Transformer hum - what to do?

A first simple step would be to switch everything off in your own house and see if the hum goes away. Even disconnect microwaves, fridges etcetera entirely.

This would at least tell you if there is some device in your house which is causing this hum.

In my case, the fridge is quite old (1993) and when it switches on, the hum increases terribly. Since the SuperNait is in a different room, it is not really an issue for me.

Thanks for that - easy enough to do at the main consumer unit.

The vast majority of mains 'conditioners' won't eliminate hum at all (and most will degrade the musicality of the system).

As MarkAH says, unplugging / isolating everything else in the house to identify internal culprits is the first step; after that...

If the hum is being induced by the quality of the mains electricity supply (i.e. an asymmetric waveform being supplied to your house), then it's usual that the loudness of the hum varies from time to time.  If the hum is constant and unvarying, then it's probably just a fact of that particular transformer (all transformers hum, it's just a question of how loud they hum).

If the hum is from the electricity supply there are two approaches that work.  One is to use a very large isolation transformer near the CU (preferably wired CTE); this should be installed professionally.  The other is to use a "DC blocking" filter near the equipment.

I would disconnect one of the power supplies, take it to a friends house and plug it in and see if it hums in this totally different location, environment, then you would be assured it's your current home, location that is the source of the problem and not the equipment.

It may be worth the trouble to at least ease your mind.

Hi Markah, you have a great system! I suffered from a randomly humming Hicap DR and similar on the 300PS but less frequently. It was quite annoying so I've bought an Isol-8 DC blocker (high current version) on an auction site just to see if it was going to work and it did, the humming is completely gone! The hicap was also suffering from a constant very low level hum that has disappeared. 

Hi Markah, very sorry to read of your situation.

First, as others have said, try disconnecting the likely culprits that are polluting the mains at home to isolate the villain. It maybe a fridge, hair dryer etc. If you find the villain, then replace it.

If this doesn't work, read Huge's post above, as he has had some success with transformer hum.

Finally, if all else fails, do a search on this forum for a thread called "suffering from those transformer hum blues?" It is one of my threads. I tried several options before finding one that works beautifully for us.

Hope this helps, FT

Thanks to all for the helpful comments so far, I'll try them out and report back.

markah posted:

Thanks to all for the helpful comments so far, I'll try them out and report back.

Happy Weekend

Good luck, hope you find something easy to fix inside the house, it's much simpler that way.

Make it a problem for your dealer to sort out

One known problem is if the house has led lighting, as this is notorious for inducing dirty electrical supplies

IT COULD BE TO THE DESIGN of the laminations and the clamping method.  or simply the position of the psu.  in 50yrs of audio I haven't any problem with hum,

Tried switching off all the other circuits in the house first of all and also plugged the NAP300 power supply (the worst offender) in a socket in another room and in all circumstances the unit still hummed. My dealer has taken it away now to try at the shop.

At least this has eliminated any other equipment or devices within the house that could have been causing the problem. I'll wait and see what he says now once it has been tried elsewhere and take it from there.

Huge posted:

The vast majority of mains 'conditioners' won't eliminate hum at all (and most will degrade the musicality of the system).

As MarkAH says, unplugging / isolating everything else in the house to identify internal culprits is the first step; after that...

If the hum is being induced by the quality of the mains electricity supply (i.e. an asymmetric waveform being supplied to your house), then it's usual that the loudness of the hum varies from time to time.  If the hum is constant and unvarying, then it's probably just a fact of that particular transformer (all transformers hum, it's just a question of how loud they hum).

If the hum is from the electricity supply there are two approaches that work.  One is to use a very large isolation transformer near the CU (preferably wired CTE); this should be installed professionally.  The other is to use a "DC blocking" filter near the equipment.

Huge - as in my previous post no "internal culprits" were found.

The loudness of the hum does vary which leads to the conclusion that it probably is a mains issue.

"Wired CTE" - could you explain what that means please? Do the two methods of eliminating the hum that you mention have any effect on the sound quality reproduced?

Thanks, Mark

Wired CTE means the transformer's secondary is wired center tap to earth.  This results in a balanced isolation transformer, in other words the voltages on the live and neutral lines are mirror images of each other (each are 115V AC, and the difference between them is 230V AC).  To ensure no detriment to sound quality the isolation transformer needs to have a high VA rating 3000VA - 5000VA are recommended.  Note this should be installed near the CU as this transformer may well hum like a beehive!

The other alternative is a series capacitor filter, there are some commercial versions available and these vary in quality.  I built my own version of one of these.

Chrissw19 posted:

It was quite annoying so I've bought an Isol-8 DC blocker (high current version) on an auction site just to see if it was going to work and it did, the humming is completely gone! The hicap was also suffering from a constant very low level hum that has disappeared. 

+1

Isol-8 DC blocker did the magic here as well -- intermittent transformer blues but nonetheless very annoying. So definitively worth a try. I got an Isol-8 DC blocker for home demo for about one week to be sure that the hum was gone before placing an order. 

My hum went away completely with isotek evo3 dc-killer, if thats your problem. Worth a try as its a very simple fix if u can demo. Br Lars

A bit late to the party... in my case 555PSs and SuperCap hum when the heating pump in the basement goes on. So in the winter I get humming PSUs and in the summer as is quiet on the Eastern front. It polutes quite badly up through the mains.

If you have more than 2 phases running into the house, you could ask your electrician to try and swap the dedidacted mains one with another. Your audio circuit might be picking up some distorted wave-forms from your neighbours, from the trafo station down the road.

Also late, but :

1st. Move, 

2nd. Forget about Naim

3rd. Take Foot Tappers Advice! 

But seriously it's those massive Transformers. in my particular case, it depends on the time of the day, Sundays are usually beautiful businesses are down, or either later in the evening, when the electrical grid is not operating at it's maximum. 

Thanks Foot Tapper, I'm taking your lead!

Is it possible to rearrange the room so that you are further away from the boxes? My 300 hums but 2m away I never notice it.

Stu

stuart.ashen posted:

Is it possible to rearrange the room so that you are further away from the boxes? My 300 hums but 2m away I never notice it.

Stu

Hi Stu,

Initially I was going to jump in here with a big "no", which holds true for the half of the room where the hifi is situated at the moment. It could be a possibility though to move the listening area to the other half of the room (that's basically what we use as a formal dining area, separated by a big archway). Food for thought................ and thanks for the suggestion.

Mark

Power supply/transformer hum that is audible from your listening position is nasty... 

My HiCap and 200 have a slight hum too but it's only audible within 2/3 ft. from the components. As suggested earlier in this topic, a DC terminator could work very well. I tried one and everything went completely silent instantly. I didn't keep it 'cos the hum doesn't bother me so there was no need to add an extra component in the mains supply. 

A good dedicated spur could solve things too. A good thing to have in any case btw. 

At least its both free and reversable Mark. Good luck regardless.

Stu

Latest update - the NAP300 power supply is still humming at the dealers, they even tried fitting a felt pad at the transformer but no improvement. They will be in touch with Naim on Tuesday to see what they say. 

Sounds like it's just a transformer that hums anyway.  It's not uncommon with large toroidal transformers the bigger the transformer the more the hum - and that's a large torroidal!

Mine also hums a bit - so I just hum along with it.
Even though it doesn't know the words (or the tune), great music still comes out of the speakers.