Unipolar vs complementary input stage

[KLe]

Hi LineSource
Interesting that this thread should reach this point ...
A question I have is ... can an Input Stage be made to produce sufficient Gain , Current/Voltage drive and a low output impedance to remove the need for a VAS?

ciao

 

[lumanauw]

Level shifting in this one is interesting. What is Q6-7, Q10-11, Q8-9? Are they current mirrors?

 

[lumanauw]

This one similiar to Mr. Cordell's principle, but the patent's aim is to get a stable current in the VAS (#5,783,970). The drop on R4 is feeded back to get apropriate CCS from T6-T7.

 

[mlloyd1]

yes.

mlloyd1

Originally posted by lumanauw ... What is Q6-7, Q10-11, Q8-9? Are they current mirrors?

 

[LineSource]

A question I have is ... can an Input Stage be made to produce sufficient Gain , Current/Voltage drive and a low output impedance to remove the need for a VAS?

ciao

Nelson Pass has several 1 and 2 stage amplifiers from Aleph through Zen. His Super-Symm topology can bridge two stage gain paths together to get higher power. The Pass DIY website has great info, as do the Pass product service manuals.

 

[roender]

A question I have is ... can an Input Stage be made to produce sufficient Gain , Current/Voltage drive and a low output impedance to remove the need for a VAS?

95dB OLG
As per low Zout, there is no need for that if you use an T output stage

 

[GK]

Said otherwise, what happens internally when an input pair has more transconductance than the input pair of the other polarity ?

The complementary drive to the symetrical VAS will be a bit imbalanced and you’ll get a little more even harmonic distortion.

Cheers,
Glen

 

[Ipanema]

Why folded cascode is seldom used in audio amplifier?

 

[lumanauw]

Why folded cascode is seldom used in audio amplifier?

Because the (not so good) output stage being used demands more gain to fix it's distortion more than the folded cascode can provide?

 

[roender]

YMHO, it is a little bit tricky to be implemented well but once done it is very stable, very fast and have wide GBW

 

[roender]

Because the (not so good) output stage being used demands more gain to fix it's distortion more than the folded cascode can provide?

Measurable distortion?
What about how it sound

 

[Ipanema]

A single folded cascode amp can have as much gain as typical two stage amp. No miller compensation required and very high open loop bandwidth.

 

[PMA]

You can start playing with structures like this. The only question is if it makes any sense for audio.

 

[roender]

You can start playing with structures like this. The only question is if it makes any sense for audio.

Pavel, please take a look at post no.66 in this thread.
It make sense, that topology sound very good and is unconditional stable. The output stage has CFP drivers plus three pears of ThermalTrack devices (NJL0302/0281)

 

[PMA]

Mihai,

what is the reason to have input cascode floating?

 

[Bob Cordell]

This one similiar to Mr. Cordell's principle, but the patent's aim is to get a stable current in the VAS (#5,783,970). The drop on R4 is feeded back to get apropriate CCS from T6-T7.

Yes, it is quite similar. Have you got a patent number for it?

Thanks,
Bob

 

[roender]

Constant Vds, very good common mode rejection, no connection to possible dirty ground

 

[PMA]

Constant Vds, very good common mode rejection, no connection to possible dirty ground

Have you built working sample?

 

[roender]

Yes, I'll open a new thread once done all the testings (in mono mode). Until then, what I can say is it sound very good, the best amp I ever made ...

 

[PMA]

95dB OLG
As per low Zout, there is no need for that if you use an T output stage

SymAsym rebuilt? You like FB capacitor to ground?