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high frequency intermittent noise

I have a noise issue that is intermittent.  Here is what the noise sounds like:

https://clyp.it/4b233bmm

Here is what I know so far:
  • The sound affects all components and is compounded if all components are turned on.  I have turned off my preamp, phono preamp, leaving just my mono blocks on, and the noise still appears.
  • I have turned off everything and unplugged everything in the house including my dimmer switch, and the noise still appears.
  • I have a pair of pro-audio monitors, self powered with class AB amps, and when I plug those into the same outlet, I hear the same noise coming through the pro-audio monitor.  So this rules out my big system.
  • The noise is primarily during the day and goes into the evenings, weekends too, early mornings it does not appear.
  • I live in a pre-war mid-rise building.  I have no ground, I'm using a Nordost QKore grounding system.  This did reduce the noise floor quite a bit, but has no affect on this intermittent noise.
  • I have a cell phone tower directly across the street from my building in Manhattan.
  • Looking at a real time analyzer, I see peak at 2kHz when the noise appears.
james1969
jea48
2,944 posts
 
@kosst_amojam,

Why is james1969 audio system able to receive the RF signal?
almarg's avatar
almarg
8,673 posts
 
AM is WAY too low in frequency. Cell phones broadcast in the 700 to 2100 MHz range.
Thanks for your informative inputs, Kosst. But of course the bandwidth of James’ audio components most likely extends only up to a frequency that is even lower than both the 540 kHz he had his radio tuned to and the 455 kHz IF frequency which I believe is used by AM radios in the USA.

So if cellphone traffic is indeed the source of the noise, his components are presumably responding to relatively low frequency modulations that are present on the near GHz carrier frequencies, which **might** also be picked up by an AM radio.

Regards,
-- Al

jea48
2,944 posts
 
Would the same logic apply if the pro-audio monitors have a balanced input?  No RCA inputs, just XLR.
Well one way to find out.
 Did you have the monitors' XLR inputs hooked up to the preamp when you used them for the test before? Or were they open ended?
 That would be leaving the balanced inputs open for the different location tests.

Someone like Al, (amarg), would have to chime in on,.... can an XLR, balanced input, be shorted out without causing any damage to the amp? My guess is yes it would be ok. But lets wait for someone who knows for sure.


almarg's avatar
almarg
8,673 posts
 
...can an XLR, balanced input, be shorted out without causing any damage to the amp? My guess is yes it would be ok.
Yes, that should be ok to do, Jim. From the perspective of the amp, shorting the three pins on an XLR input connector together would not be much different than if it were to receive a zero volt signal from a preamp having very low output impedance.

Best regards,
-- Al

kosst_amojan
2,095 posts
 
Got me. I know that sound though. My cable in my car is unshielded and if I leave my phone on it that's exactly what I get. Same thing if I put it near the interconnects on my stereo at home. Not many things use TDMA because it requires extremely accurate clocks to compensate for the speed of light so that the full packet window is utilized. That low level high pitched hum in the background is the timing reference. The major benefit of TDMA schemes is power and bandwidth conservation. You don't really need that with short distance, low bandwidth applications. There's cheaper ways to do it. If I was having this issue I'd be playing YouTube videos on my phone while moving it around all over the system. If something feet away is causing the problem, something inches away will definitely be heard. If a cell phone broadcasting near by can't replicate the problem then I'd start looking to something outside the area. Whatever is picking it up will be aggravated by a cell signal. I can't think of any other kind of signal that could be. 
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