B1 Buffer Preamp

Buffer topology

Hi,

I do not know Nelsons set-up other than that it is SE without source resistors but here is what I am using. I have tried a number of different variations on the theme but yhis is the one i like best so far. I need alot of swing and this one delivers.

Anders
 

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The one and only
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mlloyd1 said:
anything you can share at this point on the differences in the distortion spectra for these buffers built with or without source resistors?

Actually that's the most interesting part - not the source resistors
but the spectra.

The piece will be done shortly, however I have created it without
deciding on a destination for it.

:cool:
 
What's the bipolars for? It should work with drains straight to rails?

This might explain it - scroll down to the section Super Symmetrical Cathode Follower : http://www.tubecad.com/2007/04/blog0104.htm

At least for triode buffers it should be better to bootstrap the cathode follower so that it sees a constant plate to cathode voltage. But I'm not sure yet if this applies to the same degree to JFETs.
 
i understand why cascoding is done. i'm asking why it was done a certain way.
just in case my question wasn't clear ...
refer to the two buffer schematics in the attached schematic.
why cascode the current sink (j2) with a pnp (q4) instead of cascoding the current sink (j4) with npn (q3).
 

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Hi Michael,

I think the second method might be better (cascoding the current source).

Maybe Mr.Pass could shed some light on this............but then again, in the case of the B1, cascoding might not be an improvement besides you can run into stability issues when you cascode.

I can't wait for the article to come out............maybe if we found some way to prod Mr.Pass to get it out sooner.:D

Jam

P.S. Mr.Pass wrote a great article on cascode amplifier design. Here is the link

http://passlabs.com/pdf/articles/cascode.pdf
 
oops, sorry, in the schematic i posted, i forgot the "bootstrap" connection that bappe was using (the vds of the jfets is not fixed)
please remember there is a connection between the output and junction of r1 and r11 for the left hand circuit and a connection between the output and the junction of r6 and r8 for the right hand circuit.
i'll fix the schematic when i get to my other computer.

of course, we could always argue about the virtues of fixed versus telescopic cascodes ...
:D
mlloyd1



mlloyd1 said:
i understand why cascoding is done. i'm asking why it was done a certain way.
just in case my question wasn't clear ...
refer to the two buffer schematics in the attached schematic.
why cascode the current sink (j2) with a pnp (q4) instead of cascoding the current sink (j4) with npn (q3).
 
corrected schematic attached
mlloyd1


mlloyd1 said:
oops, sorry, in the schematic i posted, i forgot the "bootstrap" connection that bappe was using (the vds of the jfets is not fixed)
please remember there is a connection between the output and junction of r1 and r11 for the left hand circuit and a connection between the output and the junction of r6 and r8 for the right hand circuit.
i'll fix the schematic when i get to my other computer.

of course, we could always argue about the virtues of fixed versus telescopic cascodes ...
:D
mlloyd1
 

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