Measuring preamp output impedance

[ChrisA]

Originally Posted by kacernator

Well, the preamp is intended to drive 100W class AB unity gain power buffer, so preamp output should be around 40V at full 100W output.

I do not know how to measure it properly, I mean why so different results? Is it the problem with DMM?

The output impedance is NOT constant over such a HUGE range. Your two test points are 15K and INFINITY. That is to large. Try two loads that are spaced closer like 15K and 150K or 15K and 20K

The output impedance depends on the operating point. Try 10K, 15K, 25K, 50K and so on and make a plot.

[kacernator]

Ok, I see now. Aikido preamp has flat output impedance within small output voltages, but impedance rises with higher output voltage swings. Basically what I needed to find out was if I measure correctly or not.

Thanks.