Alex mentioned...
Looks like the "super-complementary" stage had some use in Bryston amplifiers:
http://www.bryston.com/PDF/Schematic...SCHEMATICS.pdf
(Sorry for posting transistorized links on a tube forum.)
Patrick replies now with ......
The link does does not take me to a particular schematic, but yes, I recall Ben Duncan's 1996 book I read where the use of N and P devices on each side of PP circuit are used, in order to give automatic device characteristic matching and hence less THD etc.
In the absense of much stuff about tubes, discussion of SS items should be tolerated when considering mosfets driven by vacuum tubes. Alex may surely be peeved and dismayed, and aghast at such absurdly ridiculous techniques I propose which I think do have a few saving graces IMHO, even when a dreadfully horrible IST is inserted offendingly fair smack in the middle of the signal path.
But just because I recommend the use of an IST, its actually OK because there is already room for an IST in a hybrid amp where an OPT isn't used. But the IST should be a slightly wider better BW device compared to something one may purchase from Hammond. As I mentioned, the IST has only to handle much lower voltages than when driving output tubes because the Vg-s signal of mosfets is rarely more than 2Vrms.
I had a look at the link for super-complementary follower:
http://www.valveradio.net/en/home/au...ary-stage.html
Its not too bad, and had two bjts to give +&- drive voltages and all that's OK.
But one may use a simpler method where the mosfets are arranged so two are in source follower mode and two are in common source mode.
Say you have +15Vrms powering 5 ohms at output.
The pair of Vg signals into N&P source fols are the same phase, same amplitude although DC bias is different. So Vg would be about +16.3Vrms, with Rs = 0.47r.
Vg signal to N&P common source mosfets is also the same phase and amplitude and will be about -1.3Vrms.
The -1.3Vrms comes from an anode RLa, say 2k2 to B+, and the +16.3Vrms comes from the cathode and an equal sized RLk 2k2 to a bootstrapped point connected to Vo.
Input to the concertina phase inverter is about 17Vrms, and this triode should be an EL84 in triode with low Ra, so that any distortion voltage between Vo and source follower gates is nearly all transfered to gates of common source mosfets. The only disadvantage of the scheme is that one has to use the extra triode between an input amp which needs to make slightly more than Vo. However, it should work OK and and HF gain can be adjusted with phase/gain reduction RC network applied to stop HF oscillations if thy can at all be provoked with a capacitance load of any value at Vo.
Next time I get a clear day to spend in the workshop without being driven mad by irate customers wanting their gear fixed last month, I'll try out a few of these ideas along with many more that keep coming to mind.
My own view is that the concertina phase inverter floating on Vo isn't really needed so I'll try my ideas first which are elegantly so simple.
BTW, just to illustrate why Alex should not get cranky about LF transients and his intolerance of RC and LR coupling when using SS devices, ppl should go to
http://www.turneraudio.com.au/solids...ono-mosfet.htm
Here we have RC coupling, and an OPT used with mosfets. The sound is indistinguishable from a good class A amp using 4 x EL34 per channel. There are NO BAD HABITS od bangs, pops, wheezes, farts or other BS when the amp is turned on or off. Bass is extraordinarily GOOD.
I have plans to install new PTs with E&I lams because the toroidals from Jaycar are too noisy. Then I can also include a winding for B+ and for tube input stages instead of the simple existing 3 bjts. The OP stage will be source follower mode and existing OPT BW will increase somewhat from the existing 200kHz+, and I expect excellent sound, and I'll have what will be a more interesting pair of amps with lower THD/IMD than at present.
Patrick Turner.