Dynamic Bias - Active Bias - Automatic/Self biased - Overview wanted

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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
There were two different goals that forces these ideas and concepts:

1) Only the adjust free power amp concerning bias adjust for idle current
(self biasing - I know only the Quad 405 current dumping amp and some related topologies)
2) Additional no leaving the Class A operation and low idle current at the same time
under all load conditions > 4 ohms (I know only Threshold and Mark-Levinson - Madrigal)

Where I can find an overview of a wide range of commercial brands/ models so as topologies concerning this two categories (only push-pull topologies - not single ended)?

Here patents/examples for this topologies:
Patent US3995228
Madrigal Library: Adaptive Bias
Patent US4160216
(automatic and dynamic/adaptive bias for classA under all conditions without external bias adjustment)
Patent US4077013 (automatic Bias without external bias adjustment)
http://www.diyaudio.com/forums/solid-state/1573-linear-tech-lt1166-chip.html (automatic Bias without external bias adjustment)
Patent US5216379 (automatic and dynamic bias without external bias adjustment)
http://220.232.128.43/audio/quad405/Current Dumping Audio Amplifier - PJ Walker.pdf (current dumping - ClassB without external bias adjustment)

P. S.
In this case also this threads could be of interest:
http://www.diyaudio.com/forums/solid-state/162559-new-class-super-non-switching-need-revival.html
http://www.diyaudio.com/forums/pass-labs/104399-importance-being-biased.html
http://www.diyaudio.com/forums/solid-state/58561-low-biasing-high-biasing-class-ab-amps.html
 
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P

PaulBysouth

Member
Joined 2008
There is also the Huon/Dower patent (US6-630-865), which implements a form of `Non Switching Class B' bias. This technique is quite difficult to get stable, and definitely not suitable for beginners!

The Whise subwoofers of about 5 to 10 years ago used an inbuilt amplifier using this scheme. They won the Stereophile award for the best subwoofer. Unfortunately they are nolonger in production.
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
PaulBysouth said:
There is also the Huon/Dower patent (US6-630-865), which implements a form of `Non Switching Class B' bias. This technique is quite difficult to get stable, and definitely not suitable for beginners!

The Whise subwoofers of about 5 to 10 years ago used an inbuilt amplifier using this scheme. They won the Stereophile award for the best subwoofer. Unfortunately they are nolonger in production.
Click to expand...

Thank you for this information:
Push-pull amplifiers
http://www.audiotrends.com.au/documents/WHATMOUGH_Impulse_Review.pdf
http://web.archive.org/web/20080718173445/http://www.whise.com.au/
http://web.archive.org/web/20080719141704/www.whise.com.au/ProfunderFFX25.html
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
Dynamic Bias - Active Bias - Automatic/Self biased additional URLs

TDA7250, TDA 7250
http://www.st.com/stonline/books/pdf/docs/1472.pdf
http://www.diyaudio.com/forums/solid-state/7121-high-power-amp-tda7250.html
http://www.diyaudio.com/forums/solid-state/3771-tda-7250-based-amplifier-toasted.html
http://www.diyaudio.com/forums/chip-amps/71344-tda-7250-load-problem.html
http://www.diyaudio.com/forums/chip-amps/21434-about-tda7250-tda1514a.html
Witam szukam paru schematów nord elektronik z góry dzi?kuje. (diyproject)

LT1166, LT 1166
Linear Technology - LT1166 - Power Output Stage Automatic Bias System
http://www.diyaudio.com/forums/solid-state/1573-linear-tech-lt1166-chip.html
http://www.diyaudio.com/forums/solid-state/173-anybody-played-self-class-bias-regulator.html
Output stage bias
Re: LT 1166 bias ic? john curl or?
http://www.linearaudio.nl/Miscellaneous/jc.JPG

http://www.national.com/an/AN/AN-1645.pdf
Auto Bias
Madrigal Library: Adaptive Bias
Apparatus for eliminating on-off transitional gain variations in class AB, B and C active element amplifiers
AES E-Library: The Autobias Amplifier: A New Topology for Automatically Biased Audio Amplifiers Using Power MOSFETs
Active bias circuit for low-noise amplifiers
Automatic biasing of a power device for linear operation - Patent # 7084705 - PatentGenius
ÃÈÁÐÈÄÍÛÉ ÓÑÈËÈÒÅËÜ
http://www.linearaudio.nl/Miscellaneous/renardson new class B.pdf
http://www.diyaudio.com/forums/solid-state/40877-n-channel-mosfet-amplifier-servo-bias.html
http://www.diyaudio.com/forums/tubes-valves/131455-idea-simple-bias-servo-ab-pp.html
http://www.diyaudio.com/forums/solid-state/145013-variable-operating-biass-output.html
 
S

Sebastiaan

Member
Joined 2004
soundevolution.nl
tiefbassuebertr said:
commercial products (brand and model number), that use adjust-free Class AB power amp sections still wanted (e.g. with the help of TDA7250/LT1166)
Click to expand...

the Marantz SR-5200 receiver ties the thermal sensing diode string of a Sanken SAP15 pair together with a fixed resistor. No bias adjustment. Seems to work pretty well, but most likely under biased, to be safe and sure.

I was thinking of placing a red LED between the diode string for a stable constant voltage drop, and let the diode string do the thermal adjustment.

Biasing amplifiers by hand is a night mare for manufactures in today's economy and business. I am thinking long way as well to find a cheap and simple way to avoid the manual adjustment. I think above suggestion would work well.





With kind regards
Bas
 

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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
No. Except if one can guarantee that the constant current through the chain of all diodes don't deliver tolerances/spread effects.

But the purpose of a servo is just, that certainly values of tolerances, which are always present, have no effect on the quiescent current.

An adjustment variable resistor must be still present. But after choosen the value for idle current through the output power stage this must be absolutely constant under all conditions (ambient temperature etc).
By commonly circuit concepts (VBE MULTIPLIER) I must repeat the adjustment several times, that is horrible for me
 
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S

Sebastiaan

Member
Joined 2004
soundevolution.nl
I know it is "better" to be able to adjust it. But Marantz chooses not to with above schematic. There will be tolerances, but if one keep the system under biased, so that in worst case the highest to expect bias level due tolerance difference is still below the maximum acceptable level, it can work. But one must accept a mostly under biased output-stage. The diode string will compensate for temperature tempco.

Another way to do it is with a micro controller which can read the voltage drop over the emitter resistors, and control a LDR in the bias string.

With kind regards,
Bas
 
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
an additional bias servo approach, that looks very interesting
http://www.diyaudio.com/forums/solid-state/81436-william-t-chater-power-amp.html#post2562916
http://www.freepatentsonline.com/5055797.pdf
and post #40 about
http://www.diyaudio.com/forums/soli...tter-audio-non-complements-audio-power-4.html
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.
 
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
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
http://www.diyaudio.com/forums/soli...amplification-hca-circuit-10.html#post3086470

other approaches with the same goal:
http://www.diyaudio.com/forums/solid-state/162559-new-class-super-non-switching-need-revival.html
http://www.diyaudio.com/forums/solid-state/160285-class-b-w-o-crossover-distortion-1975-a.html
http://www.diyaudio.com/forums/solid-state/88309-adaptive-bias-theory.html

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).
 
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J

JamesBrennan4

Member
Joined 2009
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.
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de

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