Semisouth SiC JFETs: SJEP120R100 or SJEP170R550 better for building amp? - Page 2 - diyAudio
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Old 10th February 2010, 06:36 PM   #11
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I'm still waiting for the P-ch power JFET!
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Old 2nd March 2010, 04:01 PM   #12
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Default In simple noob terms

Hi,

As a noob who will be mostly following instructions and parts reccommendations on others, can someone speak in non-technical terms to whether there are instances in which the R550 might be prefereable to the other SemiSouth chips? My speakers are ~97dB efficient, so I need minimal power.
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Old 2nd March 2010, 10:16 PM   #13
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It will probably work fine. I haven't received any samples of
that yet, but I expect somewhat higher thd numbers, but lower
input capacitance, so it will be more forgiving of the impedance
of the source driving it.

Of course the real excitement is the 1700 V breakdown figure,
which would allow you to stick it where many tubes will not go.

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Old 5th March 2010, 02:11 PM   #14
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Nelson,

Can you share with us, why do you think the THD number will be higher?
Is it because it has lower transconductance, and thus higher distortion on a chip to chip basis?
If the above is right, any insights on how well it works, given equal transconductance by paralleling.
I'm also thinking, whether R550 will be good for replacing the IRF610 in D1 DAC's I/V stage.

Zhou Fang
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Old 5th March 2010, 05:59 PM   #15
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All other things equal, chips with low transconductance will
have greater thd, the reason being that the nonlinearity of
Vgs vs Id will be greater.

That said, the best way to find out what you will get with a
real application is to actually try it. I don't have any of this
part, and so I have not tried it.

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Old 5th March 2010, 06:41 PM   #16
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Quote:
Originally Posted by Nelson Pass View Post
It will probably work fine.
Did you check the SJEP120R100 maybe? I've compared all specs and does NOT seem a perfect drop-in of the R125.
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Old 5th March 2010, 07:35 PM   #17
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I can only report that in the J2, the performance between
the 100 and 125 is identical.

Placed in other applications, it may be a bit different. Since
the 125 is no longer made, it's a moot point.

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Old 6th March 2010, 01:08 PM   #18
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Quote:
Originally Posted by Nelson Pass View Post
All other things equal, chips with low transconductance will
have greater thd, the reason being that the nonlinearity of
Vgs vs Id will be greater.

That said, the best way to find out what you will get with a
real application is to actually try it. I don't have any of this
part, and so I have not tried it.

Thanks for the answer!
I get it, so it is just the lower transconductance that caused your expectation of higher THD.

It is sad that R125 is no longer available.
My fear is that (as others has pointed out), when they can mass-produce SiC MOSFET, will there still be any SiC power JFET available for us?
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Old 6th March 2010, 03:08 PM   #19
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I'm not concerned - as I said, there is not a substantial
difference in practice.

Of course you can probably get SemiSouth to make the old
parts for a 6 figure check.

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Old 14th April 2010, 05:22 PM   #20
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Here is the SS-R100 capacitances graph attachment.
I have this graph in the pdf expanded and enchanced it with the additional
10V grid lines (by dividing 300V in 30 equal segments).
It has also thickened the curves, but it's not a problem.
Zero V vertical line was assigned to the left edge of the thick line.
Attached Images
File Type: jpg SS-R100 capacitances.JPG (71.0 KB, 749 views)
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