JFET input, MOSFET VAS, LATERAL output = Perfect!!

[Jay]

Originally Posted by bear

this is not a new configuration, and doesn't seem to change anything...

_-_-bear

The JLH? It is all designers' reference.

[jam]

lineup,

Do you not think it better to set the cascode voltage at between 10 to 15 volts?

Jam

[jam]

lineup,

In the 100w version would the current help reduce distortion?

Jam

[moschfet]

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

10mA and 50V

That's the reason why I have doubt. It is quite high for the difference amplifier. Thermal drift and noise could be a problem.

[MiiB]

If you make a LED based current source the thermal balance will be better...

[Jay]

Originally Posted by MiiB

If you make a LED based current source the thermal balance will be better...

I don't believe that it has something to do with thermal tracking (linearity), but LED based current source has been long known for its good sound.

[lineup]

Here a new take on JFET input, MOSFET vas and MOSFET output.
It does 48 Watt RMS before clipping in Class AB (bias is 200mA).

The only bipolar are the drivers: 2SC2911/2SA1209
I use them drivers to get 12 mA onto gates of IRFP240.

Power supply are trafos 2x24 VAC, 200VA for +/-35 Volt rails.
One trafo for each channel.

To setup you need to seek a resistance R8 that give ~5 mA through your JFET 2SK170BL at 35 Volt
Then chose feedback resistor R9 for gain like x20
After this you can adjust R1 (632 Ohm) for zero at output.

Then adjust R4 (4.95 kOhm) for 200 mA in the output devices.

Performance.
THD at 1 kHz is low.
0.0008% at 1 Watt
0.0060% at 42 Watt
The good thing is that 2nd harmonic is very dominant at all levels.
The sound is probably very MOSFETish!

Enjoy

[Dr.EM]

The 2SK/2SJ pair certainly are rare now, but maybe these could work as an alternative:

Mosfets/Modules - Lateral MOSFETs - Class D

or

ECX08N16-Z
ECX08P16-Z

These seem to be readily available laterals. Your first circuit modelled as very nice performance.

[MiiB]

Diving the Jfet right at the limit...a 10-12V cascode would be good....
What is the reason for the bipolar driver stage....can't you just pull enough current through the mosfets to drive the laterals directly..??

M

ohh sorry didn't see you changed to IRF's....

[ontoaba]

Originally Posted by lineup

The good thing is that 2nd harmonic is very dominant at all levels.
The sound is probably very MOSFETish!

Enjoy

Umm., could you explain that MOSFETish? What kind is it?

This one using cheapo MOSFETs, but this prototype is best sounded that I have, and best sounded among all amplifiers I ever tried and heard. I listen it almost all few day long (still play when I sleep) without listening fatigue. Best sound reached when driving headphones directly (most beautiful high frequency), but my motorola earpiece burned by this amp when crack input from bad connector happen. Finished in last few days.