high frequency intermittent noise

I didn't think so, but that is as far as my research went.  Glad I stopped there.

I'm not aware of any picocells or femtocells in the building.  With a cell tower right across the street, I get good reception in my apartment/building, so no need for devices like those.  All though, I cannot be certain about my neighbors, anything is possible. 

It's 4:45 and rush hour is upon us, I can hear the trains below, and the noise through my system. 👍🏻

@kosst_amojan

Faraday cage is the next logical step, if the power is clean and the Furman has no affect on the noise.  I've found some copper mesh curtains I can put up behind my system, which would create a barrier.

@jea48

Yes, this is a dedicated circuit, I have tested for this.

When I changed out the outlet, there were 2 wires connected to the old receptacle: white and red. There is another black wire not being used. I didn’t want to touch that wire, since I don’t really know what I am doing, I just copied the previous installation, using only the red and white wires previously used. The insulation seems to be fair, it’s PVC/plastic and the white looks white and did not appear brittle.

I would say the insulation is in good condition.

I will have someone come in and take a look at the circuit, maybe it can be switched out for a 20 amp circuit. So far though, I’ve never tripped the circuit breaker, and my amps are class A.  Thank you for the kind words.

It's 15.

Seems like I have been in similar odds before.  Just this weekend I ordered some parts for my turntable from KAB USA, another person with the identical name was ordering parts as well and our orders got combined which turned into an administration mess for Kevin at KAB.  What are the odds?

@toddverrone  

I agree, I've listened to people on YouTube playing the sound of cell towers through their test tools, and it sounds like cell tower noise to me as well.

What if the cell phone tower across the street is injecting noise into the electrical system?  Perhaps they have an installation issue?  The cell phone tower was installed about 2 years after I moved in.  But back then, I did not have high resolution system, and was not listening as critically as I am now.

It definitely sounds like cell phone interference to me as well. How it's getting into your system, though.. ?

@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. 👍🏻

@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 Thank you for all your expertise.  I will pick up that receptacle tester and check it out.

@jea48 Funny you should mention socket outlets, I just changed my socket outlet from a generic to a Furutech outlet (audiophile brand).  When I opened up the original socket, there were only 2 connections made with no ground.  That is how I know there is no ground.  I looked in the socket for a ground wire and did not find one, so when I swapped out the outlets, I simply mirrored the previous installation - no ground wire to connect.

Actually the new hot spot is Hudson Yards, that is where new construction is happening.  But I hear you, our infrastructure is falling apart.

If I listen carefully, I can hear the train go by underneath my building,  There is a low frequency buildup when this occurs looking at a real time analyzer, and I can actually hear the subway cars on the rails, so today I am listening carefully in between records to see if there is a correlation.

This issue is a low level issue, the noise I hear is just beneath the noise floor of the room.  So I'm chasing out the-last-bit of noise in my system. It's always that last 5% that is difficult. 🤓

I am afraid the US are sometimes a third world country, and this is one of those areas. Hope you can figure this one out. Can you find someone with a mobile phone to stand next to the subway line, or can you hear the trains when the windows are open, to confirm or refute your hypothesis?

I live in a neighborhood where we have the oldest electrical system in the city.  A few years back, an underground power transformer blew up and caused quite a stir in the neighborhood - black smoke from the electrical fire coming out of a manhole from the street. 🔥 

Nothing gets replaced unless it fails, so it would seem for my neighborhood.  I don't think the electrical company would even give me any time considering the issues they are dealing with. 😊

Those ancient subway trains can probably produce quite a bit of power line pollution, but I would expect that system to be completely separate from the domestic power, given that trains run on much higher voltages. Still, your domestic power system could perhaps pick up some noise. Did you call the electricity company?

@willemj Very good distinction.  I think the battery powered radio was a test to see if it was air born, which leads me to think it is not.  So then it is in the power.  I hope this is the case.  I have a Furman P-2400 IT on order, I'm going to give this a try.  @falconquest and @erik_squires are pointing in this direction, and I have not tried this solution yet.  I will report back my findings on the Furman.

I could not quite figure out what happened when yo used a battery powered radio. Does it come through your power lines or through the air?

As I was writing my last post I realized another important fact:

• The subway runs under my building.
  

I just noticed the noise appearing when I listened for a train to go by.  There seems to be a correlation here, perhaps it's the subway system:  when I hear the subway go by, the noise is apparent.  That would also make sense in that the subway does not run as frequent in the early hours of the day.

@jea48 The noise does present itself 24 hours a day randomly, it is only the early mornings ~ 4am to 11am it is not very frequent, but it does appear.  The building is 15 stories high.  I have already had 2 different electricians in, and they did not do anything.

@erik_squires The Furman looks promising.  The P 2400 IT looks like the way to go.

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!)

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.

@almarg I checked 540kHz and for a moment, I thought I was in that movie Contact, I did not hear the noise.  Just static.  Great idea.

@falconquest Thank you for the pointer, I will check that out.

I did lots of research into balanced power a while back and although I went with a different unit for monetary reasons this is the unit I would have purchased. Yes, it's professional grade but so what? If it takes care of your problem then it’s worth it.

http://www.furmanpower.com/product/20a-prestige-symmetrically-balanced-power-conditioner-P-2400%20IT

If you have a portable battery powered AM radio, try tuning it to an unused frequency toward the low end of the band (e.g. 540 kHz), and see if it picks up the noise.  That might help to determine if the noise is getting into your audio system via the air or via the power line.  And if it turns out that the radio picks up the noise, you might be able to determine the direction it is coming from by trying various orientations of the radio's antenna.

Good luck.  Regards,
-- Al
 

@randy-11 The cell tower..next time I see them working on the tower, I’ll wave them down...hey can ya turn it off for a few?

Another circuit, yes I’ve tried that as well. Good idea though. I wish I knew how to use an oscilloscope and had one handy. This was very interesting:

https://www.youtube.com/watch?v=BFLZm4LbzQU

I would like to measure the Furman product with an oscilloscope to see the difference.  Has anyone tried to measure Common Mode Noise from a Furman?

if you turned off all wifi routers, then try turning off the cell phone tower

or last chance, try a different circuit - wall outlet

@georgehifi He wanted to have the best possible sound off the grid, so he went with a battery power supply.

@erik_squires Good idea, I just did what you suggested, but it did not work.  I even turned off all but the mono blocks, so it was just the left channel and right channel amps on, nothing else in the household.  The intermittent noise appeared.

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

Why didn't he just get linear wall warts instead of the SMP ones? Would have been cheaper.


Cheers George

Doing research, I came across this guy demonstrating a switching power supply noise in the studio:

https://www.youtube.com/watch?v=yremMhceSyI&t=111s

His noise he demonstrated sounds similar to what I am experiencing. If this is the case then @erik_squires may have the right idea with a Furman.

I may have two noise issues in my recording in the original post - 

1. An intermittent high frequency noise
   
2. A consistent high frequency noise like a switching power supply