Preamps can color sound considerably. Surprising?

when does the preamp’s additional voltage kick in? Most preamps in most systems are still used in attenuation mode, ime.

In attenuation mode, all a pre does is add distortion if impedances are properly matched.

All volume control systems, whether active or passive, attenuate the signal from a digital system. This is because the Redbook requirement is for too much voltage for the power amp so it has to be attenuated.

Passive systems can cause the source to make distortion depending on the value of the control in the passive. In addition they can introduce colorations since they lack the ability to control the cable. Successful passive setups are due to extreme care and/or very good luck!

The dudes over at the science whatever site are all telling this is the way to go. I think there’s more to it than that personally.

You are correct. The 'dudes' have yet to realize how an interconnect can influence the sound of a system if the variables around it are uncontrolled. This is where an active line stage can be quite helpful, in addition to superior volume control (over a digital volume control).

Am I right in saying that most digital devices are designed to have low output impedance?

@antigrunge2 

No. They are likely deigned to have good sound and or good performance (which are not always the same...). Some have tube outputs and are designed to have as low an output impedance as the tube will permit... at any rate, low output impedance isn't usually the goal although its usually desired.

One of the main reasons we've sold line stages over the last 25 years and right to this day is that analog volume controls often outperform digital volume controls. With an active preamp you then set up the DAC to have the volume all the way up so there is no resolution lost, and then control the volume with an analog control.

The problem with a passive is the volume control is a series element with the output impedance of the source. This means the source impedance is raised quite a lot insofar as the interconnect cable between the passive control and power amp is concerned (and also as far as the power amp is concerned).  So controlling the interconnect cable, even if the control is 10KOhms is a lost cause. That is why passives are so susceptible to interconnect cable interaction.

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.

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...