Has anyone built the MJamp?

I've been wanting to build this one also, as usual with more power. 40 volt rails would give about 100 watts with the only drawback being that the gain depends on the feedback ratio. As you have designed it with a gain of 5 one would need 8v. peak or about 5v. rms for 100 watts out. The higher the gain, the less feedback available to correct for crossover distortion (assuming one is running the amp class AB).
There is an interesting 150 watt amp using this style of output at: http://www.ne.jp/asahi/evo/amp/J49K134/zu3.pdf
This person uses the output stage with no gain and uses small mosfets instead of transistors to drive the output beasts. He uses a very complicated front end to drive it all.

I am thinking about using a tube for the first stage and capacitor coupling it to the MJamp in a similar fashion to the one here:

What does anyone think?

There is a good substitute for the 2SK135/J50, the BUZ900 series MOSFETS from http://www.semelab.co.uk

The American distributor is:
Martinez & Associates,Inc. is pleased to announce that we have been designated the sole US distributors for Magnatec's Lateral MOSFET product Line.

We can be reached at:

Martinez & Associates, Inc.
234 Boston Post Road
Wayland, MA 01778
Tel: (508) 358-0131
Fax: (508) 358-2361
email: [email protected]

We accept payment by check or VISA, Mastercard, Discover and American
Express credit cards.
I have built several amplifiers with this scheme. It's difficult to obtain the same operation in all them. It's necessary to insert adjustable resistors in collectors of the driver transistors, and to carefully sort and match all transistors. Therefore, it's necessary to buy many transistors. This may be a problem with the expensive output devices.

But whith this care, operation is reliable, and sound very pleasant, fluid and clear. Power supply unit must be as big as possible, big transformer, many capacitors, and very short wiring. Power supply unit is 50% of an amplifier !

Regards, P.Lacombe.