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Should my power conditioner hum?

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Should my power conditioner hum?

Postby Animesh » Thu Mar 23, 2017 7:13 pm

Dear SOS Forum

I currently have a FURMAN PL-PLUS C E in my control room, which is 10A rated and has 11 outlets...but it emits an annoying humming sound that I'm convinced is louder than is acceptable in a recording studio.

It is audible from across the room c. 5 metres away. I've tried 3 different units (of the same model) and all are emitting some form of hum. So am I resigned to having to put up with this noise? Are you folk experiencing similar? It's so annoying when mixing as I'm sat quite close to it, and I'm also conscious of mics picking it up when I record soft acoustic things in my control room like vocals or acoustic guitar.

I've tried to work out the overall power consumption of all the gear currently plugged into it, I have 8 outlets in use (out of the 11 available) feeding 7 x 19" rack units (preamps and converters), and 1 x 10 slot 500 series chassis with 8 slots filled. But even still, if I've worked it out correctly I think I should be using around 4-5A - potentially less than half the units advertised capacity (I must admit I'm not that confident I worked out overall current drawn consumption of my various items correctly, though I did dutifully scrape all my manuals for power consumption info!).

I'd love your experience/help/guidance as to whether it's possible to buy a near silent power conditioning unit to serve my gear? Or is it simply a fact of life that a power conditioner will hum that I just need to get over? On a practical note, I wanted one that can be mounted into my main rack (which is easy reach from the mix position) so if there was such a beast that would be wonderful...otherwise maybe I need to let go of my dream of being able to turn on all my gear with one button!

Thanks so much for your comments :-)
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Re: Should my power conditioner hum?

Postby Martin Walker » Thu Mar 23, 2017 10:35 pm

Animesh wrote:I currently have a FURMAN PL-PLUS C E in my control room, which is 10A rated and has 11 outlets...but it emits an annoying humming sound that I'm convinced is louder than is acceptable in a recording studio.

Hi Animesh!

If this is an acoustic noise (rather than a background hum in your audio as a result of using the power conditioner) then I suspect the culprits to be vibrating transformer cores. If so, there are a few techniques that you can use to lessen the annoyance, but they all involve opening up the unit and fiddling about in close proximity to potentially lethal mains voltages.

For instance, I've successfully reduced the annoyance of buzzing transformers (often amplified by being in close proximity to a metal casing that buzzes in sympathy), by placing a small sheet of neoprene rubber between the transformer and the case (normally by sticking it inside the case and then bolting it back together so there's slight pressure between it and the transformer.

Others manage to 'pot' the transformer by applying hot wax to the transformer to damp down the vibrations, although this could be dangerous if the transformer gets warm during use.


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Re: Should my power conditioner hum?

Postby Martin Walker » Thu Mar 23, 2017 10:41 pm

Just had another thought - devices originally intended for a US market that then get converted/updated for a European one are particularly prone to having under specced transformers, and the buzz could well not be that audible in the US lab, but far more noticeable over here.

It also has to be said that 'power conditioners' can be overkill - by all means have interference suppression in your studio, but having a dedicated 'conditioner' is rarely needed unless you have problems with your mains supply :headbang:


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Re: Should my power conditioner hum?

Postby Animesh » Thu Mar 23, 2017 11:23 pm

Thanks so much for your detailed reply Martin - I was hoping you might pop in with some thoughts!

It's definitely hum from the unit rather than hum in my audio. That's interesting you mentioned acoustic noise in the vibrating transformer cores. I might kindly ask a friend of mine who's far more adept at electrical engineering than me to attempt this particular operation (unless you fancy a trip to Surrey? There's plenty of hob nobs in it for you...!)

Martin Walker wrote:Just had another thought - devices originally intended for a US market that then get converted/updated for a European one are particularly prone to having under specced transformers, and the buzz could well not be that audible in the US lab, but far more noticeable over here. Martin

I spoke to a chap over in the US who uses a similar furman and claimed no such issues...maybe this could be the reason I'm experiencing something? Would this type of hum therefore be different from the vibrating core issue you mentioned?

