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Old 25th July 2010, 12:09 PM   #11
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this approach from Marantz looks a bit like EDWIN from Elektuur
Edwin 20 watt (Elektor 1970 - May)

MCU+LDR is one of several methods (in use e. g. by Krell) - but look at post #6: this are solutions without MCU and I want to know commercial amps, where this IC's are inside.
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Old 5th May 2011, 08:42 PM   #12
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an additional bias servo approach, that looks very interesting
William T Chater power amp
and post #40 about
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?
but obviously there are very few adjustment free commercial amps; I am still looking for such audio amplifiers.

P.S.: I don't like power amp topologies like output stage (Sanken's approach) from Marantz SR-5200 (go to post #8). In case of service Sanken's output power devices is in several years a very "hard to find" part. So it is necessary, to modify the topology down to the good known Vbe multiplier circuit for using usual BjT's. Are the embedded diodes on the power BjT chip so a great advantage ??
I don't think so, otherwise the embedded diodes there must actually be inside by most power BjT versions.

Last edited by tiefbassuebertr; 5th May 2011 at 09:05 PM.
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Old 10th July 2012, 09:37 AM   #13
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Here is an approach, that I do find by one model: Sony's TA-N 902 - go to
Sony TA-N902 on thevintageknob.org
and for Service Manual:
SONY TA-N902 Service Manual free download, schematics, eeprom, repair info for electronics
associated patent paper:
Patent US4439743 - Biasing circuit for power amplifier - Google Patents
- found by post #98 about
Yamaha's Hyperbolic Conversion Amplification (HCA) Circuit

other approaches with the same goal:
New Class A, Super-A, Non-Switching : need a revival ?
Class B w/o crossover distortion (1975)
adaptive bias theory

I am still looking for currently available commercial audio amplifier devices or modules without the need of quiescent current adjust for the output push-pull power buffer (except Class-D).

Last edited by tiefbassuebertr; 10th July 2012 at 09:46 AM.
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Old 11th July 2012, 03:08 PM   #14
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I have Meridian 555 and 556 amplifiers. They do not have any bias adjustment. They use error correction on output stage, thus allowing the output stage to be biased low, but still obtaining low output stage distortion.
Additional benefit is low idle power. Unfortunately, I have not been able to obtain schematics or even detailed description of actual circuits.
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Old 29th July 2012, 01:18 PM   #15
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have anybody tested this topology?
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Old 29th July 2012, 01:58 PM   #16
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Originally Posted by tiefbassuebertr View Post
have anybody tested this topology?
At the same site you can find http://home.tiscali.nl/data.odyssey/...wLoopGevel.pdf
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Old 29th July 2012, 04:03 PM   #17
Zen Mod is offline Zen Mod  Serbia
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Nelson is having patent on opto bias
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
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