Specifications

maximum. When you turn the volume control down, the
output signal is reduced, but the noise of the circuitry
remains the same -- therefore the S/N ratio becomes worse
and worse as the volume is lowered. Since most preamps
are used anywhere between -10 dB to -40 dB for an average
listening level, this means that the S/N ratio in actual use will
be 10 to 40 dB worse than on the spec sheet.
In contrast, the S/N ratio of the VGT circuit is always at
the maximum, regardless of the volume setting. So in
real world usage, the S/N ratio is increased 10 to 40 dB
higher than a typical preamp. This results in unparalleled
resolution and retrieval of detail.
Eliminating the Preamp Stage
For the Ayre AX-5, we completely eliminated the preamp
stage altogether and simply made the gain of the power
amp variable using the VGT and added an input selector.
This is the simplest possible signal path in any audio
product ever made. Period.
" Please note that the VGT ONLY works
with circuits that have zero negative
feedback. Since very few designers have
any experience at all with zero-feedback
circuits, we are not too worried about being
copied anytime soon. "
In contrast, 2013 marks Ayre's 20th anniversary, and every
product we have ever made uses zero-feedback audio
circuitry and zero-feedback power-supply regulators.
The volume control of a VGT design demands the use
of extremely linear and low resistance switches. FET
switches will not work in this application. Thus the only
candidates for the job are relays and rotary switches.
Foolproof methods
We have a very simple, yet 100% foolproof method for
listening to the sonic eects of various switching devices.
With our method, each device has the exact same
number and type of connectors, wire, and even solder
joints. This allows us to compare the switching element
to a true "straight wire bypass" with no other variables
involved.
By far the most neutral and transparent switching device
we have ever tested is the solid-silver-contact rotary
switches from Shallco. The only change from a "straight
wire bypass" is a extremely small loss of resolution -- I
would estimate it at less than 1%, so you are getting
99%+ the full resolution of the source.
Nearly every other solution sounds broken by
comparison. One of the worst oenders are relays. (This
is especially ironic as almost all modern preampliers use
relays for either signal switching, volume control or both.)
The relay
A relay is a truly wretched device to put into the audio
signal path. There is absolutely nothing good about
it. The conductors are bad sounding, having various
alloys mixed in to the copper to make it "springy". The
plating is similarly bad, with almost all small signal relays
t: 01727 865488 e: [e-mail] w: www.symmetry-systems.co.uk
Symmetry, Suite 5, 17 Holywell Hill, St Albans, Hertfordshire AL1 1DT
Page 3
The AX-5 Story
from Ayre Acoustics March 2014