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Old 17th January 2006, 03:35 AM   #1
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Default Looking for output stage

Does anyone has an idea of output stage that has gain G=1? Not 0.99, not 0.9, not 1.1, but exactly 1?

Something like Hawksford EC or NP-PMA, but with minimal component.

I'm looking for simple EC (2 transistors maybe), that this 2 transistors can be used for setting bias, also for local Error Correction that gives G=1 exactly.
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Old 17th January 2006, 04:39 AM   #2
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The Threshold S-300 schematic (Nelson Pass) is around here somewhere. No gloabal feedback, sounds great.
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Old 17th January 2006, 05:07 AM   #3
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Hi, DJK,

Thank you.

I'm looking for somekind of "Local Error Correction" that can be implemented in low biased classAB (bias below 50mA). It is to be put on global feedback.
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Old 17th January 2006, 05:30 AM   #4
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lumanauw

Does anyone has an idea of output stage that has gain G=1? Not 0.99, not 0.9, not 1.1, but exactly 1?

Something like Hawksford EC or NP-PMA, but with minimal component.

I'm looking for simple EC (2 transistors maybe), that this 2 transistors can be used for setting bias, also for local Error Correction that gives G=1 exactly.
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Old 17th January 2006, 06:06 AM   #5
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It can't always have exactly unity gain since there is not such a thing as a zero output impedance. Error correction just puts one or two more nines into the decimal part of the gain figure.
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Old 17th January 2006, 06:09 AM   #6
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Quote:
Originally posted by Eva
It can't always have exactly unity gain since there is not such a thing as a zero output impedance. Error correction just puts one or two more nines into the decimal part of the gain figure.
This was my thinking, too.
What difference does it make, if gain is 0.98 0.99 or 1.02
as long as it is constant.
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Old 17th January 2006, 06:44 AM   #7
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Hi, EVA,

Sometime ago, I remember that you opinioned that what is called "Error Correction" is not clear, because the whole audio amp system is an EC itself You are right, but this is my thinking.

I wanted to make a "local" EC around output stage, so it can level input and output of that EC output stage as close as it can get to G=1, in order to make the work of the differential is much light-er. If the differential pair works light-er, I feel that the sonics is better.

Something in the spirit of "making the elements as linear as possible before applying feedback", so the differential pair will work much light-er (not burdened by the total mess of the whole amp)
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Old 17th January 2006, 07:45 AM   #8
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Then add another differential to the output stage
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Old 17th January 2006, 09:54 AM   #9
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Hi lumanauw

Look at: http://www.diyaudio.com/forums/showt...297#post747297
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Old 17th January 2006, 11:53 AM   #10
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Quote:
Then add another differential to the output stage
That's what I'm thinking, at least I need 2 transistors with emitors tied together or base tied together. Or input to base, and feedback to emitor (current feedback).

But trying to make with those always result in NP-PMA or Hawksford EC.

Do you have any ide to make output stage with "differential" to control input=output, that can follow full swing from +rail to -rail with G=1?

Hi, Jarek,

Thanks. I will study it.
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