🚀 go-pugleaf

Modern op amps typically have output resistances anywhere from
10's to 100's of ohms, open loop.  As an eariler poster has
suggested, however, the *closed loop* impedance of the op amp
will be much lower than this, perhaps by as much as a facter
of a hundred thousand (at d.c., that is).  The impedance will
increase with frequency.

In any case, this is a commonly spec'd characteristic.  Just
look up a datasheet from Analog Devices or T.I.

Chris