The JLH Gateway to Class-A :: 7

The Millennial March-past

The simple, yet novel circuitry of the JLH did indeed trigger the creativity of DIYers and 'circuit honchos'. Quite a few among them, who were respected designers in their own right, came out with namesake amplifier designs, and that was how we got to see the PLH, DLH etc series of amplifiers joining the Class-A cavalcade.

Guess what! The PLH amplifier which came out in 2005, was by the "grand-daddy of audio design" Mr Nelson Pass. As Mr Pass so disarmingly puts it " ... I stripped down the JLH to the simpler MOSFET topology ... and (ahem!) added my initial to the name!"

        But it is heartening to see how a great designer like Mr Pass pays his respects to another genius designer like JLH. How Pass analyzes the JLH circuit is a good lesson for enthusiasts, and the entire article is recommended (repeated) reading, if you ask me. The reader is enjoined to visit the Passdiy site for a detailed post (as is typical of Mr Pass) on the design, as also to check out the in-depth discussion of PLH on DIYAUDIO, with some slight mods thrown in. Those of you who are fond of MOSFET amplifier designs may definitely think of a build and some prolonged comparative auditions.

https://www.passdiy.com/gallery/amplifiers/the-plh-amplifier

https://www.diyaudio.com/community/threads/nostalgia-the-all-fet-jlh-plh-class-a-amplifier.203915/


Another less famous Millennial namesake is the DLH amplifier published in DIYAUDIO much later in 2017 by Horacio Diego Caminotti, an Argentinian designer, who, like Pass, was happy to append his initial to the JLH as a mark of his respect. It apparently is a very versatile and original take on the basic JLH amplifier, able to drive any speaker load from 2 Ohms upwards. To quote Mr Diego:

" This very simple design has all the ingredients to satisfy even the most demanding DIYers. The output power in pure class A operation is 15.52 W at 2 ohms (@ 1 KHz), or 7.76 W at 4 ohms, or 3.88 W at 8 ohms. THD is only 0.025 % at 15.52 W and 1 KHz (2 ohms),  0.0024 % at 7.76 W and 1 KHz (4 ohms), and  0.00091 % at 3.88 W and 1 KHz (8 ohms). 

The amp has only two stages and Voltage gain = 8,9 dB... only four transistors... performance is surprisingly good, despite its simplicity... High bandwidth ... Ultra low distortion... Output in single-ended or push pull configuration, entirely adjustable by the position of a trimpot... PSRR: 61 dB across the entire audio bandwidth."

Look at that! One of the lowest distortion figures at a range of loudspeaker load impedances. And the unique feature of being able to switch the amp between push-pull and single-ended operation. If that won't persuade you to try the build, nothing will ever, I guess. Do be warned though, if the output is set in perfect push pull configuration using two identical N-channel MOSFETs, distortion will be extremely low on account of H2 cancellation -- so it is imperative that the builder does a lot of auditions to decide which 'sound' he prefers: with the second harmonic, or without.

https://www.diyaudio.com/community/threads/dlh-amplifier-the-trilogy-with-plh-and-jlh-amps.311567/


An interesting adaptation published in 2014  of the JLH Classic is from the Tube Guru John Broskie, whose prolific and original output should be a source of inspiration for enthusiasts. Let us christen it the BLH ! (no, Broskie has not done that!)  A quality for which I appreciate Mr Broskie much is his versatility with and acceptance of "mixed topologies" (tube + solid state, which are usually 'mutually exclusive' in the minds of most other designers and DIYers ), of which he is indeed a master. Understanding and blending tube and solid state devices and circuits, as per their strengths and weaknesses, is not a strong point of many designers, it has to be admitted. 

