A new valve/MOSFET hybrid amplifier has just been released by a – surprise, surprise – UK manufacturer. Ken Kessler examines the cross-fertilisation.
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.
I’m suffering a bit of a memory block today, so I can only come up with one British manufacturer of hybrid 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 users.
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 head-banging 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.
The bass is slightly out of character with the authority shown by the amplifier throughout the midband. Extension is easily on a par with the monster amplifiers emanating from the USA, but the sense of weight is not quite so convincing. On overpowering bass extravaganzas (Sly & Robbie, most house music, Eddy Grant 12in 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 TDLs, with no hint of this condition revealed by 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 produced 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 its 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.
On the other hand, the Valfet is about as refined a performer as you’re likely to find wearing a Union Jack. It deals with delicate, detailed passages with the care and skill of an Italian model maker and it’s transparent enough to reproduce those subtle yet crucial clues to the acoustics of the recording venue; nowhere was this more apparent than on a test pressing of Water Lily’s recent Arturo Delmoni recordings.
But all is not bliss with the Valfet. Now I’ve been reamed more than once for dealing too much with non-sonic concerns but I, unlike some, am aware of other considerations which can influence a hi-fi purchaser. Admit it or not, finish and aesthetics do play a part and I refuse to ignore them on some grounds of ‘purism’. It’s easy being a purist when you don’t have to pay for the hi-fi equipment or schlep it back and forth when it needs (constant) repairs.
As far as the Valfet is concerned, it has neither the styling nor the build integrity of a £4000 purchase. As it must compete with like-priced products out there in the real world, the Valfet must be restyled or engineered if it is to challenge the likes of Krell or Rowland or Audio Research. I know that export is a high priority for Valfet; let me assure the company that the appearance of this product in a high-end audio salon in Beverly Hills or Munich would elicit the exact responses elicited by British products of yore. 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 manufacturers 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 it 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?
(Hi-Fi News & Record Review, June 1989)