multi ground question

[changes]

i´m thinking of building some effects(distortions) in one enclosure selected by a rotary switch
each one of them will be powered by a 9V bat and has negative ground
can they share the shame ground or not?
will it alter the sound of each pedal if it has the same ground with another pedal?

[Travis]

If they are all going to share a battery (or other PS) they will HAVE to share a ground.  There is no way around it.  Otherwise, with only one effect being selected at a time it really doesn't matter.

You should, however, make sure that you gorund the enclosure.  This will likely prove to be a common ground (input/output jacks).

Everything else aside, negative ground should be compatible with other negative grounds.  The sound should not be altered.