JLH Memorabilia -- The Past Perfect! :: 3

Annals of a Life in Tech - Exploring the '80s

        Exploring the 1980s is like diving deep into the ocean. Indeed it was a very fertile and fruitful decade, if we are to judge by the output from the pen of the Master. To those for whom the name JLH appears to be that of  "just another designer" from the previous century, perhaps a mere look at the variety and the depth of his articles will be enough to correct that (patently untrue!) notion.

Valves, anybody ?

        It is perhaps fitting that we ring in the decade with a glowing article on the valve -- JLH's first love. (The article was published in the  Electronics Today International magazine of Aug, 1989.) As we know, the Williamson valve amplifier that he had built as a young man was truly his first love. Only after a long period of critical audition, when he had discovered that his solid-state Class-A amplifier was subjectively indistinguishable  from the Williamson, did he happily give it away to a friend!

        The 1980s had seen the poor thermionic valve being relegated to the backbench and forsaken (in audio) in the headlong rush after the new-fangled solid-state stuff. But JLH's observation that the valve will not be forgotten is borne out very much by the valve/tube revival of the present era. Here is an excellent introduction to the theory and working of the valve, capped by a JLH design for a 30 Watt hi-fi amplifier based on the famous Williamson topology. We may note how JLH has used a linear IC (a three-terminal voltage regulator) to stabilize the bias of the 'kinkless tetrode' pair of output valves -- a happy marriage of the old and the new!  All in all, a nice 'teach-in', especially for the Gen-Z who grew up with the 'solid-state revolution'. As for me, I feel the Master should have been alive now, what with the valve revival and all that, we would surely have benefitted from quite a few "out-of-the-box" valve + solid-state designs!

https://drive.google.com/file/d/1oFBKsU4nvBsFJqxAHgjR8FH1tL8MBOMT/view?usp=sharing

ICs and MOSFETs

        What could be more suited to follow this up with than an article on "cutting edge" technology -- a detailed look inside the op-amp integrated circuits! (WW, Oct, 1981) Taking the uA741, the "universal op-amp" as an example, JLH delves into the nitty-gritty of the IC to guide the designer and enthusiast to garner an understanding of the versatile "black box" and use it in various situations. Highly recommended reading even in this day and era when definitive tomes detailing all aspects of the operational amplifier are in print. 

https://drive.google.com/file/d/1IKJ8SbyQD_NNWp2bo5Ja7Fv7LCSPXHVO/view?usp=sharing

Third Gen Op-amps

        JLH does a follow-up of the progress made in the op-amp scene in the WW, Sep 1982, article, taking an in-depth look at the third generation op-amps. For the reader of today, this carries a lot of relevance as these devices have laid the foundations of modern audio design and so it is pretty much relevant even today. 

https://drive.google.com/file/d/1Gc-0tuWC_OG3KKMrMFmm_6AmZB8fU4Oh/view?usp=sharing

LM 109 Voltage Regulator

        "Dissecting the chips" continues, with the LM109 under the microscope in March, 1982, Wireless World. Today we use three-terminal regulators with nary a thought about its inner complexity or working. A study of the inner workings of ICs is highly instructive, as JLH observes. Voltage regulators and operational amplifiers are the building blocks of today's circuits and a deeper understanding of these devices will surely stand us in good stead.

        An excellent "X-ray" analysis of the LM109 by the Master!

https://drive.google.com/file/d/1rvfM836QWHujvMjNOCu_t9QwbQx24Eq_/view?usp=sharing

The 555 Timer

        Just the number 555 is enough introduction to one of the most popular ICs of our era. It truly was an inspired design and here (WW, April, 1982) JLH takes us on a "conducted tour" of its intricacies and uses. Somehow I have a feeling that the article was "trimmed" a lot because of the lack of space, as it seems to end abruptly. But an enjoyable read surely.

