Passive Stage preamp vs Active Stage Preamp

marakanetz: while it may not be true with your transport/dac combo, some high-quality dcp's offer digital volume controls that may substitute for pots in analogue pre's. i'm personally acquainted with most of the accuphase line, having owned several of their components and listening at great length to most others. in my experience, the single-box acuphase dp-75v and the dp100/dc101 sacd/cd combo both sound significantly better when run directly to an amp of equal quality to the digital units than run through a pre, even one built by accuphase. soundstage widens and deepens and the sense of PRaT is quicker and more life-like. more importantly, the sound is cleaner, as though a veil were removed from the speakers.

i do agree with albert porter that you will not likely prefer a digital source run directly to an amp (tube or ss) if you are a diehard valve fan. a great tubed pre, like the aesthetix callisto or its sister phono stage, the io, will sooth the soul of many who'd rather be playing vinyl records than listening to a laser detect the binary reflections off a piece of metal-coated plastic. i additionally confess that i've not heard ANY source, no matter how cheap or dear, that didn't sound better played through a boulder 2010 preamp. 'course one might expect such after plunkin' down $36k. -kelly

It has been said many times that simpler is better. I believe that to be true in a lot of situations but is not always true in passive preamp. Albert talks about impedance matching being a problem in passives. It is a misnomer to talk about matching impedances because in a standard pre / power combination the output impedance of the preamp is many times smaller than the input impedance of the amp. It is the desirable low (~100 ohms) output impedance of the active preamp designs that allows the pre to drive the capacitance of interconnects without frequency degradation.
If one was to match the output impedance of the preamp to the input impedance of the poweramp you would only get half of the open circuit voltage output of the preamp into the amp. Tube amps typically have a higher input impedance that solid state but the designer is free to set the value to practically any value within reason. With the higher input impedance of a tube design it MAY be more sucessful with a passive pre. The biggest problem with a passive preamp is the higher output impedance (1000 ohms or greater) can react with the capacitance of long cables and dull the top end. I use a buffered passive design most of the time. It has a gain of one but an extremly low output impedance. I find that it can drive most power amps to full output and has the ability to drive a capacitive load with ease.

Several of the variable output CD players have a low output impedance. If they have enough voltage output to drive your amplifier to full output, I would believe you could do no better. I feel that the best sounding preamp is no preamp at all! If the system does not require the added gain or a lower output impedance, I do not feel the added switches and circuitry can improve the sound.

Chris

I recommend a "Search" in the Audiogon Forum archives, for this topic has had a lot of discussion. I don't know that there is any "importance of using active stage in tube setup": I've been happily using passive preamps with three tube power amps. You don't want an impedance MATCH between passive and power amp, but rather a power amp input impedance 5 or ten times as high as the passive's output impedance, namely, the "size" of the passive, typically 10K ohms. But I've also used a 10K ohm passive with Pass Aleph 3's, whose input impedance is only 23K ohms. I think the more crucial factor is whether your source output stages are up to driving a passive, or whether they need active preamp help. In general, don't believe what lots of people will tell you: that dynamics MUST be hurt by using a passive. They CAN be excellent, with good source output stages.

I agree with most of the above with a few exceptions. I agree that a passive pre-amp is difficult to implement, but not "always" bettered by an active. I have tried several different combinations and have found at least one that works. It requires the following 1) a front end designed to drive an amp directly 2) a very high quality passive stage 3) an amplifier with sufficient gain to make up for the lack of gain in the passive preamp. The recommendation of the Aesthetix units is right on the money. I am using the IO phono unit through a Placette passive preamp and it is very nice. However, the IO is specifically designed to have enough output to drive an amp so in that sense it could be considered a phono stage and active preamp in one. The statement about lack of balanced options is also incorrect, Placette offers a balanced version of their passive preamp.

I'm pretty much with Albert on this one. While i haven't played with a LOT of passives ( a few ), i have always had better results with an active unit. Don't know the specifics as to why, as i've tried TONS of various cables, source / amplifier combos, etc...

As to the rated sensitivity of an amp, don't take that spec as being written in stone. A single tone can generate a higher output level than a broadband dynamic signal. Since music is a broadband dynamic signal, you might need more than the specified amount of input voltage to reach full output even though the amp meets spec under test conditions on the bench with individual narrow bandwidth tones. Sean
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