[Ed345]

I've recently moved to Singapore, and am having problems with a nasty high pitched tone through my speakers. It's distracting to the point of making it very difficult to listen to music.

I am living on the 18th floor in a pretty busy environment for wifi signals etc. I also live about 200m from the local electricity substation.

The tone is a clear clean tone that turns on and off at seemingly random times. It tends to last between 5 and 30 seconds, and then 5 - 30 seconds off. It is about 7.815khz (measured from mic on laptop).

The tone doesn't seem to change base on location of amps, and it isn't anything in my apartment causing it. It is present on all of my NVA amps, although to a lesser extent on an old metal bodied AP30.

The tone is the same on all inputs regardless of anything connected and is controlled by the volume control. This makes me think it must be interference from some electrical field rather than anything to do with the mains from the substation.

Also, my old AP30 has one input that isn't wired up internally and when switched to this input the tone disappears completely. It would seem to be the wires between the inputs and the input selector that are picking up the tone?

Any ideas about any further diagnosis or, more importantly, how to deal with it?

[Shevans]

I checked the frequency allocation plans for Singapore and there should be no RF transmissions below 9kHz, its possible something is generating RF in the area. I have had an amp that picked up radio on the unused inputs when I lived really close to the transmitter, shorting the unused inputs stop it dead.

The Doc will be along soon for a diagnosis

[Daniel Quinn]

You did what !

[Dr Bunsen Honeydew]

Well it is interference from something in the building. When you switch the amp off does it die immediately or take a few seconds to die. If dies immediately then mains, if hangs around while the amp power supply discharges then RF. But it is external to the hi-fi for sure.

[Shevans]

You did what !

I'm a radio ham, so looked to see if there could be any (legal) radio transmissions at the frequency of the tone.

I would unplug and turn off everthing apart from the amp, making sure any heating / cooling / cookers / fridges / etc are all disconnected and see if the noise is still there.

[Daniel Quinn]

ten- four

[Ed345]

The tone stays on when the power is turned off. Fades away after about 10 seconds.

[Dr Bunsen Honeydew]

It is RF problem, either from unsuppressed electrical equip which is switching on and off, either yours or a neighbour or part of the building. Or strong RF from a transmitter source near by.

[Ed345]

Could easily be either. Living in close proximity to multiple apartments, and also in direct sight of an enormous electricity substation. I have already emailed the electricity company to ask them about it, but got a fairly standard reply saying it wasn't them.

As I don't want to sell my NVA setup and won't be in this apartment long term, are there any fixes for the situation?

[Fretless]

Are the amps in the old metal casings and would earthing the case help keep out the RF interference?

(off topic) I do quite a lot of translation work for a company that is investigating the health risks of RF (Wi-Fi, mobile communications, cell-phones etc.) and it is quite frightening what the possible dangers are. Especially to children: their thinner skulls offer less defence to EMR (electromagnetic radiation) and exposure to wifi/radio transmitters like phones and tablets can cause problems like: hyperactivity, insomnia and a lack of concentration.