What is a preamp?

I came upon this question when considering whether to leap for a Theta GenVII Dac/pre or maybe get a Gen Va and a good tube preamp. Theta's lit says that the GenVIII comes in 2 versions, one with volume control and one without. Somehow, just having analog volume control makes it a preamp. Do I understand correctly that switching and volume control is all a preamp is? Nothing else is happening to the signal? Why are good preamps so expensive then? And why do they vary so much in design of the circuitry? It would seem to me that the simpler the better, and volume control attached to the dac couldn't possibly be bested by a separate box with more cables, but I bet there would be lots of debate if I posted a Gen VIII vs. Gen Va and a tube preamp thread (actually I think I'll do that). What am I missing here folks? Thanks in advance. -Dave

Optimally a preamp would only switch sources and control volume without addition or subtraction to the signal. However, by simple virtue of a signal passing though another device there will be degradation and timbre change. This is subjective and incremental depending on quality of materials and design parameters.

Ulitimately, the addition or subtraction may be synergistic to the system's overall voicing. Years ago I ran bright electonics (Audionics pre and GAS Grandson amp) with Rogers LS3/5A speakers(somewhat dark and rolled off). The balance was suprisingly very decent.

Over decades of setting up systems for others and myself, I find it tiring the rhetoric of right and wrong sound. Maybe on one system the recording actually sounded better because of what the studio was using for mastering amps, type of mics used and the degree of liveliness of that studio.

Go forth, pick the preamp that sounds good to you in your system in your environment and be happy. And for God's sake listen to some music instead of to the equipment!!
Don't forget the buffering effect of a preamp because a preamp is an amp. That is probably its main advantage other than volume control and switching.

In most cases, the preamp actually runs below unity gain, which means that depending on the design of the volume control, the preamp spends most of its time attenuating the output of your CD player or phono stage. But the amp stage is still present and acts as a buffer. This can give an advantage when it comes to dynamics. Everytime I tried bypassing my preamp and running direct to amp, dynamics suffered so much that any possible theoretical advantages were swamped out. I've been using a preamp ever since.

I have found that using an active preamp rather than going direct or via a passive pre tends to produce a bigger soundstage but at the expense of some purity and micro-focus. Active preamps also tend to give you more "drive" and sometimes improved dynamics. I am not of one mind about any of this, however The larger soundstage may very well be an artificial exaggeration.