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Old 23rd October 2011, 04:50 PM   #3861
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Quote:
Originally Posted by PHEONIX View Post
Here are the results I got comparing Simetrix with LTspice simulators
Hi Arthur,

Maybe you might also run simulations of Bob's amp (see post 3824), so we could compare your results with the rest of our sims.

Cheers,
E.
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Old 23rd October 2011, 05:05 PM   #3862
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Default Trolling again?

To all (except Mike)

Did I do miss something?
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Old 24th October 2011, 09:46 AM   #3863
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Default Simetrix results with Bob's Amp

With Bobs amp I get the following results with Simetrix.

Freq THD
1Khz 0.019%
20Khz 0.976%
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Old 24th October 2011, 10:31 AM   #3864
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Hello Edmond

Its curious that the results get polarized into these two different groups of results.

Regards
Arthur
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Old 24th October 2011, 11:14 AM   #3865
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Default The user or the tool?

Thanks Arthur.

Let's tabulate the results we got till now (I hope more will come):
THD-1k (in ppm of first 10 harmonics?) of Bob's amp according fig. 19.7
Code:
Cadence-1: 259.6  (post 3826)
Cadence-2:  81.8  (post 3844)
Cadence-3  190.6  (post 3850)
MicroCap:   26.8  (post 3837)
LTspice:    26.6  (post 3824)
Simetrix:  190.0  (post 3863)
Hmm... Needless to say that these figures don't inspire much confidence in simulator platforms of various brands.
On the other hand, my THD figures obtained from MicroCap were reasonable in line with actual measurements on the 'blameless' amp, Bob's HEC amp and the PGP amp.
I also like to add that, at least to me, a figure of 26ppm doesn't sound overly optimistic.

>Its curious that the results get polarized into these two different groups of results.
Sure. But who's to blame? The user or the tool?

Cheers,
E.
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Old 24th October 2011, 07:17 PM   #3866
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Default MC10

Hello Edmond

Out of curiosity have you tried MC10 demo , it would be curious to see what results it gives.

Regards
Arthur
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Old 24th October 2011, 07:39 PM   #3867
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Default MC9 vs MC10

Hi Arthur,

As for Bob's amp 19.7, THD & 1kHz and BW = 10kHz
MC 9: 26.778ppm
MC10: 26.778ppm
As you can see, not much difference.

Cheers,
E.
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Old 24th October 2011, 07:59 PM   #3868
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So, which results should we believe, Micro cap or Simetrix?
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Old 25th October 2011, 11:23 AM   #3869
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Michael

The deal with simulators and accurate THD sims is that you need "good models" without them you dont get accurate simulated results. I am not sure of the quality of the parts used in the last simulation exercise but I dont think its fair to draw the conclusion that simulators are unreliable for THD simulations.
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Old 25th October 2011, 12:18 PM   #3870
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Default The Good, The Bad And The Ugly

Quote:
Originally Posted by PHEONIX View Post
Michael

The deal with simulators and accurate THD sims is that you need "good models" without them you dont get accurate simulated results. I am not sure of the quality of the parts used in the last simulation exercise but I dont think its fair to draw the conclusion that simulators are unreliable for THD simulations.
Hi Arthur,

As for THD analysis, there are good AND unreliable simulators. Please have a look at this thread:
Distortion simulation with LTspice
Here are some excerpts:

"After following some tips from the LTSpice mailing list, I see no practical limitation from the FFT accuracy (in LTSpice).
With compression off, alternative solver on, running
.tran 0 12m 0 .1u gives .fourier results down to 3E-6 (110dB dynamic range). The graphical FFT, selecting 65536 points and Hann window, gives a "noise floor" of -200dB. And if you join Bernhard's Church of the Merciless Noise Killing, he will most likely give you the setup for getting down to -300dB.
But these are only numbers in a theoretical game, as the active devices' models are not anywhere near this accuracy.

Regards,
Peter Jacobi"


That's okay, but now look at this one:

"Regarding the accuracy of the FFT (needed for THD analysis) within PSPICE I found the following:
http://www.<b>orcadpcb.com</b>/kb_ar...20019.asp?bc=F
an excerpt:
Simulation accuracy is limited to about 3-3.5 digits (60-70dBc). The accuracy can be improved by tightening tolerances and taking the above considerations to extremes, but not by very much. This may not be considered sufficient for some applications, but keep in mind that even the best simulation models are probably not accurate enough to provide better
[...]
Regards
Charles "


3.5 digits correspond with an accuracy of ~300ppm. If this is true, it explains a lot! Orcad

Cheers,
E.
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Last edited by Edmond Stuart; 25th October 2011 at 12:33 PM.
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