Over my years, I've owned a startling number of stereo preamplifiers. The vast majority have been gross disappointments. Preamplifiers ALWAYS change the sound, and usually for the worse.
Yes, preamplifiers have some undeniable virtues - They allow for switching among various sources, (usually) high-quality analog volume control, (sometimes) phono stages and HT bypass modes, (occasionally) tone controls and bass management, and they have robust enough output buffer amps (in most cases) to drive virtually any power amplifier. But in exchange for those virtues, you also lose some things - tonal fidelity to the source, soundstage depth and width, and the expense and hassle of having another damned box in the signal chain.
Now over the years, I can think only of a few out of the very many that I could abide. Most were intolerable. Models that I tried and found lacking came from companies such as:
Rotel
McIntosh
Conrad-Johnson
Audio Research
NAD
Lyngdorf
Emotiva
Parasound
And many, many more.
Now note that some of these "rejects" had [u]spectacular[/u] specifications - ultra low noise, higher than audible channel separation, vanishingly low distortion figures, etc. And despite these measurable virtues, their sound wasn't as good as using a variable-volume-source directly into the power amplifier(s). So obviously, specifications alone do not a great preamplifier make.
By contrast, I can think of only a VERY few preamplifiers that were tolerable or better:
The McIntosh C41 was acceptable, but not remarkable
A 1970's Mark Levinson (model not recalled) was remarkable for its transparency and imaging
A 1970's Van-Alstine modified Dynaco PAS3 was also remarkable for the same reasons (despite tube colorations)
And that's it. Those are the preamplifiers that I've been able to really admire.
And now, to that trio, I have another preamplifier that I must add to the short list as being remarkable for its sound. And I must say that my audio amigo, @garbulky, has been sold on this preamplifier for years solely from reading its specifications. He's never heard it, but he thinks it's the best in the world! And I've consistently given him a seriously hard time about being so gung-ho for a product he's never even heard. Well, he was right - I was wrong. This puppy is world class. It reminds me most strongly of the Mark Levinson line of products. And that's saying something since this preamp sells for about half or less what the ML products go for.
The product is the Chinese "Audio GD HE-1" preamplifier ( http://www.audio-gd.com/En%20audio-gd.htm ). Since there are (to my knowledge) no US distributors, you'd have to either buy used (as I did, from fellow Lounger @brutiarti) or buy directly from China. A number of things worried me about this purchase:
Even on the used market, this isn't an inexpensive product
Having purchased used, there is no warranty
The manufacturer has no authorized service centers in the USA that I know of
The circuitry and design are sufficiently non-conventional and sufficiently complex that you'd never find a shop willing to fix one of these
The darned thing is heavy and runs hot
But @brutiarti told me that it worked, and I trusted him. The trust was well-placed - the preamp looks like new and sounds AMAZING. So what's so great about the sound of this preamp that makes my system sound better WITH the preamp than without it? Now that's a complex question in and of itself. Theoretically, a preamplifier should add or subtract absolutely nothing from the signal coming in. In fact, unless tone controls, phono preamps, or bass management are in play, the EXACT analog signal coming in should be EXACT same as the analog signal going out - except for a different voltage (volume).
The McIntosh C41 was the closest to this theoretical ideal of "the straight-wire with gain." Yet it isn't my favorite preamp! Why not? The Levinson, the Van-Alstine PAS, and now the Audio GD all add something that doesn't seem to be there in the source. Now the purist would argue right there that we have proof-positive that my three favorites are inferior. Yet I prefer any of the three "winners" to anything else I've heard. Why? In a few words, detail, transparency, and imaging.
Detail - With my favorite preamplifiers, there seems to be more musical detail. I can hear "further into the midrange" and the treble (a potentially problematic issue, depending on the source) is detailed without becoming shrill. How do these preamplifiers do it? Are they rolling off the treble? Not that I can tell. The treble detail and even "ariness" are still there, but without even a hint of upper midrange screech or glare. And this is with the Oppo UDP-205 being used as a DAC (with its glassy-sounding Sabre DAC). But the Oppo doesn't sound glassy with the Audio GD preamp. What's happening here? I really don't know, but I definitely like the effect.
Transparency - This ties directly to the "more musical detail," but while some components can provide detail with a heavy hand, the Audio GD manages to sound delicate when needed. Not every preamp can do this. In fact, most fail utterly. But the HE-1 has "transparency" in spades.
Imaging - The effect of the Audio GD on imaging is virtually identical to what I hear from the MicroRendu. No kidding. That "WHOOOT - Dere It Is" experience is in full bloom with this preamplifier. I get deeper and wider imaging with this preamp in the signal path than I do with the Oppo driving the power amplifiers directly. Why? No idea - but I'm pretty sure I could consistently identify the Audio GD vs. the Oppo direct in any of the mythical "double-blind-tests." Do I want to spend my time proving that statement? Nope. I'm too busy listening. But maybe someday...
Now my introduction to this preamp is going to be very, very brief. Once @garbulky finds out that I have it, he's going to abscond with it immediately, and then become very hard to find until he's gotten his fill. Such is life, and friends are worth the sacrifice. But thanks to the Gar for stimulating my interest in this product (that I never would have heard of, otherwise) and to @brutiarti, who sold it to me.
It's been a long, long, long time since an audio purchase provided this much enjoyment this soon. What FUN!