Selim's JLH Amp

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Recently I received an envelope from Turkey. Inside that envelope were six pairs of beautifully finished circuit boards including a pair of JLH69 single ended class A amplifiers.

The boards were designed by a friend named Selim who is a member of this DIY forum. Selim is a Civil Engineer and drew the pcb layout on the trusty-old Auto-Cad computer drafting program!

This particular JLH is designed to have a reasonably small footprint and each channel is self-contained on a 5" x 5" fibre-glass circuit board that has been thoughtfully tracked and populated in a very clever manner. This made it easier for me to fit the whole thing into the enclosure, and with a minimum of external wiring this job was even easier still.

Taking a quick look at the photographs below, you can see four big 6A rectifiers on each board, I think 6A rectifiers are a good Idea for these little amps because the 3A - 1N5408 that I originally used got extremely hot. Even these big beasties get hot.

Take a look at my heatsink: This is a good example of what not to do...It is a big heatsink, but it's still way-too-small. My first selection was even smaller. This little amp was originally designed to put out around 10WRMS/CH/8R but to do that it has to burn about 25W/CH inside the output devices, and another 10W/CH inside the voltage regulator 'current-boost-transistors'. Multiply all that heat by 'two' - for stereo, and you will end up with an aweful lot of heat concentrated in a very small area (ie. six TO-3 transistors). This fact should not be under-estimated and is un-imaginable, if you are a beginner like myself.

When I re-house this amp I will use two heatsinks (one per chanel) of thermal resistance minimum 0.4-0.5 degrees celcius per Watt. These heatsinks will allow me to get the most out of a stereo pair of Selim's JLH69's.

Another mistake is my transformer! it is rated at 120VA - 0-15, 0-15 with 4A secondary windings. I thought it would be fine if I changed the rail voltage to 15VDC by simply substituting a LM7815 for the LM7824's stipulated on the silk-screen of the pcb. Once again I was wrong!

When I re-hash Selim's board into it's new enclosure I will remove the aforementioned transformer and replace it with a 160VA 0-25, 0-25 transformer and then revert to the original designs' 24Volt regulator.

The final improvement will be a seperate heatsink for each of the two current boost transistors in the voltage regulator, as they get awefully hot also: These 'other' heatsinks will need to be about 2 degrees celcius per watt minimum thermal resistance. To sum it up; I will have to add more heatsinking, much more.

OK, now you can see where I went wrong. So, don't make the same mistakes if you build one. And you should build one I reckon!


Even in the amps present configuration it has a very honest sound to it. I am not a wordsmith so I will list some things that come straight to mind:
  • Solid
  • Powerful
  • Honest
  • Clean and crystal clear.
  • Bright and tight top end that brings out the cimbals and thin guitar strings.
  • Reasonably solid bass response for such a small power output.
The amplifier boards were very easy to build and with the above re-hash I feel confident that they will punch well above their weight. It is important though, to weigh the pro's and con's of this type of 'raw' A-Class amp.

If you google JLH69, what you find is that almost-everyone loves their jlh. That said, I dont find many of the 'specifics' of their amplifiers, such as the important information that is listed above and which is so vital to making a success of your JLH69 project.

I would like to congratulate Selim for making a board that any beginner could assemble and enjoy with a minimum of fuss. Cheers mate and thanks for a good fun and functional amplifier project.

Yours sincerely, Phil Elliott
 

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Hi Phil,
I love my JLH69 also. Your description of the sound is spot on.
I have good results with the cap multiplier circuit from Elliot sound pages . I use a 250 w transformer for 2 channels
My woofer are separately powered and the deficiency in bass is not noticeable.
I have ordered some boards to try newer versions of the amp from Siliconray in this forum .
cheers and happy new year

kp93300
 
JLH

Hi
what is the output transistor in your amp ?
cheers
kp93300

Thankyou for your encouragement KP. I am like a dog on a bone at the moment and wont give up until I build the best version I can.

I used the plain old 2N3055'S. They don't work as well as the TIP35'S.

I should use some genuine MJ15003'S that I have in my parts box, because they may run cooler.

What do you think about this idea?

Cheers mate, sincerely, Phil aka farmerjack61
 
Hi farmerjack61.....6 pairs!!!
I like the sound of that...... a multi-amped system coming on perhaps?

Btw guys have you seen the very large JLH class-A thread elsewhere?
It might be mutually beneficial to move this over there.......just a thought.

Happy New year, cheers, Jonathan and while I'm relating to an Aussie is there any good reason why there is no Test Cricket on at the SCG today?
 
Hi farmerjack61.....6 pairs!!!
I like the sound of that...... a multi-amped system coming on perhaps?

:)Hi there John. Don't know much about the game of cricket, but those grass stains on the knees of the white trousers must take a lot of shifting.

