(C) The Old Valfet Audio Power Amplifier Review Page.
"The Old Valfet Audio
Power Amplifier Review Page."
REVIEW HI-FI NEWS AND RECORD REVIEW.
A NEW VALVE MOSFET HYBRID AMPLIFIER DESIGN FROM THE UK.
BY KEN KESSLER.
THE VALFET AMPLIFIER.
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 would not dream of mixing solid state circuitry with that of tubes - the trend has been to combine the two with the resulting benefits of easier parts sourcing, lower costs and greater reliability. The secret of successful hybrid-isation seems to be the ability to retain the sonic virtues of the valves themselves.
Think back a decade to the massive Radford TT100 hundred watter with a solid state front end and valve output stages and you have pretty much covered it. ( I trust that readers will inform me of the British hybrids I have forgotten...) While the Radford was an early 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. But now the British can boast a new home grown valve MOSFET hybrid, the Valfet Audio Power Amplifier.
Designer Anthony Johns has produced an unbelievably neat and compact amplifier, conservatively rated at 75W in class A or 200 watt class B into a 4 ohm load. You can actually ignore the power ratings because numbers really have no bearings on performance. 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 or 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 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 out- put terminals, a separate sub chassis for the four large electrolytic smoothing capacitors and complex but straightforward construction. The high price ( which I am saving for later ) is partly accounted for by the high quality components. The valfet includes hardware including a purpose built Arrow on off switch. Schaffner mains input filter. Molex gold plated PCB connectors. Holco precision metal film resistors, revealing no truck with cost cutting.
The on/off switch resides on the front next to an LED which changes colour according to the amplifiers mode and power output ( 4 or 8 ohm operation Class A or B operation etc ). At the back are four robust 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 1/4 inch socket plus a phono to 1/4 inch adaptor.This will be changed to a standard phono socket on production samples for domestic users.
Installation and operation were as straight forward as can be, the Valfet working admirably with a number of pre-amps. 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 - The Valfet is exquisitely neutral, imposing so little on the midband signal that you forgive it,s 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 intrude only on sparse passages and particularly crystalline sounds.
The bass is slightly out of character with the authority shown by the amplifier throughout the midband. Extension is easily on par with the monster amplifiers emanating from the USA, but the sense of weight is not quite so convincing on overpowering, bass extravaganzas ( Sly and Robbie, most house music, Eddie Grant 12 in singles etc ). The Valfet delivered the sound if not the mass. Control was never in question, with transients portrayed with a crispness which in culinary terms could only be described as al dente, but the lowest reaches can only be called lean. I should add that this was only apparent on the well extended divas and the TDL,s with no hint of this condition on the SL700s or the R1200 golds.
The treble regions were hard to fault showing a sweetness and a resistance to nastiness which again suggested valve amplification. The treble region however, is the first area to reveal any manifestations of overwork on the part of the Valfet. Although the amplifier coped admirably with every speaker and could produce ear bleeding levels it would turn rough and edgy when fed high energy material of a relentless nature. In effect, the Valfet seems to hate heavy metal music ( which some would argue is a sign of it's own good taste ), I however like to rock out on occasion and found myself asking the Valfet to do a lot more than it wanted to do, and I would have a hard time living with an amp that sneers at Guns "n" Roses.
But all is not bliss with the Valfet. Admit it or not, finish and aesthetics do play a part and I refuse to ignore them on some grounds of purism. As far as the Valfet is concerned it has neither the styling or the build integrity of a four thousand pounds purchase and must be restyled or engineered if it is to challenge the likes of Krell or Rowland or Audio Research. And if Jaguar can show the world that we can produce better styled and assembled cars than Rover 2000TCs and Austin 1100s then it,s high time our high end manufactures showed the world that this country is good for something a damned sight more appealing than a pressed steel box with flesh shredding heatsinks.
At present the Valfet is - to borrow a great phrase - a wolf in cheap clothing. It performs admirably but does not possess the perceived value needed to part someone from 4K. Given that the company is prepared to admit this instead of parrying with remarks about how many they've already sold to ( need you ask ?) British customers. It could become a global winner. Or is Musical Fidelity the only company prepared to take on the foreign hordes.
There was no interest in the product because of the criticism of the published high price and the stated tin box enclosure. The case and chassis was constructed of 2mm aluminium for good strength and to stop eddy currents flowing through this chassis and case. I have used a pair of these amplifiers to the year 2000 with no problems. I have further upgraded these amplifiers with, 1. Vishay bulk foil resistors, 2. polypropylene capacitors in the signal path. The addition of a switch to select 0.77 volts RMS or Two volts RMS input. Some parts of this design have recently been scientifically proven in electronics journals as sounding better.The recommended pick up cartridge, use the high output moving magnet Music Maker MK2 pick up cartridge supplied by the Cartridge Man of London.
Of the Five pairs of amplifiers that where sold in 1989 All The purchasers thought the solid aluminium cases that covered the chassis of the (C) Valfet amplifiers certainly were not tin box looking, and were a pleasing well thought out addition. There has never been a lack of bass or a criticism, I could only think that the reviewer was used to listening to power amplifiers that falsely accentuated the bass. Guns N Roses is synonymous with distortion, The reviewer was right, the (C) Valfet design has very good taste.
Reviewed June 1989. Hi-Fi News And Record Review.
Copyright. (C) A.W.Johns 1991 - 2013 - All Rights Reserved.