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lineup 8th April 2011 09:57 AM

JFET input, MOSFET VAS, LATERAL output = Perfect!!
1 Attachment(s)
This is the most perfect amplifier I have spiced.
It is simple but yet very, very good.

- JFET input with minimal offset problems.
- MOSFET VAS for speed and gain
- LATERAL output for be a light load to VAS

When CLass AB operation, 350mA bias, it shows only
THD 0.00018% at 1 Watt
And there is almost no increase of THD at 25 Watt output

Enjoy!! :)
For more building the final stuff and details, look for FETZILLA
in this AKSA forum: AKSA - diyAudio

ontoaba 8th April 2011 11:44 AM

1 Attachment(s)
Umm, but, could you explain that three statement? I remember that your previous thread looking for beautiful small distortion.

This is sim results distortion figure of some best output stages. Test condition is 10kHz +/-20V output and additional 10kHz, 0.5A current source connected at its output.
Single ended mosfet has higher distortion, but it has higher drop voltage compared to non classA mosfet and SE sounded better than classA. If you like distortion, you shouldn't follow many people that makes their amp suitable to drive resistors, but make your amp best to drive real loudspeaker.

gk7 8th April 2011 12:05 PM

The simulation looks promising indeed. Do you have plans to build it ?
Or does your simulation program allow to use models with some tolerances
to resemble "real world" conditions ?
I wonder how sensible this circuit will be to parameter variations, if itīs not
(with reasonable matched parts) itīs certainly worth a try.

ontoaba 8th April 2011 12:32 PM


Originally Posted by ontoaba (
Single ended mosfet has higher distortion, but it has higher drop voltage compared to non classA mosfet and SE sounded better than classA.

Edit: Single ended mosfet has higher distortion, but it has higher drop voltage and SE sounded better than normal classA with same bias (5A),

Bigun 8th April 2011 12:54 PM

I think it looks very good. I heard though, that Laterals are more obsolete than most vacuum tubes ?

bear 8th April 2011 01:49 PM

Lineup, I think Spice is lying sweetly to you... this is not a new configuration, and doesn't seem to change anything...


lineup 9th April 2011 08:37 AM

1 Attachment(s)
This is the 50 Watt version.
+/-35 Volt
and 2 pair of 2SK1058/2SJ201
Distortion is low, even at full output.

Added dc-fineadjust and bias-adjust

MiiB 9th April 2011 12:48 PM

I think a cascode would be good...So you have a little more driving force on the mosfet capacitance...will the input fets not overheat with that Voltage and current....On the limit I think..normally I like to have app 10-12 v over the fet's and then let them run close idss...

Could also be made like the balanced French concept you were toying with in the other thread...:)

lineup 10th April 2011 08:05 AM

1 Attachment(s)
With +/-50 Volt supply.
Two pair HEXFET IRFP240/9240 and cascoded JFETs.
IRF610/9610 for VAS.

100 Watt into 8 Ohm with low distortion.

Jay 10th April 2011 12:49 PM

Cool... I have been following your new circuit Lineup. This could be the "mosfet-based AKSA" I'm looking for. But I don't think I can find the ZVP mosfets. The IRF610, nah... they are horrible. How about the available lateral 2SK214 for the VAS?. Otherwise, 2 stages of bipolar is preferable imo.

And I don't understand why BD139 for the input current source?

Ups, I forget that I have been looking for the simplest topology without constant current sources...

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