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.
128x128james1969
jea48
4,022 posts
 
almarg7,616 posts11-16-2017 3:32pm
Good point by Ralph (Atmasphere) re the possibility that the amp doesn't provide grid stopper resistors in its design. If that proves to be the case, James, I would think that if you explained the situation to Vladimir he could have them installed at modest cost. It would just involve the addition of a physically small low power resistor in series with the grid of each tube.

Good luck. Best regards,
-- Al
Al,

Agree, but 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.

Jim
james1969's avatar
james1969 OP
345 posts
 
I just got off the phone with Rob at Furman. He’s a great guy, been in the pro-audio business for 24 years, 16 at Furman. He says he’s seen music studio’s go through the same issue, all of a sudden an antenna gets put up and there’s nothing to do except move. I cannot move, so then he said the next approach is to build a faraday cage and opt for better shielded cables.

This is an air borne issue, the cell tower is coupled to the air, Rob was amazed. I sent him the 2 sound samples I posted here so he could hear.
james1969's avatar
james1969 OP
345 posts
 
Well...on the positive side, I've eliminated a ground loop, and have reduced the noise floor in the music quite a bit.  The Nordost QKore took care of my ground loop issue, and the Furman P-2400 IT reduced my noise floor.  

Does anyone have any experience with AudioQuest cables? They appear to have an active shield that is battery powered...

Thank you EVERYONE who participated.  I'm a little tired...but I will get some tin foil now...
whart's avatar
whart
2,719 posts
 
Before you get all spendy on fancy audiophile cables* is there some pro level shielding material that you can buy to wrap the cables? I know that the shields typically go to ground on one end, but I gotta believe there’s a cheaper  DIY way to see if better shielding works rather than buying fancy cable.
_____
*I’m not a ’cable denier’ - I use high quality "audiophile" cable in my system, but I’d like you to solve your problem rather than just throw money at it. And cables can get spendy fast- whether they are synergistic with the sound of your system is a separate matter.
james1969's avatar
james1969 OP
345 posts
 
@whart Are you thinking tin foil as well?
More to discover