Macca's System Blog

[kazam]

Zebbo,

I've just PM'd you re: an available AG1500, just in case it is of interest..

[Dr Bunsen Honeydew]

Here is a very good article on DC in the mains. In his conclusion he shows the circuit for a classic capacitor based DC blocker. The problem is in electronics nothing is a free lunch, solve one problem and create another. This circuit will increase the line impedance of the mains supply considerably as it is a filter. This will have the effect of sitting on the dynamics and separation in the music feeding off this mains supply - so cure buzz v lose some music.

http://sound.westhost.com/articles/xfmr-dc.htm

[BilliumB]

So, I think that you're saying that there is NO negative effect, apart from the directly audible hum, from a buzzing transformer in an amplifier as a result of dc on the mains - are you convinced there are no other resultant knock-on effects? My limited experience is that the DC Blocker I'm using not only has a major effect on the buzzing, but that with it in place the music seems to 'open-up' also. Perhaps the mains is much worse than normal at my place.

What does a heavily buzzing transformer 'look like' electrically - are there any knock-on impedance effects, does it feed 'rubbish' back into the mains? What about the vibrations within the box and Impact on adjacent electronics?

I realise the blocker will have an impedance impact (and mentioned this in my post) - do have a look at the sjostromaudio.com site, they provide circuit diagrams etc; maybe the 'very thick copper traces' on the pcb are helping in this area!

Has anyone else done any experiments?

Cheers. Bill

[jammy395]

Bill (Wild Bill)...Humour me...
Nowt can be gained by fukin about with Main's .....
Trust me im a Spark....
If your hifi sounds shit......I suggest you go right back to basics.

ta

[Dr Bunsen Honeydew]

I don't think you understand, you need to read about inductance and transformers. A transformer is a DC blocker in itself, only AC can pass as an inducted signal. Put a DC voltage on the primary side of a transformer and there will be no voltage inducted onto the secondary side. So what you hear rattling from the BMU transformer is the primary coil, there will be no DC on the secondary, and that is why IF the transformer in the amplifiers connected to the BMU have noisy transformers then it is not DC causing it. Most likely cause is waveform distortion on the AC or more likely offset voltage where either the pos or neg side of the wave is over voltage, that sets up resonance in transformer coils the same as the DC does. The mains in the UK is simply CRAP and it is time we started to complain about it as the generating companies have a statutory right to keep the mains clean.

Small amounts of DC on the mains has no other effect than to make mains transformers rattle their primary coils, and the bigger the coil (transformer VA) the louder the rattle, which will also have tendency to get hotter than normal because of it.

The way some people have solved this problem completely is to install a large industrial one to one isolation transformer next to the consumer unit, this removes DC, then have a radial circuit feeding a BMU which then feeds the Hi-Fi. Most recording studios do this.

And Jammy really that is the wrong advice for hi-fi, but is the right advice for everything else.

Recording studios have the same problems we have but more so - so here you can see how complex the solutions can be. http://www.recordingmag.com/resources/r ... l/139.html

But in reality a national campaign to clean up our mains is needed, but most people don't realise, unless they are hi-fi buffs, how bad it is. AND a lot worse here than in most of the rest of the world because of our cheapskate systems installed after the war. People just put up with fridge motors failing in a few years when they should last indefinitely = bad mains. We pay top rate for it so we should get a top product instead of the crap they are feeding us.

[BilliumB]

Thanks for the detailed response. If possible, perhaps we could put my knowledge to one side (I think I do basically understand - many years ago BSc in Electronics at Southampton, plus a number of years working on fast jet aircraft audio systems, plus other relevant jobs, gave me a fair understanding even if it's a bit rusty).

So, what are your thoughts on the knock-on impacts of a loudly buzzing primary winding?

Do you think there will be more 'crap' injected back into the mains?

Do you thing the vibrations are an issue for adjacent electronics?

I'm sure we'd all like much better mains quality, but I don't realistically think I'm going to get it out here in the sticks, with milking machines and other noisy kit on neighbouring farms.

I've been considering a large transformer next to a new dedicated consumer unit (plus radial, earths etc, on a TT system and understand safety issues) - might it be better to make this a large balanced transformer feeding the radial, rather than having a transformer at each end?

Cheers. Bill

[_D_S_J_R_]

The only seriously buzzy transformers I remember were from some US import amps that usually ran silently in the home country (115V) and of course Naim amps/supplies - sometimes the supplies buzzed more than the power amps!

I've had a few NVA amps through here, currently an AP70 with two transformers in it and, apart from a 'booooooiiiiiinnnnngggg' on switch-on, there's no other mechanical noises at all...

[Dr Bunsen Honeydew]

Dave it depends on your mains, you are lucky there, and you would find the Naims would be fine. It depends where you use them and mains in this country varies from good to next to useless.

[Dr Bunsen Honeydew]

Buzzing transformers will not do any harm to anything or generate anything. The primary coil is just a bit of enamelled copper (or alluminium) coiled wire with an impedance, it is made to buzz because it is being stimulated by a "hiccup" in the AC waveform passing through it, which is the DC. The DC is there already, the mains is crap already, you are not contributing to it with the transformer.

Consumer Unit - isolation transformer - radial circuit - BMU, that is all you need. For icing on the cake use the old British standard 15 amp round pin not 13 amp fused square pin plugs.

[BilliumB]

Won't the vibration of the primary winding within its field create some sort of 'back emf' - I suppose you feel that this effect will be very small? Might the vibration of the transformer cause a vibrating field around the transformer itself, and this cause induced currents in circuits close by? I'm just thinking aloud, as the reduction in transformer buzz in my system has gone hand in glove with an improvement in 'musicality' and I'd like to understand what's happening - as I think you're telling me it should have got worse with the DC Blocker!

I understand that you don't think the physical vibrations will have any impact on anything at all - interesting.

Going back to the new radial set-up, I was wondering whether I could save on a transformer - do you not think it a reasonable approach (I seem to remember that this is the approach taken by Equitech in the USA)?

On a separate matter, what sort of improvement do you think can come from better earths (bearing in mind that I'm on a TT system, so don't have the safety problems you get with a PME set-up)? I've been considering multiple earth spikes, or some sort of earth mat (I've got a digger, so earthworks are not really a problem apart from the mess).

I'm also considering a coax earth cable (screen and conductor connected at earth end, conductor only connected at kit end, possibly with a suitable in-line capacitor to limit dc current flow for safety) in addition to normal earth cable, using the coax as a low impedance route to earth for higher frequencies - have not yet decided on best earth termination at the 'earth' end, but wondering, in addition to normal earth spikes, if I could make good use of my old water well and some stainless steel plate! Some papers seem to recommend chrome plated material for the earth 'spike'. Wondering about WT125 or something a bit more meaty for the coax. Clearly safety is paramount, then need to be sure on corrosion issues as I don't want to turn the coax earth into some sort of rf detector.

Thanks for your interest.

Cheers. Bill