yep, thanks Mike, have used those before in bigger applications...

The good news is I worked things out, thanks Ian! The placement of the "ground screw" sticker was closer to a different bolt which was the incorrect one. I had been trying to remove the wrong one.

I thought it was strange as the original amp that came with the ep600 was a phillips. Well, it turned out a bit further away is another phillips head screw which is actually the ground.

I will be testing tonight to see if the hum in the other speakers has vanished... thanks all
M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
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