Tube Rolling Advice for the Backert Labs Rhumba Extreme?

I believe this preamp uses 12AU7's. Do you know how many and is there a phono stage?

Yes, it's 2 12AU7's, Mullard reissues from Russia. 

Thanks for the suggestions! I will take @three_easy_payments' advice and live with the Mullards for a couple weeks then possibly check out the Bugle Boys or possibly another pair of Ciftes. 

My faves for my Backert.... a pair of CBS 5814a. Just a well balanced sound across the range, but with a lively presentation. I tried a bunch of 12au7s, but always come back to these!

Thanks - I'll be checking those out too.

What Backert do you have? What does the rest of your system look like? Thanks!

@1markr wow, that is some impressive gear, I bet it sounds awesome. 

I just got my FedEx alert that the preamp has delivered at home... now just 8 more hours until I can get home and start working with it!

What difference did you notice with the SR Blue fuse? Have you found an improvement with an upgraded power cable? 

The Backert is getting its first workout tonight. I'm not ready to make any gushing endorsements just yet but I am very impressed, particularly with the imaging and separation. I've noticed it's a little "soft" sounding - not syrupy or bloated or muffled, just a little polite, particularly on the bottom end. I suspect it may be the Mullards.

Thanks everyone... so it seems like there is a fair amount of burn in time required for these caps then. This could explain why I was a little surprised by what I was hearing with the "softness" in the bass, versus so many of the online reviews and marketing material that say if anything the bass is a standout feature of these preamps.

After a full day of tweaking and experimenting I can say I am very happy with the Rhumba Extreme!

Andy at Backert Labs was a great help throughout the day yesterday with further recommendations to my setup to get the best sound out of the preamp in my system. 

Here are a few observations I wrote up about the process & end results. 

I am plugging the Qutest directly into the REC OUT, which bypasses Inputs 1-4, since the Qutest is my only source. It did help with cleaning up a bit of the softness and restoring some snap and detail to the sound.

After initial setup on the glass top of my BDI Corridor Andy mentioned  that glass tops were not recommended for placement.

The BLRE went on a wooden shelf in the cabinet and the bass did focus a bit more and overall sound was cleaner and smoother. HOWEVER, because I have my Orbi satellite and Hue Bridge close to that shelf, I noticed some motorboating (digital cycling noise) in the background.

So I stole my wife's cutting board and using IsoAcoustic Oreas I replaced the BLRE on the top of the cabinet. This did result in a massive improvement in the overall sound.

I also eliminated the high level speaker wire connection from my MQ-88uSE to the JL Audio eSub and went directly from the OUT 2 of the preamp into the sub.

This restored a great deal of balance to the bottom end. I also did some further experimenting with the crossover and phase settings of the eSub, moving the crossover from 70Hz down to 60Hz. The result was a much better blend with the La Scala IIs and eliminated some directionality I hadn't noticed before.

All of these tweaks got me to the point where I no longer feel the need to swap the L509X back in to compare - currently I have solid, well-controlled bass with presence and heft, better transients and cleaner background.

This combined with the strengths of the BLRE over the 509X (massive soundstage with pinpoint placement accuracy, well-defined space around the notes, more musical unspooling of the music/greater liquidity) have me at a place where I am pretty confident I'll be able to let the 509X go to a new home, and explore further gains through tube rolling with the Rhumba Extreme.

Fit and finish of the Rhumba Extreme is top-notch. It's not an exceptionally heavy unit, but it is a solid, attractive, exquisitely machined piece. The toggles are satisfying to flip around and the remote is a heavy piece of jewelry - the best remote I've ever owned from any component. I'm really glad I was able to restore placement on the top of the cabinet with the wood cutting board because this is not a component you want to hide away in a cabinet.

The final piece of the puzzle was the delivery of a new Hugo M Scaler late in the afternoon.

Although not related to the Rhumba Extreme, the gains are jaw-dropping when feeding the Qutest dual BNC inputs at full resolution. Suddenly all boundaries between the listener and the music disappear. It's like a portal has opened to the soundstage; it's almost unreal how much of an improvement it makes. It does, on some recordings - particularly with male vocals - add a bit of thinness to the sound I've experienced when upsampling from Roon in the past.

But I chalk that up to the limitations of the Qutest more than anything else, and I can definitely see a DAVE upgrade in the next year.

A note about the M Scaler and Rhumba Extreme - I should clarify that I'm not intending to project the gains of the M Scaler to the Rhumba Extreme.

When putting the M Scaler in bypass mode, listening to the non-upscaled audio through the system is still remarkably transparent, engaging, and dynamic.

All-in-all this is very close to end-game for me.

In fact if it wasn't for the tiniest bit of thinness in male vocals when upscaling to the Qutest, I'd probably not even think about further upgrading to the DAVE, but knowing me, I'll always be nagged that there's "one last step" to achieve.

I'm excited about doing some tube rolling with the Rhumba Extreme, and will definitely explore some of the recco's mentioned in this thread.

Thanks for the heads up @milpai  I will have to do some experimenting with that myself. 

I have swapped the stock Mullards for a matched pair of Mazda Cifte 12AU7, after being so impressed with the Cifte's in my Rogue CM2. I have found the Ciftes seem to really magnify everything the Rhumba Extreme does well - they are a good compliment to the airy top end, pinpoint accurate stereo field, and authoritative bottom end without changing the sonic character of the sound in any way. 

I will pull off the tube rings this weekend and see what kind of difference it makes. I'm curious to compare; the preamp is already using terracones, sitting on a butcher board, which is sitting on 3 IsoAcoustic Indigo Oreas so I wonder what difference the stabilizers are even making at this point. 

@milpai that is interesting to hear, thanks for the follow up. I did remove the o rings on my Cifte’s for a couple of days and I could not really detect a difference to be honest. I do have mine on a slab of wood that is also sitting on 3 IsoAcoustic Oreas, so that combined with the terracones on the unit itself may make it less susceptible to noise? Or the Mazda Cifte could be less microphonic than the Gold Lions. I replaced the o rings and have left everything as-is.
A little over a month in and it is still sounding amazing with the MQ-88uSE. I did replace both power cords on the Rhumba Extreme and MQ-88uSE with Transparent High Performance PCs and I have noticed an improvement in detail, which I attribute to a lower noise floor overall in the system. 
I’m currently awaiting the Hugo TT2 to replace my Chord Qutest DAC; along with the M Scaler, I believe the Hugo TT2 will likely be end-game on the system. I couldn’t justify the expense of the DAVE and I have read rave reviews of the TT2/M Scaler combo (together surpassing the sound of the standalone $12K DAVE).

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. 

@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.