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Class A DIY kit suggestions?

Pass designs work an entirely different way - not really comparable.

The JLH uses that input transistor to provide all the voltage gain, swapping that to a fet will drop the open-loop gain to c. 1/5 - 1/10th as much (quick guess) and that means much less feedback, more noise+distortion.

ETA:
Nelson Pass did propose his own take on the JLH amp using fets - see the 'PLH' article here for a detailed read:

http://www.passdiy.com/projects.htm

-I see my guess wasn't so wrong on loop gain, although the effect on %THD isnt quite as marked. Note also the output impedance of the fet version increases significantly - it will sound different!
 
martin clark said:
Why would you want to do that? It could be done but I suspect distortion and noise would increase notably.

If you wanted very high input impedance you could just use a fet opamp as a buffer ahead of the JLH (but the standard amp is no problem for any preamp or source to drive)
Click to expand...

I needed to buffer the relatively high impedance of a valve preamp so I used a circuit from the Mullard audio circuits book. It worked fine but I can`t remember the details now, it was a very long time ago and much smoke has been released from circuits since then.
 
Thanks for the link Martin - very interesting, and informative.

I was envisaging a simple input buffer arrangement (B1 style) at input to JLH, not simply swapping a bjt for a fet.
 
If you are looking for low cost, this is the almost free PSU (Free PCB, +2.5 for power transistors.
http://www.siliconray.com/free-power-supply-pcb-for-jlh-amplifier.html

This is the high-end solution:
http://www.siliconray.com/audio-ama...wer-supply-board-with-speaker-protecting.html
large caps, onboard rectifier and speaker protector

Toroid is not listed on the website due to it's low cost/shipping cost ratio。An 15Vx2 200W should be enough.

I strongly suggest you to use our enclosures with heatsink. Basically you will need this to fit in all the boards:
http://www.siliconray.com/re3213-320x130x311-aluminum-enclosure.html

If you are thinking of upgrade in the future, these are the choices:
http://www.siliconray.com/re4015-aluminum-enclosure.html
http://www.siliconray.com/re4312hl-430x120x411-aluminum-enclosure.html
or even this if you are thinking of class A up to 50W
http://www.siliconray.com/enclosure-re4821h-480x224x424.html

Hope this could help.
gregvds said:
Hi siliconray,

Thanks to react.

Could you help me to establish a list of all I would need to build a full stereo integrated JLH with PSU inside. I need two JLH boards kit, then a PSU (yours is adapted for the JLH I suppose), but one or two? and one or two toroidals too. Then some good Heatsinks too, right. And in the end, some preamp board, for volume and source choice.
Click to expand...
 
Thanks! JLH is really a nice design, especially 2005 version built with good transistors.

Another interesting design is this tube+MOSFET class-A amp, also sounds nice although the THD isn't as good as JLH:
http://www.siliconray.com/tube-6n8p-mosfet-hybrid-hifi-audio-amplifier.html

When working with a sensitivity speaker (90dB+) the classic music sounds really great. And the looking is cool:)

new naim boy said:
That's such great value Siliconray.

Now I've never heard a JLH...... There's one way to find out :)
Click to expand...
 
I had built all 3 version of JLH from 1969 to 2005. The 2005 has the best instrument testing result (and of course the best listen performance). 1969 version use 2N3055 which is a bit slow and noisy for hifi application.

As you said class A is rughless if you use wrong parts or adjust it in the wrong way. The sequence of adjusting is important. I know at least 5 people burn speakers because the connect it at output before adjusting bias. That's extremely important
russel said:
Here is the original article, proving nostalgia is what it used to be.

http://sound.au.com/tcaas/jlh1969.pdf

If anyone does build it, make sure you use kosher parts. Class A will be pretty ruthless if you do not, be warned!
Click to expand...
 
Wow, the JLH kit offers 2N3055 trannies! The transistor that launched a thousand ships. If ever there was a workhorse, that's it. I didn't think they were rated for audio though so I'd pay the extra shekels for a better OP tranny.
 
stevec67 said:
Wow, the JLH kit offers 2N3055 trannies! The transistor that launched a thousand ships. If ever there was a workhorse, that's it. I didn't think they were rated for audio though so I'd pay the extra shekels for a better OP tranny.
Click to expand...

2N3055 is fine for the Linsley-Hood circuit, like any thing else depends how its used. Quad 303s used them, in the triple arrangement its many failings were kept well hidden.
 
stevec67 said:
Wow, the JLH kit offers 2N3055 trannies! The transistor that launched a thousand ships. If ever there was a workhorse, that's it. I didn't think they were rated for audio though so I'd pay the extra shekels for a better OP tranny.
Click to expand...

I used 2S025s in my original veroboard lashup and the 2N3055s in the permanent arrangement. Both types worked very well, the important thing is that they have reasonable hfe. Some 2N3055s I had dealings with had a gain of only 4 or 5, well below spec, these were useless in this application - and most other applications as well.
 
Barrymagrec said:
I used 2S025s in my original veroboard lashup and the 2N3055s in the permanent arrangement. Both types worked very well, the important thing is that they have reasonable hfe. Some 2N3055s I had dealings with had a gain of only 4 or 5, well below spec, these were useless in this application - and most other applications as well.
Click to expand...

Older semis were really poor performance, Mullard used to ship with about a 5% failure rate in the 70s. Now its much better, a modern 2N3055 should be much better than 5.
 
russel said:
Older semis were really poor performance, Mullard used to ship with about a 5% failure rate in the 70s. Now its much better, a modern 2N3055 should be much better than 5.
Click to expand...

Indeed, the spec is 20, these duff 3055s were some dodgy MCP items as I remember, but part of the company group so we had to use them.
 
Well that's a relief. With some useful Hfe a good '3055 might just about be up to real-time monitoring of geological processes.

I prefer to think of it as a T03 thermometer ;)
 
I built the original with MJ480 and MJ481 output devices, a ruddy great oil filled ex navy transformer and ex computer smoothing capacitors in about '73. It developed a burbling noise years later and a friend has had it for years "mending it". All this talk has me wanting it back again, driving the speakers around the computer. Maybe I will up-spec it to the 2005 version, thanks to this thread for reminding me I have hidden hi-fi gold somewhere!

I seem to remember the Motorola output pair were preferred by JLH for their massive copper mounting plate rather than the thin steel found on the 3055 and the spec of the Motorola devices had to be better than the 3055!
 
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