The JLH Gateway to Class-A :: 4

Building the JLH Classic --  Gilding the Lily

JLH Strikes again!

The avid designer and hobbyist that he was, JLH did not rest on his laurels after the unprecedented interest and dedicated following that his class-A amplifier design generated. As we saw earlier, JLH was not casually designing something for an audience; rather, his primary aim was to derive musical pleasure from his designs, which he built with his own hands. Surely we must give him credit for being updated with the contemporary happenings in the audio electronics field on both sides of the Atlantic, with a score of other designs emerging, shooting for improved performance, power etc. 

The Americans apparently were going in another direction, mostly chasing high powered amplifiers and huge speakers. This admirably fell in with their larger homes/rooms and their taste for 'big band' sound. A cursory glance at the contemporary technical journals will vouch for the veracity of this observation. Particular mention must be made of the 'Tiger' series of amplifiers by the talented designer Daniel Meyer (Popular Electronics, 1967 thru 1971)-- one could pick from a 'cat's meow' to a tiger's roar, all Class-AB and rather good! It would be of academic interest to study those designs; we will do that if there is sufficient demand for that.)

Daniel Meyer's 'Tiger' series amplifiers

While on this side of the Pond, the situation was somewhat contrary and laid back. The British, with their smaller homes and living rooms, and their love for chamber music and choral pieces, solo instrumentalists and club jazz, preferred the more intimate performance made possible by smaller, better imaging speakers and mostly Class-A or other medium-powered, but refined, Class-AB amplifiers. This major difference in tastes is very evident in the published DIY-oriented material, as well as in the  range of popular commercial offerings.

JLH was a "hands-on" kind of experimenter and builder too -- most of his published designs he had built with his own hands and evaluated over a long period of critical audition! And once he had analyzed the new designs of  his peers, it is more than likely he would have wired up and tested them, often trying out various mods and refinements. We had seen this happen even before the design and publication of his "Simple Class-A Amplifier". As a designer following the emerging trends, and as a music enthusiast listening to 'his own baby' day in and day out, it must have occurred to him to try and refine his own design and present the results to his beloved readers.

The Polished Classic

JLH admits that in the years of serious audition following the Classic 1069, he had felt that the Class-A amplifier was indistinguishable from his first love, the Williamson valve amplifier, and so he gave that away to a friend. Now the intervening 25 plus years had seen many developments and audio trends that held sway among audiophiles. And the Master was not idle -- he continued to evaluate his design in the light of contemporary thinking, and the results were published in Electronics World (formerly Wireless World), Sep 1996.

Here is the Web link to the original article:

https://drive.google.com/file/d/1xlZTfldsAhbz9HMuwOMovROpAH9Irzve/view?usp=sharing

His take on the refinements to the 1969 design were:

# An elegant means to easily set the quiescent current of Tr2.

# Switch to a symmetrical +/- power supply, so that the loudspeaker could be DC coupled -- the current trend so favoured by designers and audiophiles alike, especially by the "no capacitors in the signal path" brigade. (We shall take a deeper look at that 'audiophile clamour' in a moment.) The Master chose a simple method (so typical of his style!) to implement that. It has to be noted, though, that DC coupling of the speaker has no bearing on THD, either measured or subjective. As a matter of fact, it DOES bring in a very clear and present danger to the (expensive!) loudspeaker, in the event the amplifier experiences a fault, and DC fries the speaker voice coil -- which would necessitate speaker protection circuitry, mostly relay operated. ( Hmmmm... real audiophiles don't like relay contacts in the signal path ... LoL.)

# Nudge the output power to about 15 W, near enough to that of the Williamson amp.

# Upgrade the unregulated version of the power supply; more than anyone else, JLH appreciated the role and duty of the PSU in determining the amplifier's perceived quality. 

Letters-EW, Jan 1997

There is a minor error in the circuit printed in the EW. Refer to JLH's letter as well as to the corrected circuit diagram here.

The enhancements, as chosen by JLH, did take the amplifier into the "modern" era. Of course, it did find an enthusiastic following among DIYers, and to judge by the number of companies offering full kits of the design, it was a highly popular design able to hold its own against many contemporary commercial products. For the JLH enthusiast, here was an opportunity to "upgrade" his classic build -- and continue to use it with satisfaction! Remember more than a quarter century had passed, and the good old design was still sailing on with flying colours!

The JLH Amplifier - v.1996
(final, with corrections)

Audiophile brouhaha and all that

Since the day the Classic JLH was introduced to the world, there came onto the audio stage a score of new designs, both DIY and commercial. Most of these were higher powered Class-AB amplifiers, and as everybody knows, the "audiophile" always is hankering after more power, as if that was the ultimate determiner of sound quality. Commercial amp designers and companies knew this very well and happily continued to feed the notions of the audio hobby tribe,so that they could go on 'milking' them.