https://drive.google.com/file/d/1YsdViBp1nBFdwL6FWGrHNx76HXz-HrnM/view?usp=sharing

        For the audio enthusiasts, the next article is sure to be exciting -- An Introduction to Power MOSFETs (HFN+RR, Dec 1080). With his characteristic ease and expertise he leads the reader through the quagmire of MOS intricacies. Like in the previous case of the valve article, the theoretical discussion is capped by a very practical re-design of his Simple 30 Watt Amplifier  (which originally used bipolar devices) to use MOSFET output devices. JLH rightly predicts that it is likely that this is the direction amplifier design will take in teh future, as the "sonic delicacy and transparency" brought on by the MOSFETs makes "the nicest sounds"! Such a prophetic pronouncement!!

https://drive.google.com/file/d/1I2Y1mvD0uQ2s11FZxkyaIoI-VRinVvBu/view?usp=sharing

        Ah, that brings us, naturally, to his Simple 30 Watt Integrated Amplifier. (HFN, Jan, 1980) His aim at the time, he says at the outset, was to beat the performance of most of the commercial offerings of the time, while at the same time offering a design that the average DIYer will have not much difficulty in commissioning. The original design was published in the Nov 1972 to Feb 1973 issues of HFN+RR. The present design was the result of the requests of many for a simpler amplifier, which, of course, had improved specs. Here he goes into an assessment of the 'sound' of amplifiers, and how to realize a great sounding amplifier. The discussion of the design is an order better than what you might get in any engineering textbook. An advanced hobbyist with no technical training could easily follow the manner in which JLH develops his design philosophy. A must read for all who value an understanding of circuitry and its working. It is this power amplifier that JLH had later modified to use a MOSFET output stage (see above). 

        Being an integrated amplifier, this gets a preamp, which also gets meticulous attention from the designer. RIAA Eq and tone control intricacies are discussed at length, and he employs his famous Liniac circuit here. (Referred to in a previous post in detail.) All said and done, it sure is a design that can hold its own against many average commercial amps of today.

https://drive.google.com/file/d/1IWB8FgWqQ0-r2tMy5qu9b9D4FjmE9Y9z/view?usp=sharing

Audio Design for Everyman

        A most popular and assiduously followed series of articles were the seven-part Audio Design guidelines, published in the Electronics Today International magazine from Sep 1983 to Mar 1984. His intention here was to 'de-mystify' audio design, and coming from the Master, the series presented insights from which even the seasoned audio designer could benefit. As I said earlier, it is not often you get such a masterful handling of design theory (and practice!) in or out of EE classrooms. The series is worth its weight in gold, and served to establish the reputation of JLH as a design Guru. Anybody who has sat in a theory class knows that only somebody who has mastered things fully will be able to offer clear and simple explications of the kind you find in every paragraph of the masterly thesis.

        After discussing noise and distortion in Part-2, JLH goes into a more practical handling of those issues in Part-3. Particularly noteworthy are his prescriptions as to what is to be done about distortion and noise, the bugbear of audio designs. As is typical of JLH, an ounce of theory is always balanced by a large dollop of practice! He asks the questions that are in the minds of every designer, and then outlines step by step how to find solutions for those issues. His masterclass on tone controls should be classed as required reading for any audio designer or knowledgeable hobbyist.

        Part-3 has some topical relevance now, what with the present vinyl revival, and the need to design preamplifier modules to handle the miniscule output of Moving Coil pickup cartridges. JLH shows us how to design (and build!) a really low noise, low distortion gain block. Even passive components and RIAA Eq subtleties receive his careful attention. The result -- a simple and capable MC preamplifier. The discrete gain block could also hold some interest for the 'anti-chip' brigade today. A DIY build  is the only way to apply it to the touchstone and realize its merit. 

