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how about using J111 J175 Jfets in F5
how about using J111 J175 Jfets in F5
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Old 3rd January 2018, 10:53 AM   #61
globalplayer is offline globalplayer  Germany
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Originally Posted by AndrewT View Post
There are many Members who won't listen to the advice they don't like.
But worse, there are Members who won't read advice!
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Old 3rd January 2018, 11:00 AM   #62
sottomano is offline sottomano
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Originally Posted by sottomano View Post
[...]I'd go with MMBF5459 and 5462, [...]


Oh, and if you find they have not enough transconductance, take the lower IDSS ones (5457/5460) and parallel them. They have so much less capacity than the SK170/SJ74 ones, this certainly is no issue.
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Old 4th January 2018, 02:46 AM   #63
rhythmsandy is offline rhythmsandy
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basically i want to try parallel them and try at the input. Im planning for 4 for each type to parallel. I need to buy those and match which requires in 100 units for Lsk170 but with other cheaper alternative its worth the try.
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Old 4th January 2018, 02:51 AM   #64
rhythmsandy is offline rhythmsandy
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Originally Posted by sottomano View Post
Oh, and if you find they have not enough transconductance, take the lower IDSS ones (5457/5460) and parallel them. They have so much less capacity than the SK170/SJ74 ones, this certainly is no issue.
Aren`t they noisy? 115nV/SqHz
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Old 4th January 2018, 03:25 AM   #65
rhythmsandy is offline rhythmsandy
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Originally Posted by EUVL View Post
In the F5 Heamamp thread, you can find how the basic F5 topology can be adapted to use different frontend devices,
including BJTs, 2SK246/2SJ03, and 2N5457/2N5460 :

F5 Headamp ?

Posts #1,2,5,7,25

It is of course possible to do the same for the power amp.
But it will just not have the same performance.


Patrick
Yes just simulated in ltspice the distortion is relatively higher in these. So what is the substitute now?
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Old 4th January 2018, 05:06 AM   #66
EUVL is offline EUVL  Europe
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What is your definition of substitute ?
Same performance, no extra cost ?
Yes sure, it is called unobtainium.

This has all been discussed umteen times years ago.
F5 with BJT at input
Just pick your choice.


Cheers,
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Old 11th March 2018, 06:40 PM   #67
Mark Johnson is offline Mark Johnson  United States
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how about using J111 J175 Jfets in F5
A bit of measured data. The J113 has a lower transconductance "gm" (the slope of the curve).

~
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Old 11th March 2018, 06:45 PM   #68
rhythmsandy is offline rhythmsandy
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Originally Posted by Mark Johnson View Post
A bit of measured data. The J113 has a lower transconductance "gm" (the slope of the curve).

~
Isn`t the curve seems better? how about J175 or J176?
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Old 12th March 2018, 07:40 PM   #69
Nelson Pass is offline Nelson Pass  United States
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how about using J111 J175 Jfets in F5
If you are interested in complementary pairs for followers or as CFA
input stages, my preferred parts are the 2SK170, 2SJ74 (or the Linear
Systems equivalents). but the J113 and J176 are good enough for most
of these circuits.

For 10 mA of bias, you would put some resistance between the sources,
typically something in the 22 + 22 ohm range, taking the output off the
center (or maybe use a 50 ohm pot)

The output impedance without degeneration is about 40 ohms, for a
combined gm of about 25 mA/v, about half that of the Toshiba/LS
parts. For the F5 they result in about 6 dB less open loop gain, not
a problem.

The random noise floor for a pair of these is about 1.4 nV (per square
root Hz), compared to about 0.5 nV for the Toshiba parts, which is nearly
a 10 dB difference. A problem when your signal is 10 uV - not so much
when it's 1 volt.

Distortion driving a 10K load at 1V is about 0.015% thd, mostly 2nd
harmonic due to gain mismatch, which can be nulled out or ignored.

In short, these are workable parts.
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Old 12th March 2018, 10:41 PM   #70
sottomano is offline sottomano
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Thank you Nelson, this is really a helpful answer and in a stark contrast to those a bit less helpful ones.... Thankfully it came from you as the most respected authority here
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