transistor bias question

Started by mac, January 02, 2012, 10:29:33 PM

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mac

Let's say I have two similar 2n3904, hfe: 250, both biased near 4.3v but the bias resistors are different:

bias 1
r1: 100k (Vcc to base)
r2: 47k (base to gnd)
rc: 10k
re: 4.7k

bias 2
r1: 420k
r2: 33k
rc: 10k
re: 0k

Suppose the in caps are big enough to let all freqs through, the out caps are equal, and the emiter of the first transistor is bypassed with a big cap of nearly zero ESR.

The question is, when push hard, do both transistor distort or behave the same?

mac



mac@mac-pc:~$ sudo apt-get install ECC83 EL84

PRR

#1
What is the source impedance? Input impedance is 18K for the transistor, 12K-13K altogether.

If source is under 1K the nonlinearity is mostly gM.

If source is over 30K the nonlinearity is mostly hFE.

Many guitar-chain sources are in this zone where it is some of both.

I think the breadboard is your best friend.

I'd also point out that version 2 will drift ALL over the place with temperature or transistor change. If you are hand-picking parts and playing at home, that may not matter.
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