2SJ28 Vfet SE Amplifier - diyAudio
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Old 27th October 2009, 03:58 PM   #1
mos57 is offline mos57  Italy
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Default 2SJ28 Vfet SE Amplifier

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 , then i can post this thread on other list forum.

All suggestions are welcome.

Thanks Francesco
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Old 28th October 2009, 09:25 PM   #2
mos57 is offline mos57  Italy
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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.

Last edited by mos57; 28th October 2009 at 09:53 PM.
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Old 29th October 2009, 01:14 AM   #3
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So how does it sound?

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Old 29th October 2009, 02:04 PM   #4
mos57 is offline mos57  Italy
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Quote:
Originally Posted by Nelson Pass View Post
So how does it sound?

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.
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Old 25th December 2009, 04:22 PM   #5
housing is offline housing  Hong Kong
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Hi Francesco,

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

Thanks.
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Old 26th December 2009, 09:26 PM   #6
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Quote:
Originally Posted by Nelson Pass View Post
So how does it sound?
Yes, this I would also like to know. Even the sound compared to a IRF9640 (IRFP9240) instead of the 2SJ28 would be very interesting.
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Old 27th December 2009, 04:31 PM   #7
mos57 is offline mos57  Italy
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Quote:
Originally Posted by housing View Post
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

Last edited by mos57; 27th December 2009 at 04:35 PM.
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Old 28th December 2009, 06:52 AM   #8
mos57 is offline mos57  Italy
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Quote:
Originally Posted by mos57 View Post
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)

Last edited by mos57; 28th December 2009 at 07:15 AM.
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Old 28th December 2009, 07:12 AM   #9
mos57 is offline mos57  Italy
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Quote:
Originally Posted by tiefbassuebertr View Post
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.

Francesco.
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Old 28th December 2009, 09:32 AM   #10
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Quote:
Originally Posted by mos57 View Post
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.

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).

Last edited by tiefbassuebertr; 28th December 2009 at 09:35 AM.
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