high frequency intermittent noise

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

@erik_squires I unplugged my AV system completely, cable modem included.  It was all off and unplugged.  No affect.  Thanks for the pointer to Furman, I'll check them out.

It sounds like the cell tower is the culprit. I doubt there is a fix for that!

@yogiboy The only fix for the cell tower would be a faraday cage?  I have researched EMF curtains to put up behind my system.

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
   

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


Cheers George

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

@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.

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

or last chance, try a different circuit - wall outlet

@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 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
 

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

@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.

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.

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

@james1969 ,

The noise is primarily during the day and goes into the evenings, weekends too, early mornings it does not appear.

"early mornings it does not appear." Never? Have you checked the time in the morning the noise stops and the length of time the noise is not present? Is there a consistent pattern early every morning. The noise stops at __ am and starts up again at __ am
Same times every day?

I have a cell phone tower directly across the street from my building in Manhattan.

But the sound is not 24/7.

I live in a pre-war mid-rise building.

How many stories high?

Is there a building maintenance person on duty, someone you could speak to about the noise? If so before you talk to them see if you can pin down the time in the early morning the noise stops and the time it starts back up again.

@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.

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.

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?

@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.

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?

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. 😊

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?

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. 🤓

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

@james1969

You said in your OP the wall outlet your system is plugged into does not have an equipment ground. Not sure if it will help, or do anything, but there is a good chance the mains branch circuit wiring is installed in steel rigid metallic conduit. (Though it is possible it could be old steel armor BX cable). If it is steel rigid metallic conduit, that would be an acceptable equipment grounding conductor means. (Of course depending on the low resistance conductivity of all the electrical, mechanical, connections made with the lock nuts in the conduit to metal boxes from the metal wall outlet box all the way back to the metal box enclosure of the electrical panel the branch circuit is fed from.)

Does any of your audio equipment have a 3 wire cord and plug? (2 straight blades and a round ground pin).

I assume the old wall receptacle/s in your home are polarized 2 wire that has one straight blade slot longer than the other. Or are they really old non polarized where both slots are the same length?

How are you feeding your audio system from the 2 wire duplex wall receptacle outlet? With a grounding type 3 wire cord and plug receptacle outlet strip? If yes I assume you are using a ground cheater, (3 prong to 2 prong plug adapter), so you can plug in the 3 prong plug into the 2 wire wall receptacle. Is that correct?

By chance do you own a multimeter or access to one?
If yes set the meter to AC volts auto or a scale closest above 125Vac.
Insert one test lead probe in one contact slot hole of the wall outlet and the other probe in the other contact slot of the other in the same outlet. You should read a good steady 120Vac nominal volt reading. If not recheck your probe to outlet contact connections. Make note of the actual voltage reading.

Next.

Insert one meter test lead probe into the shorter of the two straight blade slots of the wall outlet making a good contact with the contact of the receptacle. Touch the other meter probe to the center screw of the duplex outlet that holds on the cover plate. (If the screw is covered with paint scrape off the old paint exposing the bare metal screw head.)
Does the meter read a good steady 120V nominal volts? Yes? If not make sure the two meter probes are making good contact and check again. If still you do not get a good steady 120V reading insert the test lead probe in the other contact slot of the outlet. Do you now get a steady 120V reading on the meter? (If yes the AC polarity is reversed on the outlet.) The voltage reading sold be the same as the reading you measured from the plug in contacts.

So, if after all the above you measured a good steady 120 volts, from the HOT conductor feeding the duplex wall receptacle outlet and the center screw of the outlet that holds on the cover plate, that means the metal box the outlet is mounted to is grounded to the metal enclosure of the electrical panel that feeds the branch circuit to the outlet.

**Note.
That only means that the equipment ground is present. It does not tell you the integrity, conductivity, of the equipment ground’s ability to carry any ground fault current back to the electrical panel in the event of a ground fault event. What it should do though is furnish an earth ground for the metal chassis/metal enclosure of your audio equipment that uses a 3 prong grounding type plug.

IF, after all the above has been met all that you need to do now is connect the green pigtail ground wire from the ground cheater to under the screw head of the 6/32 screw that holds on the outlet cover plate. For a better connection I would remove the duplex cover plate and install the fork of the green pigtail wire under one of the 2 screws that fastens the outlet to the metal box. Check both mounting screws to make sure they are snug and making a good mechanical/electrical contact from the outlet to the metal box.
**(Do not try to remove the outlet for a look inside. The wire conductors inside the box could be really old and the insulation that covers the wires old and brittle. Just you trying to pull the outlet from the wall box could cause the insulation to fall off the wire.)

