Shida SD-07 computer speaker set, has been used for many years. No signal also has an annoying hum. Could not bear to discard, then eviscerate many times many times, for electrolysis, for transformers, for-4558, for 2030 is 1875. never solved. This machine is an electronic volume tone, there are four kinds of sound.WvPservice manual download site
Sound board independence, powered by a was 12, increasing sound board capacitor is invalid, unplug the 12 volt sound disappears. Experiment with a 12 volt power supply separate power supply, sound disappears, so I decided to change the existing dual 12-volt single 10-volt transformer. Dual 12-volt power amplifier, 10 volts with a tone plate. Welding test machine, annoying noise and finally disappeared. +12 of tones which can be taken from dual 12 low frequency signal from the power amplifier for power series to pitch back to form self-WvPservice manual download site