Preamps for dummies that would be me

First, I have to disagree with Marakanetz about the output/input impedance ratios - a preamp output impedance to power amp input impedance ratio of 1:20 or higher will be sufficient. (For instance, if your preamp has a rather high output impedance maximum of around 1,000 ohms, try not to pair it with a power amp having an input impedance below about 20,000 ohms. As a practical matter, most preamps have an output impedance lower - and most power amps an input impedance higher - than in this example, so impedance mis-match between preamp and power amp is not usually a problem anyway). Also Marakanetz, what are you talking about with your references to preamps having to "restore" the "drastically compressed and feedbacked (sic)" output of CDP's? This makes no sense to me at all.

Randalle, the basic answer to your question is gain: active preamps offer additional gain, which might be needed to listen at the desired loud volume, depending on the source material, the source component's output level, the gain level offered by the power amp, the speaker sensitivity, and the size of the listening room.

Also, controlling volume with a passive device can sometimes become problematic due to impedance-matching issues between the resistive element used for volume attenuation and the impedance characteristics of source outputs and amp inputs, as well as those of longer cable runs. Active input and output buffering around the attenuation device, as in an active preamp, can eliminate these potential issues, which can make system matching easier by providing volume control that is relatively insensitive to surrounding conditions, and by relieving the source component from having to drive long cable runs.

Ideally, a preamp could provide gain only when it is required, but most active preamps have a fixed permanent gain factor, which is then attenuated as needed by the volume control - often (as you note) to levels below that of the source's own output level (AKA below 'unity' gain). Generally speaking, the less gain - and the less attenuation - applied to the source's signal, the more transparent the sound, so passive attenuators can have a theoretical transparency advantage for sources with sufficient output drive, as long as none of the above-mentioned impedance-matching difficulties arise. (Click on my Threads and go to the one about preamp bypass testing for more related to your question.)

There sure is some silly stuff being flung around here. I had just about completed writing a detailed rebuttal to it all, when my 'puter froze up and I lost everything. Right now I don't have the heart to start over again, so I'll just say for the time being: Randalle, keep a large grain of salt handy.

OK, let's try again...

About what Gs5556 said:
CDP's and DAC's have steep HF filters kicking in at around 20KHz to reconstruct the analog signal and keep HF digital artifacts at bay. In contrast, any competent active preamp will have its upper -3dB point (and often even the -1dB point) well out above the audioband. Given that truth, what do you propose to be the magic mechanism in active preamps that is supposed to "launder" your allegedly dirty signal coming from the CD source and make it "clean" for the power amp? As I and many others know from experience, the direct, unattenuated and unpreamped output of a CD source cannot not harm your amp, speakers, or ears on any basis other than possibly that of sheer volume.

You then posit a contradiction, by suggesting (correctly, if not comprehensively) that a passive attenuator can interact with the source's output impedance, the amp's input impedance, and the cables' capacitance, to cause mis-matching and insertion losses which can combine to roll off response prematurely at the LF and/or HF ends of the audioband, sapping signal fidelity and drive vs. an active preamp - but then put forth in the same breath your contention that a passive attenuator will pristinely pass along all of your alleged digital HF garbage to the amp unhindered vs. an active preamp, which you suggest will somehow filter this alleged spuriae that you claim is part of the CD output signal.

Well, which is it? - it can't be both. In any given situation, a passive attenuator will either preserve the fidelity of the input signal or reduce it vs. an active preamp, and the same thing applies the other way 'round; you can't simultaneously but selectively argue that passive attenuators will *both* preserve and destroy fidelity (as well as making the same argument in reverse for active pre's), depending on what's conducive to bolstering your position in the debate. As for your claim that you "personally cannot stand to listen" to a CD source not run through an active preamp, I have to assume this rhetoric is based as much on what you (erroneously) think about the output of CDP's and the action of active pre's, as it is on what you actually hear. (Which isn't to say that in any particular instance, one might not prefer the sound of their CD source run through an active preamp [especially as compared to its sound run through some other sort of attenuator, or volume-controlled in the digital domain], but that it won't be for the 'reason' Gs5556 alleges.)