One of the greatest struggles for any entrepreneur starting a new company is getting noticed. But not if you are Jay-Z, who can simply call up a dozen or so of his closest friends, like Kanye West, Madonna and Deadmau5, to join him onstage. Problem solved.But music fans thinking about throwing their leg on the table and signing up for Tidal may want to hang on to Spotify or Beats Music for a little longer. Famous musicians don't usually make very good technology executives, especially with the world of tech moving at such an extraordinary pace.And Jay-Z's pitch on Monday, asking people to pay double the price of competing services in exchange for higher-fidelity tracks and extra cash for artists, was not a seller.Folk-rock legend Neil Young has been beating the drum for high-fidelity digital music for years. His endorsement of a startup called Pono Music, which makes a portable music player capable of playing high-def audio files, helped it raise $6.23-million last year on Kickstarter.Young's involvement has not produced a very good product, though. Ars Technica, reviewing the $399 PonoPlayer, called it "snake oil".Curtis Jackson, better known as 50 Cent, bought a majority stake in headphones maker SMS Audio and installed himself as CEO. Research firm NPD Group stated last year that 50 Cent's company had less than 1% of the high-end headphones market by revenue.There are exceptions. Lady Gaga and Justin Bieber are becoming prolific tech investors, and Bono has been particularly effective with his venture capital firm, Elevation Partners. As for actually managing tech companies, Dr Dre proved it can be done. ..