Complementary diff input with JFET and BJT cascode

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mikeks

mikeks

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en.wikipedia.org/wiki/Censorship
Parasound..

...example in which the second stage's emitter is buffered from the first stage...(Q107 &Q109):
 

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Bensen

Bensen

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Joined 2003
Re: Parasound..

mikeks said:
...example in which the second stage's emitter is buffered from the first stage...(Q107 &Q109):
Click to expand...


Hi Mike,

The Audio drive from Elektor (march 2005) uses the same topology as that parasound amp. I did simulations with that topo and used the Q107 - Q110 configuration as my second diff pair+VAS. Unfortunalety it didn't give me enough gain. And using this kind of topo instead of my VAS causes unstability (3 diff pairs after each other).
This ain't a folded cascode hé? Or do I understand you wrong.

Mike, do you maybe have a schematic like the one Bocka is explaining?

Greetz
Ben
 
Bensen

Bensen

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Joined 2003
Andrew,

The protection diodes are there to protect the diff pair dual transistors against to high emitter-base voltages. The max Vbe for these devices is 5V.

I can't explain wy the voltages over R26 and R27 would be different. For me, it looks like an error on the schematic.

Greetz
Ben
 
Bensen

Bensen

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Joined 2003
Ultima Thule said:


No, something "else" will happen before "that" you interpreted wrong! :)

Cheers Michael
Click to expand...

Ultima Thule,
Do you mean when the amp is clipping? Please, tell me.


mastertech said:
AndrewT-
Hi,
any idea why the test voltages across R26 & R27 are different?

ah youre a funny Guy, is because of component tolerance

mikeks-
...that looks like complexity for its own sake....

Hi Mike youre a funny Guy
Click to expand...

mastertech ,
I first thoucht that also, but the emitter currents are the same, so base current must be about the same also, if the Hfe of the 2SA1209 and 2SC2911 is the same (these are pretty good complementary devices). Or could it be that the base current of one of the PNP driver is bigger than this of the NPN driver (upper one). Than you have a point Mastertech.


jam said:
Ben,

What kind of output stage does it use...........a CFP?

Jam
Click to expand...

Jam,
I don't know these terms good enough (CFP?). So I attached a picture. This amp uses type C as output arrangement. The only difference is that this amp uses 1 pair of drivers and no predrivers as in type C.
 

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forr

forr

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Joined 2004
ANDREWT post 58
"I've looked at that JCurl 1981 schematic and I think it is a folded cascode."

MIKEKS post 60
"In fact, the second stage is an unbuffered differential stage..."


I consider that each VAS device of Curl's amp as being purely voltage driven by the voltage between the collectors of the input differential pair. I think there is no local feedback by the 10 Ohm emitter resistance. Am I right ?

~~~~ Forr

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