source follower, emitter follower ? 4 questions

[keko]

Whats the difference between theese two?

I was looking to the Japanese Electronics 'book'  and notice those two fx.

So far I figured that each use a different tranny:..yeah, big deal  

source follower uses a J-FET (Source, Gate, Drain) 2SK30 = J201
emitter follower uses a Low frew, low noice amp (Emitter, Base, Collector)  

Low frequency low noise amplifier. Collector-base voltage Vcbo = 50V. Collector-emitter voltage Vceo = 45V. Emitter-base voltage Vebo = 5V. Collector dissipation Pc(max) = 250mW. Collector current Ic = 50mA.

paid datasheet here

is this just the only difference?

I suspect an emitter follower is like an envelope follower? i.e. depending on the strength of the signal into the base is the amout of signal that goes out from the emitter. In that case, the three outputs are just for driving several external effects?

If that's so, what can I expect from the source follower?

These looks like simple and fun build to tinker and learn with.

[R.G.]

A source follower and an emitter follower both do similar things. There is a gain of negligibly less than unity from the input to the output. The input has a high impedance, so it does not load down whatever circuit is driving it. The output has a low impedance so it can drive other circuits hard enough to avoid them loading it down.

The emitter follower is not some kind of envelope follower. It's a signal follower, just like the source follower. Both are a kind of unity gain buffer.

[keko]

So Q1 in the Tube screamer would be something like a emitter follower? (according to your FAQ if I'm not mistaken)...I guess I'll go read it again...


Is the only job of those followers to provide a low output impedance to subsequent effects in the chain?

Thank you very much R.G.


ahh...I read the FAQ again before posting, but decided to post anyway. It IS and emitter follower. R.G., be proud of yourself, you tought me something...again.

[R.G.]

A journey of a thousand miles begins with one emitter follower... 8-)

You got it! The purpose of emitter, source, and cathode (tube!) followers is to give a high impedance load to some signal, then spit it out at low impedance to drive something else.

You just lost all hope of getting yourself out of this electronics stuff - once you begin to understand it, you're addicted... 8-)