adaptive bias theory

[powerbecker]

Barry Thornton , Scientific Audio Electronics, 66th AES 1980

ppl,
after I read it, I try it! Now the powertransistors don´t cut off but instead the diodes, so it´s only a bit better than nothing!
Regards
Heinz!

 

[johndiy]

Hi powerbecker

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ppl,
after I read it, I try it! Now the powertransistors don´t cut off but instead the diodes, so it´s only a bit better than nothing!
------------------------------------------------------------
i tried it too, in 1986 it is crap, it gets in the way of alot of other
things that are actually doing a great job of keeping purity
of bias and the optimum operation of the o/p stage

regards
john

 

[powerbecker]

"formally known as classaguru"

Hello Mas..John, nice to meet You again on a for You foreign terrain 😉
Regards
Heinz!

 

[Wavebourn]

Hi,ppl.How to apply your bias system(yes,bias system only) to a normal push pull output stage???

You can't. Because base-emitter junctions are usually low voltage. That's why I used diodes in my version instead of transistors. Also, a driver transistor works as a CCS in my version, without 4 transistors extra, plus my CCS is a input voltage dependent (really adaptive) and don't cut off on a normal load impedance.

 

[ppl]

Yes them diodes caused stability issues in the PPA headphone amp when used with High speed op Amps and some Headphones so we decided to go with the conventional Class Ab Biasing however this mod (See attached) retains the current sources but ditches the diodes now the bias is not adaptive anymore but non switching in that the bias remains fixed but the Output transistors don’t turn off and no stability issues have happened I also changed the output Transistors but that was a separate mod and not related to the non switching the transistor change added more Punch and Bass drive and adding the Current sources really improved detail a lot king of like hearing a pin drop during a thunder storm.