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Old 20th March 2012, 04:39 PM   #1
popilin is offline popilin  Argentina
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Default Need help with current amp

Hi all
I come to this forum because here are more kind to me.
I need to know which is more stable circuit, DC offset, and thermal.
It's for a 25W Class A amplifier.
Thanks a lot
Johann
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Last edited by popilin; 20th March 2012 at 04:49 PM.
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Old 20th March 2012, 04:47 PM   #2
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Thermal stability depend of the low frequency gain between the thermal sense (Vgamma multiplier) and the output transistors, and the thermal coupling. The bigger the last, the better stability. Appear that circuit #1 has more DC gain.
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Old 20th March 2012, 05:00 PM   #3
popilin is offline popilin  Argentina
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Hi Osvaldo
Thaks for your feedback, but cicuit #1 has the Vbe multiplier at the base of the transistors, can it helps with DC offset?
Best regards
Johann
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Old 20th March 2012, 07:35 PM   #4
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It seems unnecessarily complex. I think you could eliminate the Q4 Q4
stage altogether and just use the Mosfets to driver the output followers.

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Old 20th March 2012, 08:49 PM   #5
popilin is offline popilin  Argentina
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Hi Mr. Pass
I am honored by your support, but I attempted to do so a few months ago, and the square wave response was so bad.
Note that cascodes are yours.
What do you think about DC offset stability? +/- 40V come from a regulated power supply.
Thanks a lot.
Johann

Last edited by popilin; 20th March 2012 at 08:57 PM.
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Old 20th March 2012, 11:09 PM   #6
popilin is offline popilin  Argentina
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I forgot to mention that the voltage amplifier is valvular and has little current capability to drive a MOSFET properly
Thanks again
Johann
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