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Old 28th December 2009, 04:08 PM   #11
mos57 is offline mos57  Italy
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My point of view is quite different: in SE circuit we can better evaluate the intrinsic component's character. In PP there are partially cancellations for some aspects or superimposition for others.

Is SE is easy to view with a scope the lower distortion of IRF 530 against IRF540 or 240: so why we not choice always the 530 i.e or better L-Mos or V-fet?
Because, on the other hand, for musical pleasure is not only important distortion but also other things as low output impedance for example, and in this way IRF540/240 are better than 530.
Whith its higher trasconductance/lower output impedance IRF540/240 are capable of better bass quality with better damping factor (read faster bass) than IRF530. Then, if not need high power it isn't need excessive voltage swing, the bigger IRF240/540 can become the first choice for the following: the difference in distortion becomes also little meanwhile the bass response remain much better than 530.
So the advantage of use IRF540/240 is to have bass much impressive and controlled and a sound more warm (ZEN amp).

But what about the high ends and details? Pheraps the little devices are better? SURE.

But more bigger devices are better always? No.
When devices is capable to manage very high current, then it become linear at very high quiescent current, value impossible in the field of linear amplification (10-20A). In the same time the parasitic capacitors (especially the input cap) becomes very relevant and tend to close the bandwith without high freq. tones.

So at the end not exist one components better for all.
I tend to have a compromise for these opposite necessity: from my experience in audio world, i prefer unipolar devices with Id from 7 to 15 A and low/medium Gm, low Rout.

Francesco.
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Old 28th November 2016, 09:20 AM   #12
bluevas is offline bluevas  Indonesia
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dear Fransesco,
I like this schematic for I have two pieces of 2SJ18 only...but I dont have 2SK79...do you have any idea if I can use other type for 2SK79 or maybe there are a
different schematic for me.
thank you
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Old 28th November 2016, 12:01 PM   #13
plasnu is offline plasnu  United States
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Have you measured the distortion? In spice model of L'amp, 2SJ28 produces more 2nd harmonics (more air?) at lower current around 20V, but I don't know if it reflects the reality...

Last edited by plasnu; 28th November 2016 at 12:05 PM.
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Old 28th November 2016, 12:52 PM   #14
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Darn if the 3a5 tube wouldn't just about drop in place of that hard to find 2sk79 about all you would need is an extra supply for the heater. And all it needs for a heater supply is 2.8v @ .11 v or 1.4V at .22v .
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Old 29th November 2016, 12:05 AM   #15
mos57 is offline mos57  Italy
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Quote:
Originally Posted by bluevas View Post
dear Fransesco,
I like this schematic for I have two pieces of 2SJ18 only...but I dont have 2SK79...do you have any idea if I can use other type for 2SK79 or maybe there are a
different schematic for me.
thank you
Hi, try to use 2SK373 OR LND150.

I recommend to see also the ultimate V-fet schematics on my website:
The last four are very low distortion design:

http://http://www.amplimos.it/e_v_fet.htm

Have a nice day
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Old 29th November 2016, 10:40 PM   #16
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I have built the L'amp with 2SJ28s and it sounds great. They are running at 1.7 amps per side. My favourite amplifier from my collection for sure.
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Old 30th November 2016, 07:13 PM   #17
mos57 is offline mos57  Italy
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Quote:
Originally Posted by plasnu View Post
Have you measured the distortion? In spice model of L'amp, 2SJ28 produces more 2nd harmonics (more air?) at lower current around 20V, but I don't know if it reflects the reality...
I have divided the original Sony 2SK82 / 2SJ28 datasheet and I rotated one of 2SJ28 for easier comparison that is posted in the attached images.
In the past, using the Locky curve tracer , I made the reliefs of the curves for both the 2sk82 and for 2sj28, that you can see in pdf.
Unfortunately, due to low voltage and current value permission from this curve tracer, it is not well adapted to assess completely power devices such as the V-FET in question.
However indicatively, in such fields of values ​​one can infer that the 2SK82 family curves are in a sense in the form of a tulip, while those of the 2SJ28 are more fan-shaped: it is' likely that for low supply voltages, the latter generate more second harmonic distortion, but this is not true at all, and changing the operating point results can be opposed.
In any case, when I designed this circuit, I wanted to make a complete amplifier, so I asked myself the question if were better to use a power stage with 2sk82 or with 2sj28.
I estimated that using the latter, became more simple and natural interfacing that power stage with the input stage using N channel devices.
This would allow you to use the only signal Vfet that was still available commercially, the 2SK79 (also 2SK63) and to be able to assemble a whole amplifier with all V-FET gain devices.
Also with the same logic you could be used alternatively in the preamp stage tubes and nuvistor (they are also N-channel). To me it seemed a huge advantage, not to you?
Those who only plans a final state does not care about this, and L'amp is just a final stage, but this one is a complete amplifier (integrated).

Best regards.
Attached Images
File Type: jpg 2SK82-Graph.jpg (17.0 KB, 220 views)
File Type: jpg 2SJ28-Graph.jpg (17.6 KB, 217 views)
Attached Files
File Type: pdf 2SK82_CURVE.pdf (39.6 KB, 13 views)
File Type: pdf 2SJ28_CURVE.pdf (37.0 KB, 12 views)
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Old 1st December 2016, 03:49 AM   #18
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I love your VFET amp.
I'll build it if find out 2SB647.

Tnx mos57!
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Old 1st December 2016, 03:24 PM   #19
mos57 is offline mos57  Italy
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Quote:
Originally Posted by jamahamvui1978 View Post
I love your VFET amp.
I'll build it if find out 2SB647.

Tnx mos57!
This transistor isn't so a critical part !!!! All high voltage/ around 1 W are good.

You can use 2SA1208, 2SB715/6.

But also 2SB649, 2SB631, 2SB1209, 2SA1358 and so on.
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Old 1st December 2016, 07:00 PM   #20
mos57 is offline mos57  Italy
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Quote:
Originally Posted by mos57 View Post
This transistor isn't so a critical part !!!! All high voltage/ around 1 W are good.

You can use 2SA1208, 2SB715/6.

But also 2SB649, 2SB631, 2SB1209, 2SA1358 and so on.
Edit: 2SA1209 not 2SB1209, sorry.
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