Single High power Mosfet for big Single Ended Amp ?

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Since I'm crazy for Mosfet SE sound signature rather than PP Class A I've built , Anyone pls tell me what type of Mosfet device that could deliver 40-60Watt Power out in 8 Ohm load with only single device per ch ....

Just finished Pavel Macura SE Amp 17Watt, love the sound but need more power for my Heavy Speaker.
Years ago I also already built some SS's Class A PP like Bebe T,JLH,Hiraga,Firstwatt F4,F5,Tumos etc
Hi Kacernator,

Thanks for the link, since the Device (2SK77b) hard to find,but its give me idea to look for the max SOA of all my Stock devices for bigest SE Pout capabilities ....


In that thread and in the Nelson Pass talk, he presents alternative with IXFN140N20P mosfet in schade feedback configuration. Check it out.

Here is the link to slides:
BAF Slides Nelson Pass |


  • baf2015-schade-mosfet.png
    144.4 KB · Views: 1,193
I need at least SE 50W/ch to free the load Spk choices due to their sesitivities, the Mosfet device candidates available out there. The problem how to reduce heatshink size , maybe the CCS usage : the Lamp,Big Resistor(do they still need the heatshink ?) or a heater element instead of a Giant Inductor...

Any suggestion wellcome.

50W into 8ohms requires an output of 28.28Vpk and 3.536Apk into a non reactive test load.
You cannot get 50W into 8ohms by any other combinations of volts and amps.

A single ended amplifier that has a fixed maximum output determined by the bias setting of the output device must be set up to achieve that 3.536A into the test load.

That determines the heat and the sink requirement.

Attach a reactive 8ohms speaker that will demand more current than a dummy load will force the SE amplifier into current clipping on fast changing transients.
That will sound terrible.
To avoid current clipping one should set up the amplifier to pass transient currents far in excess of what a resistive dummy load will demand.
Yes, I'm late to the party.

I'd say "sure, go for it" … and then be disappointed by what happens when the accumulated wear-and-tear on the MOSFET eventually causes it to melt down. I've done it, it happens. Especially when little whisker shorts somehow happen on the way from amplifier to speaker setup.

Myself, these days, I like to add active circuitry - and FAST circuitry! - to clamp current spikes on the output. Seriously. Whether you're using 1 or 10 MOSFETs (or bipolars) in parallel, you might as well include cathode / source / emitter side current-sense resistors of low value. Remember … its been 50 years since the invention of the OPAMP, and they are finally being recognized as pretty fast, pretty low-voltage, pretty stable devices. Especially for current-sense current-clamp circuits.

Just saying.

Make the beautiful design. PROTECT it from unexpected operating conditions. Sit back and enjoy the music until another wild hare enters your mind, and you need to 'do' another amplifier. REPEAT.

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.