Passive Preamp?

Do a search here and at AudioAsylum,all the info you will ever need on passive preamp is here and there

A passive preamp has no amplification stage. It is actually something of a misnomer. Typically they do not plug into an electrical source. I own two of them and they are both just switch boxes with a volume control. If you need more than this fundemental info, then you should follow Herman's advice above.

Check out the thread at: http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1159194844&read&keyw&zzno+regrets

It sounds better than most active units, it goes between your CD player or DAC and your amplifier.

It is mainly a volume control with no gain since the amplifier can handle the DAC perfectly well by itself without adding another gain stage and the problems that can come with it. A passsive volume control then will sound more transparent...you will have to do some reading in order to insert one in your system because they are system dependent:

What is your system?

Dynaco ST-70
PHILIPS 910-CD
Dynaco FM-1 tuner
Teac 330 reel to reel