How can an active preamp possibly help?

When I pipe the line level out from my CD player straight into my variable gain amp, I must turn down my amp from unity gain lest I blow out my ears. If this is the case, what value can an active preamp possibly be adding? The signal from the CD player is already "too loud" for the amp.

This leads me to question why an active preamp is needed at all. Switching and volume I understand, but can someone please explain how an active preamp amplifying the signal before it gets to the amp helps the finished product sound better (especially in light of my it's-already-too-loud example).

Some digital sources do not output enough signal to drive various amps to full power. As such, one can run into a lack of dynamics. Adding another gain stage takes care of that problem. Sean
Are you saying you're going straight line level to your amp? Does your cd player have a digital volume control for varying the gain output? Or does your amp have volume control capability?
Either way, I'VE NEVER heard ANY DIGITAL VOLULME CONTROL, or passive set up, which has proper dynamic capabilities! The sound is always less dynamic, and seems flatter over all! If you're listening to Rock, heavy dynamics, Home Theater, or other, the sound is always not as strong!
Anyone who thinks this isn't correct, needs to just hook the 6 channel out of their DVD player dirrectly into their 6 channel amp(or whatever) and process the sound in their DVD player, with no preamp/processor involved!!! You'll get WIMPY, LACKLUSTER, DYNAMICLESS soundquality everytime!..NEVER SOUNDS AS GOOD!
I've come across a ton of audiophiles that are two channel buffs, who insist on just going ANALOG out of their dvd, and into their fav 2 channel preamp! Or guy's who go out of their CD player with volume control, dirrect into their amps! This has it's drawbacks in the form of weak dyanamics and bass comparatively. You couple that with the fact that the vast majority of guy's like this use speakers that are very polite, laid back, and dynamically challenged passive auiphile speakers, and you get anything but dynamic transparancy!...EGAD!
So, if you do have some sort of volume control from either your cd player or your amp, you're still not getting the dynamic capabilities you're intitled to, I find.
Good luck
A tubed pre-amp can/does produce much more natural sounding music than CD direct to amp, IMO. My 6 tube pre-amp adds liquidity, warmth, body, and richness, and all these things are properties of live music-- and I've played guitars-- both acoustic and amplified for 40 years.

Soundstaging may be an artifact of stereo imaging, but I like it, and I like it a LOT, and tubes do it better than anything else I've heard. But on balance, it really comes down to personal preferences. I like tubed pre-amps. Cheers. Craig
Interesting feedback. But my question remains...if the signal out of my CD player is already too loud (my McIntosh amp has a gain control I can move up and down, when it's at default 12 oclock position sound is way too loud), how can a preamp possibly help? Does it lower the volume of the signal it receives and then reamplify it? If so, how can this sound better than the original source unless it's adding some sort of EQ function?
Agree with your observation, and its the same comment that would be made for using a passive preamp -- which is, in effect, the same as not using any preamp except for volume control and source switching. I have gone "passive" and will never go back -- the transparency and overall improvement is astounding, and I don't notice any loss of dynamics or bass, which are some of the arguments which proponents of active preamps make. Presumably, they would also apply those same arguments to your use of the cdp's volume control. If that's the case, why do Mark Levinson and other top names provide a volume control in their cd players. To reduce dynamics and bass? I don't think so.
I've used passive preamps, also found the sound very flat, 2 dimensional, but the bass and top end was very good, transparency great. Going back to good ss active preamp now, offering the best overall performance for my likes. Tried a tube preamp and it didn't 'do it' for me at all. Like anything else, it's something you have to try in your own system to see what works with your tastes, no amount of audiophile jargon or high flow technical theory should sway you any which way, let your ears decide.
Can anyone explain technically why people report any benefits to using an active pre, given my account above?

If the signal is already too loud and needs to be attenuated, how can an active pre possibly add soundstage?
Because many passive pre's cause an impedance mismatch with the output of the CD player, and the input of the amplifier. This causes frequency rolloff problems, and increased distortion. With an active preamp, the inputs and outputs have impedance characteristics that better match the source output impedance and amplifier input impedance, and therefore could provide better sound than going direct, thru a resistive passive pre, even though there is more stuff in the signal path with the active.

