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2.3 - Distortion Tests Electrolytic Capacitor Test Circuit
The electro under test was unbiased, and with 5.5V AC at 400Hz across the cap, the distortion rose from 0.02% to 0.022% - a definite increase, but only small. At lower voltages such as 3V open circuit (about 1.6V RMS across the cap), the distortion fell to just over 0.015%. The reason the distortion appeared to fall is simple - the connection shown forms a low pass filter, which helps to remove the harmonics that make up the distortion component of the signal. A first order low pass filter will reduce the third harmonic sufficiently to make reading the difference quite easy. Based on a very similar test done using the simulator, the distortion should be about ½ the generator value, so the cap is still introducing some distortion. As the voltage (across the real capacitor) is reduced, so is distortion, until the noise limit of the distortion meter is reached.
...............
Attempting the same test described above with a polyester cap was a dismal failure - I was not able to measure the cap's distortion , only the attenuated distortion of the signal generator. As predicted by the simulation, measured distortion was about half that of the generator alone, using a 1uF cap at 400Hz, with 5.5V AC across the cap itself. I am satisfied that the polyester capacitor's contribution to measured distortion was well below my measurement threshold.
I was not able to measure the cap's distortion
http://sound.westhost.com/articles/capacitors.htm
2.3 - Distortion Tests Electrolytic Capacitor Test Circuit
The electro under test was unbiased, and with 5.5V AC at 400Hz across the cap, the distortion rose from 0.02% to 0.022% - a definite increase, but only small. At lower voltages such as 3V open circuit (about 1.6V RMS across the cap), the distortion fell to just over 0.015%. The reason the distortion appeared to fall is simple - the connection shown forms a low pass filter, which helps to remove the harmonics that make up the distortion component of the signal. A first order low pass filter will reduce the third harmonic sufficiently to make reading the difference quite easy. Based on a very similar test done using the simulator, the distortion should be about ½ the generator value, so the cap is still introducing some distortion. As the voltage (across the real capacitor) is reduced, so is distortion, until the noise limit of the distortion meter is reached.
...............
Attempting the same test described above with a polyester cap was a dismal failure - I was not able to measure the cap's distortion , only the attenuated distortion of the signal generator. As predicted by the simulation, measured distortion was about half that of the generator alone, using a 1uF cap at 400Hz, with 5.5V AC across the cap itself. I am satisfied that the polyester capacitor's contribution to measured distortion was well below my measurement threshold.
I was not able to measure the cap's distortion
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