jbryngelson
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Healthy Tweaking is good for the Hobby
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Post by jbryngelson on Oct 12, 2021 7:35:48 GMT -5
I have a new home (built in 2017) with a dedicated 20a circuit to my equipment rack and a 15a circuit in series with other outlets. For the past few years, I have connected a BPT BP-2 Balanced Power Conditioner, similar to the Furman and EquiTech products, in my system. It uses a very large transformer as it creates balanced power instead of Neutral/Hot/Ground power. I have had a silent system, with 6 different amplifiers connected to it (L&R Main top = DIY Tube Amp, Center = DIY Tube Amp, L&R Main bottom = Hsu Research Amp, NHT Sub Amp, Adcom L/R Surround & L/R Rear Amp). I Also plug the Emotiva XMC-1 and some sources (TT) into the BPT. Other devices (Cable Box/XBox/MacMini/DROBO/USB Storage) into the 15a circuit. In summary, a silent system. Suddenly my BPT Conditioner has a cycling hum. I am not getting added sound/noise in the room (They are separate), but a fairly loud hum like the unit is suddenly taking on added load. I have disconnected everything from the unit, but I still get this cycling every 30-90 sec low hum when plugged into either the 20a or 15a circuit. Chris Hoff the retired designer tells me it is likely added DC on my electrical line. I have many dimmers, microwaves and other ugly devices that can cause this issue. Not sure why suddenly they are acting up. MY 1st QUESTION is will the CMX-2 properly block the DC which should solve my issue? MY 2nd QUESTION is, how would you configure the power in this system, knowing the outlets, the presence of a Balanced Power Conditioner, and the needs of over 20 devices in the rack. Of course I have a number of power strips... Just looking for some thoughts. Jeff in Detroit
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jbryngelson
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Post by jbryngelson on Oct 14, 2021 7:54:51 GMT -5
Does anyone have experience with DC interference on their power lines? Did you choose the CMX to solve this issue?
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KeithL
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Post by KeithL on Oct 14, 2021 9:20:05 GMT -5
DC offset on the power lines is actually a rather rare occurrence.
DC voltage does not pass through a transformer. Therefore it cannot come into your home's power "from the grid". It will only occur if there is some sort of unusual load or circuit imbalance on your side of the "pole transformer" causing it (you may or may not share a transformer with your neighbors). (The most likely causes would be something like a big motor or light controller that asymmetrically distorts the power waveform.)
If you have this problem, the symptom will be that, in devices with power transformers, the transformer will run hotter than normal, and may produce more than the usual amount of MECHANICAL hum. Toroidal transformers are especially sensitive to this because they typically have a lower DC resistance than other types.
You can measure this with some digital multimeters by putting the test leads on the AC line with the meter set to a low DC VOLTS range - like 2VDC or 20VDC. Many modern digital multimeters allow this to be done safely (your meter will list a maximum voltage that it can safely measure - and specify that it is safe to apply that voltage "on any voltage range").
BE SURE YOUR METER CAN DO THIS - AND **DO NOT** TRY IT UNLESS YOU ARE SURE. THIS IS **NOT** SAFE TO DO ON AN OLD-STYLE ANALOG METER (and will destroy the meter).
Does anyone have experience with DC interference on their power lines? Did you choose the CMX to solve this issue? |
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jbryngelson
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Post by jbryngelson on Oct 15, 2021 7:25:56 GMT -5
Keith, thanks for taking the time and explanation. I do not know for certain the cause, but my transformer based power conditioner was humming, as it generates balanced power. This hum is only at the device - from the transformer in the device, and cycles every 30-90 seconds. I emailed with the BPT Designer/Engineer and he thought it was DC on the power line causing the tranformer HUM. He suggested it could be generated via light switch dimmer, blow dryer, microwave, humidifier etc. I made sure none of those items were turned running (Dimmers off etc) and still had the issue. So I researched and bought the CMX2. When I went to the theater rack yesterday and turned on the power conditioner the HUM was gone (no CMX2 installed. Now, I am not sure if I have a power line DC issue, or a power conditioner issue. I will do more troubleshooting, but I since there is NO harm to putting the CMX2 into my system, plugging it into my dedicated 20a circuit and then putting the power conditioner behind it. I hope the hum is gone forever. System sounds great with your help last month! Jeff in Detroit. PS - I am not going to measure for DC unless it shows up again. I will use the right tools and caution based on your advise.
