Endeavouring to shine with a JLH 1969

Hello all,

I've been reading another forum thread where some say one thing some say another and then a third disagrees with both. But after a few weeks I pulled out the bit I liked, very nearly a consensus on this one ... that the transistors close to the originals would be the right way to go, it's what the circuit was designed for, commonsense? Well it would be wouldn't it.

Anyway here's a link to the original article: JLH 1969 Original Article.pdf This is not a dog eared photocopy but the cleaned up version.

And this is the circuit I'll be using

I use MA CHP-70's in FH3's which are 4.0 Ohm, I'll be using the 17V line in the table above.

More soon

Hello all,

Mistake No 1

When I began to look at this amp I found lots of schematics and kits with two little blue trimmers one for the 1/2 voltage and the other to adust the quiescent current. Thinking in my ignorance that this was the way to do it I went ahead and made this.

Tried it ... nothing ... the QC trimmer had gone PfffT! They will only take 0.5 Watts! R2 in the pic above has to be 1 Watt!! I had put stuff on veropins which was both fortunate and unfortunate, fortunate in that I was able to remove the trimmer and replace it with a fixed resistor ... still nothing ... I turned the board over and found a loose veropin, soldered that back in place and that didn't work either.

I noticed that I could push the pins into the board with my finger nails, which I was unable to do when I found a bit of old proper Veroboard ello, ello watts all dis den I thought. Looking closely at the new board I realised that the holes were not gripping the pins properly, feebly would be a better description. Every time I turned the board over with all those wires attached more pins came loose.

Ah well, there we go, such is life etc, but then I'd bought one Chinese kit with two trimmers, how did they get around the 0.5 Watt?

More soon

Cheers - J
Hello Katalyst,

The trick is a confidence one :-)

Hello all

Buyer beware (mistake No 2)
Diy Kits 1pcs JLH 1969 class A amplifier Board high quality PCB MOT 2N3055
This is what is says on the eBay listing

This is the kit assembled

The little blue trimmers are; on the left to adjust the 1/2 Voltage and on the right to adjust the Quiescent Current. I got the 1/2V easily, I used a 12V smps brick just to try it. Connecting the 10 Amp readout on my cheapo digital multimeter and adjusting the other trimmer the most I could get out of it at zero ohms was 0.58 Amps. Ahhh I thought by limiting the output with the other resistor the trimmer will not burn out.

12V x 0.58 = 6.96 Watts this is the Quiescent Current on all the time. To work out the amplifier output, I took Mr Hoods 8 Ohm speakers recommended: 27V @ 1.2 Amps = 10 Watts, 27 x 1.2 = 32.4 Watts, 10 divided by 32.4 = 0.31.

Using that multiplier 6.96 x 0.31 = 2.16 Watts and if 24V was put into the circuit that would be about 4 Watts output and is the reason no wattage is mentioned in the eBay listing title, who would buy one if it was?

On to the mechanicals the board is very nice, but, the holes are very very small and would not take any veropins. The layout is for the components they supply and no others. On another forum I see lots of folks saying they've bought this and are going to modify it ...... and then nothing! Attempts at modification would result in a right old mess.

It is also my opinion that mounting the transistors on a piece of aluminium angle is a very poor idea especially as close as they are here, it wouldn't matter with just a few amps but huge ones would be needed to dissipate a large concentration of heat. Mr Hood used direct mounting, one surface to another.

I would urge anyone not to buy this kit, I have also seen the two blue trimmers in ready made JLH amplifiers, with heatsinks that look far too small and the transistors too close together, now I know why.

Back to the source now.

Cheers - J

[edit] Even at two watts I got some sound out of it and it was very nice indeed :-)
[edit 2] In fairness to this kit I was pointed to this on YT, the person in the video did a lot better than I:
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Hello all,

This is the modified schematic I used apologies for posting this again it may help to be able to quickly refer to it.

I then looked closely at the photo of the circuit board Mr Hood used.

He used Lekrokit board, I was able to buy some Matrix board from Cricklewood Electronics very similar with single copper pads on the reverse side.

This is the Matrix board fully populated and ready to be installed, it's so easy to use and the components can be changed very easily they just slide out. I used U shaped pieces of wire to hold some parts down onto the board, soldered to the pads on the other side.

