@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. |
@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
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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. |
@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.
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@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?
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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/4b233bmmFor 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? |
@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. |
@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
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@kosst_amojan,
If the RF signal is being radiated through the air why didn't the battery AM radio pick up the signal? Wrong frequency range? What type of receiver meter device could be used to pick up the signal and identify the frequency?
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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.
That won't work. Them RF signals are sneaky. They will just go around the screen. |
It’s 4:45 and rush hour is upon us, I can hear the trains below, and the noise through my system. Coincidence? You might start keeping a log. . You said in your OP you have a pair of pro-audio monitors. By chance do you have any RCA shorting plugs? Not the dust cover caps but a shorting plug? How big is one of the monitors, and how heavy? Is it something you could carry around at different locations in your apartment without a lot of effort? You already said when you plugged them into the wall outlet, that your audio system plugs into, you can hear the noise. Was that with the monitors hooked up to the preramp or just power on with nothing connected to the input? Have you ever powered one of them up without anything connected to the input? I would think if the RF noise signal is radiated through the air it would enter the open RCA input jack and you would hear it through the speaker pretty good. If that is true what would happen if you placed one of them in the farthest room, area, as far as possible from were the audio system is now? Plug it in a wall outlet in that room. Turn the monitor speaker amp on and see if there is any difference in the sound, and strength, of the signal noise compared to the room your audio system is in. The RCA shorting plug. If you have an RCA input shorting plug install the plug on the monitor speaker amp’s input at the various locations you do the testing. Try it without the RCA plug in the input and then with it inserted in the RCA input jack. I AM SURE I DON"T NEED TO MENTION IT. BUT DON"T DO IT WITH THE AMP POWERED ON. You will get one heck of a loud buzz. My thinking is if the RF noise is being radiated it will be louder with the RCA port open than it will be if the input is shorted out with the plug. If the RF noise is traveling on the mains wiring it won’t much matter even with the RCA input shorted out using the shorting plug or the input jack is open. That is for the particular RF noise you have been hearing. |
@kosst_amojam,
Why is james1969 audio system able to receive the RF signal?
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Would the same logic apply if the pro-audio monitors have a balanced input? No RCA inputs, just XLR.
Well one way to find out. Did you have the monitors' XLR inputs hooked up to the preamp when you used them for the test before? Or were they open ended? That would be leaving the balanced inputs open for the different location tests. Someone like Al, (amarg), would have to chime in on,.... can an XLR, balanced input, be shorted out without causing any damage to the amp? My guess is yes it would be ok. But lets wait for someone who knows for sure. |
@jea48
I plugged in the socket tester and got two double orange lights indicating all is good. So I do have a ground? "CORRECT". Also the AC hot and neutral polarity is correct. There is one thing you need to before you change out the duplex receptacle from the 15 to the 20 amp. I doubt the audio grade 20 amp duplex receptacle you bought has an auto ground clip feature. You can check it to see if it does though. On one end of the supporting backstrap, that supports the recept to the metal wall box, there will be a spring clip that applies pressure to the 6/32 x 1" machine screw that supports that end of the recept to the metal wall box. I found this You Tube video doing a quick search on the net to show you the auto ground clip. It also shows the bonding jumper, grounding pigtail, I will tell you about after you watch the video. https://www.youtube.com/watch?v=VuP5Mhvu9Y8The guy did a good job for the most part with his presentation. I will pick apart one obvious mistake the guy made though, for anyone else that may watch the video. The wiring used to feed the box is NM-B cable, Romex is a trade name. Per NEC code the bare equipment ground wire must be bonded, connected, to the metal box. You will notice in the video the guy only connected it to the ground terminal on the receptacle. The receptacle cannot be used to make the bond, connection, to the metal box. james1969, If the 20 amp duplex receptacle you will be installing does not have the auto ground clip feature you will need to buy and install a green grounding pigtail wire. (Correct term is bonding jumper) Example: https://www.homedepot.com/p/Ideal-8-in-Grounding-Pigtail-12-AWG-Green-Stranded-Wire-with-10-Fork-10-...You can check around, surely you can find someone that sells in a smaller quantity. You will need to look inside the metal wall to make sure the box has a 10/32 tapped hole for the grounding pigtail to fasten. Some really old boxes does not have the 6/32 tapped hole. Hopefully yours does. If not post back. . NOTE: Just so you know.... Per NEC, and no doubt local city electrical code, you cannot install a 20 amp receptacle on a 15 amp branch circuit. Jim |
james1969 OP
267 posts 11-15-2017 4:12am
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. For now I wouldn’t go to the trouble of bringing one of them back up to your apartment for the test. Just how long are your the RCA interconnects? How long are the speaker cables? |
@james1969
Any chance you have a radio that is AC 120V powered? If you do try the same test Al, (almarg) asked you to do in an earlier post. (Page one)
One other test you might try.
You will need buy a pair of RCA shorting plugs.
