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Transformers humimg........again

Yes I'm starting a new transformer hum thread. I read through most of the others, but did not find the info I was after, sorry.
Let's start. I have a dedicated 20A line for my audio gear. Gear consists of a BPT 3.5 Signature ac isolator, Jolida JD9 II phono pre, Naim 5i-2 int. amp., two REL T-5 subs, and a Clearaudio Concept TT. Now the important part, ALL components that utilize a transformer (BPT, Naim, REL's) all have transformer hum. And yes, it is transformer hum, NOT sound from the speakers. I had a buddy, who's an electrician, over last night, and we tore everything apart from the main box to the outlet, no results. Tried many other outlets in the house, with and without the BPT unit. No difference, all transformers still humming, whether alone or not. Unfortunately, my power is fed to my house from overhead lines, but so be it. I can't change that unless I move.
Question to answer, "what can I do to stop the transformers from humming?" The hum is not overwhelming, fairly subtle actually, but nonetheless, it is something I would like to eliminate.
Can anyone offer experienced or educated replies?

Thanks :)
128x128shawnlh
yogiboy's avatar
yogiboy
5,612 posts
 
You should bring one of the culprits over to a friends house and see if it has a hum problem in another house. It might not be your house wiring causing the problem!
shawnlh's avatar
shawnlh OP
37 posts
 
I had taken a couple of the pieces down to my local hifi shop. We plugged them in, no hum. And that was straight into the wall socket, no filtering of any kind. I just happen to be cursed with bad ac into my home. I will take all suggestions here, apply them, and hope for something to work.
roscoeiii's avatar
roscoeiii
1,155 posts
 
I'll also suggest an AVA Humdinger. They have a 30 day return policy, and maybe giving AVA a call would be a good call.

If they for some reason also don't want to sell you one, shoot me a message and we can see about having you try my Humdinger out in your system.
truman
167 posts
 
PS Audio AC regenerator. PS Audio P-5 or P-10.
Should get it, I'd think.
atmasphere's avatar
atmasphere
11,749 posts
 
There are two things that cause transformers to hum, both on the AC line.

This BTW is especially true if you have toroidal power transformers.

The first is what is often called 'DC on the line' which is usually caused by a heater of some sort operating on half power so it is only drawing power when the line goes positive. This causes one half of the AC sine wave to have slightly less voltage.

This can be blocked by a fairly simple circuit- a diode and capacitor arrangement (several members have mentioned one already on this thread), that blocks the DC and thus corrects the waveform. Toroids saturate fairly easily so only a very small amount of DC (less than 1/4 volt) can make them pretty noisy. It is possible to install the DC Blocker on the line that feeds the audio room.

The second thing that can cause transformers of all types to become noisy is the 5th harmonic on the line- in the US we use the 60Hz line frequency so this would be 300Hz. The harmonic is caused by a transformer that is being used above 1/2 of its full rated capacity. This might be a transformer on a telephone pole that you and your neighbors all use. There are two solutions- have the utility replace the transformer (good luck with that, but I've seen that happen) or get a power conditioner that can block the 5th harmonic.

In regard to the latter I don't know of a 'high end audio' conditioner that can do that (OK the regenerator types can but you have to be really careful with their use to not re-introduce the same problem), but there are commercial/industrial units made that can. Elgar used to make such some years back and they are quite effective. You can find them used on ebay (the series 3000 and 6000 are the best examples). BTW they can block DC on the line too.
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