[quote name='warwickhunt' post='570062' date='Aug 15 2009, 05:10 PM']Why should problems arise if you remove all of the strings at once?
I do this and have done for the last 30 years with not a single issue... in fact most everyone (inc' reputed builders/luthiers) I know does it that way; it's the only way I know that you can give the fingerboard a clean whilst doing regular services/string changes.
Even though your string gauges are very similar, there 'is' a difference in string tension which can vary from manufacturer to manufacturer, this will have caused your set-up change. I would summise that the fact you say that your neck/fingerboard is flat means that you have very little relief in it so the smallest change in tension will require a tweak of the truss rod to get the action sorted and buzz free.[/quote]
Obviously all people and basses are different
My point was that removing all the strings COULD make the neck relax a lot more than if you change the strings one by one. More stable necks won't be affected as much, but some necks might not like, potentially magnifying the effect of putting slightly different gauge/tension strings back on.
Luthiers probably change strings like that (cutting the strings in half to get them off no doubt lol), because they're usually employed to set the bass up anyway....not just change the strings. If you undertake a full setup after each string change then great! I prefer minimal work when changing strings.
It's all hearsay seeing as we don't know what process the OP went through! I've put different gauge strings on basses before....of similar differences to those mentioned above and not needed to do anything to the neck.
Seemingly what we've ascertained though is that regardless of how you change strings, or if gauges are slightly different, it shouldn't throw a neck out like we're talking about here...."buzzing on most notes"??
Perhaps it is a weak neck, but best to get a pro luthier to look at it!
Si