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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.
128x128james1969
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almarg
9,670 posts
 
Jea48 11-17-2017
...how about when james1969 used the pro-audio monitors for the test. When he hooked them up he heard the same RFI noise. Just a guess the amps are SS.
Yes, I had thought of that, and the fact that the same noise occurred with both amps does make it seem less likely that the possible absence of stopper resistors is a factor. But note that Ralph’s comment referred to the use of such resistors in solid state as well as tube designs. (Of course, in the case of a solid state design they wouldn’t be referred to as "grid stopper resistors," that being the term I used in connection with James’ tube-based Lamm amplifiers).

Best regards,
-- Al


james1969's avatar
james1969 OP
345 posts
 
Tin foil had no affect on the power cord.
james1969's avatar
james1969 OP
345 posts
 
For those who thought the noise is GSM, I did correlate the noise with the Hf35c Rf Analyzer, but the device only correlated the noise, did not show me the frequency.  I think it was a defective unit in that the display did not work properly.
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jea48
4,022 posts
 
Tin foil had no affect on the power cord.
Did you get the conductive metallic tin foil type? Actually it is aluminum foil.

Did you also try grounding the foil to the "U" shaped equipment ground contact on the wall receptacle?  (You could also use the center 6/32 trim screw that holds on the cover plate. Just make there is not any way the bared wire could come into contact with the hot blade of the plug plugged into the outlet.)

Last thing I can think of is to try the aluminum foil on the speaker cable.

Hopefully the ferrite beads you ordered will work.

I did check on wireless building automation systems. You might want to check with  building maintenance and see if they are being used in the building. I would also ask if there are cell phone antenna devices installed in the building. That's an old building with thick outside walls made of concrete and brick, I would imagine.

https://www.buildings.com/article-details/articleid/15219/title/how-to-boost-cell-phone-coverage-in-...


http://www.facilitiesnet.com/buildingautomation/article/Pros-and-Cons-of-Wireless-Building-Automatio...




 
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