high frequency intermittent noise

if you are in NYC, you do what some sports car owners do - have a site outside the city where it is kept and subway out to it for a drive (or in your case, a listen)

a place in the Catskills could contain your most sensitive equipment and something else used in the city

It's all about the music...once the needle drops...I'm very happy.

I was on a quest to solve the noise (which I have lived with for some time) and in the process, I resolved a ground loop issue, and inserted an isolation transformer which really did solve a lot of noise from my power mains.  So the system sound has been elevated, just not 100% dead quiet like I would prefer when sitting right up next to the speaker listening for noise.

Time to move on to the next weak link...👍🏻

Hey, that's impressive use of perspective. Plenty of members on here are so OCD, they'd be miserable and only able to hear the noise.

I was that way with transformer hum, until I decided not to care

Thanks...unfortunately a move is not in my playbook at this time.  The noise is not very noticeable once music is playing.  Only when there is no music playing then it becomes noticeable.  So, it's tolerable for now.

Man, that sucks. Time to move!

@fusian  

I am not using a computer as my source.

I tried the ferrites and they had no affect on the noise.

I got a set of Sony WH-1000XM2 Bluetooth headphones and I can hear the noise very faintly in my headphones in my apartment.  So now this verifies that the noise is air borne and not from my power mains.

Thank you all who participated in this thread. 

It sounds like cheap computer noise.
Are you using a computer as your source?

@xti16 

Very interesting - parts 1 and 4.  I may try to seek these power cables for audition to see if there is any affect.  Thank you for the link.

James check out this video especially parts 1 and 4.

https://www.youtube.com/watch?time_continue=5&v=Y3RNnm8s3nQ
If you have a Raidho/Ansuz/Aavik dealer nearby and ask if you can have an in home demo. Although I don’t have any electrical problems like you I can say after adding the D-TC power cable everything became much more clear. I could also say I can play music about 2db louder. I also have the new version 2 and I can’t believe how much more ’control’ I have in the music. Not sure what you budget is but these do come with a hefty window sticker. For that reason this should be your last resort.
Good Luck

It's all resistors and it's designed to shrug off MHz range ringing because of it's crazy wide bandwidth.

We had to be careful too for the same reason.

Aluminum foil had no affect on the power cord and the speaker cable with the shorting plug in the amp.

Have you thought of wrapping cords and cables with this:

https://www.ebay.com/itm/EMF-RFID-RF-Shielding-Copper-Fabric-Roll-44-x-1-of-Material/131893330384?ss...

Using this conductive tape to seal the seams and to ground the fabric to electrical ground:

https://www.ebay.com/itm/Copper-Foil-Tape-1-5-X-10ft-EMI-Conductive-Adhesive-Ship-from-USA/162095634...

Dave

Ferrites are on order.  I still need more aluminum foil. 👍🏻

chokes are ferrites, what a bunch of us have suggested trying..

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

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.

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

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.

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.

This RF/EM signal must be picked up by the voice coil in the tweeter and it is likely a powerful megaHz signal and would be inaudible if it didnt cause problems for the amplifier(which tries to surpress distortion with negative feedback so as to match input) and the problem manifests itself in the audible range somehow due to signal saturation in the amp section making it a broadband signal.

Try adding a choke across the speaker wires to short out the HF signal.

http://audiosystemsgroup.com/RFI-Ham.pdf

See Fig 4 for an example...

almarg and or kosst_amojan, or others,
Would the copper screening work well as a shield and reject RFI from entering through the glass window?

Yes, Jim, I would think that a grounded copper screen would be effective against 700 - 800 MHz, since the openings in the mesh are far smaller than the wavelengths of those frequencies (which are about 17 and 15 inches respectively). Although as noted at the FCC link I provided earlier those frequencies can "penetrate buildings and walls easily," so keeping them from getting in via the window might not be all that helpful.

Good suggestions, though, in your previous post.

Best regards,
-- Al

@jea48 

I'm with you man.  Check this out:

https://www.select-fabricators.com/rf-emi-shielding/rf-emi-test-shielding/curtains/

I need to get more aluminum foil...

Consider snap-on ferrite beads. Relatively cheap. Worth at least experimenting on interconnects and power cords.

http://amzn.to/2hLhLG9

Best,

E

@willemj Great link, lots of interesting articles there.  Thanks.

See here for some reading in IEC standards on electromagnetic compatibility:
http://www.iec.ch/emc/

I’ve added a photo of my racks so you can see what I’ve done. Basically I’ve lined the racks with aluminum foil, then draped an aluminum foil tent over the power distribution center where all the power cords group together. Time will tell...

Using tin foil (thanks @jea48 ) I was able to reduce the level of the constant noise that was out of balance - the right channel was measuring at about 58-60db and the left channel was measuring at about 53-55db.  This was done using a Radio Shack Sound Level Meter pointing it right up at the Fostex super tweeter.  I was measuring in the early hours (no traffic, all is quiet).  My normal room noise floor during the day is 60+db.  So the noise the system is putting out usually competes with outside noise of my environment.

