Audio Note M10 Signature - Manual (Page 7)

Andy Grove, Designer in Chief for Audio Note (UK) explains some of the
development process behind our new statement line stage: -
"I realised the core concept of the M10 power supply "Galahad" while I was doing
some theoretical work on amplifier topologies. I was analysing compound amplifiers
which are connected by bridge circuits, or in other ways, such that one amplifier will
correct the output of the other by subtracting distortion from the output. QUAD
"Current Dumping" is one such configuration of the many possible.
What I came to think was that, theoretically at least, one could build a simple circuit
using a single valve which could completely reject not only all voltage fluctuations
from the mains, but which would, to all intents and purposes, be entirely isolated from
the mains in every way. Not only that but the output impedance of the supply would
be fixed, even across the audio band, and all this would be achieved without high
feedback or complex "engineer's ego trip" solutions with hundreds of active devices.
The way this would work, essentially, is that I would use a shunt valve to look ahead
at the incoming fluctuations, and to pass a current such that the fluctuations are
completely removed. This isn't possible with a feedback topology; for feedback to
work there must necessarily be an error to correct. The circuit looks at the error at the
output and tries to correct it; therefore there must be an error at the output.
The problem with the kind of setup I was looking at implementing was that they
require extremely tight tolerances to work, and valves generally do not provide that,
they age and there is sample-to-sample variation. This was the downfall of these
schemes in the past – when the circuit drifted off balance then what you are left with
is often worse that where you started.
What I realised is that by juggling the arrangement of resistors and the valve
transconductance I could eliminate, or at least minimise, the effect of drift and ease
up the effect of component tolerances, thereby creating a practical PSU topology.
The question might be asked, "well, why not just use a conventional power supply?"
The answers to that question are: -
1) All components inject colourations – even the best components.
2) PSU capacitors tend to damp musical dynamics.
3) A conventional PSU has an uneven impedance across the audio band.
I saw that the new Galahad configuration had the potential to bypass the above
problems, and I knew within my heart or sixth sense that it would work and sound
good. I'd had experience with lesser versions of it in the past, and they were very
promising, and here I was looking at the ultimate configuration.
AN INTRODUCTION FROM THE DESIGNER