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Old 6th December 2016, 11:35 PM   #21
lhquam is offline lhquam  United States
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Originally Posted by 2 picoDumbs View Post
I sssume that simulation is done with thermistor at exact same temperature as mosfet.
Generg's is mounted on heatsink.
Is it possible to simulate the effect of mounting the thermistor in different locations.
I agree that the thermistor mounting location is important. But the junction to heatsink temperature rise is only about 0.2C/W with the IXSYS SOT-227B packages. That means that at 1.3A and @24V the junction temperature is only about 6.3C hotter than the heatsink. I do not think it is a problem.
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Old 7th December 2016, 12:25 AM   #22
2 picoDumbs is offline 2 picoDumbs  Australia
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I don't think it is a problem either.
I am however interested to see the response due to the lag time required for the heatsink temperature to hit equilibrium with the mosfet.
Not concerned just interested.
Probably not easy to model I guess.
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Old 7th December 2016, 03:00 PM   #23
plasnu is offline plasnu  United States
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I'm astound by how you guys are meticulously deciphering Pa's secret message...
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Old 7th December 2016, 03:02 PM   #24
generg is offline generg  Germany
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nobody knows how the XA25 really looks.... it is only playing and enjoying and showing Pa that we can play a bit....and all his gifts were not in vain.... :-))
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Old 7th December 2016, 03:19 PM   #25
lhquam is offline lhquam  United States
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With no board photos, the XA25 is definitely more of a challenge.
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Old 7th December 2016, 05:34 PM   #26
generg is offline generg  Germany
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In the case Spice is right the very low distortion values Nelson states are for me only available with cascoded output and with some bootstrapping of the cascode transistors.

What do you think lhquam?
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Old 7th December 2016, 05:41 PM   #27
Zen Mod is offline Zen Mod  Serbia
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solder fumes time

and , if possible , cousin at IXYS , to send multiple freebies , for testing
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Old 7th December 2016, 05:42 PM   #28
Dennis Hui is offline Dennis Hui  Canada
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Originally Posted by generg View Post
And I tell you I am deeply impressed by the clarity and finesse of sound!

So Nelson real XA25 must be heavenly!
Generg, it seems you've already built a wonderful amp. Congratulations!

Cheers,
Dennis
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Old 7th December 2016, 06:01 PM   #29
generg is offline generg  Germany
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Originally Posted by Zen Mod View Post
solder fumes time

and , if possible , cousin at IXYS , to send multiple freebies , for testing
ha, ha, no cousin... but four P and four N are available at my home.



In the Sony II paper Nelson writes "There is one other detail in the output stage regulation; R17/C7 and R18/C8
which bootstrap the Cascode power transistors with about a one-sixth version of
the output waveform so as to get a little more voltage swing at maximum and
bring the output VFETs a little closer to the “sweet spot” of their load line curve."

Of course this detail is crying to be used in the "F4 beast" too.

I am only unsure where to measure the "one-sixth" waveform to get the right R.
And of course "one-sixth" might only be correct for the Sony II.

These are the limits of a box of bricks amp builder....
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Old 7th December 2016, 06:02 PM   #30
generg is offline generg  Germany
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Originally Posted by Dennis Hui View Post
Generg, it seems you've already built a wonderful amp. Congratulations!

Cheers,
Dennis
yes it is true, I now go hearing again....
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