1/. I changed this resistor until I got the Amperage I wanted, using a cheapo digital multimeter, Pos lead to the supply Neg lead to the circuit. The resistor here has to be 1 Watt or as I have used 2 - 1/2 Watt ones in parallel. There are online calculators to do this, if like the above you use two the same value then halve the resistance. To work out the Wattage output multiply your chosen Voltage by your chosen Amperage and multiply that by 0.31.
2/. There are two veropins here connected under the board, these are to take Tr1 Collector, Tr2 Emitter, R1, C1 and the output.
3/. Return the -V from the loudspeaker here.
4/. Another veropin here this goes to the Star ground
5/. The lead on R5 is soldered to the base of Tr4 then under the board to the R5 trimmer, this sets the 1/2 supply voltage at 2.
6/. A veropin where the 39k resistor and the 100uf Capacitor meet, connected to the trimmer under the board, the centre lead of the trimmer is attached to the one of the outer leads.

The pic above is a 2D of a 3D object

To make it clear that the leads from C3 to R4 are just connected to each other.

If anyone does contemplate making the amp in this way I will be only too glad to provide some large printable images of the above, please send me a nice message.

Cheers - J
Hello Katalyst,

Good of you to say that I am grateful, I've started a blog site on Googles Blogspot.
I will be doing a construction PDF, assuming that the reader knows very little about electronics.
I'm in throes of making a wooden box and into a 7 day comparison with my 3886, not from memory but by using a switch between the two as Mr Hood did.

Cheers and thanks - J


Junior Member
Watching your progress with interest. Supposedly my Rod Elliot DoZ amp is related to the JLH Class A amp. I don't know if that is true or not, though.
Hello Tillerman,

I found that DOZ amp, my goodness someone whose actually given a circuit diagram and all the trappings to go with it, brave geezer, even down to making your own heat sinks, that is; if you've got a small Bridgeport Milling machine, a Myford Super 7 lathe and a nice pillar drill. The introduction sounds (is) sour grapes at Mr Pass, they can't resist it can they :-)

The circuit is a bit like the JLH one with only a sprinkling of transistors, but, who am I to judge just an electronical dumbo.

I'm sure it sounds lovely though.

Hello Katalyst,

I will be using the same speakers, one on one side and the other on the other.
The test is proving very interesting and quite revealing not only about the amps but also my ears.

Cheers both - J


Staff member
Nice work. I started the thread on the JLH 69 amp here a few years ago. @TubeHiFiNut and @je2a3 both have the built versions. I think @je2a3 has modified his. I'm liking your work on the DIY set up. Might have to try it too.
Hello Tillerman,

Thanks for the message and yes I did look at that Class A site and the first link to the so called 1969 'article' which of course it isn't. Being a suspicious old git I wondered why and didn't look at anything else. If you would like to compare it with the actual original please use this link: JLH 1969 Original Article.pdf

This is what you find :-)

Hello opa1,

Thanks for your nice comment good of you, I found the link you provided a month or two ago it's in my faves :-) I was thinking of adding to the thread, but as things progressed I thought it best to start a new one.

I do hope that you make one, I have another old git suspicion and that is all the confusing suggestions saying that one lot of transistors is better than another lot and a lot better than the originals, is just something seen on the flickering screens of oscilloscopes and in simulating programs, bless 'em all for doing it :-) But, do they do subjective tests like Mr Hood, doubt it!

And that's another reason I'm doing this to see how it stands up to my 3886.

Good fun innit :-)

Cheers - J
Hello all,

JLH 1969 vs LM3886

I did this test for 8 days I wanted to be sure that my opinions below would reflect the time spent. I was also concerned not to use the daft metaphors one sees on, for instance six loons.

I used the setup you can see here;

Input = One channel from my CD/DVD player through to a switch with two metres of wire
Output = left loudspeaker from the JLH 1969, the right one from the LM3886

By doing this I am able to switch from one amplifier to another instantly and can use the return on the CD/DVD remote to repeat a passage in seconds.

My first reaction was there's not that much difference. After half an hour or more I realised that the JLH sounded a little brighter. This was with Mahler's 1st symphony. The following day I tried some old Jazz, Bessie Smith and Clarence Williams's acoustic recordings from the early 1920's and Lady Day's from 1937, both sounding a bit clearer on the JLH.

