Potential DC on Mains issue

[jimmen]

Hi,

I recently replied to this post from about a month ago: emotivalounge.proboards.com/post/1082890   but I am thinking that the original posters may not be following it anymore, so will paste in my question on that post here (the original post was about DC on Mains): 
-------------------------------------------

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

[405x5]

Nov 23, 2021 21:01:31 GMT -5 jimmen said:

Hi,

I recently replied to this post from about a month ago: emotivalounge.proboards.com/post/1082890   but I am thinking that the original posters may not be following it anymore, so will paste in my question on that post here (the original post was about DC on Mains): 
-------------------------------------------

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

Jim,

If I were you I would put the brakes on immediately and get with your local utility company right away.
Anything electrical outside that’s giving you something like this to contemplate inside is a no brainer problem that should be addressed by them. CMX….? I would nix that and work the problem first instead of looking for a band aid.

[doc1963]

I agree with 405x5… If there’s a service problem outside, it can affect everything in your home.

I’d document the issue as it’s occurring, if you can, and get the power company out to inspect their equipment as soon as possible.

[jimmen]

Thank you to both of you for your feedback.  I have started the process to inform the utility company about the outside transformer (had to submit an online form since this is a non-emergency situation) - let's hope they listen to my plea! 

I am going to keep the CMX-2's (and have also used a couple different conditioners and a regenerator) for now as a hopeful solution until I can work through the situation with the utility company. I have a feeling that may take a while.

Thanks again,
Jim

[jimmen]

Quick follow up in case somebody runs into the same thing. The CMX-2 arrived and totally removed the buzz from the Hegel H390.

The customer support from our power company acknowledged receiving my request to have the external transformer checked out and they said they have reported it…let’s hope it really gets looked at soon.

I had been reading that DC on mains is rare.

Jim

[DavidR]

If you have a digital multi-meter you can check for it. Just put the meter on DC Volts and measure any outlet.

[KeithL]

NOTE:

This is OK to do with most modern digital multimeters... although some few really low end ones may not be rated for line voltage.

However not all modern digital oscilloscopes can safely handle AC line voltage on their probes (120 VAC works out to about 340 V P-P).

And DO NOT try it with an older NON-digital meter... (you risk burning out the meter).

If you're not sure than better safe than sorry.

Nov 28, 2021 19:38:42 GMT -5 DavidR said:

If you have a digital multi-meter you can check for it. Just put the meter on DC Volts and measure any outlet.

[DavidR]

This is what I use

[donh50]

The outside transformer buzzing may indicate a more serious problem so definitely follow up with the power company. Various things can cause transformers to fail and generate very high levels of distortion that can inject (or mimic) DC. It may be benign, but I have seen large power transformers explode, and it is not something you want to be around.

[KeithL]

I hadn't read this in detail before...

First off, yes, a transformer will NOT pass a pure DC offset...

(Although it can pass a distorted AC waveform, which can cause noise on its own, or can cause a DC offset to occur with certain loads.)

Basically ALL transformers hum to some degree when under heavy load... 

Therefore it's not unusual that the big transformer outside hums when under heavy load - like during times when air conditioners or electric heaters are running.

And, depending on the characteristics of the transformer itself, this could also cause it to distort the AC waveform it is delivering.

(You might be able to find out from the power company what they consider to be "an acceptable pure waveform".)

And, in turn, a distorted AC waveform could cause the transformer in your Hegel to buzz.

A transformer is a bunch of wires wrapped around a magnetic core... so the core will vibrate for several reasons at the frequency of the current flowing through it.

A distorted waveform, which contains higher order harmonics, will sound more like a buzz, and louder, than a pure 60 Hz sine wave.

(A pure 60 Hz sine wave produces a smooth hum... you can get a buzz from vibration in the transformer or from a distorted waveform that contains higher harmonics.)

1)

It's possible that, due to an unbalanced load on your side of the mains transformer, or an oddly asymmetrical AC waveform, you have actual DC offset on your power line, which could cause the transformer in the Hegel to hum.

2)

It's possible that the big transformer outside distorts under heavy load, so it buzzes, and sends a distorted sine wave to the Hegel, causing its power transformer to buzz as well (rather than hum more quietly).

3)

It's possible that something upstream of the big transformer is causing the power waveform to be distorted on the main power grid.

(This may simply happen during "peak usage times".)

This could cause the big transformer to buzz and, since AC distortion WILL pass through a transformer, it will be passed on to the Hegel's transformer, causing IT to buzz as well..

The only real way to tell if the power waveform is distorted is with some sort of spectrum analyzer.

You cannot tell with an oscilloscope because relatively small amounts of distortion, up to 5% or so, may not be visible on a scope display.

(Actual clipping is visually obvious but a few percent of "warping" on the waveform isn't visible on a 'scope trace.)

The catch is that your power company almost certainly considers a slightly distorted power waveform, within certain limits, to be "normal".

It's also normal for a big outside transformer to make quite a bit of mechanical hum (and old transformers sometimes get worse).

Therefore it may be an uphill battle to convince your power company that anything is wrong (and they may simply not be willing to "fix" it).

(The specs on your local power utility supply may not be as great as you might hope.)

In most homes the "120 VAC" circuits are split across the two "halves" of the mains transformer outside...

And all of your inside circuits, whether "dedicated" or not, are connected to one of those two halves.

If you have an unbalanced or asymmetrical load on one of those sides...

Then half or your interior circuits will be "on the quiet half" and half will be on "the noisy half".

All a "dedicated circuit" means is that you have a separate direct run to that outlet from your breaker panel... it still shares that half of the big transformer outside with other circuits.

Nov 23, 2021 21:01:31 GMT -5 jimmen said:

Hi,

I recently replied to this post from about a month ago: emotivalounge.proboards.com/post/1082890   but I am thinking that the original posters may not be following it anymore, so will paste in my question on that post here (the original post was about DC on Mains): 
-------------------------------------------

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

[jimmen]

Thanks again to everybody for the great replies.  I do have a Fluke 107 meter.

We'll see what the electrical company ends up doing and what they consider to be within spec.

Based on Keith's explanation of the two halves, it now makes sense why my dedicated circuit is on a "noisy" side and by chance one of the shared circuits in the listening room happens to be on the non-noisy side and is quiet when the large transformer outside hums.

Jim 

[Boomzilla]

Source of problem = power company’s transformer that you have no control over.
Best option under your control = “whole house surge-suppressor / power conditioner (protects all electrical equipment in your home).
Best option specific to audio system = power conditioner strip and/or ballast transformer
Should power company decline responsibility for their transformer = Local TV station consumer advocate.