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Old 13th November 2012, 07:34 AM   #7541
dvv is offline dvv  Serbia
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Good reading.

Thanks, Wayne.
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Old 13th November 2012, 10:31 AM   #7542
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Ditto Wayne .

Did anyone try this with power amplifiers ? Related reading below .

http://www.essex.ac.uk/csee/research...0amplifier.pdf
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Old 13th November 2012, 11:35 AM   #7543
DF96 is offline DF96  England
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Hawksford's ideas are sometimes not quite what they seem. I seem to recall this 'current-drive' idea has already been discussed on this forum. There is more to it than simply having a very low DF, as some seem to imagine.
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Old 13th November 2012, 03:37 PM   #7544
bcarso is offline bcarso  United States
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Originally Posted by DF96 View Post
Hawksford's ideas are sometimes not quite what they seem. I seem to recall this 'current-drive' idea has already been discussed on this forum. There is more to it than simply having a very low DF, as some seem to imagine.
His arguments about some sort of hitherto-unappreciated granularity in low-level preamplification was also...errr...controversial
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Old 13th November 2012, 04:05 PM   #7545
DF96 is offline DF96  England
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Yes. He seemed not to understand that shot/partition noise (which was essentially what he was talking about) only occurs when charge carriers are uncorrelated, which does not happen in a conductor (otherwise every circuit junction would generate noise). Basic errors like that make me cautious about everything else he says; perhaps unfair, but we all have to apply filters because none of us has time to read and understand everything written on audio.
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Old 13th November 2012, 04:21 PM   #7546
bcarso is offline bcarso  United States
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Originally Posted by DF96 View Post
Yes. He seemed not to understand that shot/partition noise (which was essentially what he was talking about) only occurs when charge carriers are uncorrelated, which does not happen in a conductor (otherwise every circuit junction would generate noise). Basic errors like that make me cautious about everything else he says; perhaps unfair, but we all have to apply filters because none of us has time to read and understand everything written on audio.
He seems to appear to be having a very good time though, which I appreciate. However, while thoughtful and inventive, it seems he doesn't do a lot of background reading sometimes. And yet his name gets associated with circuits (e.g., the Hawksford cascode). What's in a name?

BTW a good albeit brief discussion of electrons in a conductor can be found in the late Peter Dunn's electronics book for physicists, Gateways into Electronics.
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Old 13th November 2012, 04:35 PM   #7547
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Does anyone here have the service manual, or just the schematics, of Harman/Kardon's legendary Citation XX?

That's one whopping legend of an ampifier. It's said that it's the best power amplifier ever made, and judging by its specs, like 500 A peak current output, it certainly looks a winner.

I know for a fact that it changed ecerything in HK, their complete topology logic changed radically. Up until it came along, they used more or less similar topologies like everybody else, just more refined; after it, they had topologies no-one else, as far as I am aware, used. Starting from HK 870 power amp, they were into sub-20 dB global NFB.

Citation XX is said to be the brainchild of three people - a Japanese engineer working for Shin Shirasuna (the company which actually manufactured HK gear), Richard Miller and Matti Otala.

I have a partial schematic, with hand jotted comments of Richard Miller, but unfortunately, it was drawn from memory (Richard Miller doesn't have its schematics ???), and has his hand written comments here and there. What is missing is the current gain stage, unfortunately, the most interesting part.

BTW, it's classic measurement specs are, shall we say, mundane, THD being given as 0.1% - hardly ground breaking. Yet, its aura is exceptionally strong. Perhapbs because (at least in part) it's so rare, it seems H/K and Shin Shirasuna had issues, like Shin Shirasuna offering exactly the same products under its own monkier, at, of course, a better price.

Has anyone here even seen it? Heard it in action?

John, I would imagine you took the time and trouble to check it out? Any views, comments, impressions?
I have pieces of the schematics, mostly the inputstage. What do you mean by current gain stage, the output stage ??

There is a member that has one and is refurbishing it, promised me schematics as he reverse engineers and rebuilds the amp. The outputstage is based on diamond topology according to the literature. The inputstage design is very different indeed, I have ever seen anything even resembling it.
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Old 13th November 2012, 05:04 PM   #7548
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The Citation XX power amp was a first in relatively high power amps to attempt to do everything 'right'. It was not the only amp attempting to do it, but at least, it was made commercially, and is still known, even today.
Most of my amps contain virtually all of the additions put into the XX, today. e.g. High Current, Good Slew Rate, Symmetrical topology, etc., etc.
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Old 13th November 2012, 06:11 PM   #7549
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Originally Posted by john curl View Post
The Citation XX power amp was a first in relatively high power amps to attempt to do everything 'right'. It was not the only amp attempting to do it, but at least, it was made commercially, and is still known, even today.
Most of my amps contain virtually all of the additions put into the XX, today. e.g. High Current, Good Slew Rate, Symmetrical topology, etc., etc.
It is something of an elusive phantom - everybody and their dog know about it, but few have seen it or heard it.

Perhaps it's the model's rarity that adds the extra aura ... Plus some really wild for the time claims, like the 500 Amp peak current capability.

@homemodder

I have that as well, but no predriver-driver-output stage at all. Ultimately, I'd simply like to have it whole, even if I don't plan on building one.
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Old 13th November 2012, 06:37 PM   #7550
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It was just 'overpriced' for its day, so that sales were low. ONLY custom built amps commanded a $5000 price, back then.
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