This thread has been resurrected over the weekend so as the OP I figured I’d chime in with my progress over the past 3 years. I have owned a Rhythm 1.3 now since last August and it was a worthwhile upgrade to the Rhumba. I am no longer using the Luxman tube amp, however; the Rhythm is paired with a Luxman M900u and it sounds spectacular. Regarding tubes, the new Rhythm came with a pair of Gold Lions, I believe, which I then swapped out with new Mullards and also a pair of Brimar CV4003s, and believe it or not I am settled back on the Mazda Ciftes. Not sure what it is about those tubes but I hope they last for a long, long time because I don’t think they are available at Upscale anymore.
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@jsqt You are indeed fortunate to have a Backert preamp. I have had the good fortune of knowing Bob for a couple decades, long before he made moves toward offering his own designs. Bob was known then for modifying preamps and to a lesser degree power amps. Most of Bob's work back then was upgrading conrad johnson units. He liked working on cj's like my PV12L because their was a lot of unused real estate inside those units so he could readily add his own proprietary circuits to improve their sound. Bob has always embraced a "purist" philosophy with an emphasis on the power supply. (Greenforce) Bob's circuits opened up the sound of cj's as cj gear is known to have a warm, rich sound. Very listenable but would obscure fine details. Bob's goal was, within my budget, to reveal all of the details in the music resulting in a more spacious soundstage when one is present in the recording. A year ago I took my modified PV12L to Bob as the volume control and selector knobs were creating a scratchy sound as I used them. Bob cleaned the knob contacts and then after asking him if there was any other circuit improvements he could install, he informed me that he could install a new gain stage dynamic linearity circuit that would be a significant step up. Done.
I wish I could hear my cj as it was before all of Bob's work and how it is now. I am quite certain the openness and musical accuracy of the modified unit would be obvious and desirable over stock.
Back in 2019 in this thread, I mentioned my embrace of Herbie's Tenderfeet. They are a nice improvement but once experiencing the musical clarity of the Isoacoustic Oreas, I now have every piece of kit sitting on them and the Tenderfeet are in the closet.
BTW...The Mazda CIFTE tubes really did sound good with Bob's circuits. The pair I had just didn't last as long as I would have liked and have been using matched pairs of Gold Lions yielding fine, balanced sound.
PS From everything I've heard about the Luxman M900u, I can imagine that it would mate well with the Backert pre. I have a Luxman phono stage. Thank God there is a vinyl revival in progress!
I recently installed the Psvane ART series tubes and they seem to make music even better than the previous Psvane series. But the point is, this preamp is amazing and tube rolling adds more fun.
@hifiman5 and @milpai thanks for the updates! I'm glad to see this thread continue, as I think there are a lot of Rhythms and Rhumbas out there but they don't get talked about much in the forums. I've done a 12AU7 inventory recently given the events in Eastern Europe and I have 4 Mazda Cifte's, 2 Genalex, 2 Russian Mullards, and 4 Brimar CV004s, so I should be in pretty good shape with the tubes I have now to weather any shortages. This weekend I'm experimenting with swapping the Brimar CV4003's back into the Rhythm and this time without O-rings. @hifiman5 were you ever curious about Bob's Xphono phono pre? I have just gotten back into vinyl since January and I have a Parasound JC3+ on order to complement my current SL-1200MK2 and my future Pure Fidelity Harmony. The Luxman and Xphono both looked really good but a little over my budget for where I'm at with vinyl these days. However since Oreas were mentioned somewhere in this thread, here's something I found - I am using an extra glass panel from my Naim Fraim to support the SL-1200Mk2, and I experimented with supporting it by either 3 Stillpoint Ultra SS vs 3 Isoacoustic Orea Indigos. The Oreas definitely seemed more natural and relaxed than the Stillpoints. Stillpoints seemed to tighten up the bass to a fault - I enjoy a bit of that analog fat bottom end (think a Fender P Bass and Ampeg cabinet) and the Oreas seemed to do a better job of tightening up the space between the notes while maintaining the natural presentation and flow of the music.
@jsqt Interesting that you mentioned not using the damping rings when you install the Brimars. I just put a new matched pair of Gold Lions in my pre last night as the tubes had been in circuit for over two years. After having read others experience with and without dampers, I installed the new tubes without the dampers. I’m looking forward to listening this weekend. I mentioned the Oreas in my previous post and agree entirely with your assessment of their impact on the system’s sound. As far as phono preamps go, I have no doubt that the Backert is great but I love what my Luxman has done for the sound of vinyl in my system. The vinyl I have been receiving is really flat and quiet. Amazingly so. I have so many silver and gold discs as well as a vinyl collection dating back to the 1970s that I plan to stay with hard media rather than adding download capabilities.
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