A friend of mine in the US was telling me about his system and mentioned he has one of these as his preamp. I've never heard of this before. Can anyone explain how it works? Anyone ever heard a preamp using this design?
Passive preamps have no amplification circuitry in them. Basically they have a volume control and various input/output switching controls.
Like any other design they have pros and cons.
Pros include - very little chance of distortion or noise being generated by a few bits of wire and a switch or two.
Cons include - sometimes can sound a bit lazy or sluggish. Probably due to input/ output impedance mismatches between the preamp and a power amp.
They have been around for many years especially in the American market, but have never become mainstream.
There are some very good examples in the UK,the best at the cheap end of the market being the Creek Audio passive pre,which has the advantage of having a motorised potentiometer and thus offers remote volume control.
At the other end of the market is the Audio Synthesis Passive,which will cost you the thick end of £600,and will compare very well with active preamps in excess of £5k(I have one of these,and can vouch for that,as will Martin Colloms from HiFi News).
The main drawback of a passive pre is that devices with high source impedance may suffer a loss of treble when put through a passive pre...otherwise,if all that you require is attentation of a source signal such as CD,then the results can be excellent.
I would agree that cheaper passives can sound constricted and slow,but the Audio Synthesis models are superb.