JLH Memorabilia -- The Past Perfect! :: 5

Annals of a Life in Tech - Nuggets from the '90s

        If the 1980s were hectic and jam packed with projects, the 1990s were more sedate. The Master was well nigh in his seventies, but neither his keen intellect nor his productivity were on the wane. The decade was marked by many significant designs from him.

        Naturally the lion's share of the articles were published in the Electronics and Wireless World magazine, the rest going to Electronics Today Internatiional, Everyday Practical Electronics and a newly launched magazine, Electronics in Action (an electronics magazine possibly with  the shortest lifespan, which soon folded up). As always his explorations into theory or the background of design are eminently readable, marked by a lightness of treatment and clarity of presentation rarely seen in technical papers. Let us examine the major articles first before going into the smaller projects.

Audio Design Masterclass -- Preamplifiers

        In June, 1990, Electronics and Wireless World announced a three-part series of articles on preamplifier design by JLH. As could be expected, this presented a detailed examination and evaluation of preamplifier design techniques over the past few decades and how it had evolved from the 1960s to the present. (This was the complement to his earlier series  on the  design of  audio power amplifiers.) Part-1 goes into considerable detail about the design of RIAA Eq preamps, examining the various pitfalls and clear solutions. Practical examples are cited and examined in detail. The article closes with an examination of the requirements of high sensitivity/low noise Moving Coil pickup preamps, including his own design which turned to an unconventional approach -- using small power transistors in a successful design to offer low input impedance and extremely low noise with standard devices.

        For the student and reader, nothing impresses more than the set of comprehensive references quoted at the end of each of the chapters. No doubt, JLH, ever the meticulous designer, had assiduously followed virtually the entire work till date by designers of note of the period.

Part-1: https://drive.google.com/file/d/1BH09NkpcqlSC81SzP8kbcLMMGG8YfhRg/view?usp=sharing

        Part-2 of the series takes up a discussion of dynamics and headroom and its importance. For the student and hobbyist wishing to go deeper into the "how and why" of preamp design, this is highly recommended reading, not an easy topic for explication. Again headroom in audio equipment is a topic that has generated so much of 'hot air' (often baseless or misguided), and JLH's masterly treatment for once establishes a solid base for our understanding of the tricky terrain.

An in-depth look at tone controls, graphic and parametric EQs is next, including a study of his famous and versatile 'Clapham Junction' tone control circuitry. (see detailed coverage in earlier posts.) For the enthusiast this series has proved to be the proverbial light shone on the black art of preamplifier design.

Part-2: https://drive.google.com/file/d/1sJClgQNpT_u6fj1TMlr4o_vwrKOyS0-i/view?usp=sharing

        Part-3 deals with apparently simple, yet critical aspects of gain controls, input switching and other such 'mudane' subjects -- which have all along remained 'mundane' and deserving of not much attention from most designers; JLH with his characteristic approach reveals how inattention to even such mundane factors is likely to affect fidelity in its totality. Last, but not the least, in any amp or preamp design is the power supply, oft ignored and sometimes abused. JLH leads us to an in-depth examination of the power supply and its importance in assuring fidelity and performance of any amplifier system. (Kindly note that in the original magazine article, a few pages were mixed up; it has been rectified in the posted article linked to here.)

Part-3: https://drive.google.com/file/d/19juV2kaQq4M9mLPIM-KP2ljYtP6pueZZ/view?usp=sharing

Hi-Q Modular Preamplifier

        Electronics Today International published a popular project in April / May, 1992 -- a High Quality Modular Preamplifier by JLH. The Editors had requested this as a complement to their top drawer 80 W MOSFET amplifier . (see 'Simply the Best Amp' in the previous post) Naturally this meant that the preamplifier had to meet or exceed the specs of popular commercial offerings of the time.

        The design offered a rather elaborate RIAA Eq pre, with a balanced FET/bipolar gain block that easily approached the performance of high quality op-amps, and probably surpassed them in HF phase linearity. Also, complex signal switching using relays was offered on par with the top-end commercial designs. The involved discussion about shunt and series feedback, distortion and noise is at text book level though considerably more lucid! Also the comparative merits of ICs versus discrete circuitry is examined.

        Notice how much design thinking has gone into the tone control, which normally designers just 'add on' with not much thought, or, at the other extreme, 'purist designers' do entirely without. A high quality class-A headphone amplifier and a dedicated regulated power supply complete the design. As always, JLH's articles are not mere project presentations -- they are indeed a 'master class' in design thinking as we have seen elsewhere time and again.

Part-1: https://drive.google.com/file/d/1uXD7xHjyq_bOwP8xroMAklGvW6JDYaqQ/view?usp=sharing 

Part-2: https://drive.google.com/file/d/1NkS7M6fIGJ80tG6b-0a-wgCdF15LplJO/view?usp=sharing

Audio Design -- Engineering or Alchemy?

