difference between an active and a passive preamp?

Should I be depressed that I am tempted to recycle posts I wrote 7 years ago, and that I remember them? 'Cause I am....

In any event, from the way-back machine in '04:

Just to add a couple more simplistic thoughts to the already excellent discussion from an absolute layman’s perspective, "volume control" generally can be achieved by two basic means, either attenuating (that is reducing) the signal that comes into the control or by amplifying it (which I have understood as adding gain). An active preamp is called that because the volume control can do both of these things--it can both reduce the signal from the input level towards zero and it can (because it has an amplification stage) amplify the signal above the input level. A "passive" preamp, on the other hand, is passive because it can only reduce the input level -- it will not have an amplification stage at all.

For most sources, the output level of the signal (which is the input at the preamp) is relatively high. Which is to say that at zero gain at the preamp (no attenuation or amplification of the signal) the volume level will be relatively loud. (Which is how passive preamps/volume controls can work -- based on the assumption that the volume associated with zero gain will be louder than you ever want or need, therefore attenuation or reduction of the signal level can provide all of the volume control range you would ever want).

Compared to just about every other source out there, however, the output signal that comes off of a vibrating pin scratching across a rotating platter of vinyl is tiny. So tiny that, without additional amplification, the signal would be too weak for a volume control designed to provide a useful range for things such as CD players to do much anything useful with at all. Thus, in order to jack the tiny output from a typical phono cartridge up into the range the your average preamp volume control was designed to operate in, you need some additional amplification. This is why a phono preamp is a separate or additional piece of equipment (or stage in your existing preamp) from your plain vanilla preamp -- it independently amplifies the signal coming from the cartridge up into a range useful for your average volume control. The gain level of the cartridge dictates how much more work the phono stage will have to do to get the signal up into this useful range. Did my layman’s understanding screw that all up horribly?

Not at all, Mezmo. I'm not technical and it made perfect sense. Audioflyer: I was recently sort of in your position. Just a few weeks ago I was posting about my passive pre. As someone who went in blind, I can tell you what I encountered. Once I had it hooked up, the level of transparency people keep talking about was immediately apparent. My cd player was completely wrong, however, because of the impedance issues already mentioned in the thread. There is a loss of that in-your-face sense of detail and some roll-off. Still, I prefer it immensely to my previous solution. I ended up replacing my cd player almost immediately for better impedance. Alternatively, I probably could have gotten a buffer.

I'm not experienced with tubes or even the "tube sound." Some friends of mine more experienced with this have said that I've achieved a bit of a tube sound with the passive--I believe other passive pre users on this site have often reported the same thing. It's been interesting how loud it can get without being uncomfortable. Before, with my active pre, which wasn't a stellar piece of audio equipment anyway (Lexicon DC-1), the high end was just too sharp and fatiguing, especially at high volume. Now, more volume just yields more rich sound.

As has been said, an input sensitivity of 20 k0hms is a bit low. What's the output impedance of your cd player? What's your budget? Knowing nothing else, if you're interested in the passive solution, I'd do what Clio09 said.

Note: I misunderstood your last sentence, Mezmo. No wonder your layman's understanding suited me so well. ;)

To be on the safe side when using a passive preamp, I would want my source to have an output impedance less than 500 ohm, source output voltage at least 2V (this also depends on the input sensitivity of your amp), my amplifier input impedance greater than 50k ohm, and total interconnect length from source to amp not longer than 6 feet. In my system, I have a autoformer passive preamp, USB DAC with output impedance of 50 ohm and output voltage of 2.5 volts, amplifier input impedance of 100k ohm (with input sensitivity of 1.25 or 2.8V depending on the amp), and total interconnect length of about 5 feet. This way I can have all the transparency, naturalness, and openness of a passive without significantly losing dynamics of an active preamp.

Dracule1 said:

source output voltage at least 2V (this also depends on the input sensitivity of your amp)

Can you expand on this?