I still wonder how much better the LF distortion would be if the receiving impedance was higher, given that most line inputs present a bridging impedance of 10K or more.I have just made measurements with 200 ohm driving impedance, load impedance remained 1.66 kohm.
Distortion vs. frequency - worse, but not as much as I expected
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Frequency response, just quick comparison to 0.056 ohm drive (I apologize for not shifting Y scale). Surprisingly still goes down to 40Hz.
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THD, THD+N at 1kHz/552mV. About 4x more than with 0.056ohm drive.
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REW and STEPS. REW sometimes goes unstable with my DAC/ADC, so time after time I use STEPS, which is stable and saves my time by no need of repeating of measurements.
Any transformer, however good, will show an increase in distortion at LF due to core saturation driving an impedance lower than it was designed for. A transformer of that size won't be happy into a 1.66k load. My transformers designed for driving a 600 ohm load are several times the size of the one in this adapter.
S.