Selim's JLH Amp

[farmerjack61]

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

[kp93300]

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

[kp93300]

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

[farmerjack61]

Originally Posted by kp93300

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

[Jonathan Bright]

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?

[farmerjack61]

Originally Posted by Jonathan Bright

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

[Jonathan Bright]

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

[kp93300]

Originally Posted by farmerjack61

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

[farmerjack61]

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.

[farmerjack61]

Originally Posted by Jonathan Bright

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).