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Old 9th March 2006, 09:05 AM   #1
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Default iteration limit reached: another numb noob Q

Hi,

when simulating my circuit in ltspice it works ok with 'universal opamp' model. if I use a certain model, be it from LT or a third party, I get an error saying: 'iteration limit reached'. The circuit works in reality.
Why is that, and how to cope?
Rüdiger
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Old 9th March 2006, 09:20 AM   #2
lineup is offline lineup  Sweden
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maybe you should build the thing ....

then is REALLY working audio circuit

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lineup
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Old 9th March 2006, 09:31 AM   #3
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He lineup,
what a worthwhile advice
It *is* build in reality, and not working in sim (anyway, better than the other way round). I did so to check what happens to happen both in sim and reality if I change something.

The sim works now, I replaced *all* opamps with their dedicated models. It seems you can't mix both universal and specific models, of course, I don't know if this is true in all cases.
Rüdiger

Edit: Wrong! It seems to work only randomly. If I change anything (e.g. add a parallel cap to Rf), then I get the error warning again
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Old 9th March 2006, 09:55 AM   #4
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Hi,

That's a common Spice engine error and opamp simulations are the worst offenders. Can mean a myriad of things from too complex of a circuit or signal to not enough info to make the calculations.

I've found that sometimes the silliest things can cure it - like varying a resistor by one ohm (99.999K instead of 100K on a feedback resistor for example) and other times it plain won't run.

Can you try another, more co-operative opamp model with similar charcteristics (like a TL072 for an 082)? The real-life difference won't be significant.

Cheers!
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