        Here is another popular series that JLH researched and wrote for the Everyday Practical Electronics magazine in (Aug, Sep, Oct) 1993. JLH, with characteristic aplomb, gets into the tricky battlefield of the subjectivists (mostly hobbyists and audiophiles) versus the objectivists (the engineers and others classed as the 'measurements gang'). As a designer of amplifiers, he admits at the outset that he is uncomfortably "sandwiched" between these opposing camps. 

        Meticulously and with well-argued examples JLH debunks the fallacies and throws light on the critical deciding factors of fidelity. It is wonderful to note how the Master asks a lot of 'unpleasant' questions, and answers them all with clarity and insight. He gets into the basics and the "nitty-gritty" of each and every component in the chain of amplification, while at the same time pooh-poohs many highly hyped topics too. Overall an excellent read for the serious hobbyist who wishes to be guided not by hype and hoopla, but by reasonable and solid facts that form the very basis of an approach to true fidelity.

Part-1: https://drive.google.com/file/d/1v47xxZ9JzRtKLSuiDNlOheKpMkU_g-HT/view?usp=sharing

Part-2: https://drive.google.com/file/d/1ebR9XFA7_VQyR8MDs5g9buPpG59AOpgK/view?usp=sharing

Part-3: https://drive.google.com/file/d/1CC0AaDSqtFrEqY8SMk_JqASUXPNbt0GL/view?usp=sharing 

Evolution of Audio Design

        The topic invites immediate comparison with the various series of articles that JLH had contributed earlier to both EWW and ETI magazines. This series appeared in a "new kid on the block" mag called the Electronics in Action, who apparently requested a series from the Master in order to pull in new readers. The new magazine was edited by the much experienced Paul Freeman-Sear, formerly with the ETI, and kicked off publication in October, 1993. JLH's series Evolution of Audio Design ran from Feb to June, 1994, inviting much reader enthusiasm. However, the magazine ceased publication abruptly in July, 1994 -- perhaps the shortest-lived magazine in the history of audio and hobby electronics.

        Be that as it may, it does not detract in the least from our interest in the Master's overview of the evolution of audio design approaches. For the readers familiar with his earlier works of a similar nature, this series is quite striking in that it is not a "carbon copy" of his earlier paper, but rather a fresh appraisal of the audio scene. This alone makes it a must read for all of us as there is nothing like "too much of a good thing" in life.

Part-1: https://drive.google.com/file/d/1Cgu5MGZDn6FjshDr3zm8e9XP8b-J9pPM/view?usp=sharing

Part-2: https://drive.google.com/file/d/1lTgk2ReE6Y7Or4X3HFNrZvggTjrtxyU1/view?usp=sharing

Part-3: https://drive.google.com/file/d/1nAr-AZS1XZNWbvVX2vVNcxeZ6jSjMMep/view?usp=sharing

Part-4: https://drive.google.com/file/d/1JBncNguq2IEvtTYZeiR_ojQ12OJ-Cqt2/view?usp=sharing

Part-5: https://drive.google.com/file/d/1Kugi9xuUX5cdN4S_abiLlr4dm4eVWBfL/view?usp=sharing 

        We will be examining the remainder of the projects from the 1990s in the next post. Until then happy reading of some rare and authoritative stuff from JLH -- which is guaranteed to make one a better-informed hobbyist or audiophile ! 

* * * * * * * * * * * *


Comments

Post a Comment

Popular posts from this blog

JLH Memorabilia -- The Past Perfect! :: 2

Image
Annals of a Life in Tech  - the 1970s            Here is a peek through the window of time into the distant past when the likes of John Linsley Hood walked the earth, and did his best to give us nuggets of audio finery, and shared his considerable wisdom with us. Through these authentic archives it is hoped that the rich legacy of JLH shall be kept alive for the benefit of the generations to come. Open Sesame !!  Transistor Theory           As we know, transistors were a novelty and a curiosity in the 1960s, and designers, most of whom had (including JLH) grown up in the valve/tube era,  were getting to grips with the fickle and not so hardy devices. This article published towards the end of 1969 illustrates JLH's preoccupation with designing for quality. His detailed analyses of transistor circuits is an excellent "teach-in" for aspiring students and designers even today, as his insights into the working of...
Read more

JLH Memorabilia -- The Past Perfect!

Image
Annals of a Life in Tech :: 1 John Linsley Hood -- a name that refuses to fade into the sunset as far as the tech world and the DIYers are concerned. It has been more than half a century since JLH came into popularity among audio DIYers with his classic "Simple Class-A Amplifier. Despite the passage of these long decades, the interest in the little amplifer has refused to die; on the contrary, fresh interest and enthusiasm among the DIYers, particularly the younger set who were not even born at the time, is kindling renewed interest in the design by the Master, and a concomitant search for his broader technical output.           One thing I have noticed while on the discussion Forums is the fact that the name JLH, though familiar to most, does NOT sort of "ring the proper bell", so to put it. People just know him as the designer of the classic little amplifier which has managed to maintain its popularity over the decades by sheer luck, perhaps. Period. The...
Read more

JLH Memorabilia -- The Past Perfect! :: 4

Image
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 ...
Read more