Bob Cordell's Power amplifier book

[padamiecki]

Originally Posted by ostripper

OS

Hi Os!
All in all I deeply appreciated the knowledge how to design good sounding gnfb amp, this was my grail for some time. True. In other words how to spoil the signal in high gain 10Hz open loop amps and then cure it with sophisticated gnfb. The solutions founded here opened my eyes and I started to believe that this is possible, I will try your proposition.
But like always, the barbarian wins, try to beat the designs like this, Modified Follower-99 With HF Transistors , impossible..

[homemodder]

Originally Posted by ostripper

Thank you , padamiecki .. for the M7 schema. It looks different than the "DBT", more like the voltage follower DB current amp (my nakamitchi 620 example). This means that Bob's "DBT" is unique to the book , no exact commercial equivalent. More "DIY" friendly as well , it can be used with any popular IPS/VAS combo plus is quite easy to thermally stabilize. I would say it's ultimate form would be with the Thermaltrack's , 2 of the internal diodes controlling the Vbe (like the leach). Njl3281/1302 is out of the reach of some hobbyist's ... 5.41 X 12 = $65usd for a 2 X 150W amps. Same power with the NJW's is only 1.80 X 12 = $21usd for the same 150W !

OS

Have a careful second look Os, The schema is about the same as the circuit that Bob proposes only its elaborated. After the Diamond buffer a driver stage is introduced to further enhance gain and the input transistors of the diamond are darlingtons. These are the only diffirences but the basics of the circuit is exactly the same. This was done to further increase gain but not only, I suspect it will increase the openloop bandwith as well. The pioneer uses this outputstage without feedback.

[jacco vermeulen]

Originally Posted by homemodder

darlingtons, output stage without feedback.

Same deal in the dynamic rail model of the early '80s.
(Technics SE-A1 competition, though Glen-K would likely have disapproved)

[ostripper]

Originally Posted by homemodder

Have a careful second look Os, The schema is about the same as the circuit that Bob proposes only its elaborated. After the Diamond buffer a driver stage is introduced to further enhance gain and the input transistors of the diamond are darlingtons. These are the only diffirences but the basics of the circuit is exactly the same. This was done to further increase gain but not only, I suspect it will increase the openloop bandwith as well. The pioneer uses this outputstage without feedback.

"Without feedback" ...at least that is different. The extra stage and the darlington's must make for 1M current gain - WOW. The CCS "mute" with the Jfets is quite unique as well. Still , Pioneer threw a lot of parts at what should be a much simpler circuit.

OS

[WuYit]

Ostripper`s implementation of the triple is technically very nice indeed, however, the single current stage is much more "perfect". Now we`ve got five nonlinear base-emitter and base-collector junctions, serious phase shifts, poor bandwidth and degraded switching performance, Pawel may also worry about the strong increase in memory distortion; a good many monotonic and random distortions to iron out (actually to live with).

[ostripper]

Ostripper`s implementation of the triple is technically very nice indeed,

#1 -It survives the abuse of the hot Tennessee summer.

#2- with the led CCS's , it is simple (well , not as simple as a EF2)

#3 - using the output pair for drivers , feel free to pile up 10 pair OP devices and run it from 90V rails. A true high current OP stage - go ahead and make yer' 1000 watt amps - fools.

#4 - Really hear what goodness your VAS has in store for you as it is not under load. Feel free to use 3-4 ma low Ic VAS's (to-92 - mpsa92/42) , resistive shunts will remain static , irregardless of output load.

#5 - It does not blow up when pushed to the rails (clipped horribly) ... fully passed the electrical abuse test with a power hungry dayton 4R subwoofer.

It's better than TMC.
OS

[homemodder]

Originally Posted by WuYit

Ostripper`s implementation of the triple is technically very nice indeed, however, the single current stage is much more "perfect". Now we`ve got five nonlinear base-emitter and base-collector junctions, serious phase shifts, poor bandwidth and degraded switching performance, Pawel may also worry about the strong increase in memory distortion; a good many monotonic and random distortions to iron out (actually to live with).

Go with a schema like the Pioneer then , it addresses many of the problems you mention, used in open loop though.

Can you show us a single current stage that can do 200w up.
Can you show a schematic of what you have in mind.

[WuYit]

homemodder,
when describing circuit topologies, for the sake of credibility, it is important to give a detailed account of what is lost, not just what is gained, otherwise the arguments will sound like coming from a marketing brochure. Nothing can be gained without giving up something. That something is usually linearity.
The common collector amplifier is not as linear as generally assumed. For instance, the very high internal feedback results in negligible isolation between input and output and together with an applied overall feedback it makes amplifier performance hugely depend on the load and signal processing become a mess. This is very far from the ideal conditions and perfection.

[ostripper]

Originally Posted by homemodder

Can you show us a single current stage that can do 200w up.

My 3 pair contraption will do that. 5-8 pair (below) would do much more. Still 40uA VAS load to run that 170 p-p waveform (4R). I don't need that much - 3 pair and the dayton sub is shaking the whole house.

OS

[Bob Cordell]

Originally Posted by WuYit

Ostripper`s implementation of the triple is technically very nice indeed, however, the single current stage is much more "perfect". Now we`ve got five nonlinear base-emitter and base-collector junctions, serious phase shifts, poor bandwidth and degraded switching performance, Pawel may also worry about the strong increase in memory distortion; a good many monotonic and random distortions to iron out (actually to live with).

Hi WuYit,

Could you describe what you mean by the "single current stage"?

Do you mean a VAS directly driving a single output emitter follower pair?

Cheers,
Bob