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Old 5th April 2011, 05:22 AM   #1
Jay is offline Jay  Indonesia
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Default MOSFET-Based AKSA Wanted! Anyone?

I have been looking forward to seeing a mosfet-based AKSA. A lateral one. Something that will have the magic of the AKSA, but also have the "air" of a mosfet. The closest professional circuit around would be Rod's P101 where one stage has been reduced. Shaan also has similar version with extra stage similar to a bipolar circuit that he calls The Magic.

I would imagine that it will take someone who understand what makes the AKSA sound as it does, to design this mosfet-based AKSA.

The P101, Magic and P3A are using NPN LTP while I want a PNP one like AKSA so I can use 2SA978 (dual PNP). A CFP mosfet also has certain merit, so I'm looking for something like the Mooly's amplifier that can be found in this site (schematic attached).

The Mooly amplifier will be modified like this:
1) PNP LTP to replace singleton and the beta enhancer
2) The VAS with bootstrap will replace the one with current source.

By this, I will have simple front end (like AKSA) and the merit of a bootstrap circuit. The rest of the job is to tweak this topology to get a favourable "distortion" if you like that terminology

My question is, anybody has similar working circuit for me to use as starting point? If not, why do you think it is not doable? If it is doable then someone must have it somewhere. If you think it is doable but will not give something different, then let me prove that to myself. I trust my ability to listen to schematic

Thanks
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Old 5th April 2011, 05:50 AM   #2
MiiB is offline MiiB  Denmark
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Do you need the driver stage...I think you could drive the laterals directly from the VAS..
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Old 5th April 2011, 06:16 AM   #3
lineup is offline lineup  Sweden
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It is a good amplifier, no doubt.
But no AKSA.
As you said, bootstrap for AKSA.
DC servo and Sziklai output is another difference. With 30mA in drivers!
The input pair is missing, like in AKSA.

And MiiB said, you could drive Laterals directly from VAS.

But the amplifier is good and will surely work well.
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Last edited by lineup; 5th April 2011 at 06:20 AM.
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Old 5th April 2011, 06:58 AM   #4
Jay is offline Jay  Indonesia
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Yes MiiB, I think I need the driver stage I think may be this is one reason why I cannot find such schematic. But even one without the driver, I think I haven't seen either

Lineup, which amp is the good amplifier? I don't have yet the schematic. I cannot try to push my (in)ability to design one because this is lateral (read: expensive)!

The Mooly's amplifier is very good. The modification I want is of course no AKSA. But the design idea/approach can be. The Mooly's amplifier itself is too complex for an "AKSA" (The opamp, CCS) tho the distortion spectrum can be close I think
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