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swiss toby
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Loc: UK
Mains hum, can I get rid of it completely? new
      #57385 - 02/12/04 06:03 PM
Having just improved my acoustics somewhat I am now even more aware of how many bits of kit in the studio have humming transformers. Will a power conditioner of some sort shut them up or is it just a case of cheap transformers hum and nothing's gonna stop them?

More precisely, I am hearing mechanical humming from the power supply for my Mackie 32:8, my UPS and my little computer monitor speakers and a slight hum through 2 of my 6 (5.1) powered monitors. Obviously it's not too practical too put all of this stuff in another room!

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Frank EleveldModerator



Joined: 30/08/04
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Loc: NL
Re: Mains hum, can I get rid of it completely? new [Re: swiss toby]
      #57401 - 02/12/04 06:36 PM
Are you sure all humming is caused by PSU transformers, or could it also be that there are other sources causing hum (ground loops for example).

Curing and preventing hum can be a tedious procedure. Transformers mostly buzz when they've to work at another mains frequency than they were originally designed for; for example, the transformer in your Mackie 8-bus PSU may be designed for the American market where the mains frequency is 60Hz. Using it in Europe, where mains frequency is 50Hz, may cause vibrations, resulting in hum. If you'd put your hand on the PSU, you'll probably feel it vibrating slightly, especially in the area where the transformer is mounted. A pad of rubber or foam between the transformer and the case may help, but be careful with mains equipment and PSUs in particular, because these contain large capacitors which may keep their charge for sustained amounts of time.

As for your monitors: you don't state what model and make you're using. It'd be helpful if you could provide more information on your setup.

A power conditioner won't improve matters as it doesn't affect the mains frequency; it only filters large variances in the mains voltage.

Cheers,
Frank


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Anonymous
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Re: Mains hum, can I get rid of it completely? new [Re: swiss toby]
      #57407 - 02/12/04 06:53 PM
Quote:

Will a power conditioner of some sort shut them up



Usually not.

Quote:

or is it just a case of cheap transformers hum and nothing's gonna stop them?




Pretty much - but even some expensive transformers hum. And some cheap ones don't. It depends upon all sorts of things like the type of transformer, the mounting method, their age, how heavily loaded they are, structure of the case/box they're living in, other random mechanical problems/failures, mains frequencies, etc. etc..

Quote:

I am hearing mechanical humming from the power supply for my Mackie 32:8, my UPS and my little computer monitor speakers



Probably down to some or all of the above-mentioned factors - or various other annoying problems.

Quote:

a slight hum through 2 of my 6 (5.1) powered monitors


Assuming that this is electrical rather than mechanical it could be down to grounding problems/PSU design or construction problems/low spec amps/interference/even PCB layout problems or something else of that ilk could cause it. (i.e. there's loads of possible causes of hum on the monitors and they could be transformer related or not.)

Quote:

Obviously it's not too practical too put all of this stuff in another room!


It'd certainly reduce the effects of the the hum from the speakers

You probably can get away with putting your UPS in another room and running an extension cable to it. It's more tricky with the Mixer PSU as there are limits to how long the DC output cable can be before you get problems. If you can get to another room on the length of cable you have then there's no harm in doing it. You can also extend most cables by a certain amount (or replace them with longer, heavier ones) to acommodate a longer run but you need to know what you're doing in the type of cable you use and how it's set up. Failing that you could use a different power supply that can help to deal with longer runs. Adding some damping material like "Deflex" sheet to the casework can help to reduce vibration noise in the metalwork of the case.

Or build a cover for your PSUs to reduce the noise.


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Martin WalkerModerator
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Joined: 28/02/01
Posts: 17483
Loc: Cornwall, UK
Re: Mains hum, can I get rid of it completely? [Re: ]
      #57460 - 02/12/04 08:34 PM
Quote 0VU:

Adding some damping material like "Deflex" sheet to the casework can help to reduce vibration noise in the metalwork of the case.




Yes, in the past I've greatly reduced buzz from some rack effects and synths with in-built PSUs by wedging a thin piece of neoprene sheet (deflex would probably be even better) between the top of the transformer and the nearest case panel (normally the top plate), which absorbs some of the transformer vibration and stops the panel vibrating in sympathy.


Martin

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swiss toby
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Joined: 09/04/03
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Re: Mains hum, can I get rid of it completely? new [Re: Frank Eleveld]
      #57646 - 03/12/04 10:17 AM
Thanks all. Monitors are Blue Sky System One and I'm assuming it must be cable routing that's causing the problem as only 2 of the 5 sats hum. Can you remind me, if signal and mains cables have to cross it should be at 90 degrees yes?

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