kdavid said:
i ... wasnt happy at all with the sound (its a martin gold us pickup)
... is an SM57 even a decent guitar mike?
For what it is worth, here is an additional 'two cents':
When performing live with an acoustic guitar, amplification is some combination of convenience, volume, and an attempt at accurate reproduction of the sound of the instrument. I think most would agree that if you are contrasting the guitar pickup with the dynamic microphone, the Shure SM57 (properly positioned and EQ'd) will provide your audience with the more accurate representation of what your guitar sounds like. If you think about how acoustic guitars produce sound, placing a microphone (or two) in front of a guitar will nearly always reproduce it's sound more accurately than transducers, magnetic poles, and internal mic's.
However...
Guitar pickups are rarely used because someone thinks they actually sound better than a microphone. There are a few exceptions, but contrast the recording studio with the stage. In the studio, there is a reason why mic's are the standard for capturing the essence of your instrument for the world to hear. The studio is a very controlled environment where dealing with feedback is just not an issue. On the stage, pickups are popular because they conveniently and consistently, from venue to venue, allow for greater amplification before feedback, something that is VERY difficult to achieve and control with a mic alone (but not impossible).
If you want to use mic all by itself, I believe you need to add some aggressive EQ in your signal path to provide you with control of the variables you will encounter. Over the years I have used a preamp with a notch filter, a 5-band parametric EQ, or a 31-band graphic EQ, all with relative success. Keep the mic close to the instrument. Where you position it, in front of the soundhole, the 12th fret, or the over the soundboard, will affect the tone as well as the susceptibility to feedback. Sound pressure levels can change radically in a small room, as people come and go, so it is nice to have fingertip control to protect the audience from that dreaded squeal. In a really large setting this is usually less of an issue. You may also want to add a foam pop filter to the mic, as raking the mic up against the strings produces a dreadful sound.
As other have suggested, if you run your pickup through a preamp it will definitely soften the 'quack-i-ness' of the Fishman piezo and add a warmer tone. That may be all you need. D-TAR Mama Bear, L.R. Baggs Para Acoustic DI, L.R. Baggs Venue DI, Radial ToneBone, and Fishman Aura Spectrum are all well-respected examples.
If you are still hungry for a better tone, you may want to consider adding the SM57 to your setup, as in, using it in conjunction with your preamp'd pickup. In this configuration, the pickup provides the volume and the mic adds the more 'natural' sound to the mix. Feedback is kept at bay by not relying totally on the mic for volume.
Then again, you may want to look into retro-fitting your guitar with an altogether different pickup system, and forego the mic altogether. A 'dual source' solution, where an internal mic is mixed with an under-saddle pickup, or a soundhole magnetic pickup is mixed with a transducer, can sometimes be just the ticket.
Then there is the new Anthem pickup by L.R. Baggs. In my opinion, it is quite an impressive solution and may bring us closer in our seemingly never-ending quest for that perfect combination of convenience, volume, and tone. Some are using the term 'holy grail' in their reviews, but I will leave that conclusion to the audience.
Finally, if you are providing your own P.A., you have complete control (relatively speaking) over your sound so you can make any decisions you like and change your setup at will. If you have to 'plug in' to a house system you can either leave the results entirely to the soundman (or lack thereof), or maintain control over your tone with a footpedal or small rack of goodies.
OK, maybe that was four cents worth, but I hope some of it proves to be helpful. I wish you great success on your quest.
Christopher
