all preamps gain and phase.

The "gain" controls how much yr pre increases the voltage of the incoming (source) signal. So, you can match it to yr amplifier (in the case of very low level phono signal you may have to increase the gain so the auditory level matches line-level sources -- as mentioned above).
The phase switch reverts absolute polarity, as some recordings or components, have reversed polarity.

Thank you for the information. as for the gain where should i have it set for cd's should I high gain or low gain?

Thanks for the responces

Russ

Low gain, typically.

Jafox: "So maybe it is only audible on certain music....or I am simply deaf!"

No, you're not deaf. Probably your listening skills are similar to mine--I can hear lots of differences but I definitely have a limit. Last fall, in a lengthy audition of interconnects, I could distinguish lots from others, but after some culling, those that passed all sounded the same--GREAT!

Each of us has a limit to our listeneing skills, and they're all different. Keep trying that signal-polarity switch; one of these days and recordings, you'll hear it.

One more point about preamp gain--linestages with high gain can create audible tube noise with high-gain poweramps. Understand that line stages amplify AFTER the volume control; that is, the volume control decreases the input voltage, not the output voltage, so the preamp's output noise is constant--unless a switch decreases it.
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Jafox--I gather the ability to hear absolute phase isn't like "normal" hearing. Some hear it, some don't. Think its called "Woods Effect" or something.