RHB Designs Rhumba 1.1 preamp

Yes, and I have been very impressed with the Backert Labs preamps, both the Rhumba and the more expensive Rhythm. You are correct, many have had CJ preamps (Audio Research preamps too) upgraded by Bob Backert. 
Since Bob and Andy Tebbe are members of our local audio club and Bob has many local customers I have had the chance to hear at least half a dozen systems using their preamps. Granted, since I know these guys very well and consider them friends, please take my comments with a grain of salt.
Nonetheless I am confident telling you that the Backert Labs preamps sound to me like they have been described in reviews; natural, rhythmic, open, airy & dynamic. They let the music flow, get your feet tapping and draw you in. 
These guys know what they are doing, and they are in it for the right reasons. Super passionate about sound quality and value. Check them out if you dare, Cheers,
Spencer

Spencer;

Thanks for the response.
Being a somewhat newbe to all the top notch components.
Can you help me, and offer a comparison to a ARC preamp sound or the CJ ET3 I just listened to.
i was hoping with the tubes( or tube rolling)  to get a warm, lush presentation( CJ style) vs super, super clean?

jeff

ps: Nice systems you have!

@sbank  The last time I was to Bob's he was working on the rollout of his own preamps.  I couldn't agree with you more regarding your assessment of Bob.  Really good guy who as you say is in it fir the right reasons.  He knows good sound and how to help you get there!

@frozentundra It's easy to change tubes to tailor the sound. Be sure to read up on the flavor that various brands provide. 12au7 tubes are a type that have been offered in many versions, so you should be able to get exactly what you seek. 
I respect both A. R.  & CJ preamps & haven't heard the ET3 so can't be to specific. Both brands have so many models each sounding different. If I must weigh in on  AR my only relative concern is that they sound  a little on the dry side of tonality, more so in the older ones. 
If you call Andy he can tell you more about which tubes they have good feedback on, etc. Cheers, 
Spencer