Need help with current amp

popilin · 04:49 PM

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

Osvaldo de Banfield · 20th March 2012, 04:47 PM

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.

popilin · 20th March 2012, 05:00 PM

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

Nelson Pass · 20th March 2012, 07:35 PM

It seems unnecessarily complex. I think you could eliminate the Q4 Q4
stage altogether and just use the Mosfets to driver the output followers.

popilin · 08:57 PM

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

popilin · 20th March 2012, 11:09 PM

I forgot to mention that the voltage amplifier is valvular and has little current capability to drive a MOSFET properly

Thanks again
Johann

20th March 2012, 04:47 PM	#2
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	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. __________________ LW1DSE

20th March 2012, 08:49 PM	#5
popilin diyAudio Member Join Date: Oct 2010 Location: Traslasierra	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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20th March 2012, 05:00 PM	#3
popilin diyAudio Member Join Date: Oct 2010 Location: Traslasierra	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

20th March 2012, 07:35 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	It seems unnecessarily complex. I think you could eliminate the Q4 Q4 stage altogether and just use the Mosfets to driver the output followers.

20th March 2012, 11:09 PM	#6
popilin diyAudio Member Join Date: Oct 2010 Location: Traslasierra	I forgot to mention that the voltage amplifier is valvular and has little current capability to drive a MOSFET properly Thanks again Johann