I connected my audio amplifier to laptop's headphone socket and got oscillations which came and went away according to hand capacitance. Does anyone have any idea what's going on please? The AX-M66 has four coaxial input sockets marked L (red), L (white), R (red), R (white). All the screens are commoned. Which pair of connections should I be using? I've connected L(red) and L (white) and the common screen to the 2 core screened wire going to the laptop. Is this correct? Why might the setup oscillate, making a sort of scratching sound?

 

If capacitance is causing issues, then most likely you have a bad ground.

 

Thanks for your reply. You may be right about the earth because the amplifier wasn't fitted with a mains earth wire by its manufacturer. It seems now that I've been watching it for a bit longer, that the clicking begins soon after the laptop boots up. Any further ideas? Also (later observation) the amplifier "farted" with no connection to laptop's headphone o/l, no PSU connected to laptop, amplifier on standby, volume control to minimum, desk fan running. This now suggests to me that there is a fault in the amplifier. I then put the amp. on and volume turned up and desk fan still running. Result was no farting. It seems as if the amp fault occurs when it's on standby. What a weird thing.