transistor biasing

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sorry Eva,

It's a little more complicated than that. Let's look at those excellent for MC transistors produced by Rohm - the 2SB737 and 2SD786 - we loved them , made heaps of MC front ends out of them , always biassed at 2+mA! for low noise with low source impedances! Then there's the electret condenser microphone preamp having to deal with sources of Mohms not tens of Ohms. Very different.


Horses for courses.

Greg
 
To do you an idea of the distribution of the noise in the bjts...
 

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amplifierguru said:


It's a little more complicated than that. Let's look at those excellent for MC transistors produced by Rohm - the 2SB737 and 2SD786 - we loved them , made heaps of MC front ends out of them , always biassed at 2+mA! for low noise with low source impedances! Then there's the electret condenser microphone preamp having to deal with sources of Mohms not tens of Ohms. Very different.


Greg


hienrich said:
before anything else
it is also customary to know which topology are you refering
for.....

because talking about noises it varies with amplifier topologies used...

for better noise rejections used the MIRROR IMAGE topology.


rgrds,

macweb

can you give some sample schematics of your preferred circuit topology for an mc stage?

thanks for helping guys.
 
the circuit from zetex is usually called discrete opamp. I've made that and currently used as mc frontend with addition of current sources. but i'm still not contented with the performance, it still has noise, about -50db i think with a 30db gain. it might be because my mc fontend has still no case.

the mc frontend circuit from armstrong looks quite like an mc headamp. i haven't tried that.
 
jondavis said:
the circuit from zetex is usually called discrete opamp. I've made that and currently used as mc frontend with addition of current sources. but i'm still not contented with the performance, it still has noise, about -50db i think with a 30db gain. it might be because my mc fontend has still no case.

the mc frontend circuit from armstrong looks quite like an mc headamp. i haven't tried that.

Any schematics for your circuit?
 
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