Buffer Question

[seten]

Well I was checking to see if I understood what fiveseven was saying about impedances, he brought up the mains.

And I didnt send that link for informational value 

[antonis]

if you put the battery across the mains,

Plz, don't do it..!! 

P.S.1
Mains impedance has absolutely nothing to do with +9V (or any other DC power supply) fed circuits..
(all AC involved parts are isolated right after rectification configuration..)

P.S.2
You're confused a bit with basic circuitry terms & definitions..
Any load fed by a power source is considered either in SERIES with VOLTAGE source's impedance or in PARALLEL with CURRENT source's impedance..
(either Thevenin or Norton)