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Old 6th May 2013, 09:24 PM   #11
forr is offline forr  France
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Each pair of transistors looks like a Baxandall super-pair :

Baxandall Super Pair

It is better known to give high output impedance at the collector of the second transistor.
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Old 7th May 2013, 07:52 AM   #12
Elvee is offline Elvee  Belgium
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As expected, bootstrapping all 4 does make a significant difference.

In addition, it also pushes the input impedance to more than 200 megohm.

BTW, harmonic is almost pure second meaning it is caused mainly by imperfect complementarity of the transistors, not an intrinsic flaw of the topology.
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Old 7th May 2013, 09:22 AM   #13
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Elvee View Post
As expected, bootstrapping all 4 does make a significant difference.

In addition, it also pushes the input impedance to more than 200 megohm.

BTW, harmonic is almost pure second meaning it is caused mainly by imperfect complementarity of the transistors, not an intrinsic flaw of the topology.
Thanks Elvee for your suggestion.
I put it even father and now distortion at 20kHz is 0.000002%.
I am going to use one of those buffers in my lineamp(no NFB) and I am not sure if the complexity is to much as the gain block is in 1ppm region. Could be that simpler version of the buffer is good enough.
Damir
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Old 7th May 2013, 11:20 AM   #14
AndrewT is offline AndrewT  Scotland
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-120dB is 1ppm.
Your sim is predicting in the tens of ppb.
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Old 7th May 2013, 11:24 AM   #15
dadod is offline dadod  Croatia
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Quote:
Originally Posted by AndrewT View Post
-120dB is 1ppm.
Your sim is predicting in the tens of ppb.
1ppm is distortion of the preceding gain block not of this buffer.
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Old 8th May 2013, 08:51 AM   #16
dadod is offline dadod  Croatia
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I've found that elvee-dado buffer oscilate when used as output for my gain block, here is compensated cascode solving the problem.
dado
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Old 8th May 2013, 11:02 AM   #17
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by dadod View Post
I've found that elvee-dado buffer oscilate when used as output for my gain block,
That is the kind of problem you be must be prepared for when using bootstrapping and similar schemes. Can you show the exact circuit in which it oscillated?

BTW, shouldn't you tie the collectors of the input transistors to the higher potential, like in my version? This should give them more E-C space to breathe correctly
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Old 8th May 2013, 11:50 AM   #18
basi is offline basi  Croatia
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Hi!!
I build this simple Buffer 2 Years ago and it works fantastic very neutral Sounding.
Greatings From Croatia!!!

Click the image to open in full size.
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Old 8th May 2013, 02:12 PM   #19
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Elvee View Post
That is the kind of problem you be must be prepared for when using bootstrapping and similar schemes. Can you show the exact circuit in which it oscillated?

BTW, shouldn't you tie the collectors of the input transistors to the higher potential, like in my version? This should give them more E-C space to breathe correctly
Hi Elvee,
I will show the lineamp where I put this buffer, later in separate thread. It is a current conveyour.
I tried your circuit first and then did the changes step by step and each one lowered distortion a bit, cascode boostrap first and then cross connection of collectors to the opposite emitter resistors.
I had the same stability problem with your circuit as with this one.
dado
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Old 10th May 2013, 05:05 AM   #20
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Elvee View Post
That is the kind of problem you be must be prepared for when using bootstrapping and similar schemes. Can you show the exact circuit in which it oscillated?
Here is the link to the complete circuit.
No NFB line amp (GainWire mk2)
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