Hi, thought this might be of interest to M500 users. Having done about 30 or so gigs with my M500 it suddenly started to have very little volume when switched on. No real response from Input Level control...and Volume control could be turned all the way up with very little effect. However...after a short while the volume suddenly surged back on...scary!....and all was OK...until the next time. When it happened again....sometimes switching on and off a few times fixed it...but....not a good situation for live gigs. To cut a long story short, having been in touch with the suppliers (who are ALWAYS very helpful), it transpires that the problem is either a loose joint somewhere internally OR a loose jumper on one of the internal boards. This is also Phil Jones personal opinion as he also was kind enough to get involved. The M500 has not been banged about and has not been abused in any way (just for the record). I will probably have to send the Amp for a Pro service as I do not want to tamper too much with it personally. Anyway.....if anyone gets this problem...I hope the post is useful..I have the full emails from Phil and the service Engineers if anybody needs them. I should add that after decades of looking for the ultimate in Bass sound..I found it with Phil Jones equipment....so I will be sticking with it.