        Coming to power amplifier design in Part-5, he sets out to cut the hype and hand-hold the reader through the quicksand of design options and solutions, again, as before, culminating in a fleshed out practical design. Subsequently, he examines the 'ins and outs' of audio recording, a very essential and popular topic in those days, there again blending theory with first-rate practice of the art. The concluding part is NOT for the average techie or hobbyist as it deals with imaginary numbers and other such esoteric stuff; but as always, he easily blazes a path through the complexities of mathematical theory, once again proving his solid technical credentials.

        On the strength of many such points of consideration, I would choose to label the (considerably abridged) series the Magnum Opus of the Master designer. Highly recommended for repeated readings -- if you are serious about understanding audio design, and if you would rather choose to read something as enjoyable as a novel (and not some dry textbooks!), you don't have to look farther than the links below.

Part-1: https://drive.google.com/file/d/1PxgXU6TrAb4vQt17XlWsZTBZgxDEL8gL/view?usp=sharing

Part-2: https://drive.google.com/file/d/1FMkQaudDGIFwK4Qnmd2TctzUtkmfrip6/view?usp=sharing

Part-3: https://drive.google.com/file/d/12cOawH4jLuURPO0ttF5X1kHP4RcaMRRs/view?usp=sharing

Part-4: https://drive.google.com/file/d/1AZG8VRZpmgcx3LpqvV9nkfwIvHRCDUpx/view?usp=sharing

Part-5: https://drive.google.com/file/d/141do84VwFAWUrmNNhGb6NOkKKI0ZqW4I/view?usp=sharing

Part-6: https://drive.google.com/file/d/13UrGaJaIB5MnpzC-PoPt12PUPZV1438W/view?usp=sharing

Part-7: https://drive.google.com/file/d/1omdVF_ISxqq-aEVneJMydk8gRyDwiL7N/view?usp=sharing

Theory into Practice

        An interesting complement to his above series was published by ETI from Jun to Sep, 1984, the Audio Design Amplifier. The design, by popular accord, reached the pinnacles of performance and perfection. It is a very high quality MOSFET output stage amplifier, and the design gets a detailed unveiling by the Master designer.

        Here the discussion of the amplifier's power supply circuit is noteworthy -- AND eye-opening for many of us. Usually a power supply is something that is "tacked on" as an afterthought by most 'designers'. Such easy shortcuts certainly are not for JLH, who realizes the importance of the power source, if the amp is to perform faultlessly to specs. For the typical 'audiophile' who specifies 'gold plated screws' for his amplifier, but who often gives a step-motherly treatment to the power supply design and components, this is a moment of  Epiphany! The power supply circuit itself at first glance appears to be far more complex than the amplifier itself ! But it is the right  complement that JLH has chosen for a great-sounding amplifier that is able to reproduce the artistry embedded in a recording -- a brave claim not often made by many amplifier makers of today! I would personally rate the amplifier as an all-time great gift to the DIY community, that raises the bar to levels not often seen in the amateur builder circles.

Part-1: https://drive.google.com/file/d/15svJTW35AfrY0PF4LYvjHUIl5dqbYn06/view?usp=sharing

Part-2: https://drive.google.com/file/d/10HWJkOMF5MIXwpJtkSw9M7CRj5UzgqL0/view?usp=sharing

Part-3: https://drive.google.com/file/d/1572io1Gho1zvKmohX6VYCcRsKWisH4Dc/view?usp=sharing

Part-4: https://drive.google.com/file/d/17DAODvLvMsuCJxzblhY4rVE-PqbpTgzy/view?usp=sharing

Erratum: https://drive.google.com/file/d/1Fg1aUz0_ojmw4gykvXlCoQNiJ354WOHJ/view?usp=sharing

Novelties of the Clapham Junction

        While it is true that JLH was favouring the HFN and ETI magazines with article after article on audio, some of his best designs (like the Classic Class-A amplifier!) were published in the Wireless World, the engineers' journal. True to form, the Oct 1982 to Feb 1983 issues carried a truly novel preamplifier design -- with the "Clapham Junction" Tone Control! This was a matching unit to the MOSFET power amplifier published in June thru August issues of the same year. (see below)

        This was a preamp of truly modular design, much more advanced than his earlier, simpler design which carried the name 'modular', and which had introduced the idea of modularity in preamp design. The key feature of the 'Clapham' preamp was the original and novel "Clapham Junction" (the name springs from a resemblance of the stepped frequency response curves to the underground railway maps) stepped frequency controls.

