JLH Memorabilia -- The Past Perfect! :: 4
Annals of a Life in Tech - More from the '80s
As we had seen in the previous post, the 1980s were a very productive period for JLH and we have a huge corpus here to survey. Let us get into the significant articles published in various magazines of the day. Perhaps it is appropriate that we "start with a bang", or rather, with the unmistakable sound of a MOSFET-amplified, crisp "pop" of a Champagne cork. The announcement of the JLH-designed MOSFET amplifier was sort of a seismic event not only in DIY circles. JLH had 'struck again', easily proving his mastery of circuitry once again with a much improved design of what he had theorized in his earlier series 'Audio Design' (see previous post), which was followed up by a high quality 'demo' build. Here was an amplifier design that raised the bar a quite a few notches. More details anon.
'Simply the Best' MOSFET Amplifier
That was how the Electronics Today International Editors put it when they broke out the champagne to announce the JLH 80 Watt MOSFET amplifier on the cover of the May, 1989, issue. Yes, it was an occasion to celebrate! JLH had bettered his own past designs with the amplifier that measured better than the best, but on top of it, sounded better than most! The proof of the pudding is in the eating and I invite the reader for a thorough reading of the original article.
The 'Audio Design' series as well as the ensuing 'demo build' by JLH had set some sort of a benchmark in audio amplifier design and performance. (See Post # 3 for details.) Moving with the times, JLH has here given some 'embellishments and refinements' to his timeless design, taking it onto another level, so to speak. As JLH puts it: "... my aim with this revised design ... is to provide a system which will be equal to or better than the best of the contemporary market offerings ..." How many amplifier designers/brands could make such a bold claim? No wonder the ETI Editors went into ecstasies while proudly announcing the design as a benchmark build, and that too for the discerning DIYer. DIY had finally "come of age", and a good DIY build could easily best most of the commercial offerings of the time!
Here again we see a sterling quality of JLH, the 'top drawer designer' of the time, as a socially committed person -- he could have easily converted the design into a pile of cash, and reached 'stardom' as the 'resident designer' of a top brand. But he, as always, chose to avoid the glitz and limelight, and gave away the designs to the DIY community with much happiness and satisfaction. He was happy to chase better sound himself, and wished nothing more than to share his discoveries with his beloved readers.
The "best MOSFET amplifier" was a very popular design of the time, to judge by the huge interest it triggered and the number of kits sold, indicating immense DIY following. Another point that garnered attention was the focus on power supply design. Perhaps for the first time illustrated with an example, JLH underscored the need to pay as much attention and design expertise to the power supply as one did to the amplifier. JLH's design for the "belt and braces" power supply employing MOSFETs was a fitting complement to the "no holds barred" design of the amplifier circuitry. Naturally, the results were sterling, to put it mildly. To most of us the amplifier circuit looked to be simple and straightforward, while that of the power supply appeared to be more complex, once again underscoring the fact that an amplifier is only as good (or as bad!) as its power supply.
Many who had built the amplifier in the '90s have been using it for decades and the general consensus is that it is a timeless design that can any day 'be there with the best' of even today's designs, and perhaps win a gold medal in comparative audition. It is time some of our senior/experienced DIYers took up a build once again and proved a thing or two about the genius and vision of JLH.
https://drive.google.com/file/d/1WhO4quhnBFVqG2E4sDrapgsQQgvsYpwO/view?usp=sharing
Designing from the Grassroots
It has to be admitted that our times bear no resemblance to the era in which JLH studied, lived and worked. With the proliferation of software design and simulation tools, the young designer of today comes more and more to depend totally on spec sheets and other such inputs (and his favourite soft tools!) while developing his designs. There always have been two schools of thought and approach -- the 'specialists', and the 'general practitioners'. The specialist knows more and more about less and less, and that's how he becomes a specialist. The GP, on the other hand, has to have a working knowledge of virtually everything within his field of work.