Disconnect the interconnects from the back of the power amp/s and plug in the shorting plugs. Check for the RF signal noise.
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james1969 OP
269 posts11-15-2017 2:09pm
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... @james1969 My idea to try the radio was to see if the noise was on the AC mains lines. From your post it appears the noise is not on the AC mains power lines. I am not quite sure though why you didn’t pick up the noise on the battery powered radio though. I suppose the static sound of the radio off station might have drowned out, masked, the signal noise you were listening for. If the noise is being radiated through the air it could be near impossible to totally filter it out. If at all. There are line filters, ferrite beads, and filter capacitors, that are designed to block unwanted signals. Problem is one size does not fit all. You have to know the frequencies you are dealing with to filter them out. I am not sure who you would need to hire for that. Al, (almarg), might know. Part of your problem could be the long 3 meter RCA interconnects you are using. You may have to try some that are 100% shielded. That can have a down side on the SQ of system. And even though the Furman P-2400 IT didn’t solve the problem and the signal noise is being radiated in the air, the power cords that feed your audio equipment will act as receiving antennas and pick up the signal and feed it into the audio equipment. As you probably already know a heavily shielded power cord can suck the air right out of the sound of an audio system. My experience with ferrite beads on a power cord can/does the same thing. Even the speaker cables can work as an antenna and send the noise to the speaker drivers. Just curious, by chance does you preamp have a headphone jack? If you have a pair of head phones it would be interesting to know if you can hear the noise through them. If you do have the jack and the phones and you still hear the signal noise though the phones disconnect the RCA interconnects from the preamp that feed the amp/s. Are these interconnects the 3 meter long ones? Jim |
@james1969 , You would need to establish a direct correlation between the subway train passing under your apartment building at the same times you are hearing the RFI noise through the speakers of your audio system. You need to start keeping a log. I have been trying to research, over the net, noise in an audio system caused by cell towers. From the Link toddverrone posted. Keep phones away from audio gear Stages are carpeted in audio gear. The farther mobile phones are away from this equipment AND (very important) their cabling, the less likely they are to interfere. Most good engineers seem to impose an effective but draconian policy on talent: absolutely no cell phones anywhere on stage or off stage. All personal electronics are to be left in the green room, no exceptions, and all those in violation, famous or not, are chastised. Engineers everywhere would be wise to adopt similar policies.
@james1969 LOL, "Do you know where your cell phone is at this very moment?" For a test turn the thing off and get it as far from your audio system as possible. What wall is your audio system set against? Out side wall? Directly facing cell tower? Adjoining wall with neighbor? When it comes to GSM buzz, not just any ferrite core will do. You must use one that has the correct number of turns and is made from material optimized for attenuating high frequency GSM signal, which can be anywhere from 800 MHz to 1800 MHz. GMS buzz? LTE? TDMA ? In layman terms please! Re: On-site Cell Tower Interference
« Reply #2 on: October 03, 2012, 10:03:56 pm »
It’s highly unlikely the cell site will induce RFI problems with any properly designed audio equipment, or any other system inside the building.
First, cellular/PCS sector antennas are highly directional. Directly below the antenna is a major null with signal levels easily being 50-70dB below on axis carrier level (based on antenna type and design) before building attenuation is considered.
Second, you can request engineering data from the cellular/PCS service provider(s) and/or tower management firm which will tell you antenna make(s) and model(s), antenna array(s) design, location(s) and ERP of each TX antenna. An outside RF consultant can assist in determining RFI potential. Logged Henry Cohen
CP Communications www.cpcomms.com
Radio Active Designs www.radioactiverf.com Tom Young http://forums.prosoundweb.com/index.php?topic=140277.0Send that guy an email, if possible. @james1969 Can you see the antennas on the tower from your window? Higher? Lower? https://www.google.com/search?source=hp&ei=mKoNWpfxCMrPmwGUyrK4Bw&q=picture+of+antennas+on+c... Here’s some EE talk. https://electronics.stackexchange.com/questions/32830/why-does-gsm-cause-speakers-to-buzzJim |
james1969 OP286 posts11-16-2017 1:35pmI
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...
You need the RCA shorting plugs for the amps inputs. |
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@kosst_amojan, As sure as I am that it’s cell phone noise, I’m almost certain it’s not that tower. Re: On-site Cell Tower Interference
« Reply #2 on: October 03, 2012, 10:03:56 pm »
It’s highly unlikely the cell site will induce RFI problems with any properly designed audio equipment, or any other system inside the building.
First, cellular/PCS sector antennas are highly directional. Directly below the antenna is a major null with signal levels easily being 50-70dB below on axis carrier level (based on antenna type and design) before building attenuation is considered. First, cellular/PCS sector antennas are highly directional. Directly below the antenna is a major null with signal levels easily being 50-70dB below on axis carrier level @kosst_amojan, So for cell phone reception in the apartment building there may be equipment to compensate for the "null zone"? If so, would you expect the equipment, or antenna, placed on each floor? Also if james1969 placed his cell phone in areas on his audio system as you did on yours he should pick up the same RFI noise as you did, correct? Another question. What if the apartment building has some type of building automation system that is remote controlled by a digital transmitted signal? Could that cause the same type of RFI noise? |
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.
