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Old 24th March 2011, 08:12 PM   #11
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Class AA, VC4, Class S (Sandman) or "true current dumping" come close, if implemented correctly.

I own a SE-A100, which is already great in it's stock form, but with a little tweaking, it beats almost every Class A amp. This kind of amplifier architecture is good for distortion harmonics lower as -120dB at 20kHz.

Another option would be V-FETs (Si-SITs, not power Junction FETs), because these typically operate at Class B at currents around 200..300mA , while Bipolars and MOSFETs achieve the optimum Class B operation around 10..100mA. They also feature a zero tempco., which means, that the Class B idle current is not dependent on thermal history.

If you ever heard a Yamaha B-I or B-2 or a Victor JM-S7, you probably know, what I mean.
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Old 24th March 2011, 10:57 PM   #12
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I concern myself only that class B cross smoothly at something significantly less than full turn-on drop of a Schottky diode. Don't worry too much what exact current that might be at any given temp. TO220 Schottkys don't run hot anyway, just please don't bolt em' to same sink as hot output devices...

I'm just sayin' that trying to control precise ClassB quiescent doesn't pay off as much as enforcing a smooth crossing, and let quiescence do as it please.

Last edited by kenpeter; 24th March 2011 at 11:06 PM.
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Old 25th March 2011, 09:38 PM   #13
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Quote:
Originally Posted by tiefbassuebertr View Post
Here the next circuit I have found: JBL's bridged T-circuit
http://www.harman.com/EN-US/OurCompa...tions/1091.pdf
The URL about Harmans T-Circuit: "An Ultra-Low Distortion Direct-Current Amplifier" from the author
BART N. LOCANTHI (James B. Lansing Sound, Inc.)
www_harman.com/EN-US/OurCompany/Technologyleadership/Documents/Scientific%20Publications/1091.pdf
is death. Here the currently URL:
http://www.aes.org/tmpFiles/elib/20110325/1091.pdf

Concerning class AA I have found this PCB devices as line preamp:
http://cgi.ebay.co.uk/NE5534-NE5532-...item1c093942eb
is it possible to prepare this PCB's in such kind, that I can add power buffer stages?

Quote:
Originally Posted by Jon Lord View Post
Class AA, VC4, Class S (Sandman) or "true current dumping" come close, if implemented correctly.
which currently amplifier models uses one of this topologies ??

the statements about
http://www.passlabs.com/pdfs/articles/seclassa.pdf
seems to be still valid.

BTW - the head line of this thread should actually be
Collection of Class B topologies <100mA Idle and Sound closest by Single Ended Class A
instead
"Collection of Class B topologies <100mA Idle and Sound closest by Class A"

Last edited by tiefbassuebertr; 25th March 2011 at 09:59 PM.
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Old 25th March 2011, 11:20 PM   #14
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by Jon Lord View Post

but with a little tweaking, it beats almost every Class A amp.
May I ask? what is that little tweak? and what the differences after tweaking?
Thanks alot before.

Quote:
Originally Posted by tiefbassuebertr
BTW - the head line of this thread should actually be
Collection of Class B topologies <100mA Idle and Sound closest by Single Ended Class A
instead
"Collection of Class B topologies <100mA Idle and Sound closest by Class A"
And without JFET input. I feel that using JFET is cheating.
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Old 26th April 2011, 11:57 AM   #15
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Quote:
Originally Posted by tiefbassuebertr View Post
Here the next circuit I have found: JBL's bridged T-circuit
http://www.harman.com/EN-US/OurCompa...tions/1091.pdf
in the meantime the AES links
http://www.aes.org/tmpFiles/elib/20110426/1091.pdf
http://www.aes.org/tmpFiles/elib/20110325/1091.pdf
don't goes open again. Therefore I have make splitting that pdf file for an attachement here.
have a look also by
Bart Locanthi

I am still looking for currently available new commercial amp products (except Class-D) with low heating but similar sound character than pure class A.
The model that I know which match closest this profile is the "Gaincard" (4706) from 47lab - go to
http://www.sakurasystems.com/products/47amp.html
http://www.6moons.com/audioreviews/4...aincard_2.html
But there must actually be much more in the meantime.

Last edited by tiefbassuebertr; 26th April 2011 at 12:14 PM.
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Old 26th April 2011, 03:40 PM   #16
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Default Technics SE-A100, Yamaha MX-10000 and Sony TA-N7B

Quote:
Originally Posted by ontoaba View Post
May I ask? what is that little tweak? and what the differences after tweaking?
Thanks alot before.
The Technics SE-A100 uses not very good OPamps for driving the power stage. With more recent ones like the LME series, you get better performance. The Class AA circuit also suffers from a kind of "thinking error", which let it operate only at sub optimal performance. The reason of this i don't know, probably patent infringement issues or whatsoever.

Nevertheless my SE-A100 does well against the mighty Yamaha MX-10000, which solves the feed forward problem with a brute force 7A standing current in the error correction stage, which means, that the MX is a room heater, while the SE-A100 is not.

Regarding the idle power, one could say, that Class AA is a kind of advanced Class B, while the HCA/Feedforward circuit of the MX-10000 is a kind of advanced Class A.

If the difference in sound (the MX is indeed a little better) really judges the approx. 400W idle power everybody has to decide on its own ...

For me the Class AA is one of the smartest approches to get the maximum performance/power with the least idle power, anyhow as many other advanced topologies the high complexity does not suggest DIY ...

There are certainly other solutions which are less complex, like e.g. the Class B power cascode (debuted 1976 with Bipolars/V-FETs in the Sony TA-N7B).

What are the advantages of such a topology ?

- Lower switching distortions due to low voltage high speed Bipolars (100 ... 200MHz Ft feasible)..
- Better linearity due to minimization of influence of Miller/Early effect.
- Less thermally induced crossover distortions, due to more thermally stable bias point.
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Old 26th April 2011, 07:43 PM   #17
Tajzmaj is offline Tajzmaj  Slovenia
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Allow me to tease a little......
Regards
Attached Images
File Type: gif 9121CMQUA-SCH-606-A1.gif (113.3 KB, 421 views)
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Old 26th April 2011, 08:13 PM   #18
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Quote:
Originally Posted by Tajzmaj View Post
Allow me to tease a little......
Regards
This topology corresponds to the paper about
http://220.232.128.43/audio/quad405/...J%20Walker.pdf
already mentioned by post #1
Unfortunately not currently available as new commercial device (or is it ?).

Last edited by tiefbassuebertr; 26th April 2011 at 08:17 PM.
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Old 26th April 2011, 08:21 PM   #19
Tajzmaj is offline Tajzmaj  Slovenia
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I have some service documentation from Quad.....those amps are almost the same....
306/520/606/707/909and I suspect also 99 mono blocks.....
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Old 26th April 2011, 08:31 PM   #20
Tajzmaj is offline Tajzmaj  Slovenia
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And some of these amps are still in production. I don't know why guys at quad like this circuit so much but I have my explanation. Because it works so good. I heard 909 once...
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