Bent Audio Autoformer vs Tube Pre

Has anyone compared the two? I'm thinking of building a fully balanced Bent Autoformer unit.

If you have compared the two, what do you think?
A Bent TVC kicked a SFL2 out. However, the rest of the system is nearly ideally suited for passives. Balanced is the way to go with these.
What's an SFL2?
I went for BOTH! I built a 26 DHT tube preamp using the Bent Audio autoformers in double duty as both the output "transformers" and volume controls. Sounds incredible! Kills my Supratek in transparency, detail and immediacy.

26 Preamp

26 Preamp Internal


That's really sweet! I'm not quite that talented of a diy'er. :-(
Neither was I until I worked at it. It just takes time, patience, lots of research, and some money to get good parts. Oh...and a patient wife...
I've got 2 out of the 4. :-)
An SFL2 is a Sonic Frontiers tube preamp.

When properly utilized in a passive friendly system, TVC and autoformer linestages usually best any active preamp regardless of technology.

I have owned many well regarded tube preamps and my Sonic Euphoria PLC has laid them to waste every time.


Amazing to me that one auto former line stage simply kills all other actives period. Wow, how have you found the time to listen to every single preamp made since the beginning of time in all the near infinite number of systems friendly to such a device. You have lots of time on your hands.

In addition, it seems your preference for sound is the standard. Most impressive!
Reading comprehension IS your friend.

"When properly utilized in a passive friendly system, TVC and autoformer linestages usually best any active preamp regardless of technology."

Read it again, this time slooooowwwwllllyyyy.....

Please use your own advice and read my statement. I clearly stated in a passive friendly system. You are welcome to your opinion and others will rightly find your conclusion pure hyperbole.
Shakeydeal ...

A Conn Yankee long haul truck driver gets lost down south and shouts out on his CB .. can anybody tell me if I'm in LOUIS-VIL

A local shouts him back .. yes you are but it's pronounced LOU-E VIL

The Yankee says well it's spelled on the map like LOUIS VIL

The local says pull over and we'll go in that eatery and ask the girl behind the counter how it's pronounced and the loser buys

They pull over and go in and the Conn Yankee walks up to the counter and says to the girl ... please tell me where we are and say it very slowly

The girl behind the counter looks the Yankee in the eye and says ,,, Bur----ger ------King

What has been your experience?
In a system friendly to passives including a good autoformer type the music can be very good indeed. To some the sound is ideal, and based on personal preference, better then actives they have tried in the same system. Reasonable conclusions based on preference.

My experience is a great tube active has sounded better in my system with components that are indeed passive friendly. I have tried several good ones from Placette, Lightspeed and Bent. The active tube has won out in my systems and to my tastes. Simply more natural, meaty and fleshed out if you will. This is just my experience and I cannot claim you or anyone else will reach the same conclusion.

Fun to try for yourself and experiment.

What tube pre do you use and what passive autoformer did you use to compare it to?
Don't you own a TRL Dude? At least that is what I have seen you post previously. Surely you must know Grannyring owns one given the TRL family is pretty well connected.

I'm guessing you probably know where I stand on this subject as well given my very open opinions about passive preamps. Although I have not compared any passive preamp to The Dude, I have compared them to many active preamps. You could do a lot worse than the Bent modules, but your system has to be optimized for it. Just for ha ha's contact Audiogon member Dgarrettson. He implemented an LDR volume control in his Atma-Sphere MP-3 preamp. Could give you the best of both worlds.
I have sold my Dude as my source is now fully balanced. I don't know your view on passives so if you can share, that would be great.
Well, yes the Dude still abides in my system and will stay! I tried a Bent product a couple of years ago that only had one input if I recall. The best passive I have tried was the Lightspeed. If money was my number one issue, and I needed to obtain the best sound I could for very little money, I would look to the Lightspeed.

