🚀 go-pugleaf

wout@dutentb.et.tudelft.nl (Wout Serdijn) writes:

>In most cases the output resistance of an op amp is formed by the output 
>resistance of a (bipolar) transistor in parallel with its biasing circuit.
>Depending on the type of op amp (especially its current consumption and
>the process parameters) the output resistance therefore can vary between 
>10 kilohms and 100 Megohms.

Eeek.  Sorry, I can't let this one go by.  Look up some data sheets:
Signetics/Philips lists 75 ohms typical for the old uA741 as the
_open_loop_ output impedance.  Many op amps are lower than this.
On the other hand, there are also things called operational
transconductance amplifiers (like the Harris/RCA CA3080) that have
purposly very high output impedances.  But you wouldn't normally
confuse them with normal op amps.

I wonder if the original poster had tried to look up the output 
impedance of a particular amp and not found it.  Often it's not
specified; sometimes instead, a closed-loop impedance is
specified, and other times, it's just not specified.