Much might be argued about why both sides are right from their respective viewpoints, but in the end it has to be admitted that there are some very positive advantages to having a solid foundation in almost all the aspects that concern your design, which alone would ensure a more "fool proof" and stable design. It is in this backdrop that the work of JLH has to be viewed and appreciated. This is no idle theory about JLH's competence, as his own rather prolific output on diverse theoretical aspects of design bear testimony to his mastery of all aspects of design, beginning with the true "grass roots" level -- in electronic design, component level. It is that aspect that is concerning us right now when we get into a study of the 8-part exposition of 'real-world' components by the Master.
The Real Components
Here is the series by JLH published from March to October, 1985, in Electronics Today International magazine. JLH kicks off the series with a detailed look at the ubiquitous, humble components -- the resistor and the capacitor, the "foot soldiers" of virtually every circuit. As we read along, we are amazed at the picture of the larger world of these humble, basic components (that in certain ways define the very working of an electronic circuit) that JLH is unveiling before us. Surely after this "lecture class", the average hobbyist is likely to have a deeper and more contextual understanding of the circuit that he is delving into.
Part-2 is an essential look at active components and it is one of the briefest and probably the best summing of what all we need to know about diodes and transistors of various types. Part-3 arms us with more in-depth knowledge about how to use these devices in real-world circuits, and by the end of the chapter, the reader has had some definitive ideas about transistors and MOSFETs and their use, particularly in audio circuits. Part-4 takes us onto a more theoretical terrain, showing us the nitty-gritty of circuit configurations and basic calculations of circuit constants. To my knowledge such a simple and at the same time accurate lessons in circuit design have not been seen in the average text books.
Another chapter on Zener diodes and LEDs follows, again, in the typical JLH style discussing the theory and background in layman's terms and capping it with real 'demo' circuits. The August instalment deals with integrated circuits and op-amps. He gives tips on how to interpret the specifications of these devices while using them in your circuits. I like to put it all as " the story of circuits ... easy and enjoyable reading" even for the average enthusiast without a formal technical background.
The next chapter gets into power switching devices like SCRs, Triacs and thyristors and their characteristics. Here again the stress is on how to understand their use in practical everyday circuits and what are the caveats we should keep in mind while using them. JLH concludes the series with a section on digital logic ICs, an essential chapter on the "cutting edge" devices of the period. An elementary, yet useful introduction to digital devices and techniques that would serve to accustom the DIYer to "test the digital waters" with some confidence.
Overall, a very useful and simple refresher for the circuit enthusiast and DIYer. I recall it was the fashion among hobby journals to have a similar "beginner's section" every once a year or so. In comparison, the very brief, highly 'distilled' words of wisdom that JLH shares with his reader stands head and shoulders above such 'teach-in' material one might find in other journals. Highly recommended reading and reference for the DIYer.
https://drive.google.com/file/d/1_MlQ8QRWTFztYpfeuv30qxCbR0fTRS_S/view?usp=sharing
Then There Were Transistors!
Part-2 in October went into more details of BJTs, FETs and MOSFETs and their various 'avatars'. To me, however, it looks as if the article was brought to an 'abrupt end' apparently because of some editorial decision linked to space constraints. This criticism could be levelled at some of his earlier theory articles too, which obviously have been at the receiving end of the "editorial scissors", again, most likely for reasons of space in the magazine. Such are the compromises we have to live with in this world!
https://drive.google.com/file/d/1CiO9hgBzQGS0geKtKunaOYtkOE3Az29_/view?usp=sharing
Audio Mixer
https://drive.google.com/file/d/15is30x7IHnZm4nVC2hxfB7H1TK-ueu20/view?usp=sharing
Distortion Meter
As we all know, every test and measurement will be only as good as the instrument we use. True to form, JLH describes a simple, yet sensitive Distortion Meter in the Jan-Feb, 1985, issues of ETI. To the hobbyist often seen juggling with THD and IMD specs, here is a wonderful opportunity to be led by the Master into the intricacies of how to measure these critical parameters. Not only that, he goes into details about how to achieve accurate THD measurements and arrives at a versatile practical design, that can function on battery power, as well as from a mains derived power supply.
