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Old 17th August 2014, 06:13 PM   #10131
FdW is offline FdW  Netherlands
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Originally Posted by MiiB View Post
Frans. I do also think Mosfets has some good properties, but they are not very symetric (both in transconductance and VGS) and in that respect worse than BJT. The cool(est) part of this circuit is the mosfet bootstrap the way it's set up it also performs current feedback
This circuit started as a diamond buffer, it then was bootstrapped (using the mosfet's) and it was great. The (my) problem was, I thought it was not great enough. So I turned the input transistors around (base to the output side) but I could not get it working, then it came to me that I needed the higher Vgs of the mosfet's to make it work, and so done. This new buffer was really amazing (in simulation). There where no current differentials, there where no voltage differentials (except in the bootstrap's) and it's simulated THD was -180dB at about 1Mohm input resistance and a good driving capability, in short, an almost ideal buffer.

Joachim did test it and it worked great, but he needed ... gain . The resistor dividers where added, the capacitors where needed to easy bias the thing, many other configurations where tested, suggestion from different people, but this is the one that survived, it works, it is easy to adjust, and it sounds real good.
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Old 17th August 2014, 10:49 PM   #10132
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I have both, the diamond with BJts and the MosFet with gain.
I prefer the sound of the Mosfet version even after i have set the gain with an Alps slider to x 1 ( like the diamond ).
The diamond punshes along as they do but the MosFet is even more transparent and " natural ".
Let Martina be the judge. She will visit me soon and we will compare.
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Old 17th August 2014, 10:51 PM   #10133
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I have now degenerated the N-channel with 68 Ohm.
That makes the N-channel quite similar to the P- channel.
I will show measurements with some more commends.
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Old 17th August 2014, 11:18 PM   #10134
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Here are the measurements.
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Old 17th August 2014, 11:23 PM   #10135
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The left diagram shows what happens when i insert a 68 resistor in the source of the N-channel.
Brown is the N.channel.
The quasi saturation knee is a bit softer but from 2V Vds they are quite similar.
The right diagram shows the situation before degeneration.
The P-channel needs nearly 3V Vgs to have the same idle then the N-channel with 2.3V Vgs.
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Old 17th August 2014, 11:58 PM   #10136
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In the right diagram red is the N-channel.
The others are the P-channel, for example magenta with 3V Vgs.
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Old 18th August 2014, 03:01 AM   #10137
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http://www.eleccircuit.com/wp-conten...nals-only..jpg
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Old 18th August 2014, 03:02 AM   #10138
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Another example of a common base driver.
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Old 18th August 2014, 12:35 PM   #10139
MiiB is online now MiiB  Denmark
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I like The VAS on that one

What is the open loop gain of the buffer/line-stage..?
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Old 18th August 2014, 01:15 PM   #10140
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Originally Posted by MiiB View Post
What is the open loop gain of the buffer/line-stage..?
Just above 60dB (measured by replacing the feedback/divider resistor by a 1G inductor).
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