opamp impedances

[downweverything]

i know you can calculate the input impedance of an inverting opamp amplifier by just looking at the input resistor.  how do you calculate the input impedance of a non inverting amp where one resistor say R1 is connected from the output to the -, the other R2 from the - to ground.  also how can you calculate the output impedance of each?

just by looking at the circuit it appears that the input impedance would just be R2 because the input voltage are equal.  is this correct?

[brett]

The input to the +ve pin of an op amp has several megohms of impedance.  But in single supply situations like pedals, we need to bias the input line, which usually involves a voltage divider (tied to AC earth by a big cap) and a resistor from the centre of the divider to the signal line (have a look at a Distortion plus schematic to get the details better than my description).  Anyway, the input resistance is essentially the same as the size of the this bias resistor (usually big, 1M in the Distortion plus and many other pedals).