I might try to further explain Esperado's amp 'advantages' to finish the 'lecture'.
In the middle-late '60's, quasi-comp output was still in vogue, as true complementary power transistors did not appear in the USA until 1966, with the introduction of the 2N3716-2N3792 complementary pair by Motorola. These devices were: 80V, 10A, and had an f(t) of 4MHz.
The standard output transistor used by Dyna, for example was the 2N3055, a VERY SLOW device best suited for DC power supplies, but the best device available was the 2N3773, that was very slow as well, perhaps less than 1MHz f(t), but very rugged, and this was used by industrial motor control amps like the Crown DC-300. It's main feature was the high 'safe area' of operation, allowing relatively high power supply voltages to be used.
What Esperado and Julian Vereker of Naim fame used, was a special power transistor series made by a European semiconductor manufacturer that had an f(t) of 10MHz or so which was a REAL ADVANTAGE, because: All else being equal, high f(t) gives a proportionally faster power amp.
So, while Marantz, JBL, and even GAS (Ampzilla) were struggling with 2-4MHz f(t) devices, even with complementary pairs, Naim and other European designers were using a 10MHz device on the output, to some advantage.
I too, struggled with 4MHz devices for almost a decade. The JC-3 power amp used 4MHz devices initially, and the big servo amp that I designed for Ampex Research used only 2MHz devices. Therefore, to make a 100V/us amp that was to be the JC-3, I had to resort to a very different input stage, namely the comp.differential fet input stage.
It is not magic as to why this made the amp faster, it is because the Gm of the first stage was LOWER than typical, and this allowed for faster slew rate.
The same thing could have been achieved by degenerating bipolar transistors, BUT then the overall amp might be noisier AND not have enough gain to hide the output Xover distortion, etc, to meet spec. Carefully, examine the AMPZILLA and see their approach, which traded lower low frequency distortion for lower slew rate.
In the middle-late '60's, quasi-comp output was still in vogue, as true complementary power transistors did not appear in the USA until 1966, with the introduction of the 2N3716-2N3792 complementary pair by Motorola. These devices were: 80V, 10A, and had an f(t) of 4MHz.
The standard output transistor used by Dyna, for example was the 2N3055, a VERY SLOW device best suited for DC power supplies, but the best device available was the 2N3773, that was very slow as well, perhaps less than 1MHz f(t), but very rugged, and this was used by industrial motor control amps like the Crown DC-300. It's main feature was the high 'safe area' of operation, allowing relatively high power supply voltages to be used.
What Esperado and Julian Vereker of Naim fame used, was a special power transistor series made by a European semiconductor manufacturer that had an f(t) of 10MHz or so which was a REAL ADVANTAGE, because: All else being equal, high f(t) gives a proportionally faster power amp.
So, while Marantz, JBL, and even GAS (Ampzilla) were struggling with 2-4MHz f(t) devices, even with complementary pairs, Naim and other European designers were using a 10MHz device on the output, to some advantage.
I too, struggled with 4MHz devices for almost a decade. The JC-3 power amp used 4MHz devices initially, and the big servo amp that I designed for Ampex Research used only 2MHz devices. Therefore, to make a 100V/us amp that was to be the JC-3, I had to resort to a very different input stage, namely the comp.differential fet input stage.
It is not magic as to why this made the amp faster, it is because the Gm of the first stage was LOWER than typical, and this allowed for faster slew rate.
The same thing could have been achieved by degenerating bipolar transistors, BUT then the overall amp might be noisier AND not have enough gain to hide the output Xover distortion, etc, to meet spec. Carefully, examine the AMPZILLA and see their approach, which traded lower low frequency distortion for lower slew rate.
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My personal view on that is waking up in an alley, with nostril powder residue, a stale taste of scotch and a strong fragrance of cheap perfume, an unzipped fly and an empty wallet.
(I'll skip the unsavory parts)
Mr D,
you are very well aware it was a metaphor.
(I'm such a romantic)
What, Spain ?
(say H to A from me)
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