From: zachary vex Date: 3/13/2001 8:37 AM Subject: Re: Can someone shed a little more light on impedance here's the basic idea. you get on a bicycle, and try to bike up a hill. you are completely frustrated... the pedals will hardly turn and you can't get enough speed to get any balance. what's wrong? well in this case, you are the source (driving the bike) and the bike's input impedance is controlled by the gears... and it's set to such a high gear that it's input impedance is too low for you to drive it. your output impedance has to do with the muscles and tendons in your legs... if they were tougher, meaning lower impedance output, it would match the bike. how do you fix it? raise the input impedance of the bike by lowering the gear ratio. suddenly, you can go, balance, and are happily climbing the hill. every source (guitar, signal generator, preamp's output, output of a pedal) has a limit to how much resistance it can drive without buckling under the stress... the input impedance of whatever it is driving has to be equal or higher to the source's output impedance (in fact, most people set it around 10 times higher for good measure) or else you'll hear degradation of the signal. low impedances require a lot of drive current. thick muscles and heavy bones are required. high impedances can be driven by skinny legs. low impedance inputs are like tenth gear, high input impedances are like first. impedance is almost the same as resistance, and in many cases measures almost exactly the same as the apparent input resistance... but the word impedance lets us include the possibility that the resistance changes with frequency (pitch) so that capacitances and inductances can be included, since so many circuits include these devices. fets are high input impedance devices because they hardly require any input current to drive them all the way on or off... they are extremely sensitive. they will detect the static on a comb from several inches away if you put a wire on the gate and dangle it in the air! hope this gives you a starting point. zachary vex