In my systems the Dude was just more pleasing to listen through. I am far more engaged in the music with it in my system compared to a passive.
Was the Bent that you tried an Autoformer and fully balanced unit?
No just the basic TAP autoformer , not balanced.
To be fair this topic has no universal 'right' answer as it depends on numerous varibles. For me however, a top quality active tube linestage is more satisfying and realistic of instruments and voice based on what I hear in live venues.Oh by the way, YMMV.
Charles, that is exactly what I shared in my previous posts. Agreed.
Jason, how has your sound changed? I know before you stated you felt like you needed a Dude (active tubed pre) in the mix due to the sonic characteristics of the Ncores. Lynx more euphonic than the Halo I presume?

The passive game is interesting. I preferred my Dude to the LSA as well, but if you are bent on building your system around a passives parameters, I guess it could work. If money is an issue, finding a DAC with pre-amp functionality seems like another pragmatic option.
What amplifier and source(s) do you plan to use with the Bent? I have tried many passive preamps and currently still use them in my system. One is balanced and the others single ended. From my experience I will say that with the right set up a passive preamp will help you achieve outstanding sound for little investment. Typically an autoformer or transformer volume control will be easier to match up with system components, but that shouldn't rule out potentiometers or resistor passive designs. In fact, a real sleeper is Roger Modjeski's pot in the box that uses a simple but high quality Noble potentiometer to attenuate the signal. LDR attenuators are also very good if built properly.
I'm using ATSAH (Hypex NC1200) amps and Lynx Hilo.

Pot in box doesn't work....needs to be remote volume controlled.
The four key specs you need to really evaluate how a passive preamp can be used in your system are the output voltage and output impedance of the source and the input sensitivity and input impedance of the amp. Neither Lynx or ATSAH provide these specs although I will go on the assumption that the Lynx outputs at least 2V and has a low enough output impedance since it is a solid state design. I do see the amp has 26 db of gain which might indicate an input sensitivity high enough (ideally below 1.5V) but the input impedance would be the more critical factor and should be greater than 50k ohms, the higher the better.

If the specs do not line up properly it is still possible to build something using the Bent modules and remote, but you might want to consider buffered outputs that would allow for better matching to the amp. Perhaps you can check with the manufacture to see if they can give you the specs.
Specs wise the amps are fine as is the Lynx. I've got that covered.

Well if you have the specs figured out and a balanced unit with remote is what your desire the Bent modules are going to be your best bet. In addition to a Lightspeed and Warpspeed (balanced) I built an autoformer volume control using the Slagleman units co-designed by John Chapman and Dave Slagle. All are very transparent and while I would give the nod to the LDR units for their increased transparency and purity in transferring the signal, building a balanced unit and one with a remote on top of it is not nearly as feasible.

I have considered building a balanced version using the Bent modules as well and may ultimately get around to it someday, but first I am having a custom direct coupled balanced preamp built that will serve as both a phono and tape head preamp with all the gain in that portion of the circuit and unity gain and buffered output in the linestage portion of the circuit. It will be interesting to compare this to the passive preamps I have.
I’ve had fun with both and I really think it comes down to system synergies and personal taste.

I’ve used a Bent TVC (S&B MK1 copper) for years and really enjoyed it. The sound is by far truer to the source and I love the remote control. My amps are not balanced so I can only take run from the DAC to the pre in balanced mode. When using the Bent I use a separate phone stage…

When I’m not using the Bent I use an Audible Illusions Mod 3b with the John Curl gold phone board. Overall I keep coming back to the AI just because it sounds so sweet with the rest of my gear. Yes there is coloration, and yes I don’t have anywhere the same control over the volume but it just works.

That being said I can’t bring myself to sell the Bent, and from time to time rotate into one of my stereos. I also defy all the odds and use 20 foot long interconnects from my preamp to the amps…

The main rig is as follows…
- Digital Sources: Levinson 360S DAC (fed from, Roku soundbridge, mac mini, Oppo 103, Levinson 17 transport)
- Analog Sources: VPI Aries, McIntoch MR 71
- Speakers: Marten Design – Dukes
- Amps: VTL Compact 100 (with NOS Mullard EL34 tubes)
- Cables: Crimson MusicLink (everywhere)
I still prefer the balanced tube preamp I'm using, which is more transparent with greater bandwidth (top and bottom) than the Bent, although the Bent is IMO excellent. My preamp has a direct-coupled vacuum-tube balanced output and can drive 100 foot cables with ease.
Of course you make (and sell) the tube preamp that you're using. :-)
Audiogon members don`t seem to mind when he touts his products on this site
Of course. I'm just sayin' though. I wouldn't expect him to like anything else publicly. Right?
Specs wise the amps are fine as is the Lynx. I've got that covered

I was not asking about specs but sound. Can we presume that the Lynx is more euphonic thus nullifying the need for a tubed pre or was it simply to chase a theoretically lower noise floor with balanced topology?

