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Old 9th August 2011, 04:17 PM   #121
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Some other research papers show that 180 mA for 2SK1058 and 2SJ162 as output devices indicates least distortion.

For the last requirement would of course require Vbe multiplier, in the current circuit it is not necessary. I have designed with MOSFET driving BJT but thermally it has never been stable without it. What are your suggestions.
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Old 9th August 2011, 04:25 PM   #122
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With BJT following MOSFET distortion seems significantly worse. Maybe you have some clues.
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Old 9th August 2011, 04:29 PM   #123
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Freq response remains good.
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File Type: pdf AC Analysis.pdf (9.7 KB, 140 views)
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Old 9th August 2011, 04:30 PM   #124
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I know, look to my pic of my test bench, and there it is, Vbe multiplier sitting on the top of BIGBT. I know it is one more transistor in sch, but it works perfectly. As I metioned before, the BIGBT temperature went well over 60C, because of the signal present on 6 ohm load at the output (no thermal runaway) without any heatsink, and bias current was still perfectly stable.

Maybe we should first simulate:
- BJT driver/mosfet output
- mosfet driver/BJT output

to see which combination sounds the best and than we can surely decide about the need of Vbe multiplier.
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Old 9th August 2011, 04:32 PM   #125
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I think we are writing at the same time.
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Old 9th August 2011, 04:33 PM   #126
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I will change my spiders web, and listen, it will take a while and I only have MJ15001 and MJ15002 available right now.
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Old 9th August 2011, 04:37 PM   #127
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OK, I heard the second combination and I just love it.

Please rearrange your spider and than report, enjoy Nico.

Last edited by Lazy Cat; 9th August 2011 at 04:39 PM.
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Old 9th August 2011, 04:49 PM   #128
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Quote:
Originally Posted by Nico Ras View Post
With BJT following MOSFET distortion seems significantly worse. Maybe you have some clues.
I see an even harmonics much more present in distortion distribution than odd ones, maybe this is the reason why the amp sounded very pleasant. The average level can be lowered significantly by proper biasing of both stages.
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Old 9th August 2011, 04:55 PM   #129
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It will take me a while to drill heat sinks and unravel the crows nests before I can try listening again. Now I have to divert my efforts to cooking instead of simulating :-)
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Old 9th August 2011, 06:33 PM   #130
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Originally Posted by Lazy Cat View Post
Thanks Hugh, it is purely my idea.
It`s a Hawksford LFD preamp concept, but nice circuit anyway.

http://www.essex.ac.uk/csee/research...D%20preamp.pdf
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