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Old 20th January 2014, 10:47 AM   #1131
PHEONIX is offline PHEONIX  Australia
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Hello Dave,

I use the Simetrix simulator. I stopped using Ltspice a couple of years ago, because its unaided convergence was not as good as simetrix.

Somebody experienced with Ltspice should have no problems simulating the loop gain plots that you want to do.

I am tempted to relearn Ltspice because it is the defacto standard on diyaudio.

Regards
Arthur
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Old 20th January 2014, 12:35 PM   #1132
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Quote:
Originally Posted by PHEONIX View Post
...
I am tempted to relearn Ltspice because it is the defacto standard on diyaudio.
Please do. I assume that improvements have been made since you left and it is certainly convenient to be able to swap ASCs.


Best wishes
David.
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Old 21st January 2014, 04:59 PM   #1133
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Quote:
Originally Posted by PHEONIX View Post
Hello Dave,

I use the Simetrix simulator. I stopped using Ltspice a couple of years ago, because its unaided convergence was not as good as simetrix.

Somebody experienced with Ltspice should have no problems simulating the loop gain plots that you want to do.

I am tempted to relearn Ltspice because it is the defacto standard on diyaudio.

Regards
Arthur
Hi Arthur,

There have been times when convergence with LTspice have indicated to me a problem in the circuit or the models.

All I'm saying is, be on the watch when you get DC convergence difficulties.

Cheers,
Bob
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Old 21st January 2014, 05:23 PM   #1134
jcx is offline jcx  United States
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I often see LTSpice struggling with convergence to operating point solution with high loop gain, particularly with op amps in the loop

while just putting up with a startup spike in.TRAN is possible – I then don't trust the .AC

I had a scary LTSpice convergence issue over xmass - I tried something related to Pass SuSy and it worked like a dream 1st few runs of the sim

I then made a few "clean up" changes - not expected to do anything to loop gain - and I spent hours getting back to a circuit configuration with any DC solution at all

now have .savebias/.loadbias file pair started up by .nodeset statement and letting that poor operating point solution bootstrap with 100 ms runs with 0 input to amp, still have to fall back to the .nodeset with some changes

I would have dismissed the whole approach if I hadn't seen the sim work in the 1st few tries

Last edited by jcx; 21st January 2014 at 05:36 PM.
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Old 21st January 2014, 09:47 PM   #1135
ihan is offline ihan  England
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Hello all,

I don't use LTspice, but with Pspice, I find that setting some initial conditions with the .IC command improves the likelihood of convergence. I assume you can do the same in LTspice.

Cheers,
Ian
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Old 22nd January 2014, 12:52 PM   #1136
PHEONIX is offline PHEONIX  Australia
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Hello Guys,

Bob as a rule I use only the models for your website along with Harry driver transitors, and I dont stray from these. Your diodes and LEDS I also use.
But I do agree with you models can cause problems.

High loop gain is where I have problems as explained by jcx with LTSpice .

Thanks for you input Ian, I will look at initial condition setup .


Regards
Arthur
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Old 4th November 2014, 06:01 PM   #1137
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Clearly, Micro-Cap is watching me:
(Courtesy of Stein who told me about it)
Attached Images
File Type: jpg STIS.jpg (156.5 KB, 199 views)
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Old 4th November 2014, 08:31 PM   #1138
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Originally Posted by Edmond Stuart View Post
Clearly, Micro-Cap is watching me:
(Courtesy of Stein who told me about it)
Or did you just send in a user article and had it approved for publication on their site?
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Old 4th November 2014, 08:34 PM   #1139
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Originally Posted by Bob Cordell View Post
Hi Arthur,

There have been times when convergence with LTspice have indicated to me a problem in the circuit or the models.

All I'm saying is, be on the watch when you get DC convergence difficulties.

Cheers,
Bob
I'm very with you! To me this has always been a hint at instability/erraticness in the schematic. Opamps can make it more suspectable to convergence problems. Simple fixes I noted amongs them was putting proper compensation across opamps, sometimes inserting a resistor in the inverting input lead from output (in case of a unity gain configuration) and a comp cap across. Base/gate stoppers can be another impactless fix.
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Last edited by MagicBox; 4th November 2014 at 08:40 PM.
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Old 4th November 2014, 08:43 PM   #1140
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@ MagicBox: Nope, of course not, as I'm not a 'registered' user of MC.
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