Next.
With the multimeter test/check the plug strip to make sure you now have an equipment ground.

Last final test! Did it help stop the noise. Or was it all a waste of your time?

Jim

@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.

james1969 OP
246 posts 11-13-2017 12:15pm

@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.

Just because there was not a ground wire in the box that does not mean the equipment ground is not present. If rigid conduit was used per NEC code the conduit is an acceptable grounding means. The conduit is the equipment grounding conductor. (Of course the rigid conduit must be electrically continuous from the outlet box all the way back to the electrical panel. It can be connected to other metal boxes and conduit bodies in it’s travel.)

Note. Just because NEC allows rigid conduit to be used as an equipment grounding conductor that does not mean your city electrical inspection department does. The AHJ (Authority Having Jurisdiction) has the final say.

Buy one of these.
https://www.homedepot.com/p/Power-Gear-3-Wire-Receptacle-Tester-50542/206212329?cm_mmc=Shopping%7cTH...
It will tell you if the receptacle outlet is grounded and if the Hot and neutral AC polarity is correct. It will not tell you the conductivity integrity of the equipment grounding conductor to carry ground fault current back to the electrical panel in the event of a ground fault event though. Not matter if the conduit is used as the equipment grounding conductor or a ground wire is used.

@jea48 Thank you for all your expertise.  I will pick up that receptacle tester and check it out.

@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.

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. 

@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.

@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?

@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. 👍🏻

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

@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.

kosst_amojan
516 posts 11-14-2017 4:03am

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.

When I first read the OP I though the same thing. It’s the cell tower or an antenna on the cell tower for some other type of technology company. But then I started reading what others had posted. Then I read Al’s (almarg) post and james1969 response.

Another thing that I didn’t think that fit it being the cell tower. If it is an antenna transmitting the signal why wouldn’t it be a constant repeating signal that would recycle itself 24/7? I then listened to the signal in the OP all the way through. It starts out as having a repeating cycle but about around half way through it peters out. Would that be typical of an LTE signal?
https://clyp.it/4b233bmm

For what it’s worth when james1969 brought into the conversation about the subway that runs beneath the building, he lives in, and said he thought there might be a correlation between the noise he is hearing through his audio system and the subway train passing by below I had a moment of deja va. Several years ago there was a posted message where a guy was having a similar noise problem as the OP here is having. He too had the subway running under his building. What are the odds?

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?

@james1969

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.

Is the branch circuit that feeds the duplex receptacle outlet a 20 amp, or is it a 15 amp? Go to the electrical panel and look at the handle on the breaker that feeds the circuit. It will say 15 or 20.

It's 15.

@james1969

99% chance the wire is #14awg. It is rated for 15 amps.
Just a guess the circuit is a convenience outlet branch circuit that feeds several other wall outlets in the room. Maybe even some ceiling lights. Have you ever checked what all is connected to the same circuit when you shut off the breaker to change out the outlet?

When you changed out the outlet for your audio system was there only the two wires inside the box that connected directly to the duplex receptacle?
Do you remember what the 2 wires looked like? was the insulation on the wires made of PVC/plastic one black, maybe red, and the other white? Do you remember how the plastic insulation looked? Was the white wire discolored kind of yellowish at the end that terminated, connected, to the receptacle. Was the insulation of either wire discolored, possibly caused by heat over the years.? Did the insulation look or seem to be hard or brittle?

.

Or did the 2 wires appear to have a cloth covering over what appeared to be rubber? One wire was black and the other was white or appeared to be white? What condition would you say the insulation was in?

I realize I am off subject with this post. I just finally got around to looking at your system on your system page. That’s a really nice system to be fed from a 15 amp convenience outlet circuit.

Jim

@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.

LTE is an evolution of GSM. It uses a combination of TDMA and FDMA. The various high speed pulses are the individual data packets broadcast in the data windows. Their intensity is the product of the frequency their transmitted on and how well tuned the antenna is to them. 
To be honest I'm surprised an antenna across a street can do this. Another possibility is that somebody very near by has a picocell or a femtocell installation in their unit. That's common in larger cities. I wouldn't be surprised if unshielded tubes picked this up. Something somewhere needs more shielding and I'd be focusing on that as much as possible. I'd be tempted to build a Faraday cage and put gear inside it to see what happens. 

Thanks kosst_amojan for the info.

@james1969
Got any of these things around or one of your close neighbors?
http://hetnet.com/what-are-small-cells-a-basic-guide-to-femtocells-picocells-and-microcells/

@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.