high frequency intermittent noise

I just got off the phone with Rob at Furman. He’s a great guy, been in the pro-audio business for 24 years, 16 at Furman. He says he’s seen music studio’s go through the same issue, all of a sudden an antenna gets put up and there’s nothing to do except move. I cannot move, so then he said the next approach is to build a faraday cage and opt for better shielded cables.

This is an air borne issue, the cell tower is coupled to the air, Rob was amazed. I sent him the 2 sound samples I posted here so he could hear.

I don't, I will go and get some...

The power cord is my antenna, I switched to a non-audiophile power cord and was able to move the power cord around, up, down, and around (could never do that with what I am using), and yes, I could affect the noise.

I'm wondering if I'm now in the market for a new power cord?

Sweet lord, you poor man.

So.. Those copper mesh curtains.. You could lay one on the floor, stack your equipment on top, then wrap the curtain up and over, creating a true faraday cage, as long as you remember to ground it to a pipe or the ground in your outlet. Test to see if an actual faraday cage works.. If so, you could build a nicer looking one integrated into your rack.

I found a set of RCA shorting plugs. I turned everything off except for one mono block, inserted the RCA shorting plug, and the noise is still present.

I tried a different power cord, and the noise is still present.

I tried an XLR cable between my power amp and preamp, the noise is still present.

I have ferrite beads (made of material 61) on order.

That is GSM noise-your (or someone nearby) cellphone is being "polled" or is polling the basestation nearby....earthing(use copper pipe in bathroom or kitchen) may well fix...if not then chokes on power cables is another avenue to explore...and of course keep mobiles charger off hifi circuit.

James, searching at eBay for "RCA shorting plugs" (without the quotes) will lead you to a number of sellers offering them at low cost.

Good point by Ralph (Atmasphere) re the possibility that the amp doesn't provide grid stopper resistors in its design.  If that proves to be the case, James, I would think that if you explained the situation to Vladimir he could have them installed at modest cost.  It would just involve the addition of a physically small low power resistor in series with the grid of each tube.

Good luck.  Best regards,
-- Al
 

I thought it was my interconnects.  I turned off everything except my amps, then I disconnected the interconnects, the noise disappears for a while...but reappeared.  Maybe my speaker cables are suspect too...

I have asked if stopping resistors are used, waiting to hear back.

No, my phone has no affect.  I wonder if it's because I'm on Verizon, and the offending tower may be a GSM tower?

I hate to say it, but this is a common problem is the audio equipment has poor RFI rejection.

There is this design aspect known as a 'stopping' resistor, that is used in tube and solid state circuits to prevent oscillation, and also has a big effect on susceptibility to RFI.

The resistor is in series with the signal and is placed as close as possible to the input connection of each amplifying device (grid of a tube, gate of a MOSFET and so on).

The resistor interacts with the input capacitance of the device, preventing it from causing oscillation by acting as a low pass filter. This is effect of RFI for the same reason.

The thing is, many audio designers don't employ stopping resistors (the Japanese really didn't use them at all for several decades) so you run into problems like this if you have heavy RF sources nearby and otherwise poor grounding.

The 'I hate to say it' part is you may have to change out gear to something more stable to get rid of this. May.

What happens if you operate your cell phone close to your stereo? Do you get interference?

Something I’ve been looking at to correlate the noise to the cell tower:

https://www.amazon.com/gp/product/B007L09DLY/ref=s9u_simh_gw_i2?ie=UTF8&fpl=fresh&pd_rd_i=B007L09DLY&pd_rd_r=68bbfce7-caf8-11e7-8cdf-51a46fae6b0a&pd_rd_w=4szrl&pd_rd_wg=JjucN&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=&pf_rd_r=T88X159BY8J205PDCWS2&pf_rd_t=36701&pf_rd_p=8f696f0a-3abd-4660-b9bd-1931764e0008&pf_rd_i=desktop

Here is an example of cell phone noise:

https://www.youtube.com/watch?v=s99i0H-nBw4

If I had the tool, I would be able to correlate with certainty.

Thank you EVERYONE who has participated on this thread for that matter.  I really do appreciate your ideas and posts.

@jea48   

LOL, Yes, I know where my cell phone is.  I tried turning it off, no effect.

My system does sit against the outside wall, which is at the same level as the cell phone tower.  I do not directly face the tower, but the tower is in direct line of sight just 2 units to my right, so for line of sight purposes, it may as well be right in front of my unit.  I also have the Empire State Building in direct line of sight, and a friend of mine thinks the Empire State Building is radiating all kinds of emissions...says I need to be wearing sunscreen while listening to my system because of the Empire State Building.

I will post a photo on my system page so you can see the towers.

The problem with the towers is they are nondescript - no signs indicating ownership or contact info.  All I see on the towers are WARNING labels everywhere.
That is an outstanding post you found on ProSoundWeb.  Thank you very much with all of your attention on this thread.  You are a real asset to the community.

The subway goes right under my building.

