Noise and DC on mains and new radial

eagle3333 posted:

Am I allowed to ask those who are happy with their dedicated mains what make/model of MCB/RCB/RCBO are you using? I'll acquire the most popular and try swapping in to see if it makes any difference..

Mine is an MK 4 way consumer unit. Two ways filled by a 100 amp DP switch, the other two each with MK 32 amp type C MCBs (I put a new circuit in two different rooms.) No RCDs.

Foot tapper posted:

Hi Ian,

If your goal is to reduce mains transformer hum from your NAP250 without reducing dynamics or speed of the system, then the Airlink BPS worked very well for me. The icing on the cake was the ability to reduce the output voltage from 240V to 230V.

I have been careful to ensure that the whole hifi is powered off the BPS, as the earthing is different for anything that is not powered off the BPS. If you link your hifi to an AV system, this is an important care point.

I do hope that the BPS works out for you after such a painful journey with the radial supply. My radial is just 10mm2 twin and earth from the main household distribution unit. 

Best regards, FT

So, the AV system link would be ok if you have an earth loop isolator, which is itself an isolating transformer?

My main question was whether the balanced PS stops the possibility of the local TT spike becoming the earth for the nearby properties and substation because it isolates the spike from the outside world?

Keith

If you have a TT earth, then that earth is connected in your property only - that's how TT (Terra-Terra earthing) works.

The problem occurs when someone connects an additional earth spike to a TN-S or TN-C-S (i.e. PME) system.

Hi Huge,

Yes, but would a Balanced PS isolate the PME from the TT connected to the hi fi, thus removing the issue? The spur (ring in my case) is earthed to the PME supply, the hifi is earthed to the spike (because the ring isn't connected at the socket end, as per Naim's method) and the two would be separated by a balanced isolating transformer, if I installed one.

So that's all good then?

The electrician says, the two earths are already isolated, by the way.

If you don't have a connection from the PME earth to the TT earth, then the earths will be isolated (as now and also with an isolation transformer).

If you connect the centre tap to the TT earth then it will be fine, it will be working as a TT system with balanced lines.

If you connect the centre tap to the PME earth and the socket earth to the TT earth, then it will be less precisely balanced but the earths are still isolated as now.  However I'd recommend against this, even though it should still be safe.

What you shouldn't do is connect the PME earth to the TT earth.
What you should do is to have an RCD on any system (or part of a system) with a TT earth.
          This is not required in the regulations but it's recommended for safety reasons, and it's unwise to not do it.

Hi Eagle, 

Does the Airlink have "in" and "out" sockets so you plug it in at the wall and the distribution block (Music Works in my case)? Is it that easy? If so, I may give it a bash, although there's not much room behind my rack. It's not very expensive so worth a punt, although I notice others are charging a heck of a lot more.

Keith

The others are more expensive because they are sprinkled liberally with magic sound dust, Keith.. 

I recommend to check out their website. They do models with outbound plug sockets; not sure if they're powered by a plug lead.. I'm getting the one without - my electrician will wire it into the 'meter' cupboard away from the hifi. (It's not impossible that it may hum at times of high DC) Wiring it in is a very modest job for the sparky. To work out which VA rating you need, Mike recommends to calculate the total draw of everything that will be connected to it, double it and get the model with the next highest rating. What's awkward for me is that if I end up having to leave the hifi on the house ring, the draw is much bigger than on the hifi radial. So I guess I have to play safe and cater for biggest - which unfortunately means a bigger spend.. 

Right, so my consumer unit is in a plastic box thing by the front door, dead close to the garage. The balanced PS would go at that end, in the garage, but not connected to the supplier earth. The TT would need to be reconnected to the radial (ring), presumably.

I would need to consult the sparks to understand properly.

I can finish off my experiences now. The BPS has just gone in and the radial had a few weeks burn in. 

1) The TT earth continued to make little or no difference to SQ. So we're using the main PME earth.

2) The BPS has killed all transformer hum. Excellent. It has had no discernible, negative impact on SQ whatsoever. Whether it's had a positive one I'm unsure because I can't remember precisely how it sounded pre-BPS. It's possible that clarity is increased.

3) The radial 'sound' is very detailed especially in upper registers. Crystal clear. And fast - it's very dynamic, but feels a little compressed. On the house ring it is definitely slower, warmer, more relaxed, more holographic, bigger staging; bass guitar is much more in evidence; the leading edges are less brittle. I prefer latter and won't be using the radial.

Maybe the dedicated radial is resulting in more honest SQ. Many people would probably be very happy with the incredibly detailed result. But it would tire me listening to it for long. If the SQ off the ring is being 'coloured' or just can't find the same quality of detail, I don't care - it's more 'musical' and involving to me. Less analytical. Less digital. What's odd is that the ring's soundstage is still so much bigger and the bass far more noticeable. 

So there you have it. I think I had a pretty good mains supply in the first place; if you do, too, don't expect all the fanfare about a dedicated supply to necessarily improve SQ for you. I discussed with Naim and they were unable to offer up any thoughts other than 'the answer is that you prefer one over the other; that's really all you need to know.' Fair enough.

Now, if only there was a way to get the BPS in the ring immediately before the hifi socket without having to take the wall apart...

KRM posted:

Yes, but would a Balanced PS isolate the PME from the TT connected to the hi fi, thus removing the issue? The spur (ring in my case) is earthed to the PME supply, the hifi is earthed to the spike (because the ring isn't connected at the socket end, as per Naim's method) and the two would be separated by a balanced isolating transformer, if I installed one.

 

Hi Keith - whether you use a balanced mains transformer or not is irrelevant .. the issue is at the master supply demarcation point  the earth and the neutral is combined with PME TN-CS supplies. With a TT supply the earth is bonded to ground instead of neutral at the demarcation. The issue comes when the PME bonded neutral / earth supply supply earth wire flows through to a bonded earth / ground electrode in an invalid wiring setup (i.e. an earth electrode is added to a PME supply) .... This would mean that if there was a fault in the neutral feed of the PME distribution from the sub station (damaged wire, JCV snagging, storm damage low voltage overhead etc), then the entire local substation could momentarily flow through your local earth electrode - possibly causing a rather short but  intensive indoor fireworks display whilst everyone's  lights dimmed in the neighbourhood/locale

So the issue is with the earthing wires - and not the balanced neutral/live downstream from the master demarcation  point.

Where the earth's are decoupled the issue becomes physical touch separation between the two earth zones.