Suffering from those transformer hum blues?

I have 2 Naim systems at home:

A mac 'n dac system in the office (mac mini, DAC-V1, NAP140, PMC wall mounted speakers)

The main system Roksan TT, CDS3/555PS, 52/SC/135s, ART Alnico speakers.

15 years ago, our house had the electricity sub-station virtually to itself.

The main system was on its own separate, 2.5mm2, radial circuit from the electrical distribution board.

The electrical supply was basically superb.

Over the last 15 years, 4,000 homes and a business park have been built, all with an infestation of switched mode power supplies, fridge freezers and other polluting electrical devices.  Worst of all, ethernet over mains, or powerline ethernet plugs, has become popular with many of our neighbours.

As a result, the power supply transformers in the main system all started to hum progressively more loudly as the years have gone by.

It reached the point where the hum was intrusive during low to medium volume listening sessions.  Much worse though has been the impact on sound quality of the system.  Female singers voices started to sound a bit relentless or "shouty" and strained.  The system became a bit tiring, harsh & relentless to listen to.

Naturally, I had several ideas about why this was occurring.  At first, I thought that it might be the "live" acoustic of the room - curtains had been replaced with wooden slatted blinds.  Some subtle acoustic treatment helped a bit but didn't solve the issue. The arrival of the ART speakers, with their far more revealing mid-range and tweeter drivers, compounded the situation.  Perhaps the new speakers were sounding a bit hard during the inevitable running-in period?  Finally, it has been a few years since the Naim boxes had been serviced, so perhaps this was the cause? 

Over the last 2 years, I have gradually worked through all of these potential root causes, addressing them in turn.  And still the system gradually worsened to the point where I have been enjoying the office system far more than either LP or CD on the main system.  If music is sounding a bit strident,  lifeless and uninvolving when played on a Naim CDS3 CD player, then something is wrong.

After consultation with several people, including Naim R&D, I have just installed a humungous Airlink Transformers balanced power supply.  It is effectively a very large mains transformer which decouples the external mains from the radial supply to the music system.  This is connected to the wall sockets in the living room with a new, 10mm2 radial circuit.  It's a beast.

N.B.: This is not something to be undertaken lightly.  And it MUST be done by a qualified electrician for reasons of safety.  Double pole isolation breakers MUST be used (Airlink fit them as standard to the balanced power supply unit).

The result?  Music suddenly sounds sweet as a nut again.  Just sit back, relax and enjoy natural, flowing music again.  No more shouty female singers.  No more harsh sounding instruments.  The sound is warmer and richer, flowing, more detailed, more dynamic and images better.  Transients like drums and cymbals jump out in a more lifelike, dynamic way.  Most importantly, It is enjoyable and emotionally involving again.

Downsides?  I suspect that it is fractionally, very fractionally slower.  It takes about a minute to adjust, then I don't notice anymore, just get on with enjoying the music and ignoring the system.

I have subsequently tried an ISOL-8 LC unit to see if it made any difference.  It made no improvement and slowed the music down a bit too much for me.  I suspect that it was trying to do what the Airlink unit had already done upstream, so there was no benefit in this installation.  Perhaps it would have helped if the Airlink unit had not been installed - we will never know for sure.

Oh, and all the transformer hum in the Naim power supplies caused by offset DC voltages?  Gone.

Ah, the wonderful sound of silence.

Food for thought for those of us with dirty mains.  

And that is becoming the majority of us in the UK I suspect...