Quad 303 triple cascade

[tiefbassuebertr]

Originally Posted by tiefbassuebertr

Only truly experienced (and unfortunately very few) developers (like Quad) achieve a design of such triple stages without any oscillation under any load condition.

I recall, that I have for checking a diy amp device, that uses also such - slightly different topology:
The name was "Equa" from German magazine "Elektor" December 1972, page 1216
This amp was an unwanted oscillator (even by p-Spice simulation and in real life only to test by current limited power supply without destroy the output devices).
Only after remove one stage in the output buffers I get satisfy operating.
About this address perhaps there is a complete Equa schematic available:
Audioclub Oost Brabant, clubavonden

I want to have basic articles about such three stage super ß quasi complementary stages. Who knows more about this?

I know too few English keywords therefore. I recall, that I have read some years ago a JAES article. But I don't know if it was the main topic.

Check out follow replies to post #3403 about
Bob Cordell Interview: Negative Feedback

[Ian Finch]

I have lost the original magazine, a UK edition but "Elektor" Summer Circuits edition 1980, had a 2N3055 "supertransitor" quasi circuit if I recall correctly. THD was quite low, bias 25-100mA. Perhaps this is of interest.

Recently, I bought a VGC Quad 303 and came across another commercial design in my searches, with the same output stage. If I can find it again, I'll post a link

[EssB]

Ian, FYI the Crimson Elektrik amps used this output stage. I think tiefbassuebertr already knows about them

[tiefbassuebertr]

Originally Posted by EssB

Ian, FYI the Crimson Elektrik amps used this output stage. I think tiefbassuebertr already knows about them

Yes; the attached file by post #2 about
Crimson (Krimson) Amp Schematics
show a schematic.

Originally Posted by Ian Finch

I have lost the original magazine, a UK edition but "Elektor" Summer Circuits edition 1980, had a 2N3055 "supertransitor" quasi circuit if I recall correctly. THD was quite low, bias 25-100mA. Perhaps this is of interest.

In the summer edition from German's magazine Elektor (1983) is in fact a beta enhancer, but with a quadruple (instead a triplett) arround a 2N3055. The actually wrong headline is follow: "2N3055 Darlingtons" (circuit number 73, page 7-92). For the positive half there is at first a NPN (BC546B), then a PNP darlington consist of a BC556B and a BD140 and then the 2N3055.
For the negative half there is at first a PNP (BC556B) and then a NPN triplett consist of a BC564B, BD139 and a 2N3055, but it seems to be a missprint, because the emitter of 2N3055 from the neg. half goes not to the negative rail.

The main issue for me by these methods of beta enhancing is the fact, that there are no clearly design rules.
Please note: by quasi complementary tripletts there are three different arrangements for the topology, and in case of a quadruple yet much more. Also by the idle current for each transistor stage there are very many possibilities.