Because I’ve had issues with noise on my mains, I am curious about balanced mains units. At the moment I have DC blocker at the power amp which works but I am wondering if I can reduce noise on power to the whole system.
Balanced mains units vary wildly in price. I’ve seen HiFi brand 1000VA, 230v, 4.35 amp twin gang units like the Russ Andrews BMU ones, then there are some more basic looking industrial options that are about quarter of the price.
If I understand the principle, instead of +230v -0v the balanced mains unit provides +115v -115v so any noise on one side is cancelled out by the ‘inverse noise’ on the other.
My system is not ultra high-end and a BMU would be hidden away so it doesn’t matter if it looks like it belongs on a factory workbench, presumably it will still provide a noise-cancelling effect or is it not worth bothering with and just wait for a pre-owned 1KVA audio-grade balanced transformer to come up?
I got an Airlink unit for my system a couple of years ago and felt it made a huge difference in eliminating transformer hum with no apparent degradation in the sound quality. Don’t use it now as I’m gone to Linn in the main system.
Thanks, that’s exactly what I was wondering. The Airlink unit is the type of thing I had in mind, industrial looking but it is still an isolation transformer with RFI & EMI screening for audio applications - probably good enough for my setup, or in any case, an improvement over the current noisy mains.
I use an Airlink 3KVA supply on my whole system and have done for years.
Don’t be drawn into the so called “audio grade” supply’s. They all do the same thing, it’s just that some have a lot more fairy dust and snake oil sprinkled over them to justify being 4 times the price. Also don’t go for a 1KVA supply. A 3KVA supply will not get saturated when your power amp is drawing on it heavily, a 1KVA will be swamped. You don’t need to hide it away either, a tin of matt black spray and it will blend in. Mine is sitting on the bottom right hand side of my rack.
A slightly more technical question - if some equipment is plugged into the balanced power supply and some is connected to standard mains, then you connect that equipment together using analogue or digital interconnects, does that create any noise/ground loop etc. issues?
For example, my naim pre-amp/source & power-amp would be plugged into the BMU but my AVR, Subwoofer, games console, blu-ray player, TV, network switch, NAS, router would all be plugged into a power strip plugged into the normal ring-main.
The network switch, subwoofer and AVR will be connected to my pre-amp (NAC 272) but not powered by the BMU. Does it matter if some components are powered by the BMU and some are not?
There are potential safety issues relating to the use of balanced mains units. Consult with the likes of Airlink and a professional qualified electrician before proceeding. HiFi forums are not the place for advice relating to electrical safety, imo.
Depends Ad nauseam where you are, we don’t know, so don’t ask, regs differ the world over. You could end up with seriously bad, dangerous or illegal advice.
Martin
Safety issues? Illegal advice? Can you be any more specific?
Usually in the UK you’re pretty safe buying consumer grade electrical equipment that conforms to British Standards etc. Plenty of retailers sell balanced mains units, could you at least hint at what you think the hazard is under normal operation assuming the BMU hasn’t been sold with a latent manufacturing defect?
Airlink FAQ for example seems to cover worst case most credible scenario:
"For an electric shock risk the following two faults would have to occur at the same time: (i) a short circuit occurring between either the mains live or the mains neutral to the case or earthed points of the equipment (a catastrophic event) and (ii) the earth connection would need to be disconnected with the equipment mains fuse blown and a short circuit occurring between the equipment live earth (a catastrophic event), current could still flow inside the faulty equipment
In other words there would need to be a catastrophic failure of the audio/visual equipment for either scenario to occur.
In a situation where just one item of equipment attached to the supply fails and takes out its own input fuse, it is the case that the neutral within that unit will still be powered to half of the mains voltage. Given the safety requirements for all consumer equipment it is highly unlikely that this neutral voltage would become hazardous as, if this were to somehow short to the equipment chassis, it would cause a neutral to earth current path which would then trip/blow the input breaker/fuse of the balanced supply."
Thanks for the replies. Stupid question time, do these Airlink BMU units not simply just plug into the wall like those shown below? Otherwise I don’t really understand the sudden concern and need to get electricians involved etc.
You can get these and plug them into a wall socket, using them like a regular mains block. There are other types which you can wire straight off the consumer unit so that the circuit going to your listening room is balanced to all wall sockets. That’s what they’ll be referring to as needing to be professionally installed.
Thanks Chris, I was confused by the all the sudden concern. Any kit I buy will simply be a domestic/consumer grade CE marked unit that plugs into the wall socket of my house (that was professionally rewired this year and has a modern consumer unit). I am also willing to risk that the build standard of my naim pre/power-amp is good enough for it not to randomly start shorting out to the chassis.
In theory it’s possible that the transformer in the balanced power supply will hum instead of the one in your Naim box. So having it located out of earshot would be a benefit of a wired in unit.
In practice I have yet to find a non-Naim transformer that hums loud enough to be annoying, and I’ve yet to find a Naim transformer that doesn’t, so I suspect this is not likely to be a problem in practice.
Here is a photograph of our 5kVA Airlink BPS as installed by a qualified electrician in the radial supply to our living room.
It’s the mid-grey cube with the blue & black isolator switches on the front:
