LTSpice Simulation Problem

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fasterbyelan

fasterbyelan

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Joined 2009
#1
I have used LTSpice to simulate two phono amps’ I have built (and work!) as a means of getting familiar with the software. Both circuits have a DC servo to remove any offsets. When the simulation is run (ie DC op.), it will not complete the action and I have to stop the calculations (the lower left corner of the screen shows something is going on!) If I remove the DC Servo element of the circuits both will simulate correctly and the results as expected.

So why can't I run the simulations and why does the DC Servo have this effect?

One of the circuits is the HPS5.1 (see here)
 
#2
fasterbyelan said:
I have used LTSpice to simulate two phono amps’ I have built (and work!) as a means of getting familiar with the software. Both circuits have a DC servo to remove any offsets. When the simulation is run (ie DC op.), it will not complete the action and I have to stop the calculations (the lower left corner of the screen shows something is going on!) If I remove the DC Servo element of the circuits both will simulate correctly and the results as expected.

So why can't I run the simulations and why does the DC Servo have this effect?

One of the circuits is the HPS5.1 (see here)
Click to expand...

Do you mean it takes longer than you are willing to wait? A servo introduces a feedback loop and feedback loop simulations can take a long time to complete.
How long did you wait?

Jan
 
#4
fasterbyelan said:
Yes, I did think that was the case and left it running for 30 mins once before ending the sim. Maybe I just need to be more patience!?
Click to expand...

I've had sims taking several hours, so maybe fire it up tonight before going to sleep 😉
There are some things that take a long time, like very small timesteps, long sim time periods (obviously) and circuits that are close to oscillations (this forces the sim to use very small steps).

Jan
 
#8
I ran a sim on the HPS5.1 (DC op.) and this did complete after about 30 mins. The DC voltages are as expected with the servo in place 😎😎

Now running an AC sim which is taking much longer, 2 hours and counting.......

Thanks for your advice Jan.
 
#9
.AC don't usually take any noticeable time at all - likely its the operating point calculation having convergence problems

sometimes the operating point calc has to be "helped" with initial conditions, nodeset statement or even doing a .TRAN 1st and saving the settled operating point values

you really shouldn't jump to .AC until after you have wrung out the circuit sim in .TRAN
 
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