I’m running Leopard while my business partner is running Snow Leopard, yet we were both experiencing the same problem with the Samson mic. We just could not get any gain. However, we were able to resolve the problem yesterday afternoon after reading and implementing the following post on a forum:

“Samson CO1U USB Gain Problem. On my Mac this has been a problem that came up when I switched the same Samson USB mics between laptops, which I have just solved. I am using two of these for stereo recording, but the issue is the same for a single mic. The source of this potential issue is the fact that even though these are mono mics they have two channels, and both channels must have their gain all the way up in order to have full gain from the mic. On a Mac, go to the AudioMIDI Setup Utility in the utilities folder, select the Samson mic in the dropdown for “Properties For”. Under “Audio Input” you will see the option of 1 or 2 channels. Select 2-ch. Down below and to the left the L & R volume sliders for both channels should be all the way to the right. Make them so and you have maxed the mic’s internal gain, which can be later adjusted down in your recording app without affecting this internal setting. You can now put the mic setting back to 1 channel without affecting overall gain. If you use two mics for stereo, set each mic like this individually, go to the Aggregate Device Editor under “Audio” on the menu bar, aggregate the two mics, and you are done. If you need to balance the gain on these mics afterward, you can do so by selecting them individually, making any changes, and then go back to Aggregate Device as the Default Input and Properties For. (There may be similar configuration setting on a PC.) Hope this helps!”