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
jea48
2,944 posts
 
@james1969

If the tester indicates the equipment ground is present then you will know it is not doing anything to help with your noise problem.
kosst_amojan
2,095 posts
 
I'm virtually 100% certain that's cell phone signal interference. That is exactly what an LTE signal sounds like when it's being picked up by an unshielded/under-shielded wire in the signal path. I doubt it's being picked up through the power lines, but I can't be curtain. If it was, you'd hear it through your TV and computer. I'd be looking at interconnects. 
james1969's avatar
james1969 OP
345 posts
 
@kosst_amojan  

My interconnects are all shielded, but they could be under-shielded.  If I turn everything off in my system except for my amps, I can still hear the noise.  So in that case we would look at the speaker cables, they are shielded too.  When I turn on my pro-audio monitors plugged into the same circuit or a different circuit, they exhibit the noise too (that rules out my system).  Keep in mind, these pro-audio monitors are self powered with class AB amps built into the speaker enclosure, so it's a self contained amp/speaker.

I do not have the noise on my TV or computer.

I did think about the tubes picking up the noise because on my amps, all the tubes are out in the open?  But then I had a solid state phono preamp in my system just recently, and that picked up the noise as well, so that rules out the tube theory.
jea48
2,944 posts
 
@james1969

How long have you had the noise problem? Did you have the noise before you changed out the wall 2 wire duplex receptacle outlet to a new grounding type outlet?

When do you think you will be able to pick up a plug-in circuit checker?
james1969's avatar
james1969 OP
345 posts
 
@jea48

This noise issue has been in my system for as long as I have used my system in my current apartment. So it was there before I swapped out my receptacle outlet.  Keep in mind, this noise is just below the noise floor of my apartment, so you have to focus to hear it.  Once you recognize the noise, then it becomes apparent in listening.  I have been on a hunt to chase out all the noise in my system, and this is the last bit of noise that I am aware of.  I can record the noise like I did above with the microphone up to the speaker.  I can see the noise in the real time analyzer as a peak around 6kHz.

I have the plug-in circuit checker on order and it will arrive tomorrow. I also have another receptacle outlet on order as well, as I will be changing the outlet receptacle from a 15 amp to 20 amp outlet receptacle. This is so I can plug the Furman P-2400 IT into the wall. I will be receiving that unit tomorrow as well, so big day for my system tomorrow. There is a possibility I will have my noise issue resolved. I will report back ASAP. 👍🏻
More to discover