Everybody knows but me

[JNorth1178]

I am embarassed to ask. What is a passive preamp? What are the other options? What kind of preamp does one want for a stereo system? JNorth1178

[Dusty Chalk]

And here I was, thinking this was going to be a thread about Anna Nicole Smith being dead...

Passive as opposed to active pre-amps. A passive is basically just an inline attenuator, either using a variable potentiometer or a stepped attenuator. Passives are fine for minimalist systems, where you want the least amount of electronics in your signal path, but you could be paying a price if you don't watch your input and output impedances of your associated gear. An active will usually provide a much nicer load to the source and to the amp. "Usually" being the key word there. I have passive volume control built in to my Manley Stingray, it's basically a dual monoblock with input selector and separate stepped attenuators.

[Feanor]

I am embarassed to ask. What is a passive preamp? What are the other options? What kind of preamp does one want for a stereo system? JNorth1178

What Dusty said; and to expand on that further, a passive preamp doesn't increase the input voltage from the source component. The "standard" or typical 2 volt output from, say, a CD player is plenty strong enough to drive most amplifiers to quite loud listening volumes; most of the time you will only want to reduce that voltage which can be done without powered electronics. I use my current Adcom GFP-750 preamp in passive mode though it's unit that can operate in active mode too.

A rule of thumb is that for passive to be viable is that the output impedance of the preamp should less than 1/10 the input impedance of the power amp, given fairly short interconnects.

[hermanv]

A truly good sounding pre-amp can run into many thousands of dollars, even tens of thousands can be spent for those pre-amps rated among the very best.

With the right system a passive pre-amp can often equal this sound quality for far less money. This is because they are remarkably simple and have no transistors, op-amps, power supplies or any of the other devices which initially appear to be straightforward, but in actuality require extensive design effort to really sound their best.

I've tried a potentiometer based passive and found it wanting. I built my own passive using a Shallco switch (silver to silver contacts) Vishay resistors with Cardas wire and RCA jacks. I would put its' sound against some of the finest pre-amps in existence. Passives have a reputation for compressing dynamics, mine doesn't seem to at all, but this is quite likely systems dependent.

The passives I've heard are quite sensitive to interconnect cables. Whether they reveal cable differences better or are more demanding as a cable load, plan on using some first class cables to get the most from a passive design.

First class inexpensive passives are made by Placette and Audio Synthesis. There are probably others but these are quite reasonable used and sound truly wonderful in the right system.

Another style of passive pre-amp uses either tapped or continuously variable auto formers (transformers) the advantage of this design style is much better control of input and output impedance, the disavantage of this technique is that it is difficult to make transformers with 10 octaves of bandwidth. These kinds of passives occasionally use pure silver wire tranformers and can get quite expensive.

Unless you are lucky enough to be able to afford a first class pre-amp, I urge everyone to give a quality passive an audition. Perhaps you too will be stunned by what your system can do with a cleaner overall signal.

[FLZapped]

I am embarassed to ask. What is a passive preamp? What are the other options? What kind of preamp does one want for a stereo system? JNorth1178

The trerm passive pre-amp is an oxymoron.

It is nothing more than a potentiometer (variable resistor)

I wouldn't waste my time with them myself.

-Bruce