The BLH Amplifier

After an excellent analysis of class-A operation, Broskie moves onto a 300B tube amplifier. As you scroll down the page, you will come to the introduction to the Classic JLH amplifier, and Broskie's mod using a Bastode (very much like a cascode topology, a sort of 'vertical' differential amplifier) input/driver/phase splitter stage.  Mr Broskie, in his typical style, then elaborates the design, in the meantime making wry comments about the "no-capacitor brigade" audiophiles and their follies. Sure does make for an interesting and educative read. Just follow the link here.

https://drive.google.com/file/d/1Nrkh-hFT1Yr5HwvALMtu1KXrjiVeZ_md/view?usp=sharing


One design that I  would happily include in the march-past of JLH namesakes is the DoZ (Death of Zen) amplifier by Mr Rod Elliot of ESP, published at the turn of the last century in 1999. Though Mr Elliot had trained his guns on Mr Pass and his Zen amplifier for his own reasons, I am happy that Elliot has acknowledged that his design bears some resemblance to the JLH Classic. When I recently took up this topic with him and requested him to change its name to ELH, (really! ... it takes true ESP ((extra sensory perception, not Elliot Sound Products!)) to design stuff that resembles each other!) he politely, but firmly, declined. With profuse apologies to him, let me refer to it here as the ELH just for our convenience. Maybe he would be kind enough to us JLH fans, and favour us with a true ELH amplifier of his design sooner than later!

The DoZ - 'ELH' Amplifier

From my experience of having built and listened to a series of DoZ amplifiers over the decades, including half a dozen modules very recently, I dare say that in sound signature too the DoZ is very near to the JLH Classic. I would solidly recommend the DoZ to any DIYer who values subjective quality and realism in amplifiers.

https://sound-au.com/project36.htm

https://sound-au.com/project70.htm


Like the Beatles, the above list also makes a "Fab Four", and you would not be far off the mark if you select any one of them for a build. The only thing that could beat that is to select perhaps ALL of them, and build and listen ... and listen ... and listen! That sure would be a RICH experience that could easily top almost all other 'rich experiences' in life !

Do read and enjoy, and build and listen AND enjoy!!

Let us see which will be faster -- your next build, or my next post!

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


Comments

Post a Comment

Popular posts from this blog

The JLH Gateway to Class-A - A Golden Jubilee Tribute

Image
Gateway to Class-A -- Building the JLH Classic-1969 John Linsley-Hood (1925 -- 2004) Audio designer nonpareil John Linsley-Hood -- Truly a legendary name in audio electronics, whose signature Class-A amplifier design has achieved cult status and the 'classic' moniker in our times. More than half a century after publication (in Wireless World, April 1969), his "Simple Class-A 10 W amplifier"  is considered unmatched in simplicity and subjective audio quality. In this series of posts my attempt is to preserve for enthusiasts and DIYers the work of this great man, and perhaps offer a gateway, a "single window", into the audio world of 'JLH' (as he is fondly known worldwide), with the stress on the Classic-1969 design. The material presented here from authentic archives and other sources in my decades-old collection, is sure to keep enthusiasts occupied for many summers and winters, reading, building, and enjoying the fruits of the build in the manner...
Read more

The JLH Gateway to Class-A :: 3

Image
Building the JLH Classic --  Milestones of the Era Today, as we look back and focus our sights on the JLH Classic, it would be educative to broadly, though briefly, survey the audio electronics landscape of the era. Unarguably that alone would reveal the correct perspective regarding the genius of JLH and his timeless design, rather than label his class-A amplifier as 'one of the typical designs' of the era. Happily the JLH Class-A was not just another 'typical design' of the period -- it had nothing that went before it, and on which it was based. Not only that, the design had many unique features despite appearing to be quite basic. Suffice to say, its apparent simplicity hid within itself many subtleties of design not easily revealed to the casual investigator or circuit hacker. No wonder it has defied the efforts of many talented designers to 'pin it down' and analyze it threadbare.  GOM and old timer Nigel Pearson has put it wonderfully thus: "It makes ...
Read more

The JLH Gateway to Class-A :: 2

Image
Building the JLH Classic --  The JLH Archives           Looking back, it can be seen that 1969 was an epochal year for JLH fans -- the Master published the iconic "Simple Class-A Amplifier" in April and later, in July of the same year, the "Modular Pre-amplifier Design" in the Wireless World magazine, the grand old dame of UK "wireless" publishing. As they often say, "the rest is history"! History continued to be made in the long fifty years plus after the publication of that article by ardent enthusiasts and DIYers.           True to the article title, the design presented an extremely simple (and elegant!) class-A power amplifier with just four transistors and a handful of passive components, which could often be scrounged from the 'junk box' of the average DIYer. As is often the case with class-A amplifiers, the expensive parts were the rather substantial (when compared to class-B amplifers) heatsinks and the heavy powe...
Read more