Valve scarcity and solid-state progress have almost forced valve
amp manufacturers to blend the two technologies. While a number of purists survive -- those who wouldn't dream of mixing solid-state circuitry with that of tubes -- the trend has been to combine the two with the resultant benefits of easier parts
sourcing, lower costs and greater reliability. The secret to successful 'hybridisation' seems to be the ability to retain the sonic virtues of the valves themselves.
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I'm suffering a bit of a memory block today, so I can only come up with one British manufacturer of hybird power amplifiers prior
to the appearance of the Valfet. Think back a decade to the
massive Radford TT100 hundred-watter with a solid-state front-end
and valve output stages and you've pretty much covered it. (I
trust that readers will inform me of the British hybrids I've
forgotten...) But while the Radford was a valve/solid-state
hybrid, it retained the less-appealing and riskiest parts of
valve amplification such as the massive, heat-generating output
tubes, huge chassis, etc. What the Americans produced were the
opposite -- valves up front and solid-state devices providing the
output -- to create smaller, cooler-running devices like the
myriad Counterpoint hybrids and the sadly-departed Moscodes from
New York Audio Labs. But now the British can boast a home-grown
valve/MOSFET hybrid, the Valfet Audio Power Amplifier from the
Valfet Audio Manufacturing Co Ltd.
Designer Antony Johns has produced an unbelievably neat and
compact amplifier conservatively rated at 75W in Class A or 200W
Class B into a 4 ohm load. You can actually ignore the power
ratings because numbers really have no bearing on performance
(viz. the 20W NAD 3020, the 15W Radford STA15, the 50W Krell
KSA-50, ad infinitum). His main priority has been simplicity,
reflected in the use of a single valve (the common-as-muck ECC83)
as a basic voltage amplifier driving a very fast, high impedance
FET input. The cubist chassis -- each monoblock measures only
190x285x280 (HWD) -- appears to be nearly 30% heatsink, necessary
because Johns has endowed the unit with selectable Class A or
Class B operation, accessible via switches at the back. Also
selectable are impedances of 4 or 8 ohms, enabling the user to
tailor the operation to suit the difficulty of the speaker load.
Removal of the lid shows the amplifier to be jam-packed, but not
quite the servicing nightmare it could be. The layout is
sensible, including whole stages on plug-in cards (connected via
computer-grade fittings), the easy-to-access valve, a
high-current power supply mounted near the output transistors and
next to the output terminals, a separate subchassis for the four
large electrolytic smoothing capacitors and complex but
straightforward construction. The high price (which I'm saving
for later) is partly accounted for by the high-quality
components, a veritable What's What of designer ingredients. The
Valfet employs hardware including a purpose-built Arrow on-off
switch, Schaffner mains input filter, Molex gold-plated PCB
connectors, Holco precision metal film resistors and other bits
and pieces revealing no truck with cost-cutting.
The on/off switch resides on the front, next to an LED which
changes colours according to the amplifier's mode and power
output (4 or 8 ohm operation, Class A or Class B operation etc).
At the back are robust four five-way speaker terminals suitable
for bi-wired systems, the aforementioned toggles for 4 or 8 ohms
and Class A or Class B operation, and an input in the form of a
1/4in socket plus a phono-to-1/4in adaptor. This will be changed
to a standard phono socket on production samples for domestic
Installation and operation were as straightforward as can be, the
Valfet working admirably with a number of preamps including the
Audio Research SP-9, Audion and Concordant and speakers ranging
from the Apogee Diva to easier loads like the TDL Studio 1,
Celestion SL700 and Monitor Audio R1200 Gold. I used the unit
almost exclusively in Class A/4 ohm mode, mainly because 95% of
my listening involved sensible levels. Major-league headbanging
required the Class B setting to avoid the onset of audible
clipping. Warm-up time was surprisingly fast, the Valfet sounding
as good as it gets after only 15 minutes.
And good it is. After all these years with me bitching about the
paucity of true high end amplifiers made in the UK, along comes
this magnificent performer without any fanfare at all. Its image
is like its sound: easy to ignore. For the former that's an
insult, for the latter a compliment. The Valfet is exquisitely
neutral, imposing so little on the midband signal that you are
prepared to forgive its few and minor faults. The sound is warm
and lush in the manner of valves (and some MOSFETS) but with
decidedly solid-state precision. Grain is only just discernible
and of such a fine texture that it will only intrude on sparse
passages and particularly crystalline sounds.
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