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-   -   2SJ28 Vfet SE Amplifier (http://www.diyaudio.com/forums/pass-labs/154009-2sj28-vfet-se-amplifier.html)

mos57 27th October 2009 03:58 PM

2SJ28 Vfet SE Amplifier
 
1 Attachment(s)
In the past weeks, i have realized a simple single ended amplifier with the V-fet Sony 2SJ28 and 2SK79 bought on Ebay in the past time.
Because seems that Papa's love Vfet as me i will post a schematic for discussion on this forum.
But if i am wrong or Mr. Pass was :mad:, then i can post this thread on other list forum.

All suggestions are welcome.:D

Thanks Francesco

mos57 28th October 2009 09:25 PM

All electrolytic caps are Mallory except for the output cap.
This last is 2x3300 mF Silmic II by Elna.

All resistors, except the power resistor, are in composite carbon by Allen B. 1/2 W.

Transformer(s) are EI type.

Francesco.

Nelson Pass 29th October 2009 01:14 AM

So how does it sound?

:cool:

mos57 29th October 2009 02:04 PM

Quote:

Originally Posted by Nelson Pass (Post 1963922)
So how does it sound?

:cool:

Its sound is very musical overall, with medium and high are present and very sweet, good air .
The bass is a little bit long and no much impressive, but however good.
The music go away without fatigue: its is a pleasure to heard.
My best amp in this sense.

But............
i would build it to bring the sound on my actual reference amp....
but the reference have still a little bit more air (in other aspect mine is almost equal or little better).

But this reference amp is my "great enigma" in my past year.

Nelson, you have been my teacher from young age, i highly regard for your script and you patent in audio, i consider you the best prolific and innovator man in audio circuit, so if i tell you what are this ref. amp now, then you just can consider me an heretical.
Because of all over, i am going to thinking that you are the only man that you can help me, also for you innate curiosity.

If one search for the " holy grail", it's a step to bring it, i think.
So need your help to discover the secret in this ref. amp.

Excuse me for my poor english, Francesco.

housing 25th December 2009 04:22 PM

Hi Francesco,

What's the quiescent current designed for the 2SJ28? What value is the trimmer at the source of the 2SK79?

Thanks.

tiefbassuebertr 26th December 2009 09:26 PM

Quote:

Originally Posted by Nelson Pass (Post 1963922)
So how does it sound? :cool:

Yes, this I would also like to know. Even the sound compared to a IRF9640 (IRFP9240) instead of the 2SJ28 would be very interesting.

mos57 27th December 2009 04:31 PM

Quote:

Originally Posted by housing (Post 2024314)
Hi Francesco,

What's the quiescent current designed for the 2SJ28? What value is the trimmer at the source of the 2SK79?

Thanks.

For full power the current must be 2 A about.

The trimmer value is 5K.

Francesco

mos57 28th December 2009 06:52 AM

Quote:

Originally Posted by mos57 (Post 2025876)
For full power the current must be 2 A about.

The trimmer value is 5K.

Francesco

But for best result, the Iq must be 2,5 A. (I am going to forgotten it) :smash:

mos57 28th December 2009 07:12 AM

Quote:

Originally Posted by tiefbassuebertr (Post 2025223)
Yes, this I would also like to know. Even the sound compared to a IRF9640 (IRFP9240) instead of the 2SJ28 would be very interesting.

Hi, at this moment i not have *9240 (i not like its much). If you are agree, i will try the more linear IRF9530 (dissipation problem permitting) or 2SJ50/2SJ56 that are most interesting for me. :p

Francesco.

tiefbassuebertr 28th December 2009 09:32 AM

Quote:

Originally Posted by mos57 (Post 2026514)
Hi, at this moment i not have *9240 (i not like its much). If you are agree, i will try the more linear IRF9530 (dissipation problem permitting) or 2SJ50/2SJ56 that are most interesting for me. :p

Francesco.

The great advantage of this circuit it is to check a wide range of power MOS-FETs and power jFETs like 2SJ28.

Because it is a single ended topology, you will not observe very large sonic differences between IRF9530 and IRF9540 (same than IRFP9140 but higher thermal resistance). Also the P-CH types BUZ905/906 and 2SJ49/50, special made for audio power stages, are unlikely to be better in this topology (in opposite to a push pull output stage).
Master Nelson Pass and his "Aleph" series represents the best evidence, where used IRF MOSFETs no special made for audio.

But I will wait to your own sonic impressions by compare.
But fact is, by this single ended topology large values of the quiescent current is a guarantee for very high sonic transmission quality. Choice your heatsink sizes so, that the temperature of your power FET itself not higher is than 25 degrees above ambient (long life condition).


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