JLH Buffer - Homage to John Linsley Hood - diyAudio
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Old 8th December 2012, 04:00 PM   #1
dadod is offline dadod  Croatia
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Default JLH Buffer - Homage to John Linsley Hood

I am big admirer of John Linsley Hood audio work and built some of his amplifiers. In other thread I needed simple but good output buffer and I remembered the one JLH used in his 80W MOSFET amp.
First is simulation of the JLH original buffer (with different BJT transistor as I do not have spice models for BC212/182). I am not sure how good are JFET models and here is just to show that buffer.
Next is simulation with better JFETs and result is quite pleasing.
dado
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File Type: jpg JLH-buffer.jpg (194.2 KB, 2376 views)
File Type: jpg JLH-buffer-new.jpg (196.8 KB, 2314 views)
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Old 8th December 2012, 04:03 PM   #2
dadod is offline dadod  Croatia
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Here is similar buffer but for higher power supply voltage and JFETs are cascoded with the same type.
dado
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Old 8th December 2012, 04:04 PM   #3
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And here the cascode made with BJTs.
dado
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Old 8th December 2012, 04:06 PM   #4
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Quote:
Originally Posted by dadod View Post
Next is simulation with better JFETs and result is quite pleasing.
dado
one more wire but with no voltage gain? ;-)
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Old 8th December 2012, 04:08 PM   #5
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Any chance you can show a sim result of the simple sk170/sj74 borbely/curl buffer for comparison using the same spice models as above ? See f6 article for example
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Old 8th December 2012, 04:09 PM   #6
dadod is offline dadod  Croatia
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Finally this one work on with +-40 V.

I used this modified JLH buffer in a line amplifier in this thread Current conveyor as a voltage amplifier
dado
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Old 8th December 2012, 04:14 PM   #7
dadod is offline dadod  Croatia
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Quote:
Originally Posted by kasey197 View Post
Any chance you can show a sim result of the simple sk170/sj74 borbely/curl buffer for comparison using the same spice models as above ? See f6 article for example
Could you show schematic?
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Old 9th December 2012, 09:42 AM   #8
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Default Compensation

Cascoded JLH buffer will oscillate if not compensated properly. I did it with R3 and C7. Here are the Gains of compensated and non compensated Buffers. I tried different compensation and this one for me worked best. I would appreciate suggestions of different or better way to compensate.
Attached needed LTspice file if someone wants to experiment and I hope show result.
dado
Attached Images
File Type: jpg JLH-DADO-buffer-gain-comp.jpg (227.2 KB, 868 views)
File Type: jpg JLH-DADO-buffer-gain-noncomp.jpg (229.4 KB, 496 views)
File Type: jpg JLH-DADO-buffer-bjtcascoded-b-gain-comp.jpg (231.1 KB, 381 views)
File Type: jpg JLH-DADO-buffer-bjtcascoded-b-gain-noncomp.jpg (232.1 KB, 429 views)
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File Type: zip JLH-buffer.zip (14.2 KB, 148 views)
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Old 11th December 2012, 08:20 AM   #9
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Originally Posted by dadod View Post
Could you show schematic?
here is one ... (only ground connection not shown) - just interested to compare the sim results here to the ones you have got since i know the sound of this one quite well (ie doenst seem to have much 'sound' at all!)

thanks for sharing this interesting work

ps. this is from one of NP's schematics in case you were wondering ! supply voltage upto 25V no problems at all
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Old 11th December 2012, 09:57 AM   #10
dadod is offline dadod  Croatia
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Quote:
Originally Posted by kasey197 View Post
here is one ... (only ground connection not shown) - just interested to compare the sim results here to the ones you have got since i know the sound of this one quite well (ie doenst seem to have much 'sound' at all!)

thanks for sharing this interesting work

ps. this is from one of NP's schematics in case you were wondering ! supply voltage upto 25V no problems at all
Here it is. It runs at Idss and in the case of my models it is 14 mA.
dado
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File Type: jpg JFET-buffer-1Vpp.jpg (187.7 KB, 744 views)
File Type: jpg JFET-buffer-5Vpp.jpg (201.5 KB, 586 views)
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