However, careful matching of the units, and careful selection of the lengths and type of cables, can mitigate this problem, but may not solve it altogether. The problem can be almost totally overcome by using transformer volume controls/passive pre, that doesn't use resistor volume controls. This would provide the advantages you allude to, and still have a good impedance match on both ends.

So, to fully answer your question, a correctly applied transformer-based passive pre, could give shorter signal path than an active pre, and sufficient gain pass through, while still providing good impedance matches, and likely would provide more transparent sound than an active pre. But an active pre, will more than likely give better sound than a resistive-based passive pre, that is not absolutely perfectly applied, including cable matching. This is primarily due to impedance matching.
Twl, Your post is an important reminder that it is possible to oversimplify with rules of thumb. The "short signal path is best" argument has been made in many posts without considering the signal in context. Many here have sold their preamps only to reintroduce them soon thereafter.
Exactly, a poor impedance matching will cause distortion. Remember: impedance is a function of frequency, therefore a good matching across the audo spectrum is important. Be sure you know what you are doing when go passive. One or two resistors do not necessarily mean "shorter path" than a few active transistors. If poor matched, it can be a "distorted path".

It is like to drive a low efficiency speakers with set amp, a wrong combo still makes bad sound.
If the output of a CD player ( or any other line level device ) can EASILY drive an amp to clipping and beyond with normal signal levels, it should be fine to use in "direct drive" mode. As Twl points out though, you may have to pay attention to line lengths and impedances to obtain optimum results.

Other than that, some analogue outputs on CD players, etc... with built in potentiometers are of low quality. Obviously, if you spend the money on a more expensive unit, "chances are" that they will have used ( hopefully ) good quality components.

Just keep in mind that some CD players do NOT output as much voltage as they are rated for. On the same hand, some power amps require more voltage to attain full power than other amps. Mating a "weak" CD player with an insensitive power amp will typically result in the loss of dynamics / flat sound that many here have commented on. One can somewhat "make" this type of situation occur due to impedance mismatches between the CD output and amplifier input. In order to get around this, a CD player or DAC should be able to deliver at least 3 - 4 volts of output without putting up a fuss. If you can do this, you should have plenty of gain to compensate for even those "quietly recorded" CD's and slight impedance mismatches. In such a situation, you will still probably even be able to overcome major impedance mismatches but sonics ( tonal balance and transient response ) may suffer. Sean
I like to simplify the ACTIVE VS PASSIVE (or dirrect source to amp) scenario like this:
...with out being technical, it's usually like the difference between a HONDA Civic that can over rev it's engine and RPMs while going 120mph, vs a Turbo Porche that has much more snap,torque, overall power, response, and performance at the same 120mph!!!
In the case of most passive set ups(or no-preamp set ups), sure you can get the overall volume level up. But what seems to happen is a lack of overall dynamic control and body to the sound, which an Active preamp set up can overcome by proper amplification of it's signal! Even weaker amplifiers with higher wattage ratings can push the volume level higher, but it's also flat and 2 dimmenstional, and strained as well! (i.e, cheap reveiver amps). I'm also not so sure that just having PROPER IMPEDANCE MATCHING is the key. I think you can still get a good impedence matcy between CD player and amp, and still not get the dynamics you would from a properly designed active preamp! Hum....
Also, for the record, I've talked to PLENTY of aduio engineers and speaker/equipment designers over the years, and they often think things are a matter of simple mathematical and physics equasions! What I find is that usally these are the guys that don't have the best sound from their systems also! There's an old saying.."if it ain't broke, don't fix it!" And the quality active preamp works for all practical purposes!
Anyway, I've yet to hear even the expensive Wadia's sound as good dirrect to an amp, as they do with a good preamp infront of it! That's what I find anyway. And I've heard a lot of passive set ups!...a lot!
THE ONLY way you'll find out the differnce, is to try both, experiment, and then you'll know!
good luck