I've installed mini-ITX motherboard into Color Classic. All works well except the speaker produce quite loud buzzing sound that changes with what is shown on the screen. The loudness of buzz increases with the contrast of the image on screen: it is loudest on full-screen linux terminal filled with white-on-black text.
The buzz was extremely loud at first until I connected the motherboard ground to chassis metal cage with a thick wire - that made it much quieter but still annoying. I am not sure what else to try to reduce the noise further so asking for advice here.
The sound input on mac harness is connected to front panel audio header of motherboard. The volume regulator input of mac is hardwired to 5V.
The buzz was extremely loud at first until I connected the motherboard ground to chassis metal cage with a thick wire - that made it much quieter but still annoying. I am not sure what else to try to reduce the noise further so asking for advice here.
The sound input on mac harness is connected to front panel audio header of motherboard. The volume regulator input of mac is hardwired to 5V.