I do know Paul at TRL (despite being anti remotes like other purist pre-amp designers I know) has used the Bent remote unit with Dudes and it apparently works well. I know one former Dude owner who said it was seamless. I am considering one for my next Dude....
You will notice that I am careful not to name names unless somebody calls me out. Its really that simple.

But at the same time, the simple fact is that direct-coupling can perform better than a coupling cap or a transformer. This is not something that I made up, its been well-known for decades. The trick is doing it.
There are very talented designers and builders who for various reasons choose a particular coupling solution.If they decided to comment on this site,each would give a convincing explanation of why 'they do what they do'.All would seem valid,that`s why listening is the determining factor.There`ll be advantages and some degree of compromise with any method chosen,
I agree completely.

I think it would be interesting if we had more interaction from more manufacturers.
Just for the record for those who could not gather it from my previous post Atma-Sphere is building the custom preamp I mentioned. While I firmly believe in the benefits of a passive preamp, one of my amps is an Atma-Sphere S-30 and after many conversations with Ralph decided that it would be worth hearing the preamp for both technical and synergistic reasons. I am moving from digital to a completely analog front end with turntable and reel tape deck, the latter taking the output directly from the tape head. Given the phono catridge is inherently balanced as is the tape deck I needed a solution that could handle the balanced designs of my sources. The convenience of getting this in a one box preamp was also influential in my decision. So for the first time in a while I will have an active circuit in my preamp. I look forward to the comparison.
My source is fully balanced so to take full advantage of that, a fully balanced pre is needed.

I had a Bent remote (ALPS) on my Dude. It's just a motor that's on the back of the Shallco attenuator. There's nothing to it.
The Bent Autoformer VC is excellent. Sixty-one 1dB steps, from -54dB to +7dB, all done via instrumentation-quality reed relays rated for billions of operations. The power they consume is used solely for the relay switching circuit. I love them in my preamp. You even get a balance control since each channel has it's own autoformer unit. The cool thing is that with a little surgery, you can restack the nickel laminations to get various amounts of primary inductance - stock they are stacked 3X3 for ~155H. That works fine with my preamp since I'm using the low Z mu-output of the plate CCS, but they can be restacked to 1X1 for ~190H if you like, or 6X6 for ~100H, etc.

They make having a remote control no detriment to the sonics, and there's nothing more ideal than adjusting the volume and balance from the comfort of your listening chair, from where you'll be...listening.
Ait, that is righteous. There is obviously a little more to its performance than meets the eye.
I think it would be interesting if we had more interaction from more manufacturers.

Absolutely. It would make this site more intellectually stimulating and more Asylum-like. The usual pattern is behind the scenes sniping and "programming" of end user/disciples to do their public bidding. Sketchy.

Tony, that sounds like an interesting and logical experiment. No more digital? I can understand that. If I did not have a 10 mo, I would love to run down the tape thing. I will have to settle for DSD and other attempts at SOTA digital....
Jason, doesn't your new dac have a pre-amp section? What is missing sonically when you go direct?
Andrew, yes the idea is to withdraw from digital completely. I will probably miss a handful of CDs but have already become more familiar with my vinyl collection which has many more nuggets than my CD collection. I am also building up my tape collection and while I understand your situation, IMO getting into tape as big a commitment either financially or time wise as some may make it seem.

DSD has piqued my interest but I have to draw the line somewhere...
Not balanced direct. Nothing missing now. :-)
Tony, if I could, I would. Paul was on me about it for a long time, but its just not practical. I have heard some early promise with hi rez, but a lot of it still lacks true analog density, etc. Maybe that will change at the software end someday.

Jason, I am surprised by that. I assumed it was balanced. Strange.