Help me work this out (electronics theory)

[disto]

ok im trying to get my head round theory of pedals... heres what i think is a nice basic easy circuit!!!

link  to image - http://distouk.tripod.com/bassfuzz.html

(ps first cap is a .22uf second is a .1uf)

whats happeneing in it though?

i guess the transistor is boosting the signal which is then linked to go from the collector back to the base (i guest this distorts the sound) the diode stopping any current from skipping the trans!! i know changing a resistance bellow the transistor (from the emitter to grnd)would reduce the distortion so what does this mean???

can anyone help me give me hints to work out why and how this unit works???!!!

[niftydog]

Wo nelly. Hang about.

What you have there is a common emitter amplifier. I suggest you read up a bit on the fundamentals of what they do first. Take note of the basics of class A amps, positive and negative feedback and look for the diagram of a common emitter amp and note the similarity to the diagram you've linked to.

Now, I would also suggest you try to understand diode operation a little better, as you seem to be basing your assumptions on an incomplete understanding. Concentrate on simple PN junctions and standard semiconductor diodes. For now, ignore zener diodes and all the other fancy stuff.

whats happeneing in it though?

put simply, it's an amplifier.

i guess the transistor is boosting the signal

It has some gain, but not all amplifiers have gain. Note carefully that a common emitter inverts the input signal. That is to say, the output is 180 degrees out of phase with the input.

This is important when you consider the diode in what we call the feedback path. Very basically, a diode only conducts in one direction. So, in this case, the positve peaks of the inverted output signal are being fed back (see "feedback" in that first link) into the base terminal.

But diodes only conduct when the diode is forward biased - usally this means the anode (arrow connected to collector) has to be around 0.7V higher than the cathode (bar connected to base). The next thing to consider is the biasing on the amplifier, but perhaps it's best to let this stuff soak in before we get into that. Read up on those class A amps and see how you go by yourself.

So yes, the diode causing the distortion, but it does not function to "steer" the current through the transistor as you've suggested.

changing a resistance bellow the transistor (from the emitter to ground)would reduce the distortion so what does this mean???

The emitter resistor (not present in that diagram) is largely responsible for setting the gain of the amplifier. Hence, making the emitter resistance something other than a short circuit will reduce the gain.