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Old 22nd March 2010, 01:58 AM   #1
PB2 is offline PB2  United States
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Default Spice Simulation of Adcom GFA-555

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.
Attached Files
File Type: txt ADCOM-GFA555.asc.txt (14.0 KB, 112 views)
File Type: txt PLB-SPICE-1.LIB.txt (20.0 KB, 96 views)
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Old 22nd March 2010, 02:39 AM   #2
infinia is offline infinia  United States
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Thanks Pete got it running in time domain.
I'm working on closed loop Bode plots at the moment
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Last edited by infinia; 22nd March 2010 at 03:01 AM.
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Old 22nd March 2010, 02:47 AM   #3
PB2 is offline PB2  United States
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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?
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Old 22nd March 2010, 02:51 AM   #4
djoffe is offline djoffe  United States
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Default 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?
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Old 22nd March 2010, 03:21 AM   #5
infinia is offline infinia  United States
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got closed loop bode plot working fine
having trouble breaking the loop for open loop shows neg gain. LOL
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Old 22nd March 2010, 03:36 AM   #6
PB2 is offline PB2  United States
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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?
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Old 22nd March 2010, 03:37 AM   #7
PB2 is offline PB2  United States
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Quote:
Originally Posted by djoffe View Post
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.
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Old 22nd March 2010, 06:22 AM   #8
anatech is offline anatech  Canada
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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
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Old 22nd March 2010, 02:29 PM   #9
PB2 is offline PB2  United States
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Updated .asc file, fixed supply caps, and added SPICE directives to turn off compression for distortion measurements.
Attached Files
File Type: txt ADCOM-GFA555.asc.txt (14.3 KB, 77 views)
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Old 22nd March 2010, 09:09 PM   #10
PB2 is offline PB2  United States
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LtSpice wiki:
LTSpice and What the New User Should Know - diyAudio
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