Overview
The role
of a pre-amplifier is to act as a
switch to control the signals from
the various source components in a
system and provide adjustable gain
to the power amplifiers. On the face
of it a straightforward task; a switch
(or two if you want a tape loop) a
volume control and a modest amplifying
stage. Nothing could be easier..........
or could it?
We must not forget that anything that
is added to the signal by the pre-amp
is necessarily going to be increased
by 20-35dB in the power amps. It follows
that there are key design points that
should NOT be included if you are
going to design a better mousetrap,
i.e.:
• Use
a volume control that adds harmonic
distortion (everything but a switched
attenuator will do this).
• Use
a metal box to house the circuit in
(flux field effects create voltage modifications
within the circuit board and corrupt
the signal).
• Use
(even the best) commercially available
voltage regulators, which (regardless
of expensive mains cleaning devices)
add as much noise to the signal as the
output of a moving coil cartridge. Their
rise and recovery times are also not
fast enough to react realistically to
the transients in the music.
This last point
is hugely important as the use of conventional
voltage regulation inhibits accurate
reproduction, adds noise, masks fine
detail, and compresses dynamic range.
The result of dispensing with convention
is "The Vibe" pre-amplifier.
Detailed
Description
Like the Groove
phono stage, The Vibe has been in development
for the last 12 years, its basic specifications
comprise:
• 5
Pairs of switched line inputs
• 1
Pair of buffered permanent record outputs
• 2
pairs of outputs to power amps
• Top
quality gold plated RCA sockets hard
wired to the circuit board
• Function
switch from 'WASP' manufacturers of
battlefield communication technology
• The
famous 'DACT' switched attenuator as
the volume control
• Proprietary
'Lithos' regulation (unique to Tom
Evans products) supplying all stages
of the circuit
Tom Evans
has been uncompromising in the keeping
to a simple design brief:
"Add nothing nor take anything away
from the signal."
To achieve this one must dispense
with 'traditional' volume controls.
Even the best have an inherent problem
with linearity and distortion, which
worsen with time and usage. The DACT
switched attenuator used in The Vibe
has a tracking accuracy between channels
of 0.05dB compared with an error of
+/- 10 % from other manufacturers.
It comprises an array of precision
surface mount metal film resistors
mounted on a gold plated spiral track
giving 24 positions to divide the
volume from its quietest to its loudest.
Its main benefits are:
• Minimal
distortion over a wide bandwidth.
• Keeping
signal path lengths to a minimum
• Providing
stunning attenuation accuracy figures
of 0.05dB between channels
In short,
it outperforms any other controlled
attenuation device on the market,
thus maintaining the nuances of fine
detail previously lost in conventional
volume controls.
The output stage utilises current
feed back technology. This approach
is superior to voltage feedback designs
as it offers far greater rise and
recovery times (less than 10 nanoseconds).
Using conventional voltage regulation
this approach is rarely used as power
supply related noise creates a marked
reduction in resolution and dynamic
range. Many of our competitors assume
that feed back is a bad approach to
design and follow zero feed back solutions.
The reason we suspect these statements
are made is that historically feedback
has been used to solve problems of
inadequate circuit design (Band Aid
Theory). This is certainly the case
using conventional technology. Intelligent
use of feed back, is a key feature
of producing a more life like presentation
as it greatly improves linearity and
bandwidth. The application of Tom
Evans' proprietary Lithos regulation
means that one is no longer reliant
on the amplifier's ability to reject
garbage as this is disposed of long
before it reaches any gain stage.
Noise is therefore virtually eliminated
with the added benefit of increased
speed and resolution far in advance
of most designs.
Because the gain stage is fully DC
coupled, to accurately reproduce a
wide bandwidth of frequencies, an
added safety feature is a DC detection
and isolation circuit. This protects
both loudspeakers and DC coupled power
amps from potential damage through
failure of any source components.
This circuit delays power up at "switch
on" for eight seconds while it checks
the system, then remains active at
all times during the unit's use and
will immediately isolate the output
if DC is detected. This only operates
below 3 Hz; its presence in the pre-amp
is inaudible.
In addition to the current feedback
technology there are marked echoes
of the award winning Groove phono
stage (in terms of error correction
and the application of psychoacoustic
principles) built into the design.
Like the Groove, The Vibe preamp again
moves the goal posts of what is possible
in reproducing recorded music.
Like the Groove, The Vibe sounds very
Tube like and has a sonic signature
that is very difficult to pin down.
Used with other source components,
The Vibe offers the sonic equivalent
of what the Hubble Space Telescope
is to traditional optical astronomy;
a far cleaner window into time and
space.
Dimensions:
Width = 33cm (12.87 inches)
Height = 9cm (3.5 inches)
Depth = 18cm (7.02 inches)
