Common to all hobbies is the threat of repetition, of the samey-ness which can kill progress -- and interest -- stone-dead. So hi-fi enthusiasts, retailers, manufacturers and journalists end up pursuing novelty not just for the sake of it but because we need the newness. Not that there's a shortage of innovation; if there was, most show reports would be a half-page long. Even fiascos like this summer's CES yielded 5000 words' worth. But there's one individual to whom I can always turn if I need a jolt of some sort, be it genuine controversy or merely a new approach to a familiar problem.
Tim DeParavicini of Esoteric Audio Research is known as, among other things, as 'the wild man of audio', 'the best tube circuit designer alive' and a few less flattering names which -- at the very least -- attest to both the fear he instills in his opposition and the respect which even his rivals hold for him; I tell you this at the risk of winning Private Eye's Order of the Brown Nose. In the past couple of years, he's wowed me with products from both ends of the price scale, the £26,000 Yoshino amplifier and the £300 EAR 834P phono amp. Then there are his awe-inspiring Revox G36 tape deck mods, his regular range of EAR electronics, his work in the recording industry, ad infinitum. But Tim's latest wheeze just might be the most 'political' move yet, something which borders on the guerrilla, and we at Hi-Fi News & Record Review are willing, nay, grateful accomplices.
What Tim has proposed comes in the form of a response to what he feels is (in the UK market in particular) an epidemic of third-rate amplifiers passing themselves off as the leading edge in tube development. He's shocked by the hype, the price tags and -- above all -- the claims of originality attributed to such designs. But this is not the place to enter into a debate about the history of valve circuit design because Tim alone could wax furiously for, oh, six hours non-stop.
Suffice to say, Tim finds a bit too much revisionism going on today, to say nothing of the wholsale 'appropriation' of others' work. So Tim has chosen to put his money where his mouth is by placing in the public domain a fresh design, one which he also markets as a regular EAR model for those who would rather not build an amplifier from scratch. He is giving this circuit away, gratis, free of charge, gornisht. So it can't be ripped off.
Lest we at HFN/RR appear coy, I should tell you at this point that we're so taken with the unit that we're offering kit versions of it (but not the bult-up version which is only available from retailers) in this month's Accessories Club. As 'collaborators', we're publishing the entire circuit diagram on p????, because Tim feels confident that skilled hobbyists can source all the parts* and build it from scratch. It's his way of raising two fingers to what he feels are the new barbarians.
But first, I should let Tim tell you, in his own words, about the Esoteric Audio Research 859 Enhanced Triode Mode SE Integrated Amplifier:
"Designing our single-ended amplifier has proven far more difficult than I first imagined. The first major problems were the reliability and quality of current production triode tubes. Most of the fashionable tubes tested (300Bs, etc) offered very poor performance. Driven hard in single-ended mode, these tubes give 10W, but with poor reliability -- only a few hundred hours' use -- and diabolical performance. I wanted a minimum of 10W of clean single-ended power, plus a good few thousand hours of valve life. Surely no customer wants to be spending hundreds of pounds on new output valves every couple of months?
"After deciding that current production directly-heated triodes were more of ornamental value than anything you would want to use in a powerful single-ended amplifier, I turned to conventional tetrodes and pentodes. Sadly, as was the case with the above-mentioned triodes, none could deliver the goods in either clean power or longevity. Parallel single-ended was tried but dismissed on sonic grounds; push-pull with the same valves sounded much better. But it kind of defeated the object somehow...
"My own 549 amplifiers provided the inspiration. They use four PL519 valves in parallel push-pull to deliver over 250W midband. Most of these are used by professionals in the studio environment, equipment which is left on 24 hours a day, seven days a week. The reliability of these valves has been superb. An average set lasts 20,000 hours -- that's three years' continuous use. After reliability tests, the similar EL509 was chosen as the output valve. It's cheap and lasts for ages.
"I was still unhappy. I really wanted a triode as an output valve, so after much head-banging I came up with Enhanced Triode Mode operation. Tests I conducted had the control grid (or Grid 1) connected to the cathode, with the audio signal fed into the valve via the screen grid (Grid 2). Operated like this, the output valve behaved as a true triode. In 'normal triode mode', the screen grid is usually strapped to the anode. This is not as successful as Enhanced Triode Mode.
"In the solid state world, MOSFETs operate in an 'enhanced' mode with the 'gate' (equivalent to a valve's grid) positive with respect to the 'source' (equivalent to the cathode). Normal FETs are biased in exactly the same way as a power valve, with the gate negative with respect to the source.
"The input circuit is a cascade to give the high 150-times gain needed to drive the Enhanced Triode Mode correctly. Actual drive is via a cathode follower, DC-coupled to the ETMs grid. A minimum amount of negative feedback is taken from the output transformer, just to make sure that the amplifier stays spotlessly clean even when driving difficult loads. DC feedback is also applied across the three stages, as a self-biasing mechanism. This provides rocklike stability, which helps to further lengthen the life of the valves as well as to improve sound quality."Continue reading about the E.A.R. 859 amp on Page 2.