I have a few main techniques to record piano.
First, dont underestimate the power of a mono piano recording, with the right mic, and placement, (and the right song of course), you can get great results. Typically, i mic piano in mono when i dont want it to take up a ton of space in a song, or when i want it focused in a very specific place in the mix and not really spread out. Often a piano is much more defined and clearer in mono when the mic is fairly close in. I will pull a mono mic back if i just want a dark, rich ambient sound.
In mono. typical signal chain might be Sony C800G, or a C12 thru an avalon or neve mic pre (or whatever's good). I'll often EQ it to tape unless i love the way it sounds coming in. I'll often also compress it a bit. again, specific EQ boxes and compressors depend on what studio i'm at, i'm not too picky, but i usually have access to nice stuff. For a tighter sound, I'll usually keep the lid on with a full stick, mic in about 14 to 18 inches off the strings roughly in the middle, cariod or omni, depending on what i'm going for. For more ambient sounds, back about 2 feet off the curve works nice for me, full stick on the lid.
For stereo micing i do two different things. If i'm dealing with a song with alot of low end content, i might choose to keep the piano brighter and not emphasis the low end. for this i'll put 2 small diaphragm condensors kind of spaced XY pair centered roughly over middle C, usually 10 to 16 inches up, one facing hi strings the other facing low strings. Mics, usually 451's, sometimes KM84's or B&K 4011's. whatever your best pair of small diaphragms are. Mic pre's i'll use the best ones i have handy.
This placement gives the piano nice attack and brightness and presence, not too much body, but great imaging.
If i want a fuller sound, I'll keep those two mics where they are and put a 3rd mic at the far end of the piano at the narrow end over the bass strings, in cardiod, and about as high up as my small diaphragms are placed. Mic's for this, either a good large diaphragm tube mic, or condensor mic. C800G, C12, U47, U87, even an AT4050 or Shure KSM would probably work well. I keep the hammer mics panned hard left and right, and bring the bass mic up the center. Just mix it in til it feels right. It adds great richness and body to the sound while keeping it tight and focused. I rarely ever have noticable phase problems adding this mic (although the hammer mics are often a problem being spaced). I blend all three together and print it as a stereo pair. Most of the time i like to record with the lid completely off if i'm going for more present sounds and this technique works well with the lid off. lid on is ok too.
-Ken Lewis
Full Time Dreamer