Tube Rolling Advice for the Backert Labs Rhumba Extreme?


Tomorrow I have a Backert Labs Rhumba Extreme 1.2 being delivered, which has been upgraded by Backert to 1.3 specs. It will be driving the Luxman MQ-88uSE and the front end is a Qutest with M Scaler (Innuos Zen MK III server/streamer). Speakers are La Scala IIs, placed about 15' apart in the corners at a 45º angle. Soundstage is excellent and expansive with remarkable placement of instruments across the sound field.

If all goes well it will be replacing my L-509X, which is currently only being used as a preamp for the MQ-88uSE, so it’s being underserved in my system and will need to find a better home.

I am interested in any advice about tube rolling with the Backert Labs pres. With the Chord digital front end, I am getting a very layered, dimensional, detailed sound and thanks to the Qutest filters I’m able to adjust filters to best match the amplification. The MQ-88uSE has a gorgeous, full, warm sound and right now the 509X’s solid state pre is giving a nice sharp, detailed, and dynamic profile to sharpen up the tube sound a bit.

I don’t want a syrupy or bloated tube sound, more airy and detailed on the top with holographic imaging with solid heft on the bottom end. I’ve replaced the preamp tube in my Cronos Magnum II with a Cifte and was really happy with the impact on the sound.

The Backert comes stock with new Mullards, which I expect may have a slightly warmer sound than what I’m chasing.

Any advice?

33c1efbf 2142 46a3 a4bb c4042a2db044Ag insider logo xs@2xjsqt
Hi jsqt,
I upgraded from the Rhumba 1.2 to the 1.3 Extreme a few months back and happier I could not be. With both of these units I saw a marked improvement in sound after just 30 or so hours with the stock tubes. Andy Tebbe at Backert mentioned it would continue to improve (and I believe it has) but around the 30 hour mark is where I saw the most dramatic change. In regards to the bass, tubes can definitely influence that but I would be patient and let it play out. My 1.3 Extreme had plenty out of the box with the stock Mullards. In terms of tubes, I have tried a bunch, most NOS including Raytheon, RCA, CBS, Mazda, Tesla, Mullards, Amperex and I am sure there are a few others. All of these were rolled in my 1.2. As @jackd mentioned, the Raytheons and RCAs are fine tubes if you happen upon some good ones and they can be had at very reasonable prices. I ran a pair of Raytheon triple mica's before I splurged on a set of early 60's Bugle Boys which were my favorites until I tried a pair of late 50's Amperex 7316s which are the bomb in my setup. Personally I would heed the advice given earlier, take your time and enjoy the ride. Everyone's system, room and preferences are different so what works for one person may not work for another. I think finding a good source for tubes is key....you can try ebay but that is a real crapshoot and you need to read the fine print. Personally I have had great luck with Brent Jesse and I am sure other dealers mentioned are also very good. Congratulations on the new acquisition and good luck on your journey! 
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.

@jsqt,Very recently I found that I prefer the sound of the Rhumba with the orange rings OFF the tubes. It felt like the sound stage widened and clarity improved so much. I don't think the O-rings that are on the tubes that the Rhumba comes up with, helps it's sound. Of course, YMMV.BTW, I use Genalex Gold Lion 12AU7 with my Rhumba 1.3. This is a fantastic preamp. The reason for my findings was that the preamp is so precise that it is scary sometimes. I played a Patricia Barber CD where the vocals were slightly to the left. And immediately after this I played Neil Diamond's 12 album, Song 2 (Hell Yeah). Here too the vocals are on left. I was damn sure that the tube on the right is dying and hence the tilt. So I shut down the system and changed the tube positions. While doing that I removed the orange o-ring and played the songs again. The sound stage did not tilt right, as I had expected. After playing another song I realized that the system was really doing pin-point positioning with improved clarity, depth, wide-stage and impact. Super happy to have made the accidental discovery of NOT using those orange rings on the tubes.

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. 
@jsqt
Would like to hear your experience after removing the rings.
Please do let me know.