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Old 1st July 2004, 03:35 AM   #11
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This amp is full of cascodes. How does it sound? Like classA? Clean?
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Old 1st July 2004, 09:15 PM   #12
gl is offline gl  United States
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The 4000A was (is) an amplifier in the best Nelson Pass tradition. It was very robust with a large power supply and lots of output devices. It sounded very dynamic and relaxed. Compared to the later Stasis two it had a bit of a darker sound. The Statis sounded a bit drier and more detailed in the midrange. These are very small nits. however. I should point out that it's been a long, long time since I've heard either one.

To answer your question, I believe that the cascodes contribute a great deal to the dynamic sound of these amplifers. I am a fan of cascoding.

There are two additional things about this design that should be mentioned. First: note the absence of VI limiters. This was the first high power commercial power amp I had come across without this feature. I had Dayton Wright XG8 MkIII speakers (modified ala the NP app note). The 4000A was easily the best sounding SS amplifer I had heard driving them.

Note too that there is no output inductor - also the first time I had seen this in a large commercial design.

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Old 1st July 2004, 11:42 PM   #13
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Some of what you may think of as cascode is the series
output stage, which I suppose technically is, but not in
the usual sense, as it's function was simply to divide the
voltage across the output devices by about 2 to share
the dissipation and keep the output devices well away from
the second breakdown region of BJT's.

By the way, if you want to see the massive output stage of the
Stasis 1, take your browser to 1.tif

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Old 5th July 2004, 05:41 PM   #14
docjoe is offline docjoe  Europe
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hello to everyone!

Today I've bought a 400a amp; realy cheap price; well, one chanel is silent; i'm planning to rejuvenate both! (i've allready succeded with a stasis II recently)

I seem to like NP stuff!

BTW, thanks for the 400/4000 drawings;

question : how much bias for optimal operation?

any info welcome!!
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Old 5th July 2004, 06:59 PM   #15
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Set the bias so that after an hour's operation you can
put your hand on the sink for 10 seconds.
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Old 5th July 2004, 07:01 PM   #16
docjoe is offline docjoe  Europe
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with nomex gloves on?
thanks i appreciate!
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