Thanks guys - well, I took the bass in to Martin at the Bass Gallery. Of course, when he plugged it in, it was on its best behaviour and seemed to be working just fine! As a result he's having to work on a very vague description of what the problem is ('Sometimes when you plug it in, there's no treble until you try twanging it . . .') and doesn't seem too hopeful that he'll turn anything up. However, he's promised to give the electronics a thorough service, checking the pots and connectors. Hopefully this should do the trick. If it happens again, though, I'll try Georgie Boy's advice and take it to Chris at the Bass Centre. I would have done that today but, of course, the one day of the year I try to use the tube to get there, the central line is paralysed because of a signal failure somewhere, so it had to be Camden rather than Liverpool St . . . Grr, I hate this city's public transport system.
K.