The Distortion Meter has an essential adjunct in the sine wave spot frequency oscillator that is described afterwards. Detailed notes follow on the construction and use of the meter in Part-3. A must read if you have plans of adding a no-nonsense THD Meter to your test bench without breaking the bank.https://drive.google.com/file/d/1Og_oqFjbnHeHrwlLbgopJHc5XfSWHS6-/view?usp=sharing
PA Amplifier
It is interesting to see JLH, a hi-fi Guru, designing a 'lowly' public address amplifier, and that too a portable one! Let us take a detailed look at the pages of ETI, May, 1986. Ah, what do we see here ... here is a portable amplifier that has been designed to work from a DC-to-DC converter that he had presented in the previous issue! (see the next entry below) Talk of putting the horse before the cart... Let us take a look.
The circuit outputs 50 Watts with about 0.1 % THD, about one-tenth of comparable PA amplifiers. In typical JLH style, he does not treat this as a "lowly design" undeserving of his attention. On the other hand, JLH goes into considerable detail examining the circuit design, and wraps up the article with a rather good preamplifier to drive the PA. At the end of it all, the knowledgeable DIYer might be left asking himself, "you call THAT a public address amp?" It IS an easy build and the rookie constructor could easily cobble one up, put in a transformer power supply, and Voila! he has a good-sounding 'blaster' for his den, and none will be wiser!
https://drive.google.com/file/d/10Le7h88jkDphV1qLcj96w1R-c2V9RWfp/view?usp=sharing
DC-DC Switcher PSU
Here is the switcher power supply that JLH had published in the April, 1986, issue of ETI, for which he had designed the PA amplifier as a companion piece. Whether you are interested in building such a DC-DC converter PSU or not, it is advised that you follow the article carefully, as JLH goes into considerable detail about the various aspects of the design of a switching converter. It is unlikely you will get such an explication of the design elsewhere. As can be guessed, the design is fleshed out fully, with construction and testing details. Hats off to JLH!
https://drive.google.com/file/d/1wACkr5cCAd2rLo4nUhofevCLO4NvkICH/view?usp=sharing
MOSFETs, and the 'Sound' of Capacitors
Here is yet another Class A/AB MOSFET Amplifier (Wireless World, Mar, 1989) which was designed to illustrate practical solutions to subjective discussions on the 'sound' of capacitors and transistors. This is where art and engineering conflict, and admittedly often scientific measurements fail to quantify aspects that could easily be ascertained subjectively. JLH, with the aplomb of the knowledgeable and wise engineer, and the discernment of the music enthusiast, wears both the hats comfortably, and walks the tightrope of the objective/subjective conflict -- and emerges with some excellent solutions for the vexing questions of 'true' fidelity.
This is an all-MOSFET design, with the less expensive and easily available BJTs only used for non-critical current sources etc, which anyway are not in the audio signal path. It is noteworthy how JLH adopts simpler solutions when there is no need to complicate things with attempts at "gilding the lily", as is often done by other designers. Here again JLH's theoretical explorations have led onto a practical design -- a rarity in engineering practice, where by and large theoreticians choose to dwell in their Empyrean Heights, often not condescending to touch the soldering iron and build (and prove!) what they have professed from their high pulpits. What we have here is an excellent debunking by JLH of the usual practice in audio circles of what is often termed 'specmanship' -- a thoroughly interesting read, if you ask me.
https://drive.google.com/file/d/1IgOII_l2DNuo7YO32jJgqXu5V6hXxPPR/view?usp=sharing
An 'Audiophile' Bench Power Supply
Although meant to power the amplifier design discussed above, this twin-rail power supply (E&WW, May1989) could easily play the role of an excellent bench supply. The ratings (+/- 0-35 V @ 4A max) make it admirably suited to its role as a test bench adjunct, but what makes it different is the 'audiophile' hat it is wearing. An audio DIYer's power supply?? Read on ...
