Coldplay are struggling to make substitutions in their US gig setlists because their performances have been ''killer''.

The 'Paradise' hitmakers - Chris Martin, Guy Berryman, Will Champion and Jonny Buckland - are experiencing a ''good problem'' during their US tour in that they are unsure where to make changes from gig to gig because each show has been a ''total belter''.

Coldplay's roadie revealed on their blog: ''The fellas are clearly having a properly great time - and the shows have been total belters as a result. San Jose were a pretty damn loud crowd. Perhaps it's been like this every night and I just spent more time with my earpieces out, taking it all in.

''They're most definitely in the zone right now. There have been tinkerings, though with some possible setlist additions in soundchecks. One of the 'Viva' album tracks that only got a rare live outing has had a workout. I really Hope it makes it back into the setlist, it's one of my all time favourite Coldplay live tracks (particularly The Ending when Jonny goes off into full on guitar hero territory).

They also played around with something from a long way back. It's all a sign of a band very much alive and enjoying themselves. The possibilities keep appearing left and right for great additions, but the set right now is so killer that it's tough to work out where to make substitutions. I'd call that a good problem to have.''

But one change the group have considered is starting up a karaoke competition in soundchecks to ensure the microphones are still being tested without harming Chris' voice.

The blog post read: ''Once the show proper is running, it's all business. Too much chatter is a pain for everyone and breaks concentration. Long soundcheck jams though, are a time when the shout system heats up and becomes a hotbed of nonsense chatter. There has even been threats of a Karaoke competition on the shout system in soundchecks when Chris usually doesn't sing, in an effort to preserve his voice.''