On this JLH there are the usual 2 NPN output transistors per channel and one PNP to carry the current over the top of a 1A voltage regulator. Six total. The power supply is a single rail regulated to 24VDC.

It's interesting that you said that because I have just finished an A/B amp that has 6 pairs of C4468/A1695 outputs. Unlike the JLH, that amp pumps most of the power into the speakers. I can run my A/B amp at well over 100W into the speakers and the heatsinks are only about 50 - 60 degrees C which is much cooler than the JLH after 30 minutes at ten watts out.

I hope you have a good break over Christmas and an even better year next.

Cheers and bye for now, Phil E aka famerjack61
 
Thanks for the explanation. Read your original post again.....makes sense now.....
I have owned a JLH '69 since about '77 it's just that my mind HAS been on a tri-amped JLH system. I've been buying up cheap transformers and heat sinks since 1973 (or possibly '74)! But now when I have the time and might get around to actually doing it I'm starting to feel guilty about global warming......life can be so cruel.
Jonathan
 
I should use some genuine MJ15003'S that I have in my parts box, because they may run cooler.

What do you think about this idea?

Cheers mate, sincerely, Phil aka farmerjack61
Hi Phil
I tried the Mj 15003 and it runs about 15 deg centigrade hotter when compared to 2n 3055 !
The rectifier is also 10 to 20 deg hotter in my set up.

I am very happy with the sound even with the 2n 3055 and i will get around to trying the tip 3055 soon.

If you have 2 v output from your source, you can try removing the pre and have volume control with the Lightspeed attenuator ( passive pre build with LDR ).

cheers

kp93300
 
MJ v 2N

Gee, that's amazing isn't it, when you consider that the 2n3055 is only $1 and the MJ15003 is $4, goes to show that money cant buy everything!

We will get to the bottom of all this heat sooner or later. Even if it means building a B class!

By the way, I am going to take your lead with the next power supply and build a 'Capacitance Multiplier'.

Will the CM dissapate less power? I think probably yes.

Cheers and bye for now, Phil E.
 
Thanks for the explanation. Read your original post again.....makes sense now.....
I have owned a JLH '69 since about '77 it's just that my mind HAS been on a tri-amped JLH system. I've been buying up cheap transformers and heat sinks since 1973 (or possibly '74)! But now when I have the time and might get around to actually doing it I'm starting to feel guilty about global warming......life can be so cruel.
Jonathan

Now look here John, I will apologise to all of my fellow greens up front for what I am about to say, but I believe it is the truth and it must be said just like the roar of the two mastadons across the frozen wastelands. (a powerful image)

Global warming is a big issue, yes. But something tells me you are more conservative than your peers, you have probably earned a 'rebate' of global brownie points. The world governments hand them out to big producers every day. I do not wish to make a knee-jerk reaction to the global worming situation but i just don't think that your A-Class monster will make a great deal of difference in the whole scheme of things.

I think me and you should design a monster together and then unleach it upon the world....If only we could program it to reject Rap, Punk, trance and dance music and just play the good stuff.

Talk soon (I hope).
 
Hi Phil, thank you for your sympathetic response. And I HAVE earned a lot of bonus points over the years as I am a compulsive "turner off" of lights in unoccupied rooms. Also I think I won't need the full 10 watts for each driver. I'm not "a head banger" and we have small rooms so may be 5 watts per driver will suffice and I can justify it more easily that way. The current plan is a tri-amped system based around 5" Kefs, 2" dome mid and a Focal tweeter and a 12' sub. So it will sort of be "a 3 and half" way system. Btw I appreciate your musical tastes too.
Also I saw on eBay a Tassie based Celestion Ditton 25 listed for under $300. I would have been interested but for the cost of bringing them to Brisbane.....interested yourself?

Btw (again) has everyone on this thread caught up with Geoff Moss's "Class-A Amp site" it is about 97% devoted to the JLH Class A amp. Exhaustive articles on grounding, PSU etc. There is a wealth of stuff there......Just Google "Class-A amp site" that usually works.
Cheers, Jonathan
 
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Small A-Class

I am starting on a small amp this week. It will be based on a 300VA 0-18, 0-18 toroid and two of the H0545 heatsinks from Alltronics. It will be dual rail & I will not be using any regulation on the rails for a few reasons;
  • Wasteful and hot.
  • Introduces another variable - voltages can vary when the bypass transistors get hot.
  • More compact layout.
  • Using the larger transformer will introduce it's own regulation to some extent. ie. less demand = full supply rail.
I also want to avoid the big electrolytic capacitor from the output (as used in the original JLH69) and see if that will improve the bass response.

I will use Mr.Self's 20W Blameless as a starting point and will make a few changes to the componentry and configuration to bring it up to date.

