Building a discrete OPamp

[AudioAngel]

Hi,

I would like to build a discrete opamp. Therefore I read articles by Nelson Pass and Enno Borbely and a lot of threads here and articles found by google.
So the basics are there but there are still some points, where I'm not sure and these points I would like to discuss.
First point is the input stage. My plan is to use JFETS for the diff-pair (BF862). For the differenial balance a current mirror. For the current mirror and the constant current source I want to use BJTs (2N5551/2N5401). Now I'm not sure. I've choosen the BF862 for low-noise. But several people like D. Self and G. Slone state out in their books that BJTs are the better choice for the diff-pair but on the other hand most discrete design which are desired to be very good and you can find here are build with JFETs. So, what are the advantages/disadvantages of JFET/BJT input stages?

Raphael

[MaxS]

Hello,

C'est une guerre de clocher, rien de plus.

Like each humans, they have their own drawback ( not the same kind of noise ) and their advantages.

JFET are a resistor driven by gate voltage and BJT are a curent source command by base current.

About the noise, to my mind, BJT get voltage noise and JFET get current noise.

All semiconductors are sensitive to temperature so you have to cool them right or you will be able to discover now kind of problema.

I think you will find many informations in BJT vs FET thread here.


Cheers,

Max

[georgehifi]

Originally posted by AudioAngel
Hi,

I would like to build a discrete opamp. Therefore I read articles by Nelson Pass

Any day now read this! http://www.diyaudio.com/forums/showt...15#post1465015


Cheers George