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Old 9th January 2009, 09:55 AM   #1101
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Quote:
Originally posted by thanh1973
Do you have any idea what I might be doing wrong?
Or is this a common problem with simulators?

common problems with simulators .............. less and less brain-time .....
and less gadgets really made

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Old 9th January 2009, 10:07 AM   #1102
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Quote:
Originally posted by thanh1973
Do you have any idea what I might be doing wrong?
Or is this a common problem with simulators?
Jfet model not that efficient maybe.
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Old 9th January 2009, 10:21 AM   #1103
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I used the jfet model for lsk170 from Linear Systems
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Old 9th January 2009, 10:31 AM   #1104
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I have this one. Changing the Beta, Idss changes. Try to see what happens (if it is not the same already).

.model J2sk170 NJF(Beta=59.86m Rs=4.151 Rd=4.151 Betatce=-.5 Lambda=1.923m
+ Vto=-.5024 Vtotc=-2.5m Cgd=20p M=.3805 Pb=.4746 Fc=.5
+ Cgs=25.48p Isr=84.77p Nr=2 Is=8.477p N=1 Xti=3 Alpha=10u Vk=100
+ Kf=111.3E-18 Af=1)
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Old 9th January 2009, 10:43 AM   #1105
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I just tried your model, but still the same result (ie mostly 3rd Harmonic with no 2nd Harmonic)
If you have LTspice, I could send you the circuit to have a look at.
I am not quite sure if I have earthed everything correctly.
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Old 9th January 2009, 10:49 AM   #1106
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Hi tanh, I havent simulated this circuit but I for one think it would display more h3 than second, playing around with values should make h2 dissapear. I dont think the guys that get h2 to be above have the exact same circuit as in the pass paper, and if I remember correctly NP himself said it would be predominantly h3.
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Old 9th January 2009, 11:22 AM   #1107
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Well I hope so.
I am learning heaps at the moment using LTspice - changing values or components looking at the effects, determining dc offset, bias currents, input impedance, and also looking at the distortion profile.
It has also been a source of motivation to try tweeking things where as before, I would be totally relying on ohers experience or guessing.

Anyway, I hope as you say it is predominantly H3, or all confidence I have in simulators will be lost.
Unless I can find the source of this discrepancy.
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Old 9th January 2009, 12:58 PM   #1108
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I just run a B1 FFT measurement again. Second order is higher than third. Mine has +/- 10V supply and no coupling capacitors. This card has 0.007% residual THD and 100dB noise floor in the last octave.
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Old 9th January 2009, 08:36 PM   #1109
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With a 23-25 V supply and 1 Khz at one volt into 10 Kohm, I routinely
see .0007% with BL parts.

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Old 9th January 2009, 08:46 PM   #1110
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I will see near that when I will get my new EMU 24bit I guess. You must be using AP2? The main question is do you still see more second than third harmonic in your FFT like I do? I used 0dBV input, volume fully clockwise, about 3k card input Z.
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