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★★ Free PCB for JLH 2005 Class-A Amplifier
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Old 27th December 2017, 02:11 PM   #311
Puffin is offline Puffin  United Kingdom
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I built one of these amps using the Siliconray boards some years ago which hasn't been used. I recently ran it for a few days and had problems with the L channel blowing the pcb fuse. Having checked it over it seems that I can't now get the dc offset down and my light bulb tester is glowing brightly when the L channel only is connected (dual mono double psu design)

I Built the board using TIP3055 transistors. My electronics knowledge has increased a little since I built that amp and I have a few questions I wonder if anyone can answer.

I used the TIP 3055's in both positions on the board, but now wonder whether they should both be the same or whether one of them should have been a P channel 2955. I am probably going to replace all the output transistors on both boards and wondered which ones would be favourite for the board's interpretation of the JLH amp.
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Old 25th February 2021, 12:55 PM   #312
Puffin is offline Puffin  United Kingdom
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I had forgotten about the above post. The amp has not been fixed. Anyone?
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Old 29th August 2021, 09:29 PM   #313
haiqu is offline haiqu  Australia
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★★ Free PCB for JLH 2005 Class-A Amplifier
The obvious thing to do is Google for a circuit diagram to answer the transistor question.
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Old 29th August 2021, 09:50 PM   #314
huggygood is offline huggygood  France
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★★ Free PCB for JLH 2005 Class-A Amplifier
this pattern has never been stable.
I tried several things but nothing worked, it swayed, I gave up.
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Old 29th August 2021, 09:53 PM   #315
nautibuoy is offline nautibuoy  United Kingdom
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Quote:
Originally Posted by Puffin View Post
I had forgotten about the above post. The amp has not been fixed. Anyone?
I have these boards, still unfinished, in a drawer...

I've attached zip file with board and schematic images. If I recall correctly there are several posts earlier in this thread that purport to describe the set-up process.

I did finish the SiliconRay headphone version and it worked well and sounded good.
Attached Files
File Type: zip Stuff4Puff.zip (53.7 KB, 15 views)
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Old 30th August 2021, 05:51 AM   #316
EUVL is offline EUVL  Europe
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Why not use the original, proven by many.
Geoff Moss's JLH-2005 design files


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Old 30th August 2021, 06:52 AM   #317
EUVL is offline EUVL  Europe
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And here the original Gerber data from Geoff Moss :
Geoff Moss's JLH-2005 design files


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Old 30th August 2021, 07:46 AM   #318
polsol is offline polsol  South Africa
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Quote:
Originally Posted by Puffin View Post
I had forgotten about the above post. The amp has not been fixed. Anyone?
Just saw this post this am.

The output transistors were specified as both being MJ15003 (NPN).
The trick (from memory) is to set both pots mid way and then adjust for quiescent current followed by output voltage (to 0V).
Repeat adjustments until the quiescent current and output voltage are stable (probably 3 to 5 times) making sure the heatsink(s) temperature is stable (at 'operating temperature') each time.

Have no issues with the amps per se. Sound is very good.

The problem is some 50Hz 'hum' in my setup which arises from the power supply I used. One really needs a lot of capacitance or something like a ripple eater to maintain a steady current to these amps with minimal ripple. Mine is 2 separate power supplies with 20,000 uF per channel (without opening the case). I think 47,000 uF per channel in a standard configuration PSU would probably be a minimum (untested).

HTH
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Old 31st August 2021, 09:51 AM   #319
polsol is offline polsol  South Africa
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Quote:
Originally Posted by Puffin View Post
I had forgotten about the above post. The amp has not been fixed. Anyone?
Found this PDF file I'd made which provides schematic and adjustments in my handwriting.
Hope you can read it.
Attached Files
File Type: pdf 15W Class A schematic.pdf (286.4 KB, 15 views)
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