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Occasional hum

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CageyH View Drop Down
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    Posted: 07 Mar 2023 at 6:36am
Occasionally, when listening to my system (through speakers or headphones) I get a short burst of a humming noise.
How do I find out what the source of this noise is, and more importantly, how do I get rid of it?

I will be checking to see if it is source dependent later today, as I noticed it yesterday when listening to vinyl.

At a guess, I would say it is probably in the 50Hz range, but it could be a multiple of 50Hz. It usually lasts for about 2 or 3 seconds.

I am thinking of fitting a filtered IEC to my mains block as a first step, as I think it is noise on the mains. Any other suggestions?
Kevin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2023 at 7:49am
There are two types of mains frequency noise: 1. 50Hz hum; 2. 100Hz buzz. In addition there is interference noise from TV and monitor screens which may have LCD (or similar) excitation frequencies, sometimes 75Hz.

There can be contact noise where a connection is on its last legs, thus removing the shielding function intermittently, resulting in "mains hum".

As you only recently noticed it ("as I noticed it yesterday when listening to vinyl"), then is there anything that has changed recently, or any new household electronics or electricals?

A mains filter cannot remove mains frequency noise because the noise is the mains frequency, and removing it removes the mains.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RichW Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2023 at 8:14am
Plug-in lamp dimmers on the same ring as hifi can induce noise.

Plug-in Adjustable Dimmer Switch for Home Lamps | eBay
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CageyH Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2023 at 8:19am
Thanks for the reply Graham.
It is not new, but yesterday on headphone listening it was there.
I had heard it before using my speakers, but was surprised to hear it yesterday.

I think I would go for option 2. 100Hz buzz.
Nothing has changed recently, but I know I have noisy mains, as we have a smart meter, power line network adapters, air conditioning and a heat pump.

So if there is nothing I can do to filter it out, I guess I will have to live with it.


Edited by CageyH - 07 Mar 2023 at 8:21am
Kevin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CageyH Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2023 at 8:23am
Originally posted by RichW RichW wrote:

Plug-in lamp dimmers on the same ring as hifi can induce noise.

Plug-in Adjustable Dimmer Switch for Home Lamps | eBay

Thanks. I don’t have ring circuits. My HiFi is on a dedicated line, but it all feeds back to the same place….
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2023 at 9:10am
Not a case of living with it. More like an ongoing investigation.

I and others can only give examples. Here's another.

I had an Hadcock GH 228 unipivot arm and upgraded to a GH 242.

Rather than being quiet, the new arm would introduce mains hum/buzz every now and then.

This was because the arm tube metal wasn't making electrical contact with the arm base, because the unipivot wasn't pressing "hard enough" together to always cause an electrical contact. Otherwise, the unipivot was doing its job as a bearing.

As such, the arm tube surrounding the arm wires wasn't an effective sheild, and then it was, and then it wasn't.

Eventually I said sod it and bought a fuss-free Technics.

We can only give you our stories in the hope something clicks (or doesn't...Wink).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RichW Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2023 at 10:48am
DC on the mains, or asymmetrical AC mains is reported to make transformers buzz.
I used to hear this intermittently but now rarely for an unknown reason..
A DC blocker might be worth a trial.

Edited by RichW - 07 Mar 2023 at 10:49am
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