I don't have a Backert brand preamp but Bob has extensively modified upgraded my conrad johnson PV-12. All of Bob's work is proprietary. The circuit boards in my PV-12 are of his design. The cj kept the textural smoothness of the original, but the sound is much more open now with superior bass slam and texture. If I wasn't as happy as I am with my current line stage I would definitely have Backert Labs on my short list.
For those who haven't met Bob Backert he is a very genuine guy who wants to help you realize the best performance possible. He stands behind all of his work. Bob is resolute about what he knows to be right in circuit design but not pushy. I can only imagine the incredible quality of units that bare his name!
I have a Backert Rhumba preamp. I haven't done much comparison with other preamps in my system, but I'm very content with this one. To my ears the sound is neutral, transparent, and lively but always with a pleasing balance of virtues. Many listeners seem to describe their impressions of this preamp in similar terms, saying that it gets out of the way so that you're listening to the music not the gear. I'd say that is a good way of putting it.
The people at the company are easy to get hold of if you have questions, and very willing to help. In my case, for example, I asked about a mono switch and they got back to me offering to convert the mute switch (which I didn't particularly need) to a mono switch. So that's what I have now.
There's another thread going on at the moment about the Backert preamps (search under "Rhumba 1.1") if you haven't seen it.
i'm not good at writings, and the following is just a simple description of my impression on Rhumba 1.1(not the Extreme version which released recently) since i have it in my system over 6 months ago.
It took me by surprise how good it sounds. With it, I came to realise that I had missed a lot of musical information with my previous Densen audio preamp ($2,200) and Audio Gd DAC/preamp ($2,000).
I mainly listen to complex acoustic and large orchestral pieces with some electronica. It is important to me that music doesn't sound compressed, muddled, smeared or veiled. The soundstage must be expansive. The Rhumba allows me to more clearly hear instruments at the rear of the stage which sounded soft and almost inaudible with my previous preamps. The Rhumba makes sounds more alive and palatable. It allowed me to discover more musical information and as a result I'm re-listening to my whole CD collection again.
The Rhumba is absolutely transparent and imposes no character of its own. Its sonics will change according to the tubes you use. Switching from the standard JJ tubes to the Amperex 7316, sonics became more balanced top to bottom. The Amperex have a natural, smooth "sparkle" to the treble, are not hard or sterile, and have low, tight, punchy bass. Not the walloping thump you get from a sub. If you want walloping bass, the JJ tubes do this well.
The Rhumba also easily allows me to hear different cables characterics.
My experience with songs with vocals are limited, so i would briefly describe the voices sound natural, and centered and accompanied by instruments just a few feet behind. Imaging / staging are not smeared. Midrange has energy and doesn't overshadow other parts of the spectrum. I highly recommend this preamp with music that has good PRaT. It sounds lively, fast and makes your speakers disappear. It doesn't sound laid back or forward, but fills up the space between and outside your speakers. Based on my auditions of other preamps in dealer demos, I felt that the Rhumba outshined preamps in the $7k range. I have heard better preamps, with a more deeply layered soundstage, but those preamps cost above $10k.
Lastly, the Rhumba has a negative which I did not experience with my previous SS preamp. It has a rather loud tube hiss which is clearly audible when i'm listening to songs with quiet passages. According to Backert Labs, hiss was greatly reduced by a new circuit implemented on later batches after my purchase (Andy at the company offered me the upgrade at a very small cost).
My system :
Simaudio 650D \ PS audio transport
YBA 1 poweramp \ MF poweramp
SS music reference \ MIT cable
Feet of Silence
HFC Interconnect CT-1E & powercord
High fidelity MC-6
The Polk thread in the previous post was about logistics - the "Rhumba reviews" thread from the Polk forum is here: http://forum.polkaudio.com/discussion/169811/backertlabs-rhumba-preamp