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Old 2nd May 2010, 01:39 PM   #1
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Default Latest LTspice giving crazy FFT results

I update my version of LTspice every so often and I found that the FFT plots from the latest version are infested with harmonics. This wasn't true before, when the usual 3rd, 5th, 7th harmonics were present in diminishing quantities. Now there are literally dozens of the things and they don't decrease so much with increasing harmonic number. (This is for a simulation of a triode-strapped EL34 PP amp). Has anyone else noticed this?
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Old 2nd May 2010, 07:53 PM   #2
jcx is offline jcx  United States
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did you remember to turn off data compression?
I always add the spice directive to the schematic:

.options plotwinsize=0
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Old 4th May 2010, 06:12 AM   #3
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Thanks for that. I find it difficult to understand mamny of the requirements of running LTspice. I haven't found the 'Help' to be particularly helpful - perhaps I'm just dumb
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Old 4th May 2010, 12:25 PM   #4
TheGimp is offline TheGimp  United States
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I understand what you mean about the help. I need to change the range of the FFT to make it more readable, but the help is less than helpfull on how to scale it.
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Old 5th May 2010, 09:06 PM   #5
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I do that by amending the frequency range. I just left-click on the X-axis of the FFT plot and enter your own start and finish values (e.g. 1k and 100k).
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Old 6th May 2010, 07:07 AM   #6
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I guess guys already know that "Blackman" is to be preferred.
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