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KeithL
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Post by KeithL on Oct 15, 2021 10:31:00 GMT -5
There's a good chance the CMX-2 will do the job.
The basic reason for the issue is that power transformers are not designed to accept DC. We all know that transformers don't PASS DC - from the primary to the secondary. However, as a result of how inductors work, a transformer's primary winding almost always has a DC resistance that is much lower than its AC impedance. (The output transformers in tube amps take advantage of this fact - and are designed to "pass the DC current used by the tubes while tapping off the AC component of the signal" and passing that on to the secondary windings.)
However, if DC voltage is present at the input of a power transformer, it results in a relatively large amount of DC current flowing through the primary winding. This current "serves no purpose", but causes the transformer to heat up, and also acts to magnetically saturate the core...
Many transformers simply produce more hum as they get warmer... (windings expand; bolts expand; sealant and potting compound get softer).
And the increased core saturation may also cause the transformer to have a higher level of waveform distortion... (And the harmonics present in a distorted power waveform tend to cause the transformer to vibrate more at higher, and more audible, frequencies).
I should point out, however, that it is normal for transformers, and especially big ones, to hum...
How much they hum depends to a major degree on the construction of the transformer... However, in many cases, transformers will hum a bit more as they get older, and the windings and the bolts securing them together loosen a bit...
You may also notice hum if the magnetic field leaking from the transformer causes a metal cover nearby to vibrate due to magnetic attraction... (if that's the case some sort of vibration damping may help.)
Keith, thanks for taking the time and explanation. I do not know for certain the cause, but my transformer based power conditioner was humming, as it generates balanced power. This hum is only at the device - from the transformer in the device, and cycles every 30-90 seconds. I emailed with the BPT Designer/Engineer and he thought it was DC on the power line causing the tranformer HUM. He suggested it could be generated via light switch dimmer, blow dryer, microwave, humidifier etc. I made sure none of those items were turned running (Dimmers off etc) and still had the issue. So I researched and bought the CMX2. When I went to the theater rack yesterday and turned on the power conditioner the HUM was gone (no CMX2 installed. Now, I am not sure if I have a power line DC issue, or a power conditioner issue. I will do more troubleshooting, but I since there is NO harm to putting the CMX2 into my system, plugging it into my dedicated 20a circuit and then putting the power conditioner behind it. I hope the hum is gone forever. System sounds great with your help last month! Jeff in Detroit. PS - I am not going to measure for DC unless it shows up again. I will use the right tools and caution based on your advise. |
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Post by rbk123 on Oct 15, 2021 16:24:59 GMT -5
If it comes back you can:
1. Turn off all the other circuit breakers in your fuse panel except the BPT's circuit and see if the hum goes away
a. If it does not, start unplugging the other devices also on that circuit and see until the hum goes away. If it still hums, something is up with the BPT
2. If the hum does go away after turning off all the other circuits, turn them back on 1 at a time to see which one(s) is(are) the culprit
Any big work going on in the houses/street around you that isn't going on anymore, to coincide with the hum going away?
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Post by vcautokid on Oct 16, 2021 7:22:49 GMT -5
The fact the noise went away is interesting. I would investigate further the possibility of a ground loop. Could be a intermittent interconnect. Also some SMPSs that power some of your devices are a great source of noise too.
