tuning down to c

Buy a baritone. Downtuning with a standard guitar/strings makes them WAY to fricken floppy, no matter what guage.

Or buy a 7 string.

Or just fuck all that downtuning crap and play at normal pitch. Like Hearse said, its what guitars were made for. They will only really intonate well at that pitch, and only play well at that pitch. Anything else is fair game.

And, man, don't play on crappy 9s. Those are like rubber bands. At least get 10s or 11s, so much better tone. I play acoustic way more than anything so I'm used to 12s all the time. heh
 
NAD said:
Change your action, adjust your bridge to make the strings sit closer to the neck. Also, check in the Musician's Discussion forum, several threads on how to change your action.

Its a little more complicated than that. First you need to adjust your truss rod. The amount of relief (forward bow) your neck should have varies by manufacturer, but in general you should have just enough to avoid buzzing from open to fret 3 on all strings. When adjusting your truss rod, never turn it more than 1/4 of a full turn in one day. Let it settle, as wood has a tendancy to shift. A useful measure of the proper relief is to press any string at the first and last fret; the space between the 7th fret and your string should be equal to the thickness of your highest string (so for 10's .01"). Use a spare string of a feeler gauge to measure.

Then you need to adjust the action. Lower it to taste, which basically means deciding on an acceptable amount of fret buzz from fret 9 on. Keep in mind fret buzz isn't really a problem if it 1) doesn't project through the amp 2) doesn't kill sustain. Keep in mind higher action = more sustain and easier bends, lower action = speed playing and easier chording (although on flatter fret boards like jackson or carvin that's not always true).

Finally, you need to intonate your guitar properly. Basically make sure that the open and 12th fret for each string is tuned to pitch. You adjust this by moving the saddles on your bridge (for fixed or tune-o-matic, never worked on a floyd rose).

When in doubt, take it to a guitar tech and get a proper set up. If you feel comfortable mucking around, these 3 steps are pretty easy to do.
 
thanks to all of you, especially to dune_666 for your advices and tips. but I couldn't solve the problem myself, so I took my guitar to the shop where I bought the new set of strings and there the tech took care of it for free. I am a happy guy!
So far I can say that C is the best tuning in this fucking world!