What To Do With Those 2SJ28's

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The last generation of Sony amplifiers used SITs to cascode bipolar devices.

Funny guys , was age of engineers crazy experiments.
Mr. Pass never stops

I don't see many designs for small SIT's Sony 2SK79 , they matched pairs are available

http://www.diyaudio.com/forums/vend...-rare-toshiba-transistors-18.html#post5053635

With two 2SK79 matched pair can we build useful front-end for stereo 2SJ28 DEF power amp stage ?

http://www.amplimos.it/images/2SK79_data.pdf
 

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So, I gather there are a number of orphaned Sony 2SJ28's out there,
so let's use this thread as a scratch pad for ideas to put them to use. :)

Other concept is SET equivalent like in tube world.
Something to amplify antique radio oh just joke !
Anyway create from the orpfans one family.
 

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with my very cheap and little speakers (20 euro 30Watt open baffle fullrange without crossover) in my studio the ACA-amp almost beats the Vfet (wich hasn´t seen real speakers due to lack of transportable case). It quite like changes with bigger speakers, but i guess it must have to do with SE magic. So I vote for little SE-kitchen-amp :)
 
with my very cheap and little speakers (20 euro 30Watt open baffle fullrange without crossover) in my studio the ACA-amp almost beats the Vfet (wich hasn´t seen real speakers due to lack of transportable case). It quite like changes with bigger speakers, but i guess it must have to do with SE magic. So I vote for little SE-kitchen-amp :)

Mating an amp with speakers is the key. The little ACA with a linear supply is almost as good as the BA-1 I just finished. Almost. The V-fet is an extremely good amp with the right speakers but with my horns I lean towards a SE . A good friend with big horns loves the V-fet better. Personal preference comes into play along with the choice of music. I love SE with my horns. The exception would be my F4. Rules are made to be broken. So many more options with efficient speakers. Even a 5 watt amplifier is more than a enough.
 
SLAPS-2sk28.jpg

4 parts and a power supply constitutes a feed forward error correcting (SUSY-ish) power amp with very low levels of distortion. 2 X voltage gain.
It has a very good damping factor, due to the feed forward EC and the NFB.

If the 2SJ28 needs a gate resistor then the amp needs 5 components per channel plus a power supply.

L1 and L2 are two windings (bifilar) on an aircored choke. Since they are very close magnetically coupled together they will force the two outputs to closely follow each other in anti-phase (hence the SUSY-"ish" feed forward error correction).

Cheers
Johannes
 
FFT-SLAPS-IRFP9240.jpg

I simulated this amp with an IRFP9240.
11.2 volts P-P output with 0.10% THD into a resistive 8 ohm load.
A nice balance of the harmonic content in the FFT graph.

All this is a simplified simulation, and should only be taken as a crude approximation of a real amp driving a real load.

Cheers,
Johannes
 
Pass DIY Apprentice
Joined 2001
Paid Member
We could approximate one by flipping a couple of the polarities in the behavioral model like so. Close enough for government work. Don't try to land a probe on Europa with it. :)

As presented, it's simply a mirror of the 2SK82, feel free to adjust to taste.

*--------------------------------------------------
*2SJ28
*GENERATED BY SIT MODELER @ AUDIOMAKER.TECH
*MODEL RANGE: -55V, -5A
*--------------------------------------------------
.SUBCKT 2SJ28 D G S ; Drain Gate Source
+ PARAMS: MU=7.3 X=1.51 K=0.157 N=2.24 VCT=0 RG=2MEG
*--------------------------------------------------
B1 D S I=-1*(K*PWR(URAMP((-V(G,S)+VCT)+(N*LN(-V(D,S))+(-V(D,S)/MU))),X))
*FOR LTSPICE
R1 G S {RG}
CGS G S 0P
CGD G D 0P
CDS G S 0P
.ENDS 2SJ28
*--------------------------------------------------

Plug in you favorite interelectrode capacitances if you're going to fool with bandwidth stuff.
 
Adapt elements from John Broskie Aikido mojo logic but for 2SJ28 stage with circuit who self-cancel his noise ?
 

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