As could be expected, the circuit offers re-entrant current limiting and excellent regulation. But a novel feature that JLH has designed into the PSU is the DC offset potential sensing at the speaker output, with the power rails going into shut down once excess DC is detected at the speaker terminal. Surely for DIYers who experiment with a range of amplifier builds, this could be a Godsend that will save their goose time and again. Conventional relay protection circuitry offers protection only for the expensive speakers from the damaging current pumped out by a faulty amplifier. The speakers are saved, but the amp smokes and most often is vapourised! Not any more! JLH has found a solution that tackles the issue at the source, and thanks to his genius, the amp under test could survive for another bout or two!
https://drive.google.com/file/d/1L5wFlhGo4Ici0PXcpzxuF2O-x_yu9m6Q/view?usp=sharing
The Beauty of Symmetry in Audio
Audiophilia is marked by periodic fads, and one that started becoming popular in the 1980s was the argument that symmetry in audio circuits contributed to 'better' sound. This took off wildly and designers were competing with each other in the late '80s and early '90s to come up with totally, fully, completely (!) symmetrical designs -- right from the input to the speaker terminal! Here (E&WW, Jan 1985) JLH is examining questions allied to this trend in an academic manner, but at the same time giving credence to the subjective judgments too. Of course, as we all know, JLH was not one to bow to commercial pressures or persuasions, but as an engineer interested in furthering the art of music reproduction, he took every step to advance the art of audio design.
Absolute symmetry between NPN and PNP BJT devices, or between N-channel and P-channel MOSFET devices, is a theoretical impossibility, as anybody should know. After the basic approach is outlined, JLH sets out to flesh out a symmetrical, sensitive, low noise/low distortion Moving Coil gain block module. This progresses to a design with JFETs offering better performance. Overall a very good exposition of the design approach to symmetrical amplification at low signal levels, and a demonstration of how this could provide a design that raises the bar in specs and performance, and could replace/beat the 'standard' op-amp based modules. Highly recommended.
https://drive.google.com/file/d/1lVFx0kC35f8M_vxzeKLamWrqA_xY7I_7/view?usp=sharing
Good Old AM Throws A Challenge
An unexpected new-year surprise awaited the readers of Electronics & Wireless World magazine in the January 1986 issue -- A low distortion, high selectivity Synchrodyne AM tuner...yes, not an FM tuner, but an AM tuner! The coming of FM had sort of relegated AM radio to the dumps, and the general assumption was that AM is such a poor system that it does not warrant high quality circuitry to receive it. JLH throws an open challenge to this situation with his very competent receiver design that takes AM quality virtually to the same level as FM.
As could be expected, JLH goes into a detailed examination of topologies and systems before zeroing in on a preferred design. To follow him here is to be led by the Master into the virtually unexplored territory of AM signal handling. Parts 2 & 3 complete the design of the extremely capable AM receiving system, perhaps only limited by the quality of the transmitted signal. DIYers wishing to be introduced to the new territory of radio reception are most welcome to sit down for a master class.
https://drive.google.com/file/d/1CBNRaB0g56V-D8pYjxg4vf9-c7Ohmy_Q/view?usp=sharing
Putting Quality Back into AM Radio
Another topic related to the above design was offered by JLH in the Oct, 1986, issue of E&WW, that explored an unusual design to try and put quality back into AM radio, a system that was treated as 'second best'. It is wonderful to see how the mastery of JLH in an uncommon topic unfolds as he examines the nitty gritty of AM circuitry and evolves his design. A complete simple, yet high quality, AM radio design is offered by the end of the article. Worth a read, if only to introduce oneself to the ins and outs of quality radio reception.
https://drive.google.com/file/d/1DFjFDDDUrCycbhDG9pQT6rCdUkJ_CFl9/view?usp=sharing
Milestones in Solid-State Audio
With the decade drawing to a close, it was perhaps time for the Master to look back and take stock, and assess how far solid-state technology has advanced vis-a-vis audio power amplifier design. (E&WW-Nov-Dec 1989, Jan 1990.) To think that this is a general overview is the first mistake the reader will make if he is unfamiliar with the meticulousness of JLH. It is a research study into the state of the art over the past few decades, starting with the inception of solid-state audio amplifiers from the late 1950s till 1970s, tracking down the subtle engineering mistakes that marked many of the designs of the era.
The opening part examines the ill effects that plagued typical early solid-state amplifiers and their causes. This had resulted in the prevalent negative comments about "transistor sound" being 'thin and lacking in warmth' when compared to the fuller and richer sound provided by valve amplifiers of the day. As JLH rightly points out, basically this issue was at the core of the emerging school of 'pure subjectivity', that openly diverged from the 'specs brigade' -- many early solid-state amplifiers had rather good specifications on paper, but did poorly in comparative auditions.
