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Old 24th November 2012, 10:41 PM   #31
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Kevin, private emails are not something to air on this forum, and bad form on any other, imo.

Sorry that you took my suggestions and inquires the way you have. My interest in what you sell is/was genuine.

I think I am out of this thread for a while... thanks.

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Old 6th December 2012, 07:36 PM   #32
Struth is offline Struth  Canada
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Hi Guys

The William Chater patent (US5,055,797) shows a bias control method using a differential amplifier monitoring the floating Re's of a mosfet output stage, feeding a precision rectifier and integrator, in turn manipulating the mosfet drive stage. AC signal is essentially ignored.

The method above is a bit complex. Self's class-A bias servo is simpler and is discrete. Other current-monitoring control circuits require just two BJTs and are unaffected by the signal.

The MF circuit is simple but tries to do too many things all at once which restricts performance.

The class-i "engine" is clever but requires matched devices to work well.

Lineup's diamond feedback circuit works very well at reducing crossover distortion if you wish to check out his thread regarding a power buffer idea.

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Old 7th December 2012, 11:29 PM   #33
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attached is the pdf of the Chater patent.

He speaks of a "turn-off transient suppressing means" and also to "...substantially eliminate crossover distortion..."

There was another amp on here that nobody could figure out if it really had immunity from turn off - trying to recall the fellow's name... it had been a commercial product. If I remember I'll post.

Coming up with a "better" and more robust method of making the class i method would be nice.
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File Type: pdf Chater auto bias pat5055797.pdf (739.8 KB, 79 views)
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Old 8th December 2012, 04:14 AM   #34
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Hi Guys

Has anyone seen the fourth part of the class-i article? It is supposed to present a practical constructed circuit.

The circuit idea is very clever in the British context, and the pitfalls all seem heavier than what gets "fixed". The previous references I gave mostly produce class-A output stages, but do not necessarily have to.

There was discussion elsewhere about the Super-A biasing. Did anyone every measure such an amp? or simulate it?

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Old 10th December 2012, 10:28 PM   #35
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subscribe to Jan Didden's Linear Audio, it has the complete article... more is yet to be published as a follow up i am led to believe...

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Old 10th December 2012, 11:06 PM   #36
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Hi Guys

One man's "substantially eliminated" is another man's "zero artifacts". The proof is in the building and measuring. Apart from being a 100% mosfet signal path, it does not look like there should be anything to keep Chater's approach from doing what it is intended to do.

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Old 10th December 2012, 11:48 PM   #37
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Is Chater's approach "error correction" or is it "non switching"?

One tries to fix it "after" the other "before".

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Old 11th December 2012, 12:59 AM   #38
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Hi Guys

Bear, is your question rhetorical?

Taking it at face value, Chater's method is in the "nonswitching" category. Elvee dismissed the method as "sampling" and being "delayed in time" when someone asked about this on the circlophone thread. I think that because there is an integration involved, Elvee saw it as not being instantly effective. I don't think that is actually a problem if crossover distortion is eliminated, and there are definitely simpler methods.

Self's method is similar inasmuch as Vq is sensed directly, but his approach uses a floating bias control circuit so is overall simpler and has no time constants. The methods shown in my books are even simpler.

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Last edited by Struth; 11th December 2012 at 01:04 AM.
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Old 11th December 2012, 03:35 AM   #39
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Quite frankly I am unclear on what this method is. I did not see your posts on the circlophone thread, I stopped looking at that some time back, and there are too many threads that i am trying to keep up with now... so the question is simply this. Are the methods you are referring to preventing cut off of each half cycle of the PP output stage or are they adjusting the overall bias over some time constant that is greater than one half cycle?

I can't determine this by simple inspection of the schematic(s).
If there is a way to do it by simple inspection, I'd love to have it explained.

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Old 11th December 2012, 03:54 AM   #40
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Quote:
Originally Posted by bear View Post
I can't determine this by simple inspection of the schematic(s).
If there is a way to do it by simple inspection, I'd love to have it explained.

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New Class A, Super-A, Non-Switching : need a revival ?
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