Spice Simulation of Adcom GFA-555

PB2 · 22nd March 2010, 01:58 AM

I did some quick LtSpice simulations of the Adcom GFA-555 and am making the asc file available here. I was in a rush used good Fairchild transistors for all the small signal devices and plan to substitute correct models as I find them. Used andy_c's output models which are probably much faster but will do for now - thanks andy! This file has SPICE directives to provide analysis of the distortion; use "view" "spice error-log" to see the results.
Remove .txt from the file names to use them with LtSpice.
I quickly collected some models that I had on this system, my main LTSpice install is on another system. These models are in the attached .LIB file. I have many models but probably not for the remaining transistors so if anyone has them please post them, especially looking for the correct outputs.

infinia · 03:01 AM

Thanks Pete got it running in time domain.
I'm working on closed loop Bode plots at the moment

PB2 · 22nd March 2010, 02:47 AM

PS caps got in there as 100,000uF should be 15,000uF.

You just uncomment the .ac spice directive, or are you already an LTspice user?

djoffe · 22nd March 2010, 02:51 AM

I notice that only Q1 has an emitter resistor, but not Q2? Is this the way the design is, or is there an omission?

infinia · 22nd March 2010, 03:21 AM

got closed loop bode plot working fine
having trouble breaking the loop for open loop shows neg gain. LOL

PB2 · 22nd March 2010, 03:36 AM

I believe that there is an example in the audio amp tutorial LTspice file. Comes with the installation. I don't think it uses any of the advanced methods. There is a "loop probe" that is probably more accurate discussed here, see andy's post #29:
Open loop gain, phase margin etc

and here:
Spice simulation

Are you a member of the Yahoo LtSpice user's group?

PB2 · 22nd March 2010, 03:37 AM

Quote:

Originally Posted by djoffe

I notice that only Q1 has an emitter resistor, but not Q2? Is this the way the design is, or is there an omission?

Yes that is how it was designed.

anatech · 22nd March 2010, 06:22 AM

Hi Pete,

Quote:

Yes that is how it was designed.

Yes, it was. I'll back you up on that.

I wish I had the time to learn how to use spice. It's great that you can.

-Chris

PB2 · 22nd March 2010, 02:29 PM

Updated .asc file, fixed supply caps, and added SPICE directives to turn off compression for distortion measurements.

PB2 · 22nd March 2010, 09:09 PM

LtSpice wiki:
LTSpice and What the New User Should Know - diyAudio

22nd March 2010, 02:39 AM	#2
infinia diyAudio Member Join Date: May 2005 Location: Californication	Thanks Pete got it running in time domain. I'm working on closed loop Bode plots at the moment __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust Last edited by infinia; 22nd March 2010 at 03:01 AM.

22nd March 2010, 02:47 AM	#3
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	PS caps got in there as 100,000uF should be 15,000uF. You just uncomment the .ac spice directive, or are you already an LTspice user? __________________ Pete Basel http://www.linkedin.com/in/petebasel

22nd March 2010, 02:51 AM	#4
djoffe diyAudio Member Join Date: Oct 2008	Is there a resistor missing? I notice that only Q1 has an emitter resistor, but not Q2? Is this the way the design is, or is there an omission?

22nd March 2010, 03:21 AM	#5
infinia diyAudio Member Join Date: May 2005 Location: Californication	got closed loop bode plot working fine having trouble breaking the loop for open loop shows neg gain. LOL __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

22nd March 2010, 03:36 AM	#6
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	I believe that there is an example in the audio amp tutorial LTspice file. Comes with the installation. I don't think it uses any of the advanced methods. There is a "loop probe" that is probably more accurate discussed here, see andy's post #29: Open loop gain, phase margin etc and here: Spice simulation Are you a member of the Yahoo LtSpice user's group? __________________ Pete Basel http://www.linkedin.com/in/petebasel


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22nd March 2010, 09:09 PM	#10
PB2 diyAudio Member Join Date: Sep 2004 Location: North East Blog Entries: 1	LtSpice wiki: LTSpice and What the New User Should Know - diyAudio __________________ Pete Basel http://www.linkedin.com/in/petebasel

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