Martin Walker wrote:It also has to be said that 'power conditioners' can be overkill - by all means have interference suppression in your studio, but having a dedicated 'conditioner' is rarely needed unless you have problems with your mains supply

Hehe, well I must say the "one button to rule them all" option was too much to resist! Saying that, if I can't easily resolve this I will switch out the power-conditioner in favour of trusty extension lead. My mains supply should be fine...the control room is on it's own isolated circuit from the rest of the building. The only problem that will then create is for my wife, as I'll then be left with a 1U space to fill in my rack!!

If I desperately did want to power up all my units at the touch of 1 button, would you happen to have any suggestions you're familiar with that world work well? (I have a feeling "extension chord with lots of sockets plugged into the wall and have your one switch there" might be the response!).
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Re: Should my power conditioner hum?

Postby Hugh Robjohns » Fri Mar 24, 2017 1:26 am

I agree with Martin that the acoustic hum is almost certainly a vibrating transformer, which is very common problem in US gear designed for 60Hz supplies when operated on European 50Hz mains.

I had a similar problem with a Mackie mixer and the neoprene sheet trick, to damp the vibrations in nearby metalwork, did the trick -- but do not mess with the insides of mains powered gear unless you are absolutely sure you know what you're doing!

If its purely the convenience of remote power switching that you're after, you could explore the various power distro options from EMO,

http://www.emosystems.co.uk/Products/Ma ... ystem.html

..or the switched mains distribution panels from any of the standard suppliers like Canford or Bryant. I use a Bryant SDU myself to power my gear up and down in a controlled way (monitor on last and off first, etc).

http://www.soundonsound.com/reviews/bry ... d-sdu-112p

There are also BES and PennElcom products that might suit.

http://www.dem-uk.com/bes/products/main ... ion_units/

http://www.penn-elcom.com/default.asp?MC=04120101&LG=EN

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Re: Should my power conditioner hum?

Postby Animesh » Fri Mar 24, 2017 10:11 am

Hi Hugh

Thanks for jumping in with your thoughts, I appreciate both you and Martin taking time out to help me - this annoying hum issues was really driving me bonkers!

That's great that you're both in agreement it's a vibrating transformer issue. It really seems bizarre to me that a reputed international manufacturer wouldn't ensure all markets it's products entered would be fit for purpose based on the dynamics of that particular market.

Thanks so much for posting links to some alternative solutions - in fact these are even better than my current solution, because I was wondering about how to bring my monitors into the "one button" solution without causing a "pop" every time the audio interface goes on and off - I'd heard of sequenced switching but never properly explored it thinking it would be cost prohibitive. But if the Bryant SDU is good enough for Hugh, it's good enough for me!

Martin, Hugh, thanks again for taking time to advise me, I'm so relieved to have found a route forward.

Wishing you both a wonderful day :)

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Re: Should my power conditioner hum?

Postby James Perrett » Fri Mar 24, 2017 1:43 pm

As others have said, humming US made gear is very common - and it isn't just the cheap stuff. My Eventide H3000 is one of the worst offenders. Mind you, I have a couple of UK made items that hum audibly too.
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Re: Should my power conditioner hum?

Postby BobTheDog » Sat Mar 25, 2017 12:27 pm

I have a USA furman, the transformer does vibrate. I found the best solution was not to screw the unit into the rack as it was transferring the "hum" to the rack which amplified it.
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Re: Should my power conditioner hum?

Postby ef37a » Sat Mar 25, 2017 1:05 pm

Bloody appalling IMHO!

In this age of superb but super cheap acoustical measuring equipment there is NO NEED for equipment NOT to have a specification for extraneous noise. I was battling this issue 40 odd years ago with 15kHz TV line whistle that many customers found drove them mad since the advent of almost Fe free chassis and <3mm plastic cabinets.

"We" went to the trouble of testing products on 60Hz mains. A big firm like Furman could surely generate 230V at 50Hz and reciprocate?

As Hugh says, do NOT tamper with the giblets. In any case there are strict rules about what damping materials may be used due to fire hazard. Also as mentioned, in UK at least we generally have a very clean (if expensive!) supply and such devices are really not needed. In fact, back in the day we found appliances like fridges needed the spike suppressor at THEIR mains point, once it "escaped" nothing seemed to stop it.

