Ok, as promised, results of tests with various filters, power cables etc...

First test on my own system, Arcam DV-79, AVR-250, Mordaunt-Short Avant
908/905C/903S speakers, B&W ASW-1000 sub, Audio Innovations Silver
Bi-Wire speaker cable.

As promised, I've been loaned an Isotek power cable (£60) in order to
carry out these tests. I was also loaned an Isotek power distribution
block (not sure of price, I think they're about £150).

For comparison, I also used a standard IEC mains cable, and an IEC cable
with a filtered plug.

I normally have my system plugged in via a Masterplug surge protected
and RFI-filtered 4-way distribution block, £8 trade or £20 retail.

For a test track I decided to use "So Far Away", from Dire Straits'
"Brothers In Arms" CD. The version in question is the SBM remaster.

Two other people were also present. One person was unsure, the other was
a complete sceptic.

First things first, I plugged the DVD player and amplifier into an
unfiltered block. I then played the test track.

I then switched power cables on the DVD player to use the Isotek, and
played the track again. This made no difference whatsoever - which is to
be expected, as the DVD player is merely acting as a transport. I
switched cables back again and played the test track to be sure, and
indeed there was no difference.

I then switched the power cable on the amplifier to use the Isotek
cable. Immediately there was an improvement in dynamics, percussion in
particular had much more presence and depth.

I switched back to the standard IEC cable and listened again to ensure
that there was in fact a difference and that I wasn't imagining things.
The sound seemed flat after switching back.

Next I tried the standard cable with filtered plug. This again made
quite a dramatic difference to dynamics. Perhaps not quite so much as
the Isotek cable, but that may be the psychological bit coming into
play. But maybe not, as later tests showed.

I then brought filtered mains distribution blocks into play, and tried
various combinations of esoteric and generic branded filters, unfiltered
cables etc.

What I discovered (and the two other people in the room also heard quite
clearly) was that a filtered distribution block makes a difference, but
there did not appear to be any audible difference between the Isotek
block at £150 or the Masterplug block. Both have RFI filtering and surge
protection, the Isotek has a metal case, the Masterplug is plastic. But
none of us could hear a difference between them.

Also, the Isotek cable sounded exactly the same when plugged into an
unfiltered or filtered block. The generic filtered cable sounded
slightly better when connected via an RFI filtered block.

The combination of generic filtered cable and Masterplug filtered block
sounded as good as using the £60 Isotek cable. Both sounded
significantly better than using an unfiltered cable.

So on this basis I would recommend the Masterplug filtered 4-way block,
£8 from CPC or anything up to £20 retail, along with a filtered plug on
the IEC cable (costs about £3.50 from CPC, not sure about retail).

However, the next part of the test was interesting. We then went around
to a friend's house, who has a similar setup to mine - Arcam CD73, A90,
B&W DM603 speakers, QED speaker cables (not sure which one, but nice and
thick).

We then performed the same series of tests, and obtained a similar set
of results. However, the differences on his system weren't anywhere near
as dramatic as on mine.

So we then shut down and unplugged his PC, in the next room but on the
same ring main, and repeated the experiments.

This time the differences were negligibly small. We heard a tiny
improvement when using either the Isotek or generic filtered cables, and
a similar improvement when using the filtered mains blocks. This time we
didn't hear any difference between a filtered and unfiltered IEC cable
when used with a filtered block.

We plugged the PC back in and fired it up again, and repeated several
times for consistency. Once again the results with filtered mains were
much more noticeable when the PC was turned on.

So, in summary:

If you don't have any computer equipment (or anything with switch-mode
power supplies) on the same ring main as your hi-fi, buy a Masterplug
RFI filtered 4-way strip, if for no other reason than it incorporates
surge protection, so will protect your kit against voltage spikes.
(Believe me, I've seen quite a few PSUs fried by this type of thing.) If
it makes it sound better then that's a bonus. If it doesn't, well, at
least you know your equipment is protected.

If you have one or two PCs in the house that aren't left on all the
time, get the RFI filtered block. Try using a filtered IEC cable and
listen, if it makes a difference then keep using it.

If you've got a miniature version of Docklands Telehouse in your attic
or spare room, stick an RFI filtered 4-way block in, then use filtered
power cables from that. It's also probably worth putting filtered cables
on your PCs and other items with SMPSUs, as then you'll tackle the
problem at source (and additionally protect *that* expensive equipment
from spikes).

In the meantime, I appear to have "won" an Isotek power cable worth £60.
They want the distribution block back, but they've said I can hang on to
the power cable for now. Might try opening up the plug and see exactly
what type of filter they've put in...

--
Glenn Richards Tel: (01453) 845735
Squirrel Solutions http://www.squirrelsolutions.co.uk/

IT consultancy, hardware and software support, broadband installation