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Backert Labs Rhumba preamp

Hello,
I am thinking of going to an active line stage for sometime now. I have a separate thread for that and people have suggested some good choices. The reason for this thread if that, while I have all along said that  don't want tubes in the system, a few have convinced me that I should try tubes in the system, especially with ProAcs.
With that said, I researched a few tube preamps, that have XLR out and the Backert Labs Rhumba is the one that has only 2 tubes, which makes me comfortable to "deal in tubes".

I would like to hear from Backert Labs Rhumba owners who moved from Solid State preamplification to this preamp. What are the differences you heard? Any improvements?

I read a review on the Stevehoffman forum and the user mentioned that there is a "hum" in this preamp. This bothers me and hence I decided to check on this forum, if anyone has experienced this with the Rhumba in their system. One poster on this forum also confirmed the "hiss":
https://forum.audiogon.com/discussions/backert-preamps-any-users

So I was wondering, if there are any users who have recently purchased this preamp and what is their experience with the hum/hiss issue.

BTW, I blame Ralph of Atma-Sphere, Almarg  and my dealer for making me consider tube amps :-) Can't believe I am creating this thread.

Thanks!
128x128milpai
milpai's avatar
milpai OP
2,420 posts
 
Folks,
One question - when I think about tubes and the demos at audio shows it was always some vocals or smokey jazz or classical. But I do occasionally listen (and I am not bashful about it) to Michael Jackson, George Michael, etc - so pop from 80s/90s. My kids do sometimes come into the room and listen to the current pop like Justin Beiber, Uncle Kracker, etc. How does this kind of music sound with tubes? With my TVC, it sounds pretty transparent and clean. Does tubes make this kind of music sound "slow and syrupy"? Will I have to keep switching between the tube preamp and the TVC to get best of both worlds? Mind you - I listen to female/male vocals, classic rock, jazz and classical 80-85% of the time.
atmasphere's avatar
atmasphere
11,944 posts
 
It also doesn't necessarily mean a balanced connection or a fully balanced design circuit (i.e MP-3) will give you lower noise or have any advantage over single ended design. Fully balance design circuit will also susceptible to hum problems too.
Just a correction here, since this statement is essentially false.
The advantage that balanced operation has is several- immunity to interconnect cables, and the system was also devised to prevent ground loop hum and it works quite well! "Fully balanced design circuit" (sic) is far less susceptible to hum problems- it is better able to reject noise in the power supply and far more able to reject hum from close by power transformers and the like. It is also possible to get lower noise, since if the balanced design is also differential, careful use of well-designed constant current sources will reduce noise while also increasing gain and reducing distortion.
The first bit: immunity to interconnect cables, is likely the most important aspect, since audiophiles are well-known to pay serious money for interconnect cables in search of the cable to rule them all. In effect, cables are the 'hidden cost' of operating single-ended preamps.
hifiman5's avatar
hifiman5
1,832 posts
 
And how does one acquire an immunity to interconnect cables?  Is it from a consistent exposure to same that you build up a natural resistance to them?  Sheeeesh!🤔😝
philipwu
214 posts
 
@atmasphere ,
with due respect and i do mean it as your preamps are a true technological marvel, not to mention its excellent sonic that many people are enjoying the transparency and speed out of tubes in your pre.
however, my encounter with preamp MP-1 is otherwise. In exactly the same setting, all variables are fixed and nothing changed (ie. interconnects, power etc..), i get hum from MP-1 , but i don’t experience hum after i swap to single ended pre. At a friend place, the same MP-1 preamp function just as great. 
i understand it could be something faulty (i’m unable to find the cause of it) at my place but i didn’t experience the benefit of balanced design preamp as compare to single ended pre at my place. so i came to understand that balanced equipment doesn’t guarantee a better sound, irregardless if the improvement in sonic is audible or not.
i don’t wish to risk a debate here and i’m only expressing my opinion with balanced designed vs single ended audio gear.
all the best,
-p
atmasphere's avatar
atmasphere
11,944 posts
 
And how does one acquire an immunity to interconnect cables?  Is it from a consistent exposure to same that you build up a natural resistance to them?  Sheeeesh!🤔😝
Proper inoculation I guess.
however, my encounter with preamp MP-1 is otherwise. In exactly the same setting, all variables are fixed and nothing changed (ie. interconnects, power etc..), i get hum from MP-1 , but i don’t experience hum after i swap to single ended pre. At a friend place, the same MP-1 preamp function just as great.
@philipwu The most likely cause is that the amp you were trying to drive wasn't actually balanced. It may have had the XLR connector (an example of an amp like this is the Lamm 1.1, also any VTL amp equipped with an XLR input), but if the circuit inside wasn't balanced you would totally get a hum. The reason is that the output of a balanced source occurs between pin 2 and 3 of the XLR, and **ignores** ground. If that's connected to a single-ended input, essentially the unused pin (usually pin 3 when this problem shows up) acts like an antenna for noise because the circuit isn't completed! There are several solutions, certain adapters can be made to work, line transformers and its often possible to modify the amp slightly so that it will accommodate a balanced input.

I frequently show at audio shows with speakers that are 105db 1 watt/1 meter and do it with no hum.


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