The thread is located on this forum under the title 20W Blameless Class A please drop in and give me a little guidance if you get the time.

bye for now, farmerjack61
 
Celestion Ditton 25 interested yourself?
Cheers, Jonathan

I am trying to extinguish my addiction to old speakers because I have too many now, and they always seem to need some repair or other!

On that subject though, I would like to point you to Audio Australia (I think they might actually be Alltronics for eBay, but), They have a range of excellent bass speakers of very high efficiency. The drivers have a pressed steel basket so I dont know how long they will hold their shape, but I just purchased 4 x 12" 8R poly woofers for $280 (the polycone is not your smooth poly but has a texture).

I am making two enclosures that stand about 4' high and 2' wide by 1' deep they have about 2m of vent that measures about 2' x 2"

The treble is covered by a vifa silk dome in each cabinet. the Vifas are attached to a 12" parabolic flare and man they fill the room with the softest clearest treble you have ever heard.

Here is a sketch and a piccie; - bye for now.
 

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I am making two enclosures that stand about 4' high and 2' wide by 1' deep they have about 2m of vent that measures about 2' x 2" The treble is covered by a vifa silk dome in each cabinet. the Vifas are attached to a 12" parabolic flare and man they fill the room with the softest clearest treble you have ever heard.....
Wow, a DIY design or a published one, Phil? It seems quite ambitious with, I imagine, sub-woofer extension. I just hope you don't run into domestic warfare over large items that compete with the furniture etc. etc.
 
Speaker Peeker

;)
Wow, a DIY design or a published one, Phil? It seems quite ambitious with, I imagine, sub-woofer extension. I just hope you don't run into domestic warfare over large items that compete with the furniture etc. etc.

Hello again Ian.

I answer to no man especially if he's a woman. (Just kidding Ma - I would do anything for you).

This is the MK2 version. MK1 was 900high by 200wide by 300deep it was a teriffic design - I sold that pair to a mate for $100 which almost covered the cost of the crossovers! But I'm not in this hobby for the money - I'm a joiner by trade.

The design has not been published in Wireless World or Silicon Chip but it has been posted here because I am sure it will appeal to some of the more ambitious and dexterous builders, who may be stuck for a very good design idea. I am pretty sure that this design will have outstanding performance based on the sound of the MK1 prototype and the design principals upon which it has drawn. I will post a Schematic and an objective review based on the listeners comments when completed. Performance will also depend on the drivers selected and I strongly suggest the ones pictured above due to their outstanding performance and meagre cost.

My first set of speakers were a brand named Sound Dynamics (phenolic dome diaphragm). They used a nice big flare on the hf. This is where I developed a taste for loud, soft rich treble that filled the room with relative ease - making speaker placement that much simpler.

I still have these speakers and have recently completely rebuilt the entire transducers lf & hf & not just the diapragms and suspension. They cost me $400 about thirty years ago but the only speakers (that I have personally heard) that sound better are a big set of 180lt JBL's that are hooked up to my brothers Harman Kardon amp.

Sound Dynamics speakers were manufactured in Canada but are no longer available.

Another brother of mine builds valve guitar amps, he bought the Fane Speaker Design Booklet years ago and I have read it from front to back because lots of the principals are the same in home audio.

I have also follow the 1/4 wave designers on this site and have seen photos and heard excellent reports of great new breathing designs.

This design has it's foundation set upon the cornerstone of all of these influences.

If some of the readers ride a Harley, Drive a V8 or play Bass they just might like this design. Those kinda fellas know the vibe that I'm on!

A speaker cabinet need not be drab and tasteless, it isnt some kind of alien in a foreign galaxy, its just another piece of furniture, but one that does more than store pots and pans. Speakers can blend with your decor, so if you are married or living with your partner, why not ask her to design the finish. She can redo your speakers when you paint the walls or she may cover them with fabric or a collage of sea-shells, or perhaps a Gaudi influenced tile mosaic. Why not try some veneer (N.G. Rosewood for example), perhaps formica or laminex are possibilities for those with a little spare cash.

There is a really fizzly pathetic and I believe unreal perception on these forums that chicks dont like good speakers. To the people that believe this, I would ask that they just go down to the local nightclub and take a look at how wet the women are, they just love to dance.

Big speakers have a big sound that can not be replicated by small speakers. I am not just talking about loudness although this is one of the more noticeable qualities of a large speaker, as Dick Smith said in his Funway into Electronics Volume 2 "Contrary to popular belief, a larger speaker will give more volume than a small speaker from the same source. If you can afford a larger speaker the results will be well worth the extra expense". [p13]

This is not to say there is no place for small speakers because the opposite is true. Small speakers are practical and can fill the need for a compact and affordabe substitute.

