Article: Beast With a Thousand Jfets

[Zen Mod]

I am happy to announce ......

That's my Pa !

 

[kasey197]

Nelson cool article !

Just one question --- in the poster attached to your article ... is that the same Morgan Jones from england who writes about valves ?

Perhaps he was on his way up in the "entertainment industry" when he crossed paths with R Corman

 

[Loudthud]

I'm wondering why the dissipation per JFET is so low. The number of JFETs could be cut in half. Is it a distortion sweet spot?

 

[Rob McCance]

He's gone CRAZY!

Amps with two devices...amps with 2,000 devices. Which is it, spits or swallows..

I love it!

Nice work, Pass.

BTW, that's the cleanest distortion waveform I've ever seen. Like something from a textbook where you use only ideal parts.

 

[chalkandtalk]

So to get a similar amp with 5W output only needs 500 ish jfets total. This comes in at under £200 - cheap as chips

 

[Zen Mod]

all Dodos are chickened



(Mighty ZM preparing Babelfish Beast)

 

[flg]

That's my Pa !

What Da Ya Mean? Papa finally adopted ZM !!!

 

[dimkasta]

So to get a similar amp with 5W output only needs 500 ish jfets total. This comes in at under £200 - cheap as chips

We could also use a transformer before one of the driving cell to reverse its phase so that we could use only 2sk170s a'la F6

 

[flg]

The buffer for the xfrmr will benifit from the comp buffer driving it. Still gonna need some P's! But that bXfrmr should drive many cells!

 

[portreathbeach]

This looks like a crazy build. Would love to make something similar.

I have a few questions.

Would this work with an unbalanced source?
Is there just 1 single 1K resistor feeding all of the JFETs, or does each cell have one each?
Are there alternative JFETs that could be used which are cheaper and more available?

 

[Zen Mod]

-yup - with much less power
-each cell is having own
-hardly , without too much compromises .......

 

[portreathbeach]

That's a shame. So there arn't cheaper JFETs with a similar spec available?

 

[jacco vermeulen]

Aargh, so late to the party, I'm a goner.

(And my Soul, from out that Shadow, that lies Floating on the Floor, shall be lifted Never more)

 

[Nelson Pass]

That's a shame. So there arn't cheaper JFETs with a similar spec available?

There are still suitable parts out there, mostly switches with high
transconductance and high Idss. You might have to degenerate them more
with higher Source resistances, but it's do-able.

I have a few rolls of Fairchild J112's and P1086's that I'm certain would work,
and you can be sure there are others.

 

[buzzforb]

Have we been thrown a bone her. I am drooling and i dont know why. Did somebody ring a bell?

 

[EUVL]

According to Mouser, P1086 is End of Life :

P1086 JFET | Mouser


Patrick

 

[EUVL]

One can of course use 2SK246BL / 2SJ103 Y or GR.
They are unfortunately also EOL.
And for the same output impedance (or total effective transconductance), you would need 5000 FETs per channel ?




Patrick

 

[AudioSan]

isn't it very good news that LSJ74 is anounced to come out this year?

 

[buzzforb]

Which year? It gives a good picture of economy of scale. We sit here thinking that they would have all the business they need, but to them, it is a market that holds no promise. Unfortunately, the audio world is the only one looking for these parts.

 

[AudioSan]

this year(2013) they said
and they know it very well the fets are maked as audio fets. maybe papa gave them a tip about this beast