It depends on the preamp. A few years ago I was looking at preamps that did one or the other and sometimes both. Many of the posts above describe the "both" situation. Many preamps have A/D conversion where the analog signal going in (from a DVD or CD player, for example) is converted to digital. Mainly this is done to apply processing such as DD,DTS,PL2 or some other music mode. Some preamps do this as a matter of course, regardless whether the signal is "processed" or not, the preamp just converts all incoming signals to digital and back to analog again on the way out. These seemed to be more in vogue a few years ago. I personally was never a fan of this concept since the sound would never be better than the DAC's inside the pre-amp. Why would someone want to have their SACD signal or signal from a high-end CD player converted, yet again, to digital?
Most pre-amps I have seen do both pure analog in and digital in. These are what are being described in the above posts where you have analog and digital inputs. The analog inputs remain analog throughout the preamp and go out analog as well. Some machines require you to use a "bypass" mode to accomplish this. Using this mode will, of course, bypass the processing of DD and DTS (and others). These same machines may have digital inputs which utilize the DAC's within the preamp for D/A processing. You would probably opt for all analog with a nice CD or SACD player for example, but might go digital in to the pre-amp if the DAC's within the pre do a better job than the CD player. If you spent big bucks on a preamp with a great digital section you may want to consider using that if you had a $100 CD player hooked up to it:-)
An all analog preamp/processor is a very rare beast, one I haven't seen since the days when Pro-logic ruled home theaters. In fact, I *think* at that time only Lexicon and Meridian (there may be others) did A/D conversion to the incoming signal. Your much more likely to find all analog preamps (no pre/pros) today.
I often lament the days where you could buy processors only that would do all the HT and music surround stuff and did not function as a preamp. I still think this is the best way to go! Ideally, you would have very high quality preamps that could accomodate 2 or more multichannel inputs and everything within the unit was analog. The processors, a separate box, could be swapped out every few years for those needing the latest/greatest in surround.
- Tony