@james1969 - alas, another quiet oasis in NYC gone to hell. 
This thread is fascinating to me for the deductive work- i know suffering the noise sucks--we've probably all had our share of imponderable issues at times- but i'm learning as i read this. 
The solution will probably be something obvious and stupid (e.g., did you plug it in?)
In the meantime, here's my tin foil hat conspiracy theory connect the dots, Elvis is an alien idea: if the subways have these critters, and the noise coincides with the passage of a subway under or near your building....?

@whart 

There is now cell phone reception in the subways too.  So each subway car or perhaps the subway tunnels are lined with these devices.

Here is another recording taken early in the morning with no subway cars under my building:

https://clyp.it/ae0xgczb

Note there are 2 noises:

1. The consistent hash/whine
   
2. The intermittent noise
   

This is the worst I've heard it in the mornings.  It only lasted for a minute and a half, enough for me to record the 1 minute clip.

The Furman has buffered me from my refrigerator noise, I would hear a *click* in my system when the refrigerator would turn on, now it's silent.

@kosst_amojan- is it possible that the building itself is set up with these devices you identified? (They seem to act like repeaters, to increase strength within buildings). Unless a neighbor set one up to improve his/her cell reception, as @jea48 alluded to, why wouldn't the building itself provide such a facility? Given the density and height of the buildings in Manhattan, I remember encountering dead spots in coverage walking around on the streets (granted, this was some years ago, I haven't done that for quite a while, and now no longer live or work in NY). 

@toddverrone

That’s a great find. Let’s say I get ferrite beads in place. I still have tubes out in the open where the audio signal goes through as well. I think there is no escape...

I found this: http://blog.rfvenue.com/2015/05/06/how-to-prevent-cell-phones-from-interfering-with-audio-equipment

It talks about cell phone noise in a pro audio setting, and mostly with phones as the source of the noise, not a cell tower. But they do mention a way to get rid of the noise that hasn't been mentioned yet. It wouldn't be the best fix, but could at least let you see if it's coming through the RCA cables. Their fix: ferrite beads on the input cables, close to the end that plugs into the amp. The article recommends specific ferrite parameters to address cell phone noise..
If ferrites on your IC cables solve the problem, you could look at more heavily shielded ICs. If not, you're only out the cost of ferrites..

@jea48   

No headphone output on my preamp.  

I just dug out my pro-audio monitor too, plugged it into a different circuit and could hear the noise, though not as loud, and nothing was plugged into the monitor either, it was simply plugged into the wall.

I put the PS Audio Noise Harvesters on the Furman P-2400 IT to see if they would stop blinking, they did not.  And when I turned on my light on a dimmer in the kitchen (different circuit), the PSNHs went crazy.  So does the Furman even do anything to filter noise?

The noise floor in the music has been lowered.  There is benefit sonically in the music though.

The Furman P-2400 IT has no affect on the noise.

@jea48 

I do not have a radio that is AC powered.  I will look into the RCA shorting plugs.

I think this is an air borne issue - cell tower...

RCA interconnects range from 3 meters to 1 meter.  Speaker cables are 2.5 meters.

@toddverrone  

Make me go and dig up the instructions..🤓  CORRECT is good all the way around, so I do have a ground.

No idea. Doesn't it say on the tester? Correct sounds to me like the polarity is correct (live wire to the narrow slot, neutral to the wide). Didn't that thing come with instructions? 😜

@jea48

I plugged in the socket tester and got two double orange lights indicating CORRECT. So I do have a ground?

@jea48 

I had the monitors connected to my preamp through a set of XLR interconnects.

I just went looking for my pro-audio monitors and just realized they are downstairs in storage.  I will dig them out if the Furman P-2400 IT has no affect.  I will be receiving the unit today.

If this noise is coming from the cell tower, I don't think there will be much I can do about it.

@randy-11

My Interconnects are single-ended RCA only.  I cannot switch to balanced because my system does not support it.  I can run balanced from my preamp to amps, but I do not have any XLR interconnects that long.

cell traffic is also likely very low in the early am when he rarely hears the noise

BTW, are your interconnects single-ended RCA type?  if so, can you switch to balanced or do the components only support SE?

...can an XLR, balanced input, be shorted out without causing any damage to the amp? My guess is yes it would be ok.

Yes, that should be ok to do, Jim. From the perspective of the amp, shorting the three pins on an XLR input connector together would not be much different than if it were to receive a zero volt signal from a preamp having very low output impedance.

Best regards,
-- Al

AM is WAY too low in frequency. Cell phones broadcast in the 700 to 2100 MHz range.

Thanks for your informative inputs, Kosst. But of course the bandwidth of James’ audio components most likely extends only up to a frequency that is even lower than both the 540 kHz he had his radio tuned to and the 455 kHz IF frequency which I believe is used by AM radios in the USA.

So if cellphone traffic is indeed the source of the noise, his components are presumably responding to relatively low frequency modulations that are present on the near GHz carrier frequencies, which **might** also be picked up by an AM radio.

Regards,
-- Al

Would the same logic apply if the pro-audio monitors have a balanced input?  No RCA inputs, just XLR.