JLH recalls how he had turned to pure Class-A operation to sidestep these unavoidable ills which were the result of the shortcomings of solid-state technology of the period. He goes on to examine how designers like Baxandall and I.M. Shaw had proposed circuit topologies capable of overcoming these limitations. He then examines the progress that led to direct-coupled circuits that promised better performance.
In Part-2 JLH continues to examine design trends and goes on to analyze 'residual effects' that still marred many designs, and how various designers were adopting techniques to move the state of the art forward. The section is an excellent and detailed introduction to 'feed forward' techniques as exemplified in various successful commercial designs, augured by Peter Walker's "current dumping" (an unfortunate name!) amplifier for Quad .
In the concluding part JLH takes a detailed look at the design of highly linear design stages, and the desirability of avoiding feedback techniques as a shortcut to correct the performance of amplifiers that had inherent design flaws. Commercial designs as well as his own tried and tested circuits are examined in some detail. Then he moves on to consider amplifier power supplies, an oft ignored part. He stresses the need for a good power supply unit, which is the only way to help the amplifier 'put out its best'.
JLH moves on to the finer aspects of test and measurement and points out how inadequacies in testing had led to many early design errors. His assessment of testing methodologies and the importance of subjective evaluation of 'quality' are indeed eye-opening. He argues for valid and standardized norms for testing all aspects of the 'goodness' of an amplifier, which unfortunately we have not been able to develop fully. Here again we come face-to-face with the subjective/objective dichotomy, and the voice of JLH is perhaps a rare one arguing for an educated balance in such situations. He nails the basic problem of specs and measurement thus: " There are certainly other things which also have an effect on sound quality which we could measure -- if only we knew where to look". Knowing and deciding on what all to measure is something on which the jury is still out.
The series provides an overall enjoyable read for the circuit enthusiast and DIYer as JLH, with his characteristic aplomb and expertise, not to speak of simplicity, clarity and erudition, throws light on design issues that had remained vague and dark. A fitting series on audio nuances to mark the end of the decade, in my opinion.
https://drive.google.com/file/d/1XAdfAnaPcZPZkFzA3gJkScaT6J0-oo0X/view?usp=sharing
The Bias Report from JLH
JLH is at his humorous best opening the article on bias in the September, 1986, issue of ETI. Yes, bias means tape recording HF bias without which hi-fi recording is impossible.
Today we do not care (or know!) much about this arcane topic. In his typical style JLH takes us along from first principles to the complexities of the topic, delineating how setting the correct bias is of prime importance in tape recording. A great introduction to a topic that to my knowledge never received much exposure in the technical press. Most recommended.
https://drive.google.com/file/d/1BOywJgVQ_ZjI7FwWqR3F5eQsziYnaFrS/view?usp=sharing
FM -- From the Beginning
Here is a great series on FM radio, capped by a top-notch PLL FM Receiver build.
An excellent introduction to FM radio was published in the ETI in Dec, 1986 - Jan 1987, which was a preamble to the high quality FM tuner that was to follow in the February, 1987 issue. From the basics of FM radio broadcast and reception, JLH moves on to details of good FM receiver design in the second part. He also illustrates modern practices like a chip-based high quality FM receiver. For the reader whose ideas about FM radio is somewhat sketchy, an excellent opportunity to polish up his technical competence.
Part-1: https://drive.google.com/file/d/13BR2f5RRJqn5lwD9-YZMGjmUUwbmzHBU/view?usp=sharing
Part-2: https://drive.google.com/file/d/1bj5IvTPwsDsUZ-XSY-AisZZbArtQiPEX/view?usp=sharing
Low Distortion Stereo FM Decoder
ETI February, 1987, issue saw the publication of a practical low distortion stereo FM decoder board, which followed after his previous background articles. JLH discusses all aspects of the system before coming to the circuit of the decoder and its building. As we know, a high quality decoder is at the heart of any good stereo FM receiver, and here was one that bettered most of the commercial offerings of the day.
https://drive.google.com/file/d/1l71Q7c1fLgkINTnO_6HN4m-J7PwcpCgZ/view?usp=sharing
PLL FM Tuner
The discussions of the previous months in ETI naturally led to the design of a state-of-the-art PLL FM tuner in the March, 1987, issue. Needless to say, this design by the Master in fact was a very popular project at the time, and set the trend which was soon followed by many commercial products. The quality offered by the low distortion / high fidelity design stole the hearts of music lovers, and the simple implementation made it the darling of DIYers.
