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bjt jfet CFP diff input stage
bjt jfet CFP diff input stage
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Old 16th December 2012, 11:13 AM   #11
Lazy Cat is offline Lazy Cat  Slovenia
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Originally Posted by robydream View Post
Any schematic more?
This triple is only a building block replacing single BJT to get better performance. Schematics suitable are any one would like to use, it's up to your imagination.
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Old 17th December 2012, 09:10 PM   #12
robydream is offline robydream  Croatia
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What about this amp?

Input stage is what i need just need to add jfet..so what you guys think about this?

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Old 27th June 2014, 08:05 AM   #13
UltimateX86 is offline UltimateX86  France
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It is possible to use this config for output stage ?

CFP + mosfet cascode

Last edited by UltimateX86; 27th June 2014 at 08:09 AM.
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Old 26th July 2014, 05:08 PM   #14
Bigun is offline Bigun  Canada
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bjt jfet CFP diff input stage
I don't see why not.
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 27th July 2014, 04:29 AM   #15
Calvin is offline Calvin  Germany
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refferring to the schem of #1, the JFETs require to be high Vgs types which the SK170/SJ74 are certainly not.
The BFs may be useable, but I'd prefer the 4391 due to their higher Vds.
Apart from the BFs and the 439x probabely all other suitable parts are long obsolete.
While a depletion mode device is a elegant way to create the CFPs supply it should be noted that there will be no real complementars to the N-JFETs.
You may be able to find devices for a differential SE input, but not for a complementary symmetrical input.
Also the Drain-Source voltage may be too restricted for a high power amplifier (>50W).
It could well be that the JFET itself needs to be cascoded too.
Further on keep Gate leakage in mind.
From app Vds/4 on and high current and high temperature conditions Gate leakage 'explodes' and could lead to a fatal Latch-up of the device.
The DS values for Gate leakage are given for absolutely non-realistic conditions.

For the CFP BJTs standard BC5xx or BC3xx (and their SMD equivalents BC8xx) are very suitable, easy to source and lowcost.

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