Quote Originally Posted by DMK
I had a weird experience with the Creek passive and another passive I tried out ... Perhaps an impedance mismatch, as you said.
Here's a guideline from Enjoy the Music ...

Enjoy the Music.com Review Magazine:

The question a prospective buyer must ask him or her self is: Should I employ an active or passive pre-amplifier? When that question is answered with some assurance, then, questions like which and what type can be answered.

Q: Who should use a passive pre-amplifier?

A: People who can say for sure the following are true about their systems.

1. "I do not need phono equalization." If you have a turntable and you play black vinyl discs, then you need some sort of RIAA equalization (filtering) to restore your source signal to its original form. This usually will take the form of some sort of active "phono" stage with the proper RIAA time constants inserted between a pair of "buffer" input and output stages -- with or without gain. Usually this stage has anywhere from 24 - 78 dB of gain, depending on the needs of the associated MM or MC phono cartridge. And, very often this phono stage is associated with an active "line-level" stage which may have a gain of less than 0dB or it may have as much as 10 or even 20 dB of gain. (Remember, every 3dB of gain represents approximately a doubling of the music's apparent loudness!)

2. "All of my line-level sources (my tuner, my CD player, my cassette, etc.) have enough gain to drive my amplifier directly." This means every source should have an output of (at least) .75 volts. A 2 volt output is industry standard.

3. "The impedance of my sources is low enough and the load impedance of my basic amplifier is high enough that their direct connection will not seriously roll off my system's high frequencies or compromise its transient response." This means that every source component should have an output impedance of no more than 1000 ohms (less than 300 ohms is best) and that your amplifier should have an input impedance of at least 10,000 ohms. 20,000 ohms (or more) is better.

4. "I do not plan on using interconnect wires more than two-meters long." Longer lengths of wire connecting pre-amplifiers to amplifiers present greater capacitance and therefore create low-pass filters with lower turnover frequencies thereby rolling off more of the music's higher frequencies and reducing the illusions of luster, brightness or transparency as well as transient attack. In other words longer lengths of interconnect can cause the reproduced music to appear dull.

The perspective passive pre-amplifier user should always do two things: First consult manuals and/or manufacturers to determine if the above conditions are easily met. And second, you must try the passive preamp in your own system to make sure it does not screw up your music. These types of audio component interfaces are (in reality) quite complicated and typically possesses too many variables to be predictable -- therefore a home audition is essential.