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JLH 10 Watt class A amplifier
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Old 20th February 2020, 10:00 PM   #5961
Alan Frobisher is offline Alan Frobisher
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Join Date: Jun 2010
Great to hear that the JL-H is still arousing interest.Split rail amp. is much better,eliminates the op. cap. Tried building the amp. with Toshiba 2SC5200s (watch out for fakes!). The sound was extremely "bright",not surprising as the op. was still flat at 250KHz.!It is well worth reading the JL-H section on the Class A Amp. Site. now hosted by Elliott Sound Products.
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Old 21st February 2020, 01:38 AM   #5962
grunf is offline grunf  Croatia
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Location: Šibenik, Croatia
I played with JLH69 for over two years, the starting position was a dual-power version. I then added power sources for Q3 and Q4. I spent most of my time trying out various transistors, primarily for the Q3, which I realized had the most impact on amplifier sound. I dropped the C3 and adjusted the current through the Q4. For Q3, low Cob fast transistors are good.Q3 with low Hfe will not sound good. Q1 and Q2 must have higher Hfe.
Of the equipment, I only have an oscilloscope and a voltmeter, but on scop I have an FFT analysis and you can see the difference in Q3 selection.
The other important thing is the power supply, it has to be as good as possible with less ripple and noise, initially I only used capacitors, so I added the resistors so I had a CRCRC combination with a 2V voltage drop, now I added the regulators with an additional 3V voltage drop. I have a total of 180,000uF in power supply.
The JLH69 amplifier really sounds great and I have no intention of changing anything for now.
In my opinion it is not necessary to change a lot according to the basic scheme, it is enough to add CCSs, but special attention should be paid to the choice of parts (especially Q3) and power supply quality.
Attached Images
File Type: gif 1969 design with dual supply rails (Option 1).gif (6.9 KB, 119 views)
File Type: png JLH69 new.png (55.7 KB, 122 views)
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Old 21st February 2020, 07:07 AM   #5963
Rallyfinnen is offline Rallyfinnen  Sweden
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Join Date: Jan 2017
Originally Posted by Rallyfinnen View Post
0.00x% should be possible with some tweaking, but maybe not with the 3055. I have seen figures like that in Arta around 1W into 8ohm load, but I prefer to look at the FFT and not plain numbers. EDIT: not sure now, maybe it was only 0.01 something.. anyway, distortion around -90dB is definitely possible.
Just did a quick test of my PNP JLH to refresh my memory. Load is actually 7.2ohm, not 8.
There are some spikes from noise pickup that should be disregarded at 8kHz and 16kHz, and some 50Hz and multiples of that.
Attached Images
File Type: jpg PNP JLH 1W 8ohm 1kHz.jpg (202.6 KB, 100 views)
File Type: jpg PNP JLH 8ohm multitone.jpg (258.8 KB, 94 views)

Last edited by Rallyfinnen; 21st February 2020 at 07:10 AM.
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Old Yesterday, 10:42 PM   #5964
horu5 is offline horu5  Germany
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Join Date: Apr 2012
Location: Munich, Bavaria
Hello you Guys,

I am bulding the high power esl version from Geoff Moss. http://www.kaschei.com/classa/jlheslfig1.gif

I've measures output transistors Type MJ15003 with my Lab-PSU and a thermometer to get the hfe at 85°C. -> Post 5901 Link: JLH 10 Watt class A amplifier ..Thanks for your advice fredbloggstwo!

The transistors have gains between 102 and 129.

Does it make sense to always combine a strong and a weak one on each "side" for Example Q1, Q1A gains = 109 + 125 = 234 Q2, Q2A gains = 104 + 129 = 233.

As far as described in the TCAAS-Design Notes for the 1996 Version the Q1 and Q2 should be matched, Q1 should have higher gain.

Do gains sum up the way I've been thinking of? Is it a "clean" solution? Hope you could give advice! Help would be very much appreciated!
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