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Old 29th January 2012, 05:13 PM   #11
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Quote:
Originally Posted by studiostevus View Post
I am a beginner in LTSpice and tried to get this to work... unfortunately the log file shows the measurements FAIL'ed.... any ideas what could be wrong?
Can you submit your schematic? The best way is to zip content of the whole directory, where schematic is located. It is hard to say without loking at your simulations.
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Old 30th January 2012, 09:06 AM   #12
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This is the schematic and the files.... thanks for you help!

Archive.zip
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Old 30th January 2012, 07:16 PM   #13
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Hello,
You have to place analyzer symbol on your schematic and connect it's output to your amplifier input and analyzer input to amplifier output. The same way as if you are using real measuring equipment.
I modified your schematic. It is in zip file, together with 2 plot setting file (*.plt), that you may use to display frequency or amplitude sweep results. You can also see control file example for amplitude sweep.
Pictures show transient plots for amplitude sweep and distortion plots for your circuit, frequency and amplitude sweeps.

Don't hesitate to ask any questions.

Eugene.
Attached Images
File Type: png gomes_tr.png (23.6 KB, 362 views)
File Type: png gomes_FR_THD.png (7.9 KB, 307 views)
File Type: png gomes_AMP_THD.png (12.4 KB, 303 views)
Attached Files
File Type: zip Gomes_MOD.zip (1.6 KB, 66 views)
File Type: txt Analyzer_Controls.txt (10.4 KB, 87 views)
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Old 15th August 2013, 09:37 PM   #14
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Hi, Eugene,

Thanks a LOT for so excellent and useful piece of software!

I would like to ask about data representation and interpretation of graphs (please look at the picture attached). Bottom graph is the most valuable total, 2nd and 3rd harmonics.
Input voltage of DUT changes:
.STEP dec param Ag 0.01 1.0 2

What I would like to display on 3rd graph is THD% = F(V_out). Yet there is something strange. X axis starts from zero and ends with 1. Does this mean input voltage?
Then, -51 dB THD = 0.28%
Looks like Y axis (on third graph), labeled with "m", is a strange notation of THD %.

Q: Is it possible to display graph THD% = F(V_out), or better just to export data to spreadsheet and draw graph here?
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File Type: jpg 1.jpg (79.6 KB, 174 views)
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Old 17th August 2013, 05:07 PM   #15
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Hello,
Yes, your X axis is "ag" by default. Then 1V is your maximum setting of generator amplitude from .STEP command.
To change X axis to output RMS value, click on horizontal axis (on numbers).
You will see "ag" in the top tab. Change it to "fundamental_v_rms" and set corresponding limits in lower tabs.
In notation 280m=0.28, as soon as it is in present, 280m means 0.28%.
I was not able to figure out how to display preset notation on the scale in this case. That's why the name represents meaning.
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Old 18th August 2013, 12:46 PM   #16
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Quote:
Originally Posted by Eugene Dvoskin View Post
To change X axis to output RMS value, click on horizontal axis (on numbers).
You will see "ag" in the top tab. Change it to "fundamental_v_rms" and set corresponding limits in lower tabs.
Hi, Eugene,

Thanks for feedback.
"fundamental_v_rms" doen't exists in your LTSpice script,
Did you meant "fundamental_out_v_rms"? In this case graph is displayed correctly.

BTW, did you tried to use LTSpice to predict instability problems, caused, for example, by grid leak resistor of too large value? Looks like this is working in *some* degree. Oscillation is not shown, but rather unusually low output voltage.

I would be glad to hear your opinion. Your LTSpice skills seems to be on the highest level possible.
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Old 18th August 2013, 03:22 PM   #17
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Yes, you right. I just looked at my old script.

I'm always using LTSPICE to evaluate many kings of instability's.
I'm not very familiar with models for tubes, however your simulation is as good as your model is. You have to understand your model limitations. You also have to evaluate stability in different modes of operation, different offsets and etc. All circuits are non linear, parameters are changing. You have to make sure that your simulation covers this. Including some cases that may be considered artificial - like clipping. And that you also included parasitics.
If models are good (well, that's a common problem) I would use both AC and Transient analysis to predict possible instability.
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Old 13th December 2013, 02:56 PM   #18
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Hi Eugene,
I'm not an LTspice expert, only pre-breadboard user mostly.

If I put the directive for power measurement and outputpower as baseline, the resulting diagarams represent amplitudes THD and Pout THD. Is it correct?
Does my setup is correct, in general.

Thanks.
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File Type: jpg Pout_1.jpg (74.1 KB, 37 views)
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Old 13th December 2013, 06:25 PM   #19
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I think that you are correct.
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Old 13th December 2013, 06:47 PM   #20
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Thank you.
Btw, thanks for the nice tool.
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