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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.
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Showing 7 responses by erik_squires

erik_squires
15,912 posts
 
Um, do NOT "short" your speaker wires!

The example in fig. 4 is fine, but it is most certainly NOT a short, it is the opposite, a choke.

Given however that you even have powered speakers having this issue, the problem is probably too late by the time it gets to your speakers. You need to think further upstream.

I did by the way recommend cheap RF chokes above.

Best,

E
erik_squires
15,912 posts
 
Consider snap-on ferrite beads. Relatively cheap. Worth at least experimenting on interconnects and power cords.

http://amzn.to/2hLhLG9

Best,

E
erik_squires
15,912 posts
 
I'm afraid it turned into a long thread. Very sorry the Furman didn't work out for you. :(

I'm not clear on something. Does this problem occur with just the bare amps / powered speakers, or does it require a preamp / interconnect to be present?

Best,

E
erik_squires
15,912 posts
 
James, one other thing to try, use an extension cord if you must, but maybe you have other AC lines which are less noisy, or perhaps a place in your apartment where the noise pickup is less?

Just throwing out ideas that are cheap. :)

But yeah, I like Furman for noise and value (especially if you can find them on sale!)


erik_squires
15,912 posts
 
Make sure you look at a Furman with LiFT and SMP.

The SMP surge protection is, by design, a low pass filter. Unlike most other AC filters it works in the audible band, but not sure how low.

LiFT is active filtration. The one thing about Furman, they seem to have 100 different models, so be careful that the exact model you look at or test includes both.

Not sure about common mode noise, but most linear power transformers filter that out anyway.
erik_squires
15,912 posts
 
One final check:

Go to your electrical panel and turn off everything except your hi fi gear.

This will make sure you didn't miss something inside that is causing the noise. If the noise is still present then it is external, either from RF/EMI or elsewhere in the building.

Best,

E
erik_squires
15,912 posts
 
Do you have any sort of Wifi or security system? Also disconnect incoming network and cable TV cords as well if any.

If this is purely a power issue, in the audible spectrum, Furman power conditioners with LiFT and SMP are really really good for removing noise at an affordable price.

Best,

Erik
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