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jbryngelson
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Healthy Tweaking is good for the Hobby
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Post by jbryngelson on Oct 19, 2021 7:33:16 GMT -5
If it comes back you can: 1. Turn off all the other circuit breakers in your fuse panel except the BPT's circuit and see if the hum goes away a. If it does not, start unplugging the other devices also on that circuit and see until the hum goes away. If it still hums, something is up with the BPT 2. If the hum does go away after turning off all the other circuits, turn them back on 1 at a time to see which one(s) is(are) the culprit Any big work going on in the houses/street around you that isn't going on anymore, to coincide with the hum going away? This is solid troubleshooting advise. Yes, my Audio Rack has a dedicated Circuit, and I can turn off all the breakers but the Audio circuit, which has only one outlet - in my rack. As you point out, if it is gone then, I can start turning on the breakers looking for the circuit with the source of the HUM. Again - solid contribution and thoughts. |
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jbryngelson
Minor Hero
Healthy Tweaking is good for the Hobby
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Post by jbryngelson on Oct 19, 2021 7:36:06 GMT -5
The fact the noise went away is interesting. I would investigate further the possibility of a ground loop. Could be a intermittent interconnect. Also some SMPSs that power some of your devices are a great source of noise too. Yes it is interesting. Today, still no HUM. I added the CMX2 anyhow to the power chain, but when I connect the BPT directly to the dedicated circuit, it still is - gone. I did have an issue with an interconnect earlier this year that was the source of a big amp issue for one of my subs. When I replaced it with a different interconnect my troubles went away. Put the troubled interconnect back in, and the problems returned. I took it out, cut it and tossed it! Put the replacement back in and happy as can be...... |
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Post by vcautokid on Oct 19, 2021 8:03:43 GMT -5
The fact the noise went away is interesting. I would investigate further the possibility of a ground loop. Could be a intermittent interconnect. Also some SMPSs that power some of your devices are a great source of noise too. Yes it is interesting. Today, still no HUM. I added the CMX2 anyhow to the power chain, but when I connect the BPT directly to the dedicated circuit, it still is - gone. I did have an issue with an interconnect earlier this year that was the source of a big amp issue for one of my subs. When I replaced it with a different interconnect my troubles went away. Put the troubled interconnect back in, and the problems returned. I took it out, cut it and tossed it! Put the replacement back in and happy as can be...... I stopped counting how many inteconnects cause noise issues. Of the many folks I have helped and the miles of cable that was bad that was tossed away. |
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jimmen
Seeker Of Truth
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Post by jimmen on Nov 22, 2021 15:00:19 GMT -5
Hi - I am having a similar problem that didn't show up until I got a more powerful integrated amp - a Hegel H390 (which has a much larger transformer than the Hegel H190 that the H390 replaced).
We are in a new development (18 months) all new underground wiring with a huge transformer/box outside that I assume services a couple of our neighbors too. I have a dedicated 20amp circuit brought into the sound room. Normally, the transformer in the H390 is totally silent - I have to put my ear on top of the case to even hear it. But, when the transformer outside is starts buzzing during certain (random) times during the day, the transformer on the H390 starts buzzing like crazy.
What's really odd, if I plug my system into one of my normal (non dedicated) 15amp circuits in the house when the transformer outside is buzzing wildly, the transformer on the H390 doesn't buzz "as much" as when it is on the dedicated 20 amp circuit. I can also get some buzz when our microwave runs, and I understand that; it doesn't buzz when the fridge is on.
Just in case this is a DC on Mains issue, I have order two CMX-2's for both our systems. I was going to call our utility company, but Keith's comment about how any DC issue on the outside transformer can't come into the house was interesting. I am trying to figure out why I get the transformer buzz only when the outside transformer on the street is buzzing.
Any thoughts appreciated.
Thank you,
Jim
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Post by localnet on Mar 4, 2023 20:41:14 GMT -5
Jim, I know this is an old post, but I am doing a bit of electrical work right now and stumbled upon this thread, as I own a couple of the CMX-6 units for their mount ability and the fact they can use a power cord that I supply. First thing I would do is check the outlets, get the proper screw driver from HD or Lowes, the one electricians use to tighten screws on outlets and breakers, they have the square head on them, around $10. The outlets, most new construction homes use cheap contractor outlets, they buy in bulk, are cheap and will pass inspection, other than that, they are junk. I would go with a quality brand like Leviton. Get the ones with the screws, not the ones you stab the wire into the back of the outlet. Electricity, it vibrates, and will loosen screws on outlets over time, and it will also break wires, especially in those stab connector outlets. Check your outlets, I bet there are issues with those. Then the microwave hum. I would swap the breakers around, the microwave on say the left breaker box rail and the audio equipment on the right side rail. And I would check the outlet at the microwave, replace if one of those .50 contractor outlets. And if you do discover you have those cheap outlets and switches, change those things out. Go with Leviton, or another quality brand. I would go through the entire house and change them all out, switches and outlets. That hum, you should not be getting any hum, there is more than likely something wrong in your electrical connections/wiring. I do all of my own, and the microwave is on the same rail as my audio gear, I get no such hum or noise. I have a Siemans box and use their QT breakers. I would also check the wiring in the panel, make sure all of the connections are secure, turn the main panel power off first before checking. If you do not feel this is something you are comfortable with, hire a good electrician. |
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