output impedance Z

hi to everyone.

i was wondering if someone could explain in simple terms on how to measure the output impedance of a preamp  

i know in pro audio the impedance is 10 to 1 and a MIC preamp input impedance  is 1500 ohms 

my luxman M03 input impedance is 47 K

i read this on the net  the document was copied from someone's post 

thanks