I did read everything but unfortunately cannot think of anything else, especially since Al and Ralph already commented. It could be the power cable, speaker cables or both. I listen to recorded noise and watched youtube video showing sound of different type of interference. Judging by >1s gap between occurrences I would suspect that it might be intelligent power meter. They repeat readings from each other for each household or apartment on "Mesh Network" at 900MHz few times a day. Where is it located? It could be also that it picks up all the sources - cell tower, trains, power meter etc. What about getting metal conduit in Home Depot (it is cheap) and cut it to the size of power cable and speaker cables. After running cables thru it ground them well. Look for alternative grounds like faucet or radiator. It is only to check what it is. If noise goes away then we can start removing conduits one by one. If it doesn't then either filtering from the Furman is too weak or amp itself is picking up noise and needs better grounding. Most of shields are not perfect Faraday cage and have to be grounded in order to work. For instance to make high frequency current flow on the outside because of skin effect (cable shield or metal box) it needs place to flow to - a ground. Amplifier box should be grounded with separate wire directly to good ground. I would experiment with different grounds. If faucet pipes work, than running long ground wire is better than suffering from audible noise. Perhaps speaker box also needs shielding? (Shadorne suggested it). If it is difficult to do/check replace it with very small speaker (even plain individual) and shield it.
Jim, speaker cables are antennas for the electrical noise since amplifier has low output impedance only for low frequency signals. Induced noise enters amps input thru the feedback loop.
As for the ferrite - on one hand you need highest permeability, but on the other high frequency response. Self Resonant Frequency (SRF) specification might be useful since above this frequency impedance of the choke for common mode signals will drop like a rock. Read this: https://www.coilws.com/index.php?main_page=page&id=128
I've been once in the company that had so much of the noise pollution (multiple high frequency seem welders) that nothing worked - not even telephones. Technicians there told me that common rules, like grounding shield on one end only don't even work. At the end they had to put every power cable in conduit. We had to put our equipment, we sold them, in the metal NEMA box with metal mesh screen on the front door glass.
I have a police station down the street, and a fire station down one block from me. So the public safety GSM band would probably be in high usage during the daytime (like what I experience now). I'm up at early hours to enjoy my system (when the city is asleep) and there are no sirens to be heard. The subway still comes and sometimes I hear the noise, we have cell phone service now down in the subway system.
James1969, It is possible. I had for few days CB like transmission loud voice coming thru pretty much everything at home - TV (turned off in stanby), speakerphone, radio. I noticed every time the same unmarked car with many antennas passing by. I suspect that his transmitter was out of whack. FCC intervenes only when somebody complains. Intensity of electromagnetic field drops in linear fashion with distance. When you are close it can be pretty strong.
Thank you for that clarification. I too got a Furman device, I got the isolation transformer, the P-2400 IT. It basically removed the noise floor from the music in my system. I am still getting the intermittent GSM signal in my system, that is why I am exploring power cables with better shielding.
I inserted an isolation transformer (Furman P-2400 IT) into my system, so everything plugs into the isolation transformer. This had no impact on the specific noise I am targeting, but it did have a big positive affect in sound quality - removed any noise I was hearing in the music, and effectively lowering the noise floor quite a bit. But it had no affect on my intermittent noise. I called Furman directly and spoke to one of their reps and he was shocked to hear the Furman had no affect on the noise problem I am experiencing, he then said it was air born, not in the power line. Which I agree with him.
So I powered down my entire system (and apartment) for that matter and left the dedicated circuit on for my system. I put an RCA shorting plug on 1 amplifier’s input, I put a basic power cord on the amp and turned the amp on. I was able to affect the noise when I lifted the power cord and moved it around and it behaved like an antenna. So I am thinking of trying a new power cord to see if that will improve/change the situation.
I was able to identify the 700-900MHz frequency range by using this device: https://www.amazon.com/gp/product/B007L09DLY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 It will play the frequencies it’s detecting through the speaker, and I was able to correlate the intermittent noise to the 700-900MHz frequency range which is a dedicated cellular band for emergency first responders. So that made more sense, because when I hear sirens or the subway below, I usually hear the noise.
James1969, Yes, twisting signal wires will reduce it - if it is coming as common mode. In the case of power cord your signal wires are hot and neutral (return). Pitch of the twist should be many times smaller than wavelength (17" for 700MHz) Twisting them with 1" pitch should be fine but I would twist as tight as I can. Noise might be getting in as common mode or normal mode. Transformer should be good defense for common mode as well, but there is capacitive coupling between primary and secondary. For that transformers have grounded shield (between windings). You could also attempt to use common mode choke, winding power cable around toroidal ferrite core. That would create inductance in series for the signals flowing in the same direction in both wires (common mode) but would be zero inductance (cancellation) for normal mode (signals flowing in opposite direction). Unfortunately it is difficult to do (connectors, thickness of cable, etc.) When noise already is or converts to normal mode you can't do much except for filtering. Electrolytic caps inside present high impedance at these frequencies because of their high inductance. Placing low inductance cap in parallel would help, but might create parallel resonant circuit with said inductance. External filter should help but it might create big voltage drops since most of the gear takes power in short current spikes of very high amplitude. That would appear as reduced dynamics of power amp. I bought Furman Elite 20PFI conditioner that has power factor correction. It supposed to present resistive load to the mains. Other than very tight non-sacrifitial over/under voltage protection it has huge inductor and huge capacitor to deliver required current spikes to the load while presenting constant load to the mains. With my amp (150W) it does not reduce dynamics.
