"Glenn Richards" wrote in message
...
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 this friend who believes his ears demand fancy speaker cables had never
noticed that his computer was degrading the sound of his system?

With two friends, you had the opportunity to do the test blind. Why didn't you?

Does anyone know what frequencies are removed by mains filters? How should I
choose between them? Is there a standard? Do they all offer the same
attenuation?

If not then, as with fancy speaker cables, what explains the variety when they
all have the same purpose?

cheers, Ian

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