Who makes the best passive volume control?

The Lightspeed is the best we have tried.

However all passives have certain limitations, and if you exceed those limitations, they will color the sound quite noticeably, and rob you of dynamic impact, regardless of how good they are.

The primary limitation is cable length. By the time the cable is even 6 feet long, the loss of bass and impact is easily heard. At full volume it will not be such a problem, but as you back off on the volume control, it will be very much like operating a sort of tone control that rolls off the bass. This is caused by an interaction between the output impedance of the source, the resistive value of the passive unit at the particular volume control setting, the characteristics of the cable and the input impedance of the amplifier. That's a lot of variables.

It is for this reason that you will see an on-going debate about whether or not active preamps can be more transparent and more dynamic, with greater bandwidth. Some active preamps are much better at this than others! In theory, the active line section should control the cable so that it has no artifact. In practice, this is rare although there are examples (most of them being balanced designs). However, if it does control the cable the passive will not hold a candle to it.

i duno if they are best, but they are certanly very good:
(using them for more then 3 years with various amps)

http://www.positive-feedback.com/Issue19/endlerattenuators.htm

or

http://www.icl.co.jp/audio/english/Model5/m5-1.htm

What about Burson stepped attenuator?

Atmasphere,

A little OT but how can you tell if an active is controlling the cable in the way you describe? Any good way of measuring this? In something like Stereophile's equipment measurement, any particular that will give agood idea of cable control, degree of cable control or likelihood of cable control?

Marebg, those are one passive approach I have not tried, but
it sure does help to eliminate an IC, for reasons Ralph
alludes to. I would have a bit of an issue with the
ergonomics of the Endlers, but I suspect they sound very,
very good.

That being said, there are several aficionados of passives
that have tried the gauntlet, including Endler, that once
trying the Lightspeed have concluded it is the best sounding
passive of any topology. I do think that Endler-type
Lightspeed would sound the best, but it would be a bit more
complicated to design and that is not the designers way -
though I am sure there would be a market for it - get rid of
the IC, the final frontier:)