The JLH Gateway to Class-A :: 8

Following in the Master's Footprints

        The audio world, as most of us know and admit, is peopled largely by "itchy fingers", and the JLH Classic too did not escape their 'itchy-bitchy' labours. While quite a few of these tweaks/mods could be classed with the proverbial exercise of transforming a horse into an a** ...oops! donkey, many did indeed add to the elegance in performance and the simple topology of the famous little amplifier. What astounds many is the fact that this labour of love is continuing to this very day as is borne out by that marathon thread in DIYAUDIO on the JLH amplifier (nearing 500 pages and 10,000 posts) -- truly a testament to the timeless appeal of the Master's design.

        It is probably in the present century young designers, who grew up in the world of Circuit Simulators and theoretical explorations of the "what-if" kind, wanted to "play" with the classic design. They little realized it was a design that was conceived and perfected by a designer who had come through the trial by fire of the tube and early solid state era. More than that, JLH had attempted to best his Williamson tube amplifier with its 'life-like' sound signature.

        It is funny to note how today's designers  endeavour to reduce distortion to immeasurable levels in the belief that it is the 'magic bullet' that could give them the 'perfect amplifier', and who often quote Matti Otala and his proclamations about IMD, believing that he was the true 'Messiah of Distortion' who single-handedly transformed the world of audio. Sadly many of them were not born when the grand old man Williamson said more or less the same thing about distortion and issued a caveat to aspiring designers to not treat feedback as a shortcut to "improve" an amplifier with mediocre specs.

        But it is heartening to note that over the past years ... rather, decades ... the collective efforts of a lot of designers and devoted hobbyists have spawned quite a few offshoots of the classic JLH design. Let us explore some of them now for what it is worth.

Bigun's TGM9

        Though not begun as an attempt to 'mod' the Master's design, TGM9 by Bigun has a lot going for it, especially when you consider it as an inspiration for other DIYers. He had a lot of stuff in his junk box which he wanted to use, and that led on to a totally unexpected 'variant' of the basic design. Funny that his build took a fair number of years, but as they say, all is well that ends well, and it was true in the case of Bigun's build too. The results were more than rewarding.

        I would say the aspiring builder of the 1969 Classic should definitely spend some time reading up Bigun's account of his build. He has promised to once again install the old JLH Classic amplifier in his home system and share his experience and insights after all these years. Do check out his link which is likely to be a confidence booster for the hobbyist contemplating a build of the JLH 1969 Classic.

https://www.diyaudio.com/community/threads/tgm9-my-version-of-the-jlh-69-class-a-amplifier.268846/


The 'Sublimed' JLH

        Another noteworthy 'modded' build was by Haik Kokorian, who also 'dared' to use a switching power supply -- that too for a class-A amplifier! Of course, much later we see designers like Nelson Pass advocating the use of switcher power supplies to drive class-A amplifiers. Don't be carried away by all that, though. All along, switchers were infamous for their broadband noise output, and most cheap switchers follow suit even today. Only a handful of makers/brands have SMPSs of  'respectable performance' that you could employ to drive hi-fi amplifiers. 

        Mr Kokorian called his concept the 'sublimed' JLH. As we all are aware, there is an almost universal mistrust/distrust of "capacitors in the signal path" (though its vocal supporters easily forget that the signal currents have to traverse the power supply capacitors too!) Here the 'sublimed'  design eliminates the large electrolytic output capacitor by using a pair of large electrolytics to create a 'virtual ground' at half-supply voltage for the speaker return. It is interesting to read through Kokorian's arguments about the amplifier functioning with a constant current 'circulating in its veins' etc. But, according to him, the results after his mods were truly 'sublime' both at the LF and HF ends. I would recommend the 'sublimed JLH' to the DIYer with an open mind as it is fairly easy to try out the mods and hear it all by oneself, and then choose to believe or not! Here is to sublime experiences!

https://www.diyaudio.com/community/threads/sublimed-jlh1969.329553/


Hennady's 'Mod' JLH

        Another interesting 'take' on the good old JLH Classic amplifier is the thread posted by Hennady Kovalsky -- a much-modded version for the 'mod' times. It is a 'sliding bias' sort of circuit, in that it operates up to about 9W in class-A, and at higher power, slides into class-AB. It is a pretty interesting thread as Kovalsky moves from one idea to another, and he shows quite a few interesting 'takes' on the JLH.

        For the DIYer driven by 'what if' and other such fanciful questions, the  thread is likely to offer many ideas and lots of inspiration. Mr Kovalsky is meticulous in his presentation so that the hobbyist following him will not be left high and dry! But then building different versions and comparing the 'sound' to that of the classic is the ultimate icing on the cake, if you ask me. Here is the link for adventurous circuit surgeons to explore:

https://www.diyaudio.com/community/threads/hennadys-take-on-the-1969-jlh.409972/


The JLH Magic

        Quite a few builders, who are knowledgeable designers themselves, have opined that it is pointless to try a few mods in order to 'perfect' an already perfect design that JLH had conceived. On that note, I would say the serious JLH fan should be more concerned about adapting and building the classic amplifier with the components available to him currently, and how best that build could be 'tuned' to be close to the sound signature of the original design. In our times with the preoccupation with achieving ever lower levels of THD and TID and such like, it is moot whether we are moving up the right alley vis-a-vis obtaining improved sound quality that makes an amplifier indistinguishable from the "real, live thing".

        Admittedly, it is the "realistic sound" of the JLH classic amplifier that has made it the darling of hobbyists who care about 'natural sound'. Perhaps it is fitting to close this section with the comments of a diehard JLH fan who had designed and built a very high powered JLH-style amplifier for a client, and  who himself had a high-bias JLH Classic for his daily enjoyment. (At least we have to accept that he knew what he was talking about!)

        "... the JLH sounds like honey amongst lemons...Imagine that you designed a product in 1969, and in 2024 still people are arguing how to make a perfect design better... I don't think any of you can claim anything even close (to the JLH Classic), with or without simulators... JLH's second "improved" design, the one that I also have, do not even come close to his original(1969) ... "

        Our upcoming task is to try and collect together the many 'versions' of the JLH that have mushroomed all over the world over the past decades. It is hoped that these diverse 'modern movements' in the great Symphony that the Classic is, will serve to inspire and encourage DIYers and designers to attempt and add to the timeless euphony of the Classic design by JLH.

        In the meantime do read, comment and share, and with renewed inspiration, plan a build that bears your signature!

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