Of course, there were occasions when you needed higher power to drive inefficient speakers to realistic levels. But then a high power class-A amplifier was as good as a room heater, and about a hundred times more expensive. The sensible thing to do in such a situation was to ditch such speakers and move on to efficient and simpler speaker designs. Try and have a listen to a 2 -- 3 Watt single valve amplifier driving an efficient speaker, and you will jettison all your notions about power and sound levels! About 4--5 Watts is more than enough for any normal, average living room, and 15 W will drive the speaker twice as loud. (The power relationship is geometrical, with a 4 W amp sounding twice as loud as a 2 W amp, and it would take a 16 W amp  to sound twice as loud as a 4 W amplifier! Well, that is another story!)

Banish the Caps!

God knows who injected this notion into the "audiophile" mind. It was with the coming of the DC coupled amplifiers that this notion spread worldwide. Naturally companies wanted to have exciting "new developments" that made their amplifiers uniquely superior, and here was great ad copy -- " no dirty capacitors in the sacrosanct signal path that degrades the sound in our amplifiers...". And the rest, as they say, is history -- the entire audiophool crowd took lustily after the Pied Piper.

It doesn't take a PhD to know that there are good capacitors, and not so good ones in this world. But it is the duty of the designer to select and specify a part that meets his design requirements. Of course, in engineering there is a bit of "over-spec-ing" to take care of spreads in manufacturing, aging of the component over time and other factors. If the designer has selected a particular part on the basis of its specs, and okayed it after measurement of the completed equipment, and in the case of an audio amplifier, found it more than satisfactory after a slew of subjective listening tests etc, then I believe the average hobyyist should leave it at that. We all know commercial designs have to meet the "bottom line" and it is a fact that often corners are cut to maintain profitability. But certainly not so in the case of a DIY design. Especially when the designer happens to be "designing to satisfy himself", like JLH was doing.

It is funny how the "anti-capacitor" brigade forget certain basic engineering truths, probably out of their over-enthusiasm coupled with sheer ignorance. As we all know (or should!), the amplifier handles AC signals. Even though the amplifier might be totally DC coupled, the output devices act as (in simple layman's parlance) taps controlling the flow of music signals into the speaker. They are only controlling faucets, but the power is coming from an overhead tank -- the power supply filter capacitors! Don't those capacitors affect the flow of the audio signals across them? Ha ha, the laugh is on you! (No wonder Jean Hiraga always listened to music with his Le Monstre amplifier connected to a set ofheavy forklift battteries, as he thought no conventional power supply was able to mimic a huge battery as a power source -- absolutely no compression of music dynamics because the wimpy power supply couldn't supply the oomph !!)

Here a humble experiment may be suggested to the DIYer. Listen to an amp and "get to know it" well over a period. Go and build a "no holds barred" power supply to replace the built-in one, and then do an audition. What do you hear? If you did not hear a change (good, or bad!), you are not qualified to be in the hobby, I daresay.

Capping it up

So, what is my take on caps?

Select the caps, particularly electrolytics, for low ESR and make sure their values meet the circuit requirements adequately, then over-rate a bit, and you should be home comfortably. JLH has specified four capacitors in the Classic v.1969, and just two in the v. 1996. Try various brands/types, slight changes of values etc (in the case of the Classic1969 output capacitor, some capable designers have recommended more than 20,000 uF!) one by one only on ONE channel; do comparative auditions over a couple of weeks, preferably including some late-night longer sessions to identify if there are any new 'listener fatigue' factors at work. Select what you find as improvements, and be done with it. And DO NOT FORGET to give equivalent TLC to those humble power supply reservoir caps and the decoupling caps, and you are sure to be not far off the mark, if you ask me.

No need to pollute your 'golden ears' with blah-blah from the "knowledgeable" crowd -- believe in your own ears; seeing is believing ... hearing it oneself is believing, and phooey to critics and naysayers!! It is your home, your amp, your music. Period.

We would be fools to imagine that JLH would be content to take it easy and rest on his laurels. For him chasing the ultimate audio quality was a perennial quest. His continual labours of a quarter century bore fruit, and the JLH fans were lucky to get newer "enhancements" of the design from the Master himself.

Many designers (two names crop up often, those of Geoff Moss and Graham Maynard, who held JLH in high esteem) have suggested improvements to the basic design and we will take that up in one of the future posts. 

Until the next post, read, share and comment, and plan your build based on these inputs I have been able to gather for you.

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