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-   -   no current mirror, current mirror, cascoded current mirror, bjt or jfet VAS? (http://www.diyaudio.com/forums/solid-state/121745-no-current-mirror-current-mirror-cascoded-current-mirror-bjt-jfet-vas.html)

maxpou 21st April 2008 05:00 PM

no current mirror, current mirror, cascoded current mirror, bjt or jfet VAS?
 
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Hi Guys,
i started my tests with Borbely super buffer topology. But i modified the OLG because i thing that 40dB of feedback is too high and drop to 15dB. I checked hte FFT with my cd player with cd test at 1Khz to 0dB because i don't have a good sine wave generator and he has 0.0068% THD. I have cheap PS with regulator 7812 and 7912. The output for my all test is 2V rms. Any comments is welcome. Thank You! Maxpou

maxpou 21st April 2008 05:01 PM

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FFT test.

maxpou 21st April 2008 05:03 PM

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Now I changed the drain resistor to 560ohms.

maxpou 21st April 2008 05:06 PM

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I changed the drain resistor for current mirror and i have a better result.

maxpou 21st April 2008 05:08 PM

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sorry the schematic for current mirror.

maxpou 21st April 2008 05:15 PM

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And if I change the jfet VAS for a cascode bjt and i changed R9, R10 of 270ohms to 75 ohms.

maxpou 21st April 2008 05:16 PM

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my last test is cascoded current mirror.

maxpou 21st April 2008 05:17 PM

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and the FFT

peufeu 21st April 2008 06:23 PM

Re: no current mirror, current mirror, cascoded current mirror, bjt or jfet VAS?
 
Quote:

i thing that 40dB of feedback is too high
Why ?

maxpou 21st April 2008 08:40 PM

Hi Peufeu,
because in my experience, i have a better sound when i reduce OLG in my cd player, line stage, power amp and i listen a old audioresearch 100.2 ( 6 dB of feedback) in my friend home and i loved the sound. I listened the Ayre audio system too and my jaw fell to the ground. So because I find it difficult to build a pre-amp without feedback I want to reduce as much as possible. thank you! Maxpou


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