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Old 2nd January 2009, 10:56 AM   #581
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Quote:
Originally posted by ostripper
Yes , in simulation on LT , microcap , NI 10 ,and with the onset
of clipping. (trying to put a little more H3 into the picture).
They can't all be wrong..
OS
Good morning OS,
I'm not saying that they are wrong, just to take the results with a grain of salt, especially if you have used the same models in each sim.
Likewise for compensation. The sim will give a close approximation and show the effect of different compensation schemes. It will not hit the nail on the head though, as it doesn't use real devices, on a real board in a real environment. Too many other variables.


Gotta go...
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Old 2nd January 2009, 11:50 AM   #582
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Os,

looks good, I was wondering why you were neglecting cfp as input, wonder why the 5th is not coming down too, strange, you can manupulate the spectrum a little with the cfp in the input, the higher the current through the first transistor the more ....... eheh you experiment, youll be learning something useful.

H3 is not that bad, amp tends to sound more detailed, but dont have it above H2, again subjective preference but try get rid anything else after H3. At these THD levels you can only really hear any difference at higher powers. Another reason why I think carlos finds class a muffled, it drops H3 plenty with relation to H2.

I would recommend a jfet in the input for the cfp, there is high voltage jfets available if you take the trouble to seach for them so no cascode required upto a certain voltage. There are some issues with using the jfets like this but compromises have to be made. The jfets have a more relaxed sound, strangely enough they raise H3 and odd order more than anything else.
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Old 2nd January 2009, 11:50 AM   #583
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About to have a real board..
added CFP ,base resistors at OP, diodes at signal ground,
must document the package now. very nice board..
Attached Images
File Type: gif fa3_parts.gif (35.1 KB, 304 views)
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Old 2nd January 2009, 12:04 PM   #584
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Quote:
By homemodder - wonder why the 5th is not coming down too,
the plot I did not show, the one with the darlington.., had
5 DB less H5 ,so that is why I will order 4 Ksa700/800's
from mouser (why not) . board will take all the mods discussed here , , and still look good.OS
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Old 2nd January 2009, 12:12 PM   #585
jaycee is offline jaycee  United Kingdom
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The FFT results I showed were full power (ish, 42V p-p with 2V p-p input) at 1KHz with a resistive 8 ohm load.

I've now uploaded the LTSpice files, and a 10KHz full power FFT image.

It seems if you're going to add degeneration, the place to add it is the collectors of Q18/19.
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Old 2nd January 2009, 12:33 PM   #586
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Quote:
I've now uploaded the LTSpice files, and a 10KHz full power FFT image.
I just ran your .ASC file with my models (ksa992/1845 -
njw0281/0302) fast amp.. very good..
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Old 2nd January 2009, 02:54 PM   #587
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Jaycee, I just tried to simm your circuit but at 20KHZ, dont you find any oscilation problem ??? What version ltspice you using?? Os any problem??
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Old 2nd January 2009, 03:16 PM   #588
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Quote:
Jaycee, I just tried to simm your circuit but at 20KHZ, dont you find any oscilation problem ??? What version ltspice you using?? Os any problem
I ran it normal no hangups.. but when I clipped it
it broke out in oscillation when VAS saturated.

I added degen at CFP (22r) and it behaved unconditionally.
Also 10pf lead comp. at vas made for "whacked" LG plot.
I use LT4,by the way...
OS
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Old 2nd January 2009, 03:29 PM   #589
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I use LT4 too, but models from a japanese factory, slightly better with jaycee s models, this is nuts, I must try that degen. Whats happening here??
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Old 2nd January 2009, 03:53 PM   #590
AndrewT is offline AndrewT  Scotland
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Quote:
10pf lead comp. at VAS made for "whacked" LG plot.
what does this mean?
Is it good or bad?
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regards Andrew T.
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