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Old 12th April 2010, 11:01 AM   #1
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Default Dynamic Bias - Active Bias - Automatic/Self biased - Overview wanted

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)
Linear Tech. LT1166 chip (automatic Bias without external bias adjustment)
Patent US5216379 (automatic and dynamic bias without external bias adjustment)
http://220.232.128.43/audio/quad405/...J%20Walker.pdf (current dumping - ClassB without external bias adjustment)

P. S.
In this case also this threads could be of interest:
New Class A, Super-A, Non-Switching : need a revival ?
The Importance of Being Biased
low-biasing or high biasing in Class-AB amps

Last edited by tiefbassuebertr; 12th April 2010 at 11:14 AM.
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Old 12th April 2010, 02:06 PM   #2
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I have I have got away with a design that uses a Vbe mulitplier but not on the heatsink so long as I keep the bias current low.

This works well with some designs.

I also built a quasi and found that needed the bias transistor on the heatsink.
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Old 19th April 2010, 10:11 AM   #3
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Today's commercial amplifier mainly use still for the idle current adjust the good known Vbe multiplier for the cumbersome manual adjustment procedure - I guess there are still over 90%.
I miss progress (not only in this case) even after such a long period of audio power amp experiences in Class AB.
Also in the diy-aera I note this situation.
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Old 19th April 2010, 11:02 AM   #4
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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.
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Old 19th April 2010, 11:23 AM   #5
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Quote:
Originally Posted by PaulBysouth View Post
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.
Thank you for this information:
Push-pull amplifiers
http://www.audiotrends.com.au/docume...lse_Review.pdf
http://web.archive.org/web/200807181....whise.com.au/
http://web.archive.org/web/200807191...nderFFX25.html
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Old 12th July 2010, 06:18 PM   #7
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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)
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Old 24th July 2010, 08:46 PM   #8
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Quote:
Originally Posted by tiefbassuebertr View Post
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)
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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Old 25th July 2010, 10:57 AM   #9
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Quote:
Originally Posted by Sebastiaan View Post
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
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

Last edited by tiefbassuebertr; 25th July 2010 at 11:03 AM.
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Old 25th July 2010, 12:27 PM   #10
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Quote:
Originally Posted by tiefbassuebertr View Post
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
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

Last edited by Sebastiaan; 25th July 2010 at 12:35 PM.
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