Balanced dynamic mics can normally be used with the phantom power switched on. Caution, unbalanced mics can be damaged!! - it's best to check with the microphone manufacturer and also ensure you have balanced connecting leads.

I should also add, don't use a dynamic mic like the SM57 with an unbalanced lead.
If you're not sure about the difference between balanced and unbalanced leads I'll be happy to explain.
Hope this helps. :) :)

MikeG
Is the difference that one is low impedence and the other high impedence? I'm assuming you mean use a 3 prong cannor cable?
Please correct me if I'm wrong. I'll be recording this weekend and a frind lent me some CAD drum mics that I plan to use along with a couple of Marshall condencer mics and a SM57.
Thanks for replying.

No it's not to do with impedance, it's all about using balanced leads and a balanced source.

Check that the microphone leads you are using are connected in a balanced configuration. Assuming you are using XLR to XLR connecting leads then the connections on the lead will be pin 1 (screen) on the male XLR to pin 1 female XLR, pin 2 (Hot(+ve)) male to pin 2 female, pin 3 (Cold(-)) male to pin 3 female.
i.e. 1 to 1, 2 to 2 and 3 to 3.

On an unbalanced lead pin 1 and pin 3 are linked and connected to the screen, pin 2 is the (Hot(+ve)connection.

DO NOT use either unbalanced leads or sources with the phantom power switched on as the voltage on pins 2 & 3 of the XLR connector can cause damage to the microphone.

Your SM57's on a balanced mic cable will be fine so don't worry.
But it is important to make sure only use balanced sources and balanced connecting cables to the mixer when the phantom power is on.

Meant to add that your "3 prong Cannon" is an called XLR