Are you hearing this through your headphones or monitor from the mixer or from your recording device? I have a crappy ber. mixer as well, and I have no problem with gain structuring between the mixer and the weak preamps of my recorder with any of my mics, none of which are fantastic (sm57. sm58, MK 319, 603s).
What is the mic? Try switching out your mic cable, it might be bad. The gain on the preamp (the small black knob by the input) should not have to be turned up too high. Is there achance that you have the volume ont he headphones cranked? The noise might not even be from the mic/preamp combo. If the mic is cheapo it could have a lot of self noise, if there is a lot of electo-magnetic interference and you balanced cables are crappy/shoprting out, that could pick up noise, etc.
For the most part, if you put all the pots (gain on the pre, volume on the channel, master volume, and the volume on the amp/headphones) about halfway, you should not be addig too much noise.
If you have a condensor and are jhsut getting used to it, you might be hearing the room, the first time many use one of these types of mics, they start to hear everyhting going on in their houses.
If you have no techincal issues like described above, your mic may jsut be very noisy, you could cut some of the highs in EQ< but that will lose some of the signal you are trying to capture, a bad option.
Daav