Passive Preamp - What makes it work?

I want to try a passive preamp, such as Creek's OBH 12, as an inexpensive pre to replace my current Denon AVR1700. I've read a bunch on here that output levels from the CD and input impedance of the amp are crucial factors. What should I be looking for to see if this is a good idea for my system? Is the goal to make the impedances match, or should one be higher than the other? Also, are there any passive pre's with a home theater passthru?

My system:
Joseph Audio RM22si signatures (86 db sensitivity)
McIntosh MC-2105 amp (input impedance 200k)
Music Hall CD25

A passive preamp is essentially a potentiometer (really, 2 for stereo). Used only to attenuate (decrease) the level of the source feeding it.

In order for a passive pre-amp to operate ideally in your set up, you would want to make sure the CD player has a output that is high enough for you to be happy with the listening level in your room. A pre-amp's job is to take an input signal from a source component, and either attenuate it, or add voltage gain (thus making it an active preamp requiring a powersupply) in order to for you to choose a comfortable listening level. One good way to see if your CD player has enough juice, is to hook it up directly to the McIntosh power-amp. Pick a CD that you know has a piece that starts out very quietly so that you dont kill your ears or blow your tweeters (classical music is good for this). If the level is loud enough for you, then you're all set. You should know that this is as loud as it's ever going to get with a passive pre-amp (In an ideal world, with the volume turned all the way up).

Output impedance, in this case, is really not going to be an issue. Your McIntosh's 220k input imedance is high enough that unless the output impedance of your CD player is outrageously high, the passive pre-amp (essentially a potentiometer) should not affect things that much. Impedance matching is definately not wanted in this case. At line levels, you want a maximum amount of Voltage transfer. This occurs best with a very low output impedance feeding a very high input impedance.
What does a passive amp do that's better than one that's not? Does it have benefits? I'm not educated enough to know what a passive amp is used for?

Would not a regular pre-amp always be better than a passive?
Theresa, there are (as always) several views on this subject.

Some say that passive preamps are superior and follow the "less is better" rule. A passive preamp can only cut signal. It cannot increase signal if needed, nor can it actively impedance match between multiple components.

Others believe active preamps are better because they can more effectively manage all types of signals. Active preamp's have many more parts, require power and process the signals fed into it, often adding their own personality (for better or worse).

Some Audiogon members go the no preamp route. Instead they choose a CD player with a volume control and drive direct into the amp.

All three answers are correct provided you have the right combination of equipment.
I just copied the Q&A section from Placette Audio's website in an ad I posted for a passive ( It addresses your question and you may find it interesting. I think the Q&A section was listed on the bottom of the list on the left hand side of their home page.

I tried the Creek between an Odyssey Stratos and MSB Nelson dac, shortest possible IC's ( 1.5ft) and hated it. The soundstage became very flat, entirely 2d. Bass and trebble extension was outstanding, imaging was just ok, vocals where hollow and lost presence, overall just didn't sound "right," was only a stereophile class "C" component for a reason. For the cash it can't be beat, but there are many better preamps out there for not much more on the used market. Still, you must try it for yourself in your own system to see what you like. I would suggest trying the Adcom 750 pre as a good alternative that has an active and passive section, and can be had for around $600-700 used.
Types of passives should at least be mentioned. There's a transformer type I know zilch about, and three resistive types: (1) potentiometers, (2) series stepped attenuators, and (3) ladder stepped attenuators. Almost everyone would agree that (3) is much superior to (2): I've built both with identical resistors and comparable rotary switches, and the difference is easily heard. Some very costly pots may be competitive with (3), but most are clearly not, IMHO. Whether passive or active is better is an unending dispute, but everyone would agree that it depends heavily on the system, in several ways, and that passives are trickier to deal with. In my opinion, they're well worth it, but others will disagree. It's a much-discussed topic in this Forum: maybe you could look up those discussions.
The FT Audio LW-1 is an excellent passive preamp. I'm using it with a Pass Aleph 30 amp and Kimber Silver Streak ICs. The sound is alive and the soundstage is 3 dimensional. Awesome clarity and warm sound. With passives, the right combination can really swing. Paul Lam of FT Audio recommends Kimber cables (the Select KS-1020 or at least the Silver Streak) as these are highly transparent and clean. This preamp is $500 new (you hardly ever see them new, a real testament to their quality). Both my sources have enough output to drive this syetm easily plus my speakers are easy to drive. The LW-1 has a 30 day trial period and Paul will help you understand if it is a good match for your system. The Placettes are also highly regarded.