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Old 24th September 2009, 10:11 PM   #11
forr is offline forr  France
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Around 1990 I think, I added the Margan's non-swithing circuit to a JLH bipolar amp. For an unknown reason, I disliked the sound and soon dismantled it. As PMA sugests, I would prefer to explore the Blomley approach.
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Old 25th September 2009, 01:42 AM   #12
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Hi,
If you are interested in Non Switching Class B designs, then the following references may be useful:

P. Blomley `New Approach to Class B Amplifier design’
Wireless World, Feb. 1971

S. Tanaka `New Biasing Circuit for Class B Operation’
AES 65th Convention, paper 1615, Feb. 1980

E. Margan `Crossover Distortion in Class B Amplifiers’
Electronics & Wireless World, July 1981

Marcel van de Gevel `Audio Power with a New Loop’
Electronics World, Feb. 1986

Huon, Dower US Patent 6-630-865
Oct. 2003

I think the most interesting of these is the Gevel and Huon ideas (Huon and Dower’s patent is an extension to van de Gevel’s work), in which the bias is constantly adjusted during each cycle so that the `Off’ output transistor never actually turns off, but settles to a minimum current. Getting the Huon scheme stable, however, is a bit of a challenge! Incidently, the Whise 319A active sub woofer (no longer in production) used an amplifier designed around patent 6,630,865.

Paul Bysouth, September 2009.
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Old 25th September 2009, 08:33 AM   #13
bambo is offline bambo  Netherlands
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Hi Forr and Paul,

thanks for your feedback! I know the references you provided Paul, and saw them in an earlier post of yours. I was hoping the keep-alive scheme (after Douglas Self) by Margan would be a good, relatively simple solution. Albin seems quite satisfied, Forr provides an opposite opinion... Anyway the circuit mentioned in E&WW july 1987 (not '81) appears to have been described originally in Electronics & Wireless World October 1985. So I would like to track down the original text. Can't find in a nearby library though.... And, as explained, the rewrite (?) in Журнал " РАДИО" № 2, 1987 (in that website presented as a retro schematic !!) doesn't really work for me .

Cheers,
Mark
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Old 21st October 2009, 07:51 PM   #14
bambo is offline bambo  Netherlands
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Quote:
Originally Posted by Erik Margan in E&WW, Oct.1985 View Post
Add-on current dumping

Recently, several “non-switching” class-B amplifier circuits have been published. Some of these are complex, some have thermal runaway problems, and some require careful matching of devices.
This circuit is so simple that it can be implemented in any class-B amplifier, yet it is effective enough to cure all of the problems that traditionally result in crossover distortion.
The idea is to make sure that the output device is always turned on, by configuring it as a constant-current source when it would be normally be turned off. The principle is not new, but the realisation is.
Transistor Tr2 is forced into constant-current mode by collector current of Tr4. This transistor senses the fall in Tr2 collector current as I2RC falls, so I4RB4 directly compensates IORE negative feedback through Tr2 being the regulating current-derived negative feedback prevents thermal runaway without the need for special thermal feedback.
Take care selecting base resistor values RB3,B4. Lower values of around 200Ω are preferred to prevent creation of an additional pole within the desired bandwidth.
Drive current ID needs to be set at about twice the value of Tr3/Tr4 maximum collector current to allow the drivers to work in class-A throughout the full-voltage swing. Quiescent current is set by I3 and RB/RE.
Making RC equal to RE simplifies calculations.
Generating bias voltage with diodes allows a simple output current limiter to be added in the form of D3,D4.

Erik Margan
Ljubljana
Yugoslavia
Hi there,

for all interested, I have carefully retyped the original text of Margan's circuit idea. The scan of Albin's reprint thereof was very welcome, but I could see why Albin called it tatty. Anyway, I hopped into the technical university library last week to reclaim from history a couple of words that apparently had fallen of....

Enjoy your favourite records, without switching
Mark
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Last edited by bambo; 21st October 2009 at 07:56 PM.
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Old 21st October 2009, 08:19 PM   #15
AndrewT is offline AndrewT  Scotland
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here we go again.
Ensuring that devices pass a minimum current, rather than turn off, does not make a ClassA stage.

Imagine the circuit as two single ended stages with that extra transistor added (to each half) to ensure the main pass devices always conduct.
What happens to the output when the deviation of the output current exceeds the bias current? It clips!
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regards Andrew T.

Last edited by AndrewT; 21st October 2009 at 08:22 PM.
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Old 21st October 2009, 09:00 PM   #16
bambo is offline bambo  Netherlands
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Quote:
Originally Posted by AndrewT View Post
here we go again.
Ensuring that devices pass a minimum current, rather than turn off, does not make a ClassA stage.

Imagine the circuit as two single ended stages with that extra transistor added (to each half) to ensure the main pass devices always conduct.
What happens to the output when the deviation of the output current exceeds the bias current? It clips!
Hi Andrew,

ehhh, I dunno? By strict definition, I would be tempted to allow a "class A" badge. But I agree, heat- and trickery-wise, 'non-switching B' is not A.

I am afraid I don't grasp the reasoning behind the second part of your post. Clipping,,, WHY? The measurements published in Margan's article "Crossover distortion in class-B amplifiers" show not even a faint hint of clipping in NSB operation at levels exceeding bias.

regards and enjoy your albums!
Mark
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Old 22nd May 2011, 04:43 PM   #17
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Are there any news?
I would like to know commercial amplifier devices, where non switching ClassB is in use - except class XD from Cambridge Audio, go to
Amplifier Class-XD™
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