Well there we go Ian, I hope I answered that question - I don't believe in one liners so I hope you have a better 'feel' for what I am on about.

BTW I am not familiar with the term 'subwoofer extension' if you could elaborate I may be able to shed some more light on this particular design.

On the subject of sub-woofers (as in Surround Sound system Subbies) I thought they were only used to compensate for the small speakers that everyone seems to use for satellites these days!

Cheers mate, Go the big Nana, bye for now.
 
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;).........If some of the readers ride a Harley, Drive a V8 or play Bass they just might like this design. Those kinda fellas know the vibe that I'm on!
Hey, we have whole suburbs full of those guys up here. They go rides of up to 300 in a bunch and the cops then thin them out a bit. Utterly Scary! 'Got three bass players in my street, not including me but we're all bad. V8s? Nearly all dead now or locked away for times of cheaper fuel (ok,ok - just locked away)
BTW I am not familiar with the term 'subwoofer extension' if you could elaborate I may be able to shed some more light on this particular design. .
Ah, a piece of shorthand, translated in full as "with the extension in bass register of a subwoofer" Apologies for the excessive brevity.

Most here have probably dabbled in speaker building.
40 years ago I began a set of massive transmission lines that occupied about 16 cubic feet and consumed masses of chipboard, fine longfibre merino wool and the dearest drivers I could afford as an undergrad. I won't describe them now but I was very pleased with myself until Dad told me to dice them or move out. These were Mother's instructions originally. She danced all right but not to ZZtop :D.
I tackled about 20 simpler and much smaller pairs and quite a few kits too. Some for me, most to sell. Some good, some fair and a couple I couldn't ever part with. Somehow they became smaller over the years and when subwoofers became popular, I just used small satellites with one. This was tidy but expensive for the quality demanded by those designs.

I still get a longing to build something sensitive enough for JLH or any small class A amplification. I have a cheap driver in mind now for a 25l box @ 30Hz tuning. 'Big problem is; how to treat mids with an 8" driver? It's not easy and i don't like the chances of a cheap 3-way. 'Feel inclined to design in 8 ohms at 91 dB sensitivity?
 
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Btw (again) has everyone on this thread caught up with Geoff Moss's "Class-A Amp site" it is about 97% devoted to the JLH Class A amp. Exhaustive articles on grounding, PSU etc. There is a wealth of stuff there......Just Google "Class-A amp site" that usually works.....
Hi Jonathan
Well I visit the site and continue to gravitate there as a source of inspiration. I feel a time warp every time I log in or out. I also recall the hundreds of hours i wasted debating with audiophiles over such designs in their day. I'm not sure whether it's nostalgia or a need to grasp a piece of history or the curiosity to see how simple audio electronics can work so well for us. Probably all of the above to keep me interested.

There are a couple of other sites feeding this Brit-fi interest and I've had communications with guys in the UK like Paul Kemble who are happy to assist with searches for material that is not published on the web. This applies particularly with magazine articles you may find reference to, where author's copyright can drag on in perpetuity. I don't have as much singular interest in JLH's class A amplifier designs as some of the forum but this is a great site as is Paul Kemble's site which has a lot more JLH works than just audio.

Don't forget Douglas Self's site (The Self Site:D) is a goldmine of even earlier Brit-fi memorabilia for valve-tech now too. I could say there's a lot of other wierd and ancient industrial technologies there too if you're inquisitive. Fascinating stuff, all Googlable.
 
Hi Ian. Ta. yes, you are right about Paul Kemble's site, good reminder. I was aware of it but not your reference to magazine articles; thanks. We took LSL last year and I chased up some JLH stuff in the British Library only to find some Visgoth had knocked off some of the 1984 ETI (UK) editions I wanted....and further investigation revealed NO OTHER source in the UK institutions. Sad.
It is interesting what DOES actually motivate us......I initially liked the JLH Class A because it was simple and I thought I could build it and secondly I was born a few miles away from his home in Somerset! But over time I came to appreciate his mixture of scientifically grounded objectivism and his subjective response to circuits. I thought the balance was right. A lot like Nelson Pass in that regard.
Cheers, Jonathan
 
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ETI

I'll wager there are a few UK denizens who have salted away every copy and delicately savour a little now and then in a quiet moment. Why not post a list of articles wanted and sit back in anticipation? There are a few guys here who have expressed familiarity with '80s ETI articles. I'm sure a few cages could be rattled for some help at least.

I was equally disappointed on my carefully planned visits to British libraries only to find nothing of value or pertinent reference. It's literally unbelievable and I always suspected outdated references. I thought the material was actually out on loan to other institutions or, as in other countries, in private hands.

Somerset eh? then you might still have an identifiable accent as my Chard relatives retained from a young age. I've toured about the county a bit - Great Western territory, beautiful and warm in summer!
 
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