I use an iPad on stage for synths. While setting up at soundcheck for a gig, I was told by the sound tech that the 3.5mm jack-to-stereo RCA cable I'd brought 'wouldn't work' for their DI boxes (even though the DI box in question had RCA sockets) and would fry my iPad's headphones socket as soon as the phantom power was switched on.

This seemed odd to me.

Firstly, I've never heard of phantom power being used for synths or devices with headphones-out, only mics. Second, I'd been using that exact cable at previous gigs with no discernable problem.

Since then, I've been using a 3.5mm jack-to-stereo 1/4" jacks cable just in case. But I'm curious; was this guy mistaken or did he actually know what he was talking about?