2. tech-talk
  3. 132315-8612

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
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. 
randy-11
1,913 posts
 
cell traffic is also likely very low in the early am when he rarely hears the noise

BTW, are your interconnects single-ended RCA type?  if so, can you switch to balanced or do the components only support SE?
james1969's avatar
james1969 OP
345 posts
 
I just went looking for my pro-audio monitors and just realized they are downstairs in storage.  I will dig them out if the Furman P-2400 IT has no affect.  I will be receiving the unit today.

If this noise is coming from the cell tower, I don't think there will be much I can do about it.

@randy-11

My Interconnects are single-ended RCA only.  I cannot switch to balanced because my system does not support it.  I can run balanced from my preamp to amps, but I do not have any XLR interconnects that long.
james1969's avatar
james1969 OP
345 posts
 
@jea48 

I had the monitors connected to my preamp through a set of XLR interconnects.
james1969's avatar
james1969 OP
345 posts
 
@jea48

I plugged in the socket tester and got two double orange lights indicating CORRECT. So I do have a ground?
More to discover