FirstWatt J2

[audiodesign]

I have seen now the schematic on forum pag. 49

There is a current locker so these mosfet are not like lateral

 

[Zen Mod]

I see 29 pages - that's browser/user dependable

be more specific - which post exactly

 

[bobodioulasso]

This one?
http://www.diyaudio.com/forums/pass-labs/151909-firstwatt-j2-50.html#post2175400

There is a current locker so these mosfet are not like lateral

Not mosfets but power Jfets

 

[flg]

What is a "Current Locker"?

These SiC JFETs are lower threshold like Laterals though. And that seems to be an issue with the output biasing that is not quite typical Pass? Even the 1.25V version of TL431 might not cut it? Or maybe no one makes it anymore???

 

[flg]

O.K. Page 50 explains a little more. A TL Reg may work but Papa says it is less stable or "would need adj..."

"Current Locker" you mean the over current protection Q1?

 

[Zen Mod]

I=2A

40C : Ugs=1V576
70C : Ugs=1V581

TempCo

 

[flg]

.16mV/C Are you kidding? Is that in the data sheet?

 

[Zen Mod]

let's say just that Mighty ZM measured that

not thoroughly with CCS biasing , but with plain power resistor between PSU and drain

gate was tied to drain , of course

in any case - let them bleed ......... and do not worry too much

 

[audiodesign]

this

 

[Zen Mod]

what with this ?

that's plain CCS .

rephrase question , so we can answer

 

[audiodesign]

yes, the FirstWatt J2 use a CCS on output stage to fix the current also when temperature increase.

 

[Zen Mod]

nope

 

[Tazzz]

Here is all one need to know about the output stage topology used in the J2 in order to make a clone that's close enough to contain the interesting characteristics!

The Good Old Days & More SRPP

(Scroll down to "Even More Impedance-Multiplier Circuitry")

 

[flg]

let's say just that Mighty ZM measured that

not thoroughly with CCS biasing , but with plain power resistor between PSU and drain

gate was tied to drain , of course

in any case - let them bleed ......... and do not worry too much

Very good ZM! Time to get back to the Circlotron circuit. With JFETs this time...

 

[bobodioulasso]

Looks like J2 thread is awaking

 

[Zen Mod]

not with me , Bubba

 

[Tazzz]

My J2 clone is done and dusted

 

[bobodioulasso]

I still need to buy some Sic Jfets first.
Nah, to many amps there.
Need to sell some.

 

[nicoch58]

bobodioulasso you can gift one to me

 

[bobodioulasso]

Do you want speakers also?