The Kiwanuka article in Linear Audio 11: Douglas Self

[PB2]

Hello Scott

Might well, but as it stands it's just an opamp... R8 will give some of the slew-reducing effect described in APAD6- the current-source base needs to be firmly held at a low impedance to prevent transients feeding through its Cbc and reducing the current.

I'm hoping to expand the 'History of power amps' chapter in APAD6 into maybe a whole book. (if there might be a market for such)

I'd be very interested in tracking down the first power-amp with an LTP input, and the first with a current-mirror. I'm not very familiar with the USA literature so you probably know more about this than I do.

One data point: Daniel Meyer's Tigers That Roar amplifier (Popular Electronics July 1969) had an LTP but no mirror.

I see that you're looking for the first power amps with diff pairs and mirrors but you
might find this paper by Walt Jung interesting that covers the history of OP amps including
tube types:
https://www.analog.com/media/en/training-seminars/design-handbooks/Op-Amp-Applications/SectionH.pdf

It seems that the GAP/R P-65 was the first SS OP amp to use a transistor diff pair in 1961.

 

[ejp]

A power amplifier with LTP input stage appears in the Mullard Transistor Audio and Radio Circuits, 2nd edition 1972, 50W Amplifier p.137, and in the RCA Transistor, Thyristor, & Diode Manual, 1971, Technical Series SC-15, Circuit 15-12 p.718. The Harman-Kardon Citation Twelve has been said here to be based on this circuit.

 

[Bonsai]

I think Bart Locanthi’s JBL amp is the earliest I can locate. Here is a write-up

Locanthi’s amplifier from 1966

But, I believe the LTP was already in wide use in tube based opamps used for computational applications in the 50’s already.

I’ve commented on Locanthi’s design in the article above because it’s the first sensible design I have been able to locate where the designer seems to understand feedback and use it sensibly. YMMV.