FirstWatt J2

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#664
even if it's close to original ( and it isn't so close ) , I think that no one with enough insight in difference with Real McCay will give proper comment,
from one sole reason - it seems that Pa isn't so keen to reveal original schm , most probably because of cloners

I'm not saying that you need to abandon J2 , but you will not likely be given with answer - in public

J2 is one of few FW products without "just 100 pcs" tag

go figure
 
#666
Zen Mod said:
well - looking at first post schmtc , it isn't

xformer is phase splitting device here ........ so - type of outputs modulation is already chosen

of course that you can drive lower one as presented , with upper one connected in Mu fashion

design permutations are countless .......... as Papa said several times :rofl:
Click to expand...

I once made a transformer-coupled driver stage that consisted two N-FETS, the output having a capacitor coupling; and it worked wonder well. I used an opamp to drive the transformer (and had feedback across this phase splitter). With 60 volts Vb+ ; Vb is all at once irrelevant once you drive the FETs that way.
 
#668
Matching two 2SJ109

May be someone knows......

I always thought, using two 2SJ109 to drive the Semisouth like Nelson did, they had to be of the same Idss.

But what is about this idea of a friend and me.....

The two halfs within an 2 SJ109 are fairly close matched, I suppose for Idss and for xconductance...
Normally you would say I take one doubleJ-fet for the positive input and one for the negative input. So I have to care for a similar Idss of the two doubleJ-FETs .

But now let us use two not so close matched SJ109, one with 7,2mA and one with 8,5mA....
Is it possible to take one half of the left doubleJ-fet and one half of the right doubleJ-Fet (7,2 +8,5 = 15,7mA) for the positive input and one half of the left (again 7,2mA) and one half of the right (8,5mA) resulting again in 15,7mA for the negative input side?

Of course there will be a small difference of the sums because the FETs are internally not completely matched.

This way of matching would offer me the possibility to use the different SJ109 I have......!

And if some one uses J74 he had to care only for two very good matched pairs and no more for a quadruple!

Is it possible or is something wrong in our reflections?😀😀
 
#669
Seems ok although i dont know if the jfets not being equal would caus eissues with sharing current. In theory, it should be like unequal resistors proportionately sharing current based on their resistance, but i donr know what it would do to their performance. Have you tried a pot across ouput Rs to play with harmonic distribution? Part od me wonders if the jfet trick you are speaking of would yield similar results, imfluencin gthe harmonic nature an dlevel of distortion.
 
#670
buzzforb said:
Seems ok although i dont know if the jfets not being equal would caus eissues with sharing current. In theory, it should be like unequal resistors proportionately sharing current based on their resistance, but i donr know what it would do to their performance. Have you tried a pot across ouput Rs to play with harmonic distribution? Part od me wonders if the jfet trick you are speaking of would yield similar results, imfluencin gthe harmonic nature an dlevel of distortion.
Click to expand...

Thanks Buzz!

Interesting ideas...! 🙂
 
#677
generg said:
sometimes an offset of 300mV gives the tight mixture of k2 and k3 you only have to get the offset away again and to keep the distortion spectra....

hm, hm.....😀
Click to expand...

Very true. From my listening experience with my different J2 attempts and original J2,

the original J2 is extremely fine-tuned to just add the right proportion of 2nd harmonics without shading any details in mid and high frequencies.
Like in tube amp times, 'voicing' an amp by fine-tuning parts values is the art, that will lead the way to the original j2 sound.
 
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