It says ASU doesn't have it, "Sorry, but this item is not currently available from your library." And no information, that I can see, to create a login.
Which is I posted. Can someone get me a copy? Thanks! ...Jim Thompson
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| James E.Thompson | mens |
| Analog Innovations | et |
I have just finished reading Linear Audio Volume 11, and once again Jan Didden is to be congratulated on a generally first-class job.
But- as you might imagine, I make an exception for the Michael Kiwanuka article, which contains a lot of criticism aimed at me.
The amplifier circuit Kiwanka is complaining about is Fig 15.1 in Audio Power Amplifier Design. (6th edn) A copy is attached. The biasing system controls TR1 input-pair tail-current, with the bias voltage passed to VAS current-source TR5, crucially via resistor R23. This looks like a sound piece of penny-pinching but actually has a unexpected limitation in positive slew-rate, which I duly explain and cure. The same scheme was used in the original EW article in Sept 1994. I think all my amplifier designs, for the last 10 years at least, have used separate biasing for the two current-sources to avoid this issue.
Kiwanka's Figure 1 has a biasing system that controls the current through the VAS source TR5, and no bias sharing, which is of course a completely different situation. Whether this change was deliberate or accidental I don't know, but the rest of the article is naturally irrelevant to anything I have written, so you needn't try to make sense of it.
If you are wondering about all this 'Thompson' business, the Russell & Solomon paper just makes the bare statement that a current-mirror in the input-pair stage for differential-to-single-ended conversion was first used in an opamp by J E Thompson at Motorola in 1966- so far as the authors are aware. No reference is given. I don't know who first applied it to a power amplifier, and if anyone can tell me I would be most interested. However that seems to me no reason for calling the configuration a Thompson. Many people are known to have contributed, and you might as well call it a Blumlein (input-pair) or a Miller. (compensation) My Blameless name refers to later developments such as heavy local feedback in the input pair.
I read the article and yeah, I don't have any idea why the author is using Mr. Thompson's name on the topology in Fig. 1 either. It looks like the topology used in just about every solid state audio power amplifier ever. Maybe he was the first to use a current-mirror as a differential pair load on a chip or something
I never personally claimed the configuration myself, but Tom Frederiksen, in several of his missives attributes it to me... though, actually, his attribution is incomplete, there's substantially more to it in regards current matching... I first applied it ~1963.
Kiwanuka has written yet more fallacious diatribes... watch "audioXpress" for the coming retribution >:-} ...Jim Thompson
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| James E.Thompson | mens |
| Analog Innovations | et |
Sure, most audio amp papers are all pretentious waffle.
Its a complete waste of time to design for symmetrical slew rates. All that matters is that the input referred amp slew rate is reasonably larger than the input slew rate, and no one will notice.
Like, the world is run with mp3 on iPhones and piss tiny in-ear phones, that usually aint. I am probably one of the 3 in this universe that actually owns a real Hi-Hi amp, well....non of my acquaintances have one for sure....
"However, a resistive load doesn't amplify its internal noise, and therefore possesses the advantage of producing somewhat less noise than would be generated by the current mirror or active current source."
Pretty sure this statement is easily proved to be false when comparing two power amplifiers with the same slew rate and open loop gain, AFAIK there is literally no advantage to not using a current mirror load for the input pair other than not having to use two transistors
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