I'd listened to these recordings many times and realised that I was listening to what I expected to hear i.e. the 3886 and 3876 before it and not what the JLH was giving me. The JLH still sounded a bit brighter though.

Next up was Norah Jones and 'What am I to you' this time I listened to her and realised that her voice was more up front with the JLH, this is where the switch came into it's own, being able to swap amps instantly identifies ones thoughts like nothing else.

The piano version of the Enigma Variations was next and one particularly loud and fast variation sounded quite brighter on the JLH but a little dull from the 3886. Oh dear I thought there must be something wrong with my speaker on the right.

I removed the drive units and the input lugs from both, resoldered them and undid and re-tightened the cables, I then swapped the speakers left for right and right for left.

Back to the variations and the same result, it wasn't my speakers at all! I thought now I'm on to something here. @Poultrygeist mentioned shimmer in a post with reference to Cymbals. My goodness! A bright light in ones brain, that awoke a recent memory, I'd never heard of the term as aural only as pictorial and thanked him.

Straight back to Norah Jones and yes there it was, a rather dull Cymbal from the 3886 and a clear and fast Shimmer from the JLH. What's going on here I thought and back to the Variations, there it was again that instant brightness as I listened carefully to the JLH.

It then dawned on me what was going on (forgive me I'm just a slow old cheapskate git) it was the ADSR the JLH gives me the spike between A and D the 3886 doesn't;

After that I tried Glenn Gould's Goldberg's I could hear him better on the JLH, maybe not such a good thing! Then Julian Breams BBC series Guitarra I could hear his breathing and his jacket rustling and his fingers sliding up the fret (not just the squeaks) at first I didn't believe it and played them over and over again on a couple of days to make sure.

Back to Mahler and the 1st symphony by this time I was used to the brighter sound and listened for the bass drums in the background, a dull rumble on the 3886 I'd never taken much notice of, on the JLH a clearer more concise sound, by this time I wasn't surprised at all everything the 3886 did was a little better on the JLH.

I'd saved Tangerine Dream for a few days, this is the new trio with their wall of full frequency sound recorded at high volume (into the red as I found out in Audacity), deep bass to high treble and everything between. Clarity is what I got from the JLH and a slight confusion from the 3886.

I tried other recordings of course I won't bore you with the names the ones above were the occasions when something dawned on me and was repeated with lots of other music.

The last eight days have been rather strange I did have to look for differences they were not immediately apparent. The 3886 is a fine amplifier no doubt about that, the JLH is slightly better being brighter, faster and more analytical.

What will I be listening to now for the foreseeable future, the JLH :-)

Cheers -J

[edit] onto the box and the finish next
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Staff member
So your using a switching power supply. What voltage? Also what transistors are you using? Sorry if this has been answered. I'm about caught up on some of my other projects. Might be time for a audio project. :)
Hello OPA1,

Thanks for the question, only too glad to answer.

The Schematic and board layout are on this post: Endeavouring to shine with a JLH 1969

I'm using 4 Ohm speakers so I followed the 3 Ohm line in the table under the schematic, I bought an 18V 5Amp smps, the voltage can be adjusted by 15% either way.

24V will be fine for 8 Ohm speakers. No need to use 10 watts though I did the comparison with 6 Watts.

Cheers - J


Junior Member
What you have observed in your trial is consistent with my own listening experiences with a couple of class A amps (Rod Elliot DoZ and Pass F3 clone). Excellent write up of your experience.
Hello Tillerman,

Thanks for the message good of you to say that about the Class A amps it reinforces my own opinion. On another forum I had some detractors saying that basically 'bright' was not 'right'

But then from one of the experts was this quote from Mr Nigel Pearson;
"Really good valve amplifiers have an analytical sound that is bright and fast. Less good valve amplifiers sound soft and pleasing. Most valve lovers let their designs drift towards the soft. A true Williamson which is rare are not soft."

Mr Hood said this in the 1969 article
"The "Williamson" and the present class A design (the JLH) were both better than the other valve amplifier, and so close in performance that it was almost impossible to tell which of the two was in use without looking at the switch position. In the upper reaches of the treble spectrum the transistor amplifier (the JLH) has perhaps a slight advantage."

Interesting stuff and I agree about the 'fast' I must include it in my review.