Cables

Testing mains regenerators falls outside the normal run of HFN lab reports so I've built some special equipment to do so. The first uses an inline Hall-effect current transducer from LEM Components that can record currents of up to 80A at slew rates of greater than 60A/μs over a bandwidth exceeding 100kHz, while adding a series resistance of only 0.18mohm. Built into a box with flying leads terminated in a mains plug at one side and a mains socket at the other, it can be inserted in the mains feed to any component to measure mains charging current.

Tested by powering-up a Naim Audio NAP 300 amplifier, itself outputting 85W continuous on each channel into a 4ohm load, the charging current waveform from the wall socket [red trace, Graph 1 below] is significantly improved by the P20 [black trace]. The P20's current pulses are almost textbook whereas those from the wall socket have a lower peak value and longer duration as a consequence of the mains waveform being flat-topped and the source resistance being higher.

Distortion measurements must accommodate mains regenerators that have unbalanced, balanced or floating outputs, for which I've built a balanced resistive attenuator that feeds an INA217 low-noise, low-distortion instrumentation amplifier. Together these give a voltage output one-hundredth that of the difference between the live and neutral lines, with much lower inherent distortion than a transformer-based solution. Once again, obvious differences are seen between the voltage waveforms from the wall socket [red trace, Graph 2], the P20 on its low distortion sine wave output [black trace, Graph 2] and on the highest MultiWave setting [green trace, Graph 2]. The test table lists individual amplitudes of the first four odd harmonics (each referenced to the 50Hz fundamental) plus a THD figure calculated from the first 14 harmonics. While the P20 correctly reported output distortion as 0.1% on sine wave, it still said 0.1% with MultiWave output selected. KH