At 700MHz shield should be a good defense against noise, since anything induced would flow on the outside of the cable - shield, because of the skin effect. The only problem might be shields inductance. I suspect that better cables have better shielding in that respect.
@james1969 OP > My power cords appear to be picking up cellular activity in the 700-900MHz range.
Blindjim > sorry. I’m curious as to how you determined it is your PCs specifically which are inducing this extraneous noise and not some other cable, component, or power irregularity.
My power cords appear to be picking up cellular activity in the 700-900MHz range. So you say twisting them will help reduce the cellular signal I seem to be picking up?
Power cable hot and neutral conductors are carrying the same current in opposite directions being, in a sense, "balanced". Twisting them will make them exposed to external fields evenly causing cancellation. Same goes for radiated field from the cable. This works perfect as long as pitch of the twist is shorter than wavelength of the offending signal (4.9" for 2.4GHz). This makes practically no noise induction in ground wire. Twisting also increases capacitance (not important) and reduces inductance (important).
As for balanced circuitry - it does not reduce normal mode powerline harmonics the same way as balanced audio amplifier does not remove harmonics of the music - it only reduces harmonics produced by amplifier itself and only even harmonics (does nothing to odd harmonics). Balanced input supposed to reduce common mode noise. Power supply transformer does that already. Shield, in instrumentation/measurement amps cables, is usually driven with common mode input signal. This scheme eliminates capacitance between shield and signal wires for common mode noise reducing greatly capacitive pick-up. It works quite well, but I’m not sure if it makes any audible difference with power cables.
Regarding induced current in the “neutral” conductor, one reason to use balanced power is that both the “hot” and neutral conductors are energized, each at 60 volts, but 180 degrees out of phase with each other. This not only avoids the induced current problem but, as with balanced circuitry, causes powerline harmonics to cancel each other out.
I had s disaster ofDynerhistic shielding 14 receptacles between Power cords ,interconnect ,and speaker cables ,plus Which really ticked me off they use wall warts .to get the better wall warts then the ones it comes with $400 Each scam city and less then $10 of mini circuit board resistors and a few other things If I am spending $ 1200 for interconnect the $10 in parts better wall warts should come with it . My friend had non active csbles From Verastarr for less or similar money and was a much more natural cable .I havd sold all my synergistic and Verastarr are my New go to cables .beware of all the optional add one before buying. Anything.
All of my cables have some form of active shielding and it is very effective but with some caveats. Battery powered shielding, such as DBS from AudioQuest is painless and easy to use but don’t disconnect the batteries as it will take 48-72 hours to fully reform the field and in the interim the cables will sound thin and edgy. I have all AQ interconnects and a number of AQ power cables (btw the new Dragon power cords are quite astounding). Mains powered shielding such as on older SR Cables is also very good but you need to be prepared to invest in the power supplies. There is an extensive thread (search Spallone) on the value in upgrading the wall warts that come with the SR active cables and I can attest to the impact - you get even better results with a dedicated supply such as the transporter. The newer SR cables drive the shield directly without need for external power but the introduce the need for a separate ground, which is another story and complication
in summary them active shielding works but it brings a level of cost and complexity along with it and you need to be prepared to tweak things to get the best out of it
I’ve experimented with different cable architectures/geometries for many years and settled on the helix design because I found it to be the most noise-free geometry I had tried.
As an example - I built a cable using high quality Furutech bulk cable - I then removed the internal conductors and braided them - the improvements were immediately noticeble - I then built the Helix design using the Furutech conductor as the live and the improvements were even greater
I have compared the Helix to power cables up to $1500 and the Helix proved to be better each time
The first Helix cable I made was to prove the theory and was built from Romex - It outperformed the braided Furutech cable - but since solid wire is not permitted by code, I now use the stranded conductors listed in the link.
I feel that the materials listed in the link provides a :"great value" option, but I encourage anyone trying them to experiment with different conductors suited to their own budget.
I have a few which do not have active shielding. I have tried a few which did. Needless to say, results will vary, though I found no ostensive value to active shielding when it came to sonic improvements over those of most other power cords which did not use an energized network.
The aforementioned experiences occurred while I was using actively shielded IC as a main, and active shielded speaker wires. Presently I use but two sets of actively shielded cables, and both are speaker cables. Both are Synergistic Research but different models and lengths.
The active power cables I tried were as well, sR. this was some time back and the tech may have and likely has changed. Improved? Dunno.
The usual answer on these topics sits wsquarely on the Ops shoulders. They will have to give some a try to find out for themselves in their own system, location, etc. to be certain.
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