2. amps-preamps
  3. 1427575925

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 :)
shawnlh

Showing 3 responses by atmasphere

atmasphere's avatar
atmasphere
12,174 posts
 
A balanced transformer does not seem to sort the problem of DC on the line although it does have advantages.

There is a simple circuit consisting of a bridge rectifier and four electrolytic capacitors (bypassing the rectifiers in the bridge in reverse bias mode) that can block DC. They are effective enough and cheap enough that they are often included in equipment to help prevent the noisy transformer issue.

http://www.diyaudio.com/forums/solid-state/2080-dc-filter-16.html
Scroll down to post 159.

They can also be inserted in the AC line although this should be done by a qualified technician. The circuit is compact enough that it can be installed in an electrical junction box.
atmasphere's avatar
atmasphere
12,174 posts
 
What is your line voltage? It should not exceed 125V for more than a second. If its high that could explain the problem. The PS Audio should be able to correct that.
atmasphere's avatar
atmasphere
12,174 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.
More to discover