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Old 27th August 2009, 08:49 PM   #1
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Default Beast with a Thousand JFETs

Jam called me up and asked if I have ever paralleled up a
bunch of 2SK170's and 2SJ74's to make a power output
stage.

I guess it's time to unveil the Beast with a Thousand JFETs.

Here's the first teaser, a circuit panel to hold 588 JFETs and
associated resistors.
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File Type: jpg BEAST 01.jpg (92.5 KB, 5249 views)
File Type: jpg BEAST 02.jpg (94.9 KB, 4944 views)
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Old 27th August 2009, 09:01 PM   #2
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How do the capacitances compare with an equivalent group of power fets? I'm curious to see what you can do with this Will you need to do any matching? (or just wing it) Pardon my ignorance, I'm not a huge ss designer.
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Old 27th August 2009, 09:04 PM   #3
Salas is offline Salas  Greece
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Quote:
Originally Posted by Nelson Pass View Post
Jam called me up and asked if I have ever paralleled up a
bunch of 2SK170's and 2SJ74's to make a power output
stage.

I guess it's time to unveil the Beast with a Thousand JFETs.

Here's the first teaser, a circuit panel to hold 588 JFETs and
associated resistors.
He, he, mega!
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Old 27th August 2009, 09:37 PM   #4
Bigun is offline Bigun  Canada
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Wow, that's impressive - I hope you're using a Pick n Place machine, no hand soldering on that thing.

How does the cooling work ?
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Old 27th August 2009, 09:50 PM   #5
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Quote:
Originally Posted by Bigun View Post
Wow, that's impressive - I hope you're using a Pick n Place machine, no hand soldering on that thing. How does the cooling work ?
Hand soldered. Hand matched.

What cooling?



currently ripping: Outernational Sound, Thievery Corporation
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Old 27th August 2009, 09:57 PM   #6
mjf is offline mjf  Austria
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Quote:
How does the cooling work ?
perhaps with a few (cpu) fans.........
and if that does not work put it into a refrigerator.
greetings.........
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Old 27th August 2009, 09:59 PM   #7
gl is offline gl  United States
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Nelson,

As I recall you did something similar once before many years ago - paralleling lots of JFET's.

If this beast has a thousand JFET's then there must be two of these panels required? And with 2SJ74's the voltage rails will probably have to be in the Firstwatt power amp range?

By golly the thing is starting to look like a simplified version (did I actually say that out loud?) of the F4.

Graeme
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Old 27th August 2009, 10:10 PM   #8
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Quote:
Originally Posted by Nelson Pass View Post
Hand soldered. Hand matched.
EEEK
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Old 27th August 2009, 10:13 PM   #9
wicked1 is online now wicked1  United States
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Quote:
Originally Posted by Nelson Pass View Post
Hand soldered. Hand matched.


currently ripping: Outernational Sound, Thievery Corporation
Doing that by hand is almost crazy, but I've gotta tell you... Thievery Corp is the perfect music for such activities.
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Old 27th August 2009, 10:32 PM   #10
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Since J74 is not that easy to source, I will go single ended.
In fact, as a premonition, I started to source the 170 months ago...

Heat? I heard someone immersed some amp on oil...maybe vaseline, with its many uses , could also work.

Regards,
M
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