I'd like to learn about volume controls

I've been researching preamps (I currently am very happy with an FT Audio LW-1 passive preamp) and I'm very curious about volume control designs. I know there are different types and different quality. Where can I learn about volume control design, or can anyone briefly explain the differences? Thanks.
I'll try to help you, with what I know about them.

All volume controls cause a loss of some kind, in the signal path. One of the goals is to try to get the least signal loss, and still retain control of the volume. Higher quality Potentiometers, which are actually "variable resistors" like Alps, and Noble, are a common solution. Some go further, and used "Stepped Attenuators" which have rotary switches in them instead of infinitely variable potentiometers. These switch progressively incremented resistors into the circuit, depending on how far you turn it. One of the drawbacks of this design, is that you can't get any "in-between" volume levels between "clicks". The advantage is, that the individual high-quality resistors give a less degraded signal. Due to cost, sometimes the "clicks" are 4-5db apart, and cause difficulty in attaining the exact listening level you want. From what I have read, the minimum steps available are 1.2db each. This amounts to alot of Caddock or other expensive resistors, and can increase cost dramatically. These controls can cost upwards of $600 just for the part, not the component. There are several different designs for these, such as "ladder step" and "shunt", and maybe some others that I don't know about. They have pro's and con's. From my understanding, the ones that route the signal through only one resistor for each step, and don't progressively add resistors to a stack, are the best sonically.

There are also some "add on" remote control volume controls, that connect into the tape-loop of your preamp. Generally these are voltage controlled amplifiers, and are easily controlled by the remote control. I have not used any of this type, but from what I have heard, they are sonically not as good as the other types, but more convenient.

Next, I have heard about some new variable transformer volume controls, that people say some good things about. I have never used them. I would like to hear them to see how they perform.

Finally, there are digital volume controls, that are sometimes used on CD players. These do some manipulations in the digital domain instead of the analog domain, like the others mentioned above. They have been derided as signal destructive devices, that drop "bits" to alter the volume. Most of the threads on this forum that have discussed this issue have concluded that the digital domain volume control is not good for sound.
Twl pretty much covered most of what we need to know. I would just like to add a couple of points. First off, as we know, volume controls are really attenuators. When you connect a cd player directly to a power amp you are getting the full output and you need a way of taming it via an attenuator. You can use either the cd players' output control or gain controls on the amp.

As TWL mentioned, many cd output controls are in the digital domain. And yes, you will lose bits (resolution) as you attenuate. In theory you lose 1 bit for each 6db of attenuation. That's how we get 96db s/n ratio for a 16 bit device. Divide 16 into 96 and you will see what I mean. 24 bit devices (in theory) get you 144db of resolution.
As an aside, 24 bit devices are usually more like 20 bit because of various limitations like thermal noise, etc.

Personally, I prefer to use an active preamp, staying away from external volume controls and passive preamps.
I seem to recall a article written in The Absolute Sound about a year or so ago, about a product called a Silver Rock Transformer Potentiometer from a Swiss company called Audio Consulting. In addition to a high quality transformer (for noise reduction I believe) they have a unique passive volume control that seems to work differently than most. Sorry I don't remember more about that volume control or the way it works, but I think it would be well worth investigating. Here is a site that may help you start on your journey www.referenceaudiomods.com
Hope this help and
Thanks for listening,
BAT's website (balanced.com) has a description of their research into various types of volume controls that you may find informative. Click on the "resources" tab to get to the "white papers" -- the one you want is titled the "i-series white paper".
I think Melos, Big Dog(?) and TacT have/had some interesting volume controls.