I measured the performance of the Miyajima Wo-1 with my Audio Precision SYS2722 system.1 When I connected the preamplifier’s output to the analyzer and switched it on, the AudioPrecision’s gain-ranging kept changing. Ken Micallef had told me that he had heard “pops” when he turned the preamplifier on, likely the result of a DC voltage somewhere in the audio circuit. An obvious place to look would be on the wiper of a conventional volume control potentiometer; however, I would not have thought the Wo-1’s unusual “shunt” switched-resistor volume control would suffer from this problem.
I powered down the Miyajima, connected a Fluke DC voltmeter to the left channel’s output, and turned the preamplifier back on, leaving the volume control set to its minimum. The voltmeter immediately registered a DC offset of >30V, which slowly declined, the DC voltage dissipating, perhaps across the voltmeter’s very high input resistance, perhaps via some other route. I repeated the procedure with the Wo-1 connected to a 100k ohm load. Again when I powered up, there was an initial DC offset
