Using Many Small Signal Transistors Paralleled in place of one output Transistor

[tiefbassuebertr]

Originally Posted by tiefbassuebertr

I am still looking for commercial audio amplifier brands, where are in use a bunch of small or medium signal transistors in the output power stage instead only one or only few BjT power device in each half.

any news?

[tiefbassuebertr]

Originally Posted by tiefbassuebertr

This approach seems to be very good in view to the sonic quality. Thule's integrated amp IA120 work with a bunch of paralleled TO-126 (unfortunately I haven't the schematic).
Mr. Nelson Pass does basicly the same by this project:
Beast with a Thousand JFETs

Who knows more commercial brands with a bunch of small signal transistors in the output power stage instead only one BjT power device in each half?

commercial amp devices seems to be very rare. But where are the best schematics for diy projects in this matter (except the above mentioned and the follow:
http://www.diyaudio.com/forums/solid...amplifier.html )
In respect of ultra low impedance loads this approach seems to be the best from my view.
Thanks for advices.

[jacco vermeulen]

http://www.diyaudio.com/forums/chip-...ml#post4402617

[tiefbassuebertr]

Originally Posted by jacco vermeulen

http://www.diyaudio.com/forums/chip-...ml#post4402617

Very interesting. What about sound? Are there experiences with the use of AD797 in this kind ?

[jacco vermeulen]

For the output section of Mr Self's design, AD797 would require double the number of opamps and make it rather expensive.

(I picked other opamps for the front end, plus fet-input opamp for the servo instead of OP177, use it as headphone amp for an AKG)

[cbdb]

1 thing. The drivers see all those output transistor input capacitance in parallel. Don't know how this compares with one high power transistor.

[tiefbassuebertr]

Originally Posted by cbdb

1 thing. The drivers see all those output transistor input capacitance in parallel. Don't know how this compares with one high power transistor.

The main advantage for operating in parallel mode is the absence of the typicall disadvantages in comparsion to MOSFET's.
The actually question is here, what kind of audible effects and distortions occurs on the different circuit topologies (with and without global NFB so as with global NFB only for LTP/VAS like used in Nelson's STASIS series)

[Mark Tillotson]

An advantage of using many smaller transistors is that secondary breakdown is avoided, so long as adequate current sharing emitter resistors are used. A single power transistor die is large and thermal gradients can build up between different parts of the die leading to hot-spots (the mechanism of secondary breakdown).


Another advantage I can see is that if one device fails short, it will be vaporized quickly by the opposite side devices acting in concert, becoming open circuit and leaving the amp still functioning - cascade failure is less likely. Against this is the fact that failures are more likely with more devices, and severe voltage spikes are going to affect multiple devices anyway.

[greenocean]

krell fpb-300c Krell FPB-300C - Manual - Stereo Power Amplifier - HiFi Engine