Burning Amplifier BA-2

OK, matched pair it will be. The footprint is shown here. Was just curious if some kind of creative twisting for face to face offered any advantage in operational stability. Most likely not worth the trouble in this application ;)

Thanks.
 

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The middle pin of the 7 does nothing
The two sets of the outer 3 are the jFET pins.
One is reversed relative to the other.

holes 3 and 5 are the Source pins.

Turn the left jFET 90° anticlockwise after insulating the Gate lead.
Turn the right jFET 90° anticlockwise after insulating the Gate lead.

You now have a pair facing each other ready for Thermal Coupling.

One of the biggest advantages of the j109 is the Thermal Coupling.
The specified tolerances of matching are not worth buying.
Most pairs achieve much better matching than the tolerance.
But this can still be bettered by hand matching over a range of Id (<Idss).

With (very labour intensive) hand matching and Thermal Coupling you can end up with a better matched pair than using a j109.
 
Full-fat BA-2

I was playing with the design of a J2-esque/F4 combination for producing comfortably more than 100W into 4 ohms for my Maggies.

But such an approach isn't ideal. When driving the F4 you've got those SemiSouths burning up a lot of heat which is wasted on the F4's 47K input.

Here's another idea which doesn't require the compromises of having the J2-esque also be a good stand-alone amp. While it started as a J2-esque IS, a BA-2 VAS, and an F4 OS, it ends up looking more like a Full-Fat version of a BA-2:

1) rails increased to 46V
2) LTP cascoded
3) LTP CCS changed from single JFET to BJT feedback pair
4) VAS CCS changed from bootstrapped load to BJT feedback pair
5) OS shortened to 4 pairs

Comments appreciated.

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