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-   -   Beast with a Thousand JFETs (http://www.diyaudio.com/forums/pass-labs/150048-beast-thousand-jfets.html)

Nelson Pass 27th August 2009 07:49 PM

Beast with a Thousand JFETs
 
2 Attachment(s)
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.

Boris_The_Blade 27th August 2009 08:01 PM

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.

Salas 27th August 2009 08:04 PM

Quote:

Originally Posted by Nelson Pass (Post 1908474)
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!:D

Bigun 27th August 2009 08:37 PM

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 ?

Nelson Pass 27th August 2009 08:50 PM

Quote:

Originally Posted by Bigun (Post 1908500)
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

mjf 27th August 2009 08:57 PM

Quote:

How does the cooling work ?
perhaps with a few (cpu) fans.........
and if that does not work put it into a refrigerator.
greetings.........

gl 27th August 2009 08:59 PM

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

jacco vermeulen 27th August 2009 09:10 PM

Quote:

Originally Posted by Nelson Pass (Post 1908507)
Hand soldered. Hand matched.

EEEK :eek:

wicked1 27th August 2009 09:13 PM

Quote:

Originally Posted by Nelson Pass (Post 1908507)
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.

maxlorenz 27th August 2009 09:32 PM

Since J74 is not that easy to source, I will go single ended. :cool:
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 :D, could also work.

Regards,
M


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