OpenLoop Gain and compensation

Voegelchen · 23rd September 2010, 06:16 PM

Hello world

I have an amp simulated and as real device, but I've some problems to simulate it's open loop gain. Is there anything out as info that can you recommend to read ?
Next problem is the compensation of the amp....At the moment there's only the capacitor across B-C of the VAS transistor...but there I must put >300pF in to get the amp stable at any load (in the real world). What's about a second order pole in the feedback ? In the simulation that works fine...but in real world ?????

Thanks.....

Federmann · 23rd September 2010, 06:34 PM

And the whole scheme?

Voegelchen · 23rd September 2010, 06:45 PM

as PDF:
http://www.ac-vogel.de/TheAmp_MK2/20...2010-06-30.pdf

and see pic

Voegelchen · 23rd September 2010, 06:48 PM

R22 and C5 are not placed (R-C across VAS)
C2 is 300pF (across VAS)

lineup · 23rd September 2010, 07:04 PM

You have a supply rail filter D4 + R37 (10 Ohm)
I would rather put this before the VAS Constant current source.
So I should move them to the right of T7.

Current sources benefit from clean, constant voltage supply.
And this is what the filter D4 + R37 helps to give. su

Voegelchen · 23rd September 2010, 07:06 PM

Yes :-)
Error known and will be corrected in next "session" :-)

ostripper · 07:27 PM

strange , this is almost the same as my "AX" which runs stable down to 22pF ??

edit , GET RID of the Darlington drivers !!! (tip 102/107) most likely they are the problem.

OS

Voegelchen · 23rd September 2010, 07:27 PM

Ok... I've found something about testing OL gain in simulation (making the feedback R from output to some MOhms and replacing the feedback resistor to ground by 10F (!) ).

So I've Open Loop gain... the compensation in the simulation works fine (just where I want it) and I also get best results in simulation... but bad results in real world :-(
One prototype (breadboard) is performing well... the PCB type seems to be instable.... mhhhh... can the emitter resistors make an amplifier unstable ? There where other types on the breadboard than on the PCB....

Voegelchen · 23rd September 2010, 07:29 PM

Quote:

Originally Posted by ostripper

strange , this is almost the same as my "AX" which runs stable down to 22pF ??

edit , GET RID of the Darlington drivers !!! (tip 102/107) most likely they are the problem.

OS

Why not darlingtons ? capacity too high ? They make unbelievable current gain

ostripper · 23rd September 2010, 07:36 PM

Quote:

Originally Posted by Voegelchen

Why not darlingtons ? capacity too high ? They make unbelievable current gain

Oscillation city... standard MJE15032/33 drivers will give 2k hfe in a standard EF2 output stage and will allow the "blameless" to run on a single 33/47pF Cdom rock solid. I don't lie , i'm building my 10th pair of your amp "ax" below.
OS

23rd September 2010, 06:48 PM	#4
Voegelchen diyAudio Member Join Date: Jun 2010 Location: Germany and www.aca-vogel.de	R22 and C5 are not placed (R-C across VAS) C2 is 300pF (across VAS) __________________ Designing audio electronics isn't a job, it's a mission

23rd September 2010, 07:04 PM	#5
lineup diyAudio Member Join Date: Dec 2005 Location: the north	You have a supply rail filter D4 + R37 (10 Ohm) I would rather put this before the VAS Constant current source. So I should move them to the right of T7. Current sources benefit from clean, constant voltage supply. And this is what the filter D4 + R37 helps to give. su __________________ lineup

23rd September 2010, 07:06 PM	#6
Voegelchen diyAudio Member Join Date: Jun 2010 Location: Germany and www.aca-vogel.de	Yes :-) Error known and will be corrected in next "session" :-) __________________ Designing audio electronics isn't a job, it's a mission

23rd September 2010, 07:25 PM	#7
ostripper diyAudio Member Join Date: May 2008 Location: Albany , NY (smallbany)	strange , this is almost the same as my "AX" which runs stable down to 22pF ?? edit , GET RID of the Darlington drivers !!! (tip 102/107) most likely they are the problem. OS __________________ Mongrel website , always current and updated : http://www.fidelityforce.com/ostripper Last edited by ostripper; 23rd September 2010 at 07:27 PM.

23rd September 2010, 07:27 PM	#8
Voegelchen diyAudio Member Join Date: Jun 2010 Location: Germany and www.aca-vogel.de	Ok... I've found something about testing OL gain in simulation (making the feedback R from output to some MOhms and replacing the feedback resistor to ground by 10F (!) ). So I've Open Loop gain... the compensation in the simulation works fine (just where I want it) and I also get best results in simulation... but bad results in real world :-( One prototype (breadboard) is performing well... the PCB type seems to be instable.... mhhhh... can the emitter resistors make an amplifier unstable ? There where other types on the breadboard than on the PCB.... __________________ Designing audio electronics isn't a job, it's a mission


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23rd September 2010, 06:34 PM	#2
Federmann diyAudio Member Join Date: Oct 2009 Location: Kunovice - Moravia	And the whole scheme?

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