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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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james1969's avatar
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james1969 OP
347 posts
 
Try adding a choke across the speaker terminals to short out the HF signal.

@shadorne 

What is a choke?  How would you implement this?  I'm not an electronics guy, learning-as-I-go-here.
atmasphere's avatar
atmasphere
11,841 posts
 
I got my phone steaming videos last night and put it INSIDE my F5 right up against the left amp board.
Nelson knows his stuff.

If the amp is not properly stopped, it will be almost impossible to make this problem stop (if you will pardon the expression...).

Sometimes the amplifier circuitry is OK, but RFI gets rectified right at the input. RF beads of the right value can help, if added right where the signal gets to the amp circuit.

If the amp makes this sound with the inputs shorted, there really isn't much you can do about it but replace the amp or have it repaired.
erik_squires
16,134 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
shadorne's avatar
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shadorne
7,477 posts
 
A choke is an inductor that chokes off high frequencies.

The reason I think it is coming from the speakers and back into the Amp is because you have tried other steps.

An very strong HF signal hitting the tweeter coil might also cause core saturation (hystersis) in the tweeter and this converts HF to broadband noise.


toddverrone's avatar
toddverrone
840 posts
 
chokes are ferrites, what a bunch of us have suggested trying..

man, i hope you're single at the moment! all that foil
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