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Old 25th November 2003, 07:51 PM   #1
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Default Ultra low noise dual jfet

Djeez, this dual jfet has 0.3 nV/sqrt(Hz) at 100 Hz. Great for a MC amp isn’t it:

http://www.interfet.com/pdf/DS_IF3602.pdf at

http://www.interfet.com/

Only problem is minimum order is $500

Cheers
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Old 6th December 2003, 10:46 AM   #2
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...and it has a gm of 750 !!! This would be really worth a try!?
input capacitance is not low. Doesn't it count?
Someone found a source for purchasing say 20 items or so?
Rüdiger
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Old 6th December 2003, 12:07 PM   #3
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GM=750mS=0.75

Other potential problem is low power dissipation of 300mW for entire device.

Petter
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Old 6th December 2003, 12:14 PM   #4
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Quote:
Originally posted by Petter
Other potential problem is low power dissipation of 300mW for entire device.

Petter
Do you usually need more for typical low-noise applications
like MC input stages? Seems quite sufficient IMHO.
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Old 6th December 2003, 12:24 PM   #5
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Quote:
GM=750mS=0.75
Sorry, this definitly can't be true. You'll end up with a damper instead with an amplifier...
Rüdiger
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Old 6th December 2003, 01:45 PM   #6
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Hi,

A Gm of 750 mS looks a bit high indeed. Here is a bit more about the chip:

http://www.interfet.com/pdf/P_NJ3600L.pdf

No need to e-mail Interfet, they simply will give you not more info than what is on the WEB-site.

Note that this is simply a very large area jfet-chip that acts like many smaller jfet-chips in parallel. The large input capacitance is not an issue IMHO regarding the 50-100 ohms resistance involved with MC amps.

I got this hint from an old colleague at the University of Delft. For that 500 bucks you get app 25 fets. It is excluding VAT and duties. Interfet does not keep them them in stock, they produce on order. He measured a real 0.7 nV/sqrt(Hz) at 10 Hz and room temperature. He has still a lot in his drawer but refuses to sell me a pair

At the moment I use the 2SK389’s but these become rare and expensive nowadays. Also these are not well tailored to low source resistances regarding noise.

Cheers
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Old 6th December 2003, 01:54 PM   #7
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Quote:
For that 500 bucks you get app 25 fets
At that price it is a theoretical discussion at all...
There seem to be just a few fets suitable for audio (that are obtainable), if one searches the archives here.
Rüdiger
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Old 6th December 2003, 02:10 PM   #8
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Quote:
At that price it is a theoretical discussion at all...
Dunno, but if cost is no objective... It is the lowest noise dual jfet I came across, especially with low source impedances and at low frequencies.

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