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Old 25th April 2008, 04:19 PM   #1
sreten is offline sreten  United Kingdom
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Default margan : non switching class B

http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf

Hi,

Anyone know anything about :

References
1. E. Margan, Add-on current dumping,
Electronics & Wireless World, 1985, October,
p.40.

Referred to in the above article ?
is it really non switching class B ?
Is there a good explanation of it anywhere ? (I cannot find any info).

How does S2 in figure 2 work ?
it looks like it will blow the amplifier up ........

/sreten.
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Old 25th April 2008, 04:46 PM   #2
KSTR is offline KSTR  Germany
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Default Re: margan : non switching class B

Quote:
Originally posted by sreten
is it really non switching class B ?
Is there a good explanation of it anywhere ? (I cannot find any info).
The idea behind is seems to be the following:
Basically the output is an emitter follower in a CFP-like configuration. Under normal conditions the current sense circuitry around the top and bottom 0.4R resistors is off (the transistors are off). When the current starts to cease as the output current increases for the opposite side, the voltage increases across the sense transistor's Vbe junction, starting to turn it on (the diode provides a bias point for this). This in turn spreads the bias (as established by the primary bias circuit) due to voltage drop on the 200R base resistor which now gets pulled towards the rail. Which increases current up to an equilibrium point, a feedback loop in the end. Therefore the outputs never turn completly off.

You might want to check out the LT1166 bias generator, which does more or less the same thing but a bit more clever, without the additional sense resistors, using the drop across emitter resistors directly.

Quote:
How does S2 in figure 2 work ?
it looks like it will blow the amplifier up
If it's a bad design, it will. Otherwise it's just a worst case reactive test load, some people use even higher values (3uF, 10uF).

- Klaus
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Old 24th August 2008, 09:40 AM   #3
albin is offline albin  United Kingdom
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hello there
re non switching class B amp by Erik Margan.find july 1987 issue
electronics & wireless world.there is a full test circuit & results by the man himself.I built 2 pairs of these for myself and I still use them.
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Old 3rd October 2008, 07:18 AM   #4
albin is offline albin  United Kingdom
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hello
this topology was 1st published as a circuit idea in Electronics & Wireless World in october 1985,I have a tatty reprint.
regards
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Old 3rd October 2008, 07:32 AM   #5
PMA is offline PMA  Europe
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How about Peter Blomley approach?
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Old 3rd October 2008, 11:57 AM   #6
Mooly is online now Mooly  United Kingdom
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Quote:
Originally posted by PMA
How about Peter Blomley approach?
Doesn't that just move the switching problem to an earlier stage ?
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Old 4th October 2008, 03:07 PM   #7
Elvee is offline Elvee  Belgium
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Default Re: margan : non switching class B

Quote:
Originally posted by sreten
http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf

Hi,

Anyone know anything about :

References
1. E. Margan, Add-on current dumping,
Electronics & Wireless World, 1985, October,
p.40.

Referred to in the above article ?
is it really non switching class B ?
Is there a good explanation of it anywhere ? (I cannot find any info).

How does S2 in figure 2 work ?
it looks like it will blow the amplifier up ........

/sreten.

Interesting.
I had never seen the original Margan circuit, though I heard it mentioned from time to time.
I reinvented myself very similar circuits. I am not bitter about it, because, at the time, this enabled me to have a totally fresh and unbiased view on what I thought were "my" circuits.
I came to the conclusion that this type of bias did indeed do a great job of eliminating crossover distortion, but at a cost (there are no such things as free lunches in engineering).
When the NSB circuits are active, they introduce a supplementary, local NFB. In short, each circuit tries to keep constant the current in the output transistor it controls, and thus "fights" with the principal loop gain, which tries to change this current according to the input signal.
The net result is a reduction of gain in all the region where the circuit is active. This is much less obstrusive than raw crossover distortion, but this nevertheless introduces gain non-linearities in the transfer function.
These non-linearities are relatively modest and can easily be dealt with by the open-loop gain of the amplifier, but if perfection is the ultimate goal, different strategies have to be adopted.
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Old 4th October 2008, 05:13 PM   #8
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Hello

Does this current dumping resistors ideas can be apply to a Self type 2 output ?

Thank

Gaetan
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File Type: jpg self ef type 2 output.jpg (60.1 KB, 599 views)
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Old 4th October 2008, 08:02 PM   #9
albin is offline albin  United Kingdom
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Default elvee erik margan nsb

your reply enlightens me
i made two pairs of these ghetto style.no pcb.I learnt a lot
more about earthing, power distribution, decouplng,and what works from these than anywhere else.for me they were magic.
I think because I believed in them and the man.
thank you
regards
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Old 24th September 2009, 09:24 PM   #10
bambo is offline bambo  Netherlands
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Quote:
Originally Posted by albin View Post
hello
this topology was 1st published as a circuit idea in Electronics & Wireless World in october 1985,I have a tatty reprint.
regards
Hi there,

on the net I can find (I think...) the Margan article titled "add-on current dumping." It's, however, in cyrillic so that I cannot understand much more than that it was published in journal "Radio" in 1987 (words like transistor etc. are recognisable ). Perhaps a rewrite in Margan's mothertongue (?).

Anyway, if you, Albin, would be able to send me a little scan of your reprint, I would be eternally thankful! I am much interested in using a scheme like this.

kind regards,
Mark
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