I am sure all the gear could easily be started/stopped from one outlet. If you want to avoid monitor "pop" but keep them on the same run to avoid earth loop problem, use a wireless mains switch. These default to off so the next time you power up the monitors will be off.

I find the wireless switchers most handy for gear where the mains outlet is down among the spiders and fluff.

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Re: Should my power conditioner hum?

Postby Animesh » Sat Mar 25, 2017 1:39 pm

James Perrett wrote:My Eventide H3000 is one of the worst offenders.

Hi James - thanks very much for posting! Did you manage to deal with your hum issue somehow or is it still ongoing? Did the advice offered by Martin & Hugh also potentially help you as an avenue to explore?

BobTheDog wrote:I have a USA furman, the transformer does vibrate. I found the best solution was not to screw the unit into the rack as it was transferring the "hum" to the rack which amplified it.

Hey Bob - thanks so much for sharing your experience. I have tried your suggestion and unfortunately the unit still does have quite an audible hum, but I'm really glad this worked for you. I also compared my existing unit with a brand new unit (sent to me by my suppliers out of the rack completely), and both emitted an acoustic hum, but the brand new one slightly higher pitched so even more annoying!

ef37a wrote:Bloody appalling IMHO!

In this age of superb but super cheap acoustical measuring equipment there is NO NEED for equipment NOT to have a specification for extraneous noise.

Thanks so much for posting Dave! Yes I completely agree with you I would have thought it standard QA practice if you're shipping internationally.

ef37a wrote:If you want to avoid monitor "pop" but keep them on the same run to avoid earth loop problem, use a wireless mains switch.

Wonderful, thanks so much for the tip there. I'll look some up!

This has been fantastic, I'm incredibly grateful to you all for taking time out to offer your experience and advice.

I think in light of all the advice and info, I've decided to part exchange my Furman unit for something akin to what Hugh has - the individually switched PDU. Though I'll also be looking into Dave's suggestion of a wireless mains switch. Either way, I think my love affair with Furman has ended...
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Re: Should my power conditioner hum?

Postby James Perrett » Sun Mar 26, 2017 10:43 pm

Haven't fixed the H3000 as it is mainly used as a comfort reverb for vocalists who are in a separate room.
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Re: Should my power conditioner hum?

Postby Guest271017 » Mon Mar 27, 2017 12:09 am

I googled why does power conditioner hum and got similar results. Interesting read here;

http://forums.stevehoffman.tv/threads/d ... um.145281/

If you had an O-scope, you could look at what's coming out of the wall.
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Re: Should my power conditioner hum?

Postby Animesh » Mon Mar 27, 2017 9:52 am


Thanks so much, that's incredibly kind of you to research this on my behalf! Sadly I don't have an O-scope...but perhaps the next time we have the electrician round we might take a look. I'm hoping to part-exchange on one of the Bryant individually switched PDUs that Hugh mentioned this week - so I'll report back on whether my control room is now hum free :-)

Thanks again for taking time out to help me, I really appreciate it!!
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Re: Should my power conditioner hum?

Postby ef37a » Mon Mar 27, 2017 11:23 am

I very much doubt there could be enough of a DC component on UK mains to come close to "saturating" the inductor in such a power conditioner.

Especially so since the poster stated "there was very little load on the system". Light load means low current so surely not a low enough path R to cause saturation? In any case a decent amount of DC would, IMHO cause other problems such as fuses blowing or breakers tripping out?

Suggestions of messing about with diodes and caps and MAINS should be firmly ignored!

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Re: Should my power conditioner hum?

Postby Guest271017 » Mon Mar 27, 2017 12:27 pm

DC riders are one part of it, but a mangled sine wave is another.

Not an electrical engineer or anything close and not questioning the veracity of anything said, but why are UK mains immune to this?

As stated in that article and others, both could be introduced inside the residence or down the street by a number of devices. Are there filters or conditioners on every service, at each building?

Just trying to get my head around it.

All I can think of is Keeping Up Appearances where Hyacinth Bucket rings the electric provider demanding she get clean, never been used electric delivered to her home lest it brush against her wall paper or fail to de-shoe before entering the residence.
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