I have a Roland Rd700sx running through a Yamaha Stage pas 500.

A few things seem very strange .. and are probably fixable but I've run out of ideas.

1 - The headphones only work when there is a lead running from the output to the amp... !?
the amp doesn't even need to be turned on... and without that cord plugged in, it sounds very very quiet and turning the volume up to full gives me a very quiet and distorted sound.
my first thought was 'earthing' or maybe power supply.. but I have no idea about those.

2 - When the keyboards volume is at full it always distorts.. (that's manageable, just wondered if it was normal)

3 - during live gigs, there always seems to be an issue with going straight from the board.. it's some kind of lack of volume and light buzzing. that turns into a LOT of buzzing when the volume goes up... I have tried a DI box.. with the earth lift switch... but that switch seems to cut out 90% of the sound... this issue has always been fixed by running it through my stage pas mixer/speaker FIRST then out of that to the sound guy's desk. The sound guy always shakes his head in disappointment at my board... .. I've tried asking them but their answer for things is usually "it's fucked"
WHY OH WHY can I not simply give him an out straight from the keyboard??! Or even from a DI box?!

I imagine all 3 problems could easily be related somehow...
any help on ANY of the 3 is awesomely appreciated... And I have a big question mark around 'POWER SUPPLY' and 'EARTHING' but don't know enough to keep going..

Cheers guys

- Ruben

That should be a big clue. This is a balanced signal out right? Ans XLR jack on the Roland? I bet one side of the balanced signal is dead/disconnected and it was using the ground shield on the cable as the return path, you lift that sound mostly goes away.

You are going to have to get a meter set on AC volts or a scope and look at the outputs.. If you don't have the test equipment of know how then take it to some one who does.

I think yu guessed right about some kind of ground issues but I'd pretty sure the problem is inside the keyboard. THe ground lift switch killing to signal tells me the signal is not "balanced".