I've had my Benchmark LA4 in my system for a couple of months now. I've used it in place of my Conrad Johnson Premier 16SL2 tube preamp.
My Thiel 2.7 speakers are being driven by CJ Premier 12 tube monoblocks. I use a Benchmark DAC 2L as my digital source, and a good turntable/phono stage for vinyl.
My impressions so far:
Negatives:
1. I share some of the list of gripes posted by Rich B so won't repeat them. I also find the volume knob a bit plasticy and clicky, feels more toy-like than I'd want. I actually find the volume knob on the DAC 2L preamp section to be more luxurious - it's turns smoothly and quietly yet also provides a subtle clicking sensation as I dial the volume, which I like. I really love the minute volume steps offered by this product as I HATE pre-amps with coarse volume steps. On the other hand I've found the remote control of the volume to be more fussy than my CJ remote controlled pre-amp. It seems like I start pressing the volume up, barely hear a change and then suddenly it increases quickly and I can over-shoot. My CJ remote operates more smoothly. Also, the CJ remote offers discrete input selection, very helpful when I'm switching between my digital and LP source. (And sometimes I'm doing it to compare the two). Where the LA4 forces me to toggle through "dead" inputs to get back to a source.
Finally, I'm not very big on the aesthetics of the plain looking box. I do like a bit of audio jewellery and love the look (and glow) of the CJ preamp.
Positives
2. Operation/Sound!
First, while I'd like a smoother feeling volume knob, I nonetheless do appreciate a volume knob over my CJ pre-amps volume, which use"down" and "up" volume buttons. A knob is much simpler to use, and was one of the attractions of the LA4 for me.
I also like, if conceptually, the synergy of having a Benchmark DAC hooked up to a Benchmark preamp. Feeling of confidence. I also enjoy on a conceptual level - or a pride of ownership level - that the LA4 represents such a high level of no-B.S. engineering, and that it seems to be at about the top of the heap in terms of objectively verifiable performance (neutrality/low distortion etc).
As I said, some of that is "conceptual" pleasure because, given I use some old tube amps and often listen to vinyl as well, my system isn't going to be taking full advantage of the performance of the LA4. But my motivation in buyin the LA4 wasn't to achieve best possible (and likely inaudible to me) transparency, but rather "more neutrality/transparency than my tube preamp" which is a lower bar to clear, it seems to me.
In other words, it just had to give me something more neutral than my preamp in my system.
Beyond all that I have nothing technical to offer - all that is in Amirm and other people's measurements, and that's not my expertise anyway.
So on to my
subjective uncontrolled listening impressions -
my advice is to stop reading now if such things annoy you
My listening impressions are that the LA4 is a damned impressive addition to my system! All this is in the category of "subtle differences" but (presuming FTSOA they are there) these can make large subjective impact to those who care about such things.
I'd always found the CJ preamp added a slight bloom to the sound (images seem to expand a little bit) and a sense of roundness and body (where a voice sounds a bit more corporeal and occupying solid space between the speakers, rather then a see-through apparition). Also a tiny bit of "sheen" and "texture" that seems to make voices and instruments a bit more vivid and present (and to my ears slightly more "reminiscent of the real thing."). Though it all came at the cost of a very slight generalization, a mild coloration I was aware of, even though I love it.
With the LA4 any such suggestion of those colorations from the preamp are gone. It just sounds eerily transparent and neutral, yields a psychological sense of "very quiet" where incredibly subtle details - e.g. a drummer in a quiet passage tapping his hi-hat super softly - seem to just occur in the room with no sense of an artificial haze around the sound. Super, super clean. Similarly, there is the sense of hearing every iota of information in a track, down to the most quiet, distant, subtle detail. That triangle lightly struck, mixed waaaay back and deep in the mix in it's super subtle halo of reverb? Effortless to hear with total clarity. There's also a sense of cleaner timbral character to everything - from how drum cymbals are differentiated, to drum skins, to the character of a sax vs trumpet etc. There isn't that slight sheen added that slightly generalizes the timbre, and so instruments and voices seem that much more differentiated. One of my main gripes with the CJ preamp is that drum cymbals sounded a bit too similar and high hats especially could tend to sound a bit more like "modulated bursts of white noise" where on the LA4 the particular timbre of metal is preserved, making that aspect of drums more convincing. The brassy metallic quality of a trumpet vs the reedy quality of a sax is a little bit more revealed. Which I love.
It's definitely been an audiophile occasion to listening to lots of music again, re-appreciating various aspects with the LA4 in place.
Am I going to fully replace my CJ preamp with the LA4? I'm not sure yet. There are still pluses and minuses to each, subjectively. The CJ is a bit more richer and filled out and seems to produce a slightly more consistent "sense of thereness, density and realism" to my ears, at the expenses that I've noted, the LA4 more neutral, detailed and transparent to the source, which can sound a "bit on the thin side" but which can also often sound "more real" given the recording. It has lots of allure to my ears. I haven't put my CJ pre-amp back in for quite a while, so it will be interesting to see what I think after having lived with the more neutral LA4 for quite a while.
My apologies if all this is a distraction to the thread, but wasn't sure where to put it otherwise.