Non-feedback parametric linearisation in FETs - diyAudio
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Old 27th December 2004, 06:46 PM   #1
x-pro is offline x-pro  United Kingdom
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Default Non-feedback parametric linearisation in FETs

This is my small Christmas present for those who like zero NFB single-ended class A amplification

I've worked in my spare time (for last year and half) on a home project to make a very linear single-ended transistor amplifier without NFB and one of my ideas I've described in a small article on my web site here:

http://www.ant-audio.co.uk/Theory/Pa...earisation.htm

The performance of this circuit, despite the simplicity of the concept, is quite impressive - here is one example:

For a voltage amplifier stage using this idea I've measured distortion levels vs RMS current in the load resistor. Idle DC current was 4.5 mA, for 0.15 mA RMS current THD were 0.0025%, for 0.5 mA - 0.03%, for 1.15mA RMS (that is a swing from 3 to 6 mA (!) ) - only 0.16% .

It is possible to make this approach work even without the source resistor, thought it requires very careful transistors selection. THe circuit of my headphone amplifier (A.N.T. Audio "Amber") includes a voltage amplifier stage based on this idea.

Merry Christmas and Happy New Year!

Alex Nikitin
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Old 27th December 2004, 06:52 PM   #2
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Interesting, Alex. Is there info on the ANT headphone amp on the 'net? Does the 'T' stand for "Technology"?

Jan Didden

Edit: found it. Beautifully executed, very professional looking. Where do you get those enclosures?
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Old 27th December 2004, 06:58 PM   #3
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Quote:
Originally posted by janneman
Interesting, Alex. Is there info on the ANT headphone amp on the 'net? Does the 'T' stand for "Technology"?

Jan Didden
Jan,

look at my web page: www.ant-audio.co.uk . There is also a review of it on head-fi :

http://www4.head-fi.org/forums/showthread.php?t=88528

And well guessed - A.N.T. does stand for Alex Nikitin Technology

Alex

P.S. - enclosure is a standard Hammond case.
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Old 27th December 2004, 10:44 PM   #4
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damn
i cannot see pictures in your link
seems intersting...
could you attach these figures?

cheers
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Old 27th December 2004, 11:16 PM   #5
x-pro is offline x-pro  United Kingdom
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Quote:
Originally posted by darkfenriz
damn
i cannot see pictures in your link
seems intersting...
could you attach these figures?

cheers
Here is the link to a PDF file:

http://www.ant-audio.co.uk/Theory/Pa...earisation.pdf

Cheers

Alex
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Old 27th December 2004, 11:42 PM   #6
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Hi X-pro,

Best new years wishes for you and thx for the PDF.. looks very interesting .. enough to keep me spice-ing for a week ... at least....;-),


cheers,
thijs
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Old 27th December 2004, 11:55 PM   #7
Bricolo is offline Bricolo  France
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what's the difference with a cascode?
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Old 28th December 2004, 12:10 AM   #8
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Quote:
Originally posted by Bricolo
what's the difference with a cascode?
Hmm - 8-10 times lower distortion? However it is only true for a specific combination of the "upper" and "lower" transistor parameters and for the right value of the drain current.

Alex
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Old 28th December 2004, 01:25 PM   #9
Hennie is offline Hennie  South Africa
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Very interesting indeed. To avoid opamps some I/V converters for DACS use valves. They rely on something like a 50 ohm resistor to ground followed by a valve voltage amplification stage. Would you say this topology is suitable for this purpose? That would be great, because few CD players have space for valve stages.
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Old 28th December 2004, 01:52 PM   #10
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Quote:
Originally posted by Hennie
Very interesting indeed. To avoid opamps some I/V converters for DACS use valves. They rely on something like a 50 ohm resistor to ground followed by a valve voltage amplification stage. Would you say this topology is suitable for this purpose? That would be great, because few CD players have space for valve stages.
This topology can be used in many applications, including this one . For 50 Ohm and, say, FS 1 mA RMS output current of the DAC, the maximum input voltage would be 50 mV - near the "sweet spot" for this circuit, with a possibility of a very decent performance - with the distortions about 0.002% (mostly 2-nd order) and SNR about 100 dB.

Alex
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