[ BJT amplifier circuit, v_be negative ]

[texane]

Hi,

I am learning about BJT transistor and I understand them quite well know... I guessed
until I saw the following simple circuit:
http://www.reconnsworld.com/audio_simplepreamp.html

What I do not understand: passed the first AC coupling capacitor, the voltage can be
negative. Usually, the transistor is base voltage biased in such a way there is an offset
so that negative voltages are not an issue. But in this schema, there is no offset. I built
it, and it works: I get some Vbe < 0 and get a correct Vc with no clipping...

How is it possible, can someone explain to me what I am missing? I guess there is
something with a current involved from Vcc to C1 as the voltage accross C1 becomes
< 0, and that it acts as the Vbe offset I do not see... but not clear at all to me.

Thanks!

Best regards,

texane.

[Tube_Dude]

Hi

Take out of circuit C1, and check, if then, you have around 0,6 Volts VBE, if not, or you have a faulty transistor, faulty R3/R2, or wiring error... 

[texane]

Thanks for answering.

I think I found my mistake... I left the oscilloscpoe to AC coupling and obviously was seeing
'negative' voltages instead of the real one... for my defense, let say this is an old scope
Of course, having Vbe negative would have clipped the voltage on the other end.

Best regards,

Fabien.

[Tube_Dude]

Happy End!! 

[texane]

yes, but I spent a lot of time thinking that my understanding of BJT was wrong or incomplete...
still a lot to learn by the way

[Tube_Dude]

We all (almost all...  ), learn with our mistakes...