Measuring Amplifier Output Impedance

13533329_1340106839336356_6538344959771332536_n

Measuring the output impedance of an amplifier does not require technical gear like a VNA, though that will make for a nice quick and accurate measurement. You can also do it using your multi meter and a scope. Here is how:

Connect the output of the amp to the swiper of a 10K pot or better yet, a decade resistor box.

13528977_1340107616002945_8318913652801389010_n

And measure the resultant waveform on the scope.

13510895_1340107646002942_4297484531567183411_n

Starting with the pot set to 10K ohm, adjust the pot until you have 50% of the amplitude of the signal.

13483003_1340107769336263_7781115297360550022_o

Remove the pot from the circuit and measure its resistance, this value is equal to the output impedance of the amplifier.

New Bitmap Image

You can then use a transformer turns calculator to determine the turns ratio for transformer for your circuit. Not hard now is it.

Facebooktwittergoogle_plusredditpinterestlinkedin