Preamps can color sound considerably. Surprising?

when compared to a good passive, it's just no contest.

I've tried many passive preamps, thinking "that must be the answer". It isn't--they  are all dry and flat.

Passive Volume Controls are very susceptible to interconnect cable interactions, combined with the output capacitance of the source and the input impedance of the amp. If properly set up they can be excellent and if anything is off the very same unit can sound 'dry and flat' because of adverse interactions.

In any event you have to be careful of the interconnect cable; if you've auditioned cables and heard differences you know what I'm talking about.

Active tube preamps usually have output coupling capacitors which, no matter the quality of that part, will color the sound. In addition they are often single-ended circuits and so too are susceptible to interconnect cable interactions.

If you really want to hear what the recording sounds like, you have to eliminate the interconnect cable as a variable. The balanced line standard (AES48) offers a means to do that, but you have to adhere to its tenents to do that and most balanced high end audio preamps do not. 

I use recordings I made that are on LP and CD so I know what the recording is supposed to sound like. They are very helpful when a reference is needed (is it too lush or too dry or whatever...) to know what is going on...

@atmasphere,

could you kindly also get into the differences between attenuation and amplification? It seems hard to get across that most dacs only need the former whereas adding a pre by definition adds distortion. (While this may run counter to commercial interests, a degree of intellectual purity seems desirable in this discussion…)

Pretty much all capacitors inside a preamp Color the sound. Are capacitors the sole culprit in coloring the sound? Great capacitors, like Teflon, allow the dynamics to be where they should be. The peeks and the valleys are respected. Assuming you have a great amplifier to go along with us.

You hear preamp manufacturers touting our device gets out of the way it doesn't interfere with the music.  This could not be further from the truth. 

Call it is what it is.

could you kindly also get into the differences between attenuation and amplification? It seems hard to get across that most dacs only need the former whereas adding a pre by definition adds distortion.

@antigrunge2 

The problem we're all up against is that Redbook requires for more voltage than any power amplifier would ever need. So the signal has to be attenuated to do any good.

That means that in the case of a passive the control value becomes critical. Lower values like 10K work better, but most sources won't support driving 10K- they are more comfortable driving higher impedances. This can result in a loss of bass and distortion on the part of the source if its having issues.

Active preamps do indeed add distortion. However they tend to be less susceptible to interconnect interactions. There are four functions that any line stage should have:

1) volume control

2) input switching

3) supply any needed gain

4) control the interconnect cable to prevent interaction

Of these the 4th is least understood in home audio but well understood in pro audio, which is why they can use inexpensive cables and still get neutral sound.

If the active line stage is good at controlling the interconnect cable it stands a very good chance of being more neutral than a passive device and possibly also lower distortion, depending on the passive device to which its compared.

So its a mixed bag, which is why this conversation persists.

@atmasphere 

If the active line stage is good at controlling the interconnect cable it stands a very good chance of being more neutral than a passive device and possibly also lower distortion, depending on the passive device to which its compared.

So its a mixed bag, which is why this conversation persists.

Such a keen point. 
I n theory and on paper, the passive approach should be more invisible/transparent, more out of the way. Yet in practice, a high quality active will often yield the better or more realistic sound quality. It is indeed a “mixed bag.”

Charles