The idea presented here has not been tested, nor is it for the novice. It is something like a thought experiment. If you do build it, please, send us your results.

SE Transformer Testing
    Here are some thoughts on how to test a single ended transformer. Since distortion increases with a higher impedance source, the worst case distortion will result from feeding the transformer from a modulated current source, as shown to the right. This circuit enjoys some nice touches: the MOSFET is protected from destruction from the removal of the transformer from the circuit by the collapsing of the voltage source reference voltage; the power supply noise should not define much of a current variation in the transformer, as it is current source loaded (except for the parallel 1 meg resistor); the IC op-amp needs only a single 12 volt supply voltage.

         Distortion = I_h / I_f · R^' / X_p , where
           R^' = rp || (R_o · ratio²)

   Complementarily (since distortion decreases with a lower impedance source), the best case distortion figure will result from feeding the transformer from a voltage source, as shown to the left. This circuit boasts some nice touches: the potentiometer can be adjusted for the lowest distortion from the transformer; the medium-high voltage current source would only current load the transformer; a low distortion IC buffer may not require a regulated power supply; the transformer's primary DC resistance is nicely offset by the RC network defined by the 1M resistor and the 1.5µf capacitor.  // JRB

pg. 8

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