Try this. Do you have a roll of metallic tin foil in the kitchen? Unplug all the other power cords from the AC power outlet. Reason? To eliminate the chance they will/are acting as receiving antennas and induce the RFI signal into the power cord of the mono amp. Wrap the tin foil around the speaker cable for the one mono amp being used for the test. Be careful to keep the tin foil back from the amp terminals as well as speaker terminals. An inch or two is fine. (metallic tin foil is conductive). For the test the foil should not need to be grounded. Plug the mono amp directly into the power wall outlet. Check for the RFI signal noise. Still there? Next thing to try. Wrap tin foil around the power cord for the mono amp. Just the cord not the plug body or the IEC connector. (remember metallic tin foil is conductive). The tin foil will shield the hot, neutral, and equipment ground wire. The tin foil should not need to grounded for the test. The tin foil should reject the RFI noise, if it is radiated through the air, from entering the conductors of the power cord. Plug the mono amp directly into the power wall outlet. Check for the RFI noise. If the noise is still present you might try earth grounding the tin foil. Though I think it would not be needed for the test. You will need a piece of wire. Any size will do. Bare one end of the wire wrap it around the tin foil, at the plug end of the power cord, a couple times or so and then twist the wire to itself to secure it around the tin foil. Bare the other end of the wire, amount stripped depending on the wire gauge of the wire. You may need to fold it over itself a few times to increase its’ effective size. Insert the wire in the "U" shaped equipment ground hole of the wall receptacle. |
Got Tin Foil? Has to be the metallic kind.
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almarg7,616 posts11-16-2017 3:32pm
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
Al, Agree, but 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. Jim |
Tin foil had no affect on the power cord.
Did you get the conductive metallic tin foil type? Actually it is aluminum foil. Did you also try grounding the foil to the "U" shaped equipment ground contact on the wall receptacle? (You could also use the center 6/32 trim screw that holds on the cover plate. Just make there is not any way the bared wire could come into contact with the hot blade of the plug plugged into the outlet.) Last thing I can think of is to try the aluminum foil on the speaker cable. Hopefully the ferrite beads you ordered will work. I did check on wireless building automation systems. You might want to check with building maintenance and see if they are being used in the building. I would also ask if there are cell phone antenna devices installed in the building. That's an old building with thick outside walls made of concrete and brick, I would imagine. https://www.buildings.com/article-details/articleid/15219/title/how-to-boost-cell-phone-coverage-in-...http://www.facilitiesnet.com/buildingautomation/article/Pros-and-Cons-of-Wireless-Building-Automatio... |
kosst amojan said: Might mu metal be more effective than aluminum foil? @kosst amojan Probably, not sure. I just figured he could pick up the aluminum foil locally. By the way I think you are right in thinking the cell tower is not directly the cause of the noise. It may be indirectly caused by the cell tower because of cell phone equipment installed on the floors of his building though. There may be one on his floor. In the corridor or a housekeeping closet or a small mechanical/electrical closet. A suspended acoustical tile ceiling is a great place to hide the small antenna. The old prewar apartment building could have thick outside walls made of concrete and brick. Hard to say. James1969 could see how thick by just looking out the side of the window for how thick the outside wall of the building is. Floors can be thick concrete as well. It depends on the type of construction and building materials that were used. |
james1969 OP
296 posts 11-17-2017 3:58pm
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. @james1969 , By chance does the Analyzer have the ability to indicate signal strength as well? If so walk around your apartment and see where the signal is the strongest. Next go out the entrance door of your apartment to the central House hallway, corridor, of the floor you are on. Walk the hall in both directions and check for a hot spot in signal strength. Point the device at both walls on each side as well as the ceiling as you walk down the hallway. |
@james1969, I missed the Big Glass Window directly behind your audio gear when looking at your system pictures before. Just a test you can try, if you are up to it. Cover the entire window with at least two layers of aluminum foil. Tape the foil in place. Overlap all splices by at least a couple of inches. Overlap the second layer by 1/2 the width of the aluminum foil. If possible wrap the foil over the window inside trim to the adjacent wall, window sill, and above window trim. Ground the aluminum shield to the mains equipment ground with a piece of wire. For the ground connection of the wire to the aluminum foil you could try removing the insulation from the wire several inches and then tape the bare ground wire to the foil the entire bared length. If by chance it works, fingers crossed, you might then try copper window screening to cover the glass window. EDIT: If you do try the experiment, experiment with the foil shield grounded and un-grounded to the mains equipment ground. Example of copper screening. https://www.dkhardware.com/bronze-copper-zinc-60-screen-wire-50-BRZW60-product-49932.html?gclid=EAIa...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? |
