difference between an active and a passive preamp?

The passive has no active circuitry and therefore no gain.

And, as a result of having no active gain, passives are generally more transparent, and provide more bang for the buck if gain is not an issue. If you have only one source, check out Luminous audio axiom

Passive has no gain stage.
Active has a gain stage (at least one)
In all other ways they are about the same physically.
electrically though, they are different.
The passive preamp depends entirely on the source component to 'drive' the amp.
So using a passive preamp means you MUST have a robust source device. (or the result will be thin, weak sound)
Generally most CD players can drive a passive preamp 'good enough' That is it will sound no worse taht an active preamp.
For a passive preamp to excel.. the source must have a great ability to drive the amp.

With an active preamp none of that matters. any source can be used and a good result will occur.

Some sources actually state i nthe specs do not use with a passive preamp. (nice to have that info. My Audio Research PH-2 specifically states do not use with passive pre._
So.. IF you can find out the ability of your source to drive the amp, a passive will be good..
If it cannot do it well, then you either have to get a source that can drive a passive, or get an active preamp.
When you get up there in money spent on a preamp.. the actives get pretty good.
In the lower ranges is where the passive shines in comparison to an Active pre. IMO,