Today when the hobbyist more often "plays with black box chip modules", the series by JLH offers an excellent opportunity for the electronics enthusiast to update himself with the "how and why" of the workings of advanced circuitry. Certainly a must-read, as I see it.
Part-1: https://drive.google.com/file/d/1sjJPbA4qlPIluU6CKNDU2IcenvRtQDad/view?usp=sharing
Part-2: https://drive.google.com/file/d/1uUWiVedTX-6HFl1zewvlaIxNM-ird3F9/view?usp=sharing
Active Filter Calculations Made Easy!
Every engineer know what a pain it is to design and calculate the values for active filter modules. Here (WW, Feb, 1984) JLH has simplified the procedure considerably, using the Texas Instruments and Hewlett-Packard programmable calculators.
More involved active filter calculations by Kamil Kraus is appended to the article here. Not for the faint of heart form whom maths is not a strong point!
https://drive.google.com/file/d/1Dt-qEGY0N2BfsQBXYXsAf1KfVVnAXWgC/view?usp=sharing
Necessity, they say, is the mother of invention!
So true in the case of the master inventor and designer JLH! As we know from his own admission, whenever he felt a need for something or other, be it a cassette recorder, an amplifier, or an accurate test instrument, he would set about designing and building one ... and sharing it with his beloved readers!
Here are a few more such instances when his necessity spurred him on to invention !!
Simple Capacitance Meter
For long the hobbyist has been handicapped by the lack of a simple instrument to measure and verify the value of capacitors. As a 'hands-on' hobbyist, JLH was only too aware of this difficulty.
Here (ETI, Nov, 1984) JLH sketches out the design of such a simple instrument and its construction. A simpler and cheaper capacitance meter you could not find, then or now, if you ask me. Go read, and build it!
https://drive.google.com/file/d/10M9dGITIDL-vukhfak9uLCSII0cHIrEY/view?usp=sharing
Strain-gauge Weighing Scale
JLH the engineer and designer had another hobby -- photography. And here are a couple of serious and practical projects triggered by his hobby needs.
Back in those days film / print development called for extremely accurate mixing of chemicals that made up the developer solutions. Rather than buy an expensive chemical balance, JLH set out to design and build a highly linear and sensitive electronic scales with a range of 0.1 gram to 1 kilogram.
The design (WW, Oct, 1983) is noted for its mechanical ingenuity and electronic wizardry. Whether today you need such an instrument or not, it makes for excellent reading if you are a "true blue" hobbyist who wishes to be inspired by greats like JLH.
https://drive.google.com/file/d/1w1zRnoDTLtPXwa0KoQrZvXpVkLknyWBC/view?usp=sharing
Automatic Enlarger Timer
Here is the second project from JLH, the master photographer! As old timers know, the dark room was the 'work shop' of the ardent photographer and the creative process that began with the clicking of the camera shutter ended only with the final print made with the help of the enlarger. And exposure was critical at both these stages.
There are quite a few practical issues to be addressed here while designing an automatic enlarger timer, and JLH examines them in detail here, and emerges with a great design. (WW, May, 1985) The circuit offers 'real time' exposure measurement and control.
Great reading if only to familiarize yourself with the arcane world of black & white photographic practices from the last century!
https://drive.google.com/file/d/1Pc0d_r1ucOqCUcLBLvQvJOXM_XWYI1DS/view?usp=sharing
In the next post we shall move on to the exciting 1990s and examine the contribution of JLH to the advancement of the art and science of audio design.
Until then, read, enjoy, comment and share.
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Very useful article indeed 👍😍
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