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Old 30th September 2015, 04:58 PM   #1
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Default Jfet input stage better in sound quality compared to a BJT input?

thinking to start working on Jfet input amplifier but is it worth enough to use jfets at input stage?
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Old 30th September 2015, 05:01 PM   #2
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There are probably hundreds of threads here in the forum about this, searching around will give you many different opinions and proven designs to back up those opinions.
There is no better, there is different flavours.
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Old 30th September 2015, 05:06 PM   #3
RJM1 is offline RJM1  United States
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Only if it is being driven by a high impedance source.It might be useful if you are using a tube preamp but not with anything that can drive a 1K load.
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Old 30th September 2015, 05:08 PM   #4
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Ask yourself what exactly you want to do, what your design specifications are, then design to that. FET input might be better, we don't know.

Where is Bruno when you need him? Penultimate slide: http://www.hypex.nl/docs/papers/AES123BP.pdf
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Old 30th September 2015, 05:32 PM   #5
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John Curl, Nelson Pass, Charles Hansen, and Constellation Audio design with and bought up all the Toshiba jfets - guess why
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Old 1st October 2015, 05:31 AM   #6
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How to increase the voltage operation of this circuit to +/-100V?
http://m.eet.com/media/1196048/F11large.jpg
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Old 1st October 2015, 06:20 AM   #7
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Quote:
Originally Posted by rhythmsandy View Post
How to increase the voltage operation of this circuit to +/-100V?
http://m.eet.com/media/1196048/F11large.jpg
Add a cascode between the Jfets and mirror.

Using the jfets in a blameless .... your would have the "voice" of the
current sourced VAS.

There are better circuits to take advantage of a jfet LTP. Older
sansui 3 stage designs or a cascoded "symasym" would be the
ticket.

I've built and heard both BJT/FET IPS's , less gain with FET's. No
real SQ differences. The VAS and output stage are bigger factors.

The other guru's buy up the fet's to perpetuate another urban legend.

Edit - (below) is a far more advanced version of what most 1970-80
Japanese JFET LTP audio amps were. Works flawlessly with just
about any Jfet.

OS
Attached Images
File Type: gif old sansui.gif (42.2 KB, 601 views)
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Last edited by ostripper; 1st October 2015 at 06:32 AM.
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Old 1st October 2015, 06:34 AM   #8
kamis is offline kamis  Serbia
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Quote:
Originally Posted by ticknpop View Post
John Curl, Nelson Pass, Charles Hansen, and Constellation Audio design with and bought up all the Toshiba jfets - guess why
They made a huge stock of Toshiba j-fets, created a good audio story, and are selling them slowly more expensive than diamonds. They say that LS j-fets are not good enough compared to Toshiba.
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Old 1st October 2015, 07:01 AM   #9
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I think these days the secret is to stock good parts..
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Old 1st October 2015, 09:00 AM   #10
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Quote:
Originally Posted by ostripper View Post
Add a cascode between the Jfets and mirror.

Using the jfets in a blameless .... your would have the "voice" of the
current sourced VAS.

There are better circuits to take advantage of a jfet LTP. Older
sansui 3 stage designs or a cascoded "symasym" would be the
ticket.

I've built and heard both BJT/FET IPS's , less gain with FET's. No
real SQ differences. The VAS and output stage are bigger factors.

The other guru's buy up the fet's to perpetuate another urban legend.

Edit - (below) is a far more advanced version of what most 1970-80
Japanese JFET LTP audio amps were. Works flawlessly with just
about any Jfet.

OS
BJT or Jfet cascode?

1. Any other better transistor than 2N5401? as ON semi and Fairchild have stopped them so how about using KSA1381? the cob is impressive but im sure any other transistor with lower cob?
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