I lined my right rack (I have two racks next to each other) with aluminum foil along the left and right sides, what little I could in the rear, and I also lined the rear wall behind my right rack.

Now my left and right channels are producing the constant hash (the carrier signal) noise at even levels.  This is a step forward, as before with out the aluminum foil, my right channel was emitting the noise up 5db from the left channel.  Very unpleasant to hear something artificial that is out of balance.  Now they produce the noise at an even level, so I've altered the cellular signal where my right amplifier sits (in the right rack).

Using the Analyzer, I was walking around my apartment trying to visualize what a cellular signal would look like - all I could think was it must look something like a solar flare - magnetic in nature?  So that would explain why I would walk around and hear various levels of signal strength.

So it appears the aluminum foil has altered the cellular band of signal around my right rack with my right mono block.  Now both channels are closer in output level of the noise.  We shall see/listen/hear as the day/week progresses.

@erik_squires 

No problem, I have 30 days to return the Furman.  But I think it's a keeper.  The issue presents itself with only the bare amps turned on.  I was using only 1 amp only for some testing.  Even the powered speakers have this issue.

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

Here is some interesting shielding:

https://hollandshielding.com/content/Filemanager/PDF_Catalog%20cable%20shielding%20[English]_November-18-2010-219pm.pdf

@jea48 

The signal strength is an audible on the Analyzer, not a visual indicator, the speaker emits the raw signal noise.  I walked around on my floor and the Analyzer was pretty quiet.  I circled the entire floor...nothing.

@almarg Terrific find. That would explain why some days it’s quiet, and other days it’s busy. Early mornings 4am to about 11am it’s quiet most days. And it goes on late into the evenings. Yesterday it was very busy all day long.

I also used the Hf35c Rf Analyzer to walk around my apartment with all the power turned off, to find quiet zones, unfortunately I do not have much flexibility in my room arrangement for the system. It’s called living in a shoebox.

I’m not too bad off, the noise is a low level noise, just-at-the-natural-noise-floor of the room. Its traffic outside, people, cars, bikes, skateboarders, road construction, building construction, air planes above, I hear quite a bit.

I have a police station down the street, and a fire station a block down, so I hear a lot of sirens, which may also contribute to the public safety band Al had mentioned above. So between the subway, the cops, and the firemen, my stereo should keep me in the loop.

... the frequency my stereo is picking up is in the 700 - 800MHz range.

James, check out this link:

https://www.fcc.gov/general/700-mhz-public-safety-spectrum-0

The band extending from 698 to 806 MHz is used by public safety services, with part of it also apparently being used in some locations for cellphone or other mobile device communications.

Hope that helps. Regards,
-- Al

unless... the cell tower is somehow causing the lower freq. noise - maybe drawing on a power supply or something

Playing with the Hf35c Rf Analyzer I pointed it to the cell towers across the street, and the noises it makes is higher up in in the frequency range of 1600 - 1900MHz.  Where as the frequency my stereo is picking up is in the 700 - 800MHz range.  So I guess it's not the cell tower.

Yes, concrete and brick, 14" thick barrier wall. I’m in a concrete box basically with brick on the outside.

I did not ground the aluminum foil the first try.  I will try again.

For those who thought the noise is GSM, I did correlate the noise with the Hf35c Rf Analyzer, but the device only correlated the noise, did not show me the frequency.  I think it was a defective unit in that the display did not work properly.

Tin foil had no affect on the power cord.

Jea48 11-17-2017
...how about when james1969 used the pro-audio monitors for the test. When he hooked them up he heard the same RFI noise. Just a guess the amps are SS.

Yes, I had thought of that, and the fact that the same noise occurred with both amps does make it seem less likely that the possible absence of stopper resistors is a factor. But note that Ralph’s comment referred to the use of such resistors in solid state as well as tube designs. (Of course, in the case of a solid state design they wouldn’t be referred to as "grid stopper resistors," that being the term I used in connection with James’ tube-based Lamm amplifiers).

Best regards,
-- Al

@james1969 - no, I was not. I was thinking of that braided stuff that is sold by electronic parts wholesalers or specialty suppliers, like the guy that sells the Duelund? cable that in certain cases needs shielding.

I reserve tin foil for hat lining, but make sure it covers the back of my neck. :)

@whart Are you thinking tin foil as well?

Before you get all spendy on fancy audiophile cables* is there some pro level shielding material that you can buy to wrap the cables? I know that the shields typically go to ground on one end, but I gotta believe there’s a cheaper  DIY way to see if better shielding works rather than buying fancy cable.
_____
*I’m not a ’cable denier’ - I use high quality "audiophile" cable in my system, but I’d like you to solve your problem rather than just throw money at it. And cables can get spendy fast- whether they are synergistic with the sound of your system is a separate matter.

Well...on the positive side, I've eliminated a ground loop, and have reduced the noise floor in the music quite a bit.  The Nordost QKore took care of my ground loop issue, and the Furman P-2400 IT reduced my noise floor.  

Does anyone have any experience with AudioQuest cables? They appear to have an active shield that is battery powered...

Thank you EVERYONE who participated.  I'm a little tired...but I will get some tin foil now...