        Tone controls, then and now, largely followed the (Peter) Baxandall design. Here was an original re-think of the tone control circuitry, and to my knowledge, this design has not been upstaged till date. Truly a preamplifier that ticks all the boxes, but one which the serious DIYer has not noticed or tried yet, chiefly because he hasn't had the opportunity to learn more about its novel topology. It is high time to heat up the soldering station and plunge in to claim the sublime rewards of tonal clarity!

Part-1: https://drive.google.com/file/d/1UmFN9wrbKv9nENrKWonFhO6nezVB0Ib7/view?usp=sharing

Part-2: https://drive.google.com/file/d/1Ms45EG_rU5fTQDE5PQQEeyDD4peJDbVF/view?usp=sharing 

Part-3: https://drive.google.com/file/d/1GAqw60ESq6Zj8HIzHfNKU94z58dmZtPd/view?usp=sharing

Part-4: https://drive.google.com/file/d/1vadzQuwB_pi71U4vyxuJ03IAGsMytptK/view?usp=sharing

 Letters relating to the Modular Preamp (above) and the MOSFET Amplifier (below) (WW, June, 1983) with important points answered and some corrections given:

https://drive.google.com/file/d/1hLftFvK3IeXNjn8DfdwjIM2YpfYMSxDs/view?usp=sharing

MOS Power Play

        As mentioned above, this was the high power MOSFET Amplifier that matched the 'Clapham Junction' preamplifier. Published in the Wireless World from Jun thru Aug, 1982, the first part dealt with the issues that cropped up while using MOSFETs. JLH presents his design approach to these issues in the second part, and distills the final design in Part-3, as was his usual style, by transforming all that theory into a practical, real-world circuit that performed in a truly admirable manner.

        The icing on the cake was the loudspeaker protection circuit that bore the signature of the Master that wrapped up the design. One keeps looking with wonderment at the fertile mind of JLH and his prodigious output of original designs.

https://drive.google.com/file/d/1Q4DX9pa2rK9bM8HaVXMqUCaCI-p-t4gj/view?usp=sharing

Corrected Circuit Diagram

Warning: Several errors had crept into the circuit diagram of the amplifier printed on P-28 of the August issue. Here is a correction note published by the editors. The errors, unfortunately, are serious and so the reader is enjoined to refer to this note and make suitable corrections in the final circuit of the amplifier presented. 

Wien Bridge Test Oscillator

        The venerable Wien-bridge  network has served as the mainstay of a good audio test oscillator for long. However, there are factors that make it impossible to reduce its inherent distortion beyond a point. Here (WW, May, 1981)  JLH explores a truly novel circuit incorporating an opto-electronic device (for the first time!) to take distortion elements down to 0.001%.

        A good read for the hobbyist, as rarely does one get a chance to be enlightened of the inner circuit workings as with the Master JLH.

https://drive.google.com/file/d/1921xVpcy4wV_NRmn_e0k389x33oCUD5u/view?usp=sharing

         We have only managed to touch some of the major articles of the 1980s (though not in strict chronological order) in this lengthy post. Quite a few more remain to be examined, surely in the next post, which hopefully will cover most, if not all, of them. I am sure my readers will agree that it is not an easy task to "get a handle" on JLH, one of the more prolific among designers and technical authors, who was equally at home in theory and hands-on practice!

        So, until next time read and enjoy some of the rare gems from the JLH collection, and may some of these designs inspire you to take up new and highly rewarding builds!

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