I've played with both, it is a tough call IME. Now that Nick has introduced a C core version. Which is supposed to be even better. I personally would try it before any of the others just because of the different winding technique.
The Bent was the better built of the two. It's easy to describe the sound differences between the pot and a TVC.
For me it was like taking a bottle of Windex and a rag and cleaning a cloudy window. This was using a noble pot for comparison..there simply was no comparison in sound.
Bass was cleaner and deeper, the highs had more of a shimmer. And the soundstage layers became more revealing.
The only reason I do not use a TVC now is because I needed more gain for my amplifier. So the results vary depending on the components used. After owning several TVCs, you couldn't give me a component that uses a pot for the volume control..it doesn't matter what it is.
I've never heard the Promitheus, but have made a TVC using Stevens & Billington TX-102's supplied by Bent Audio when they could still be had. Since you ask about
RVC's too, resistor-based passives, let me say that I found my TVC to outperform two RVC's, both using Shallco switches (as does my TVC), one with Holco resistors and one with Audio Note Japan tantalum resistors. Then I made a shunt design RVC using Texas Components TX2352 Vishay resistors, and it competes well (without beating) my RVC. I use low capacitance interconnects, and though they're 9' long I have none of the oft-cited problems with RVC's. Those TX2352 resistors are simply great--I've made huge improvements in three phono preamps by using them as 47K ohms input loading resistors, for example. I hope this info is useful--feel free to email me for more detail.
I don't have personal experience in comparing the Promitheus TVCs to Bent Audio, nor do I have enough personal experience with resistor-based passives to say anything particularly insightful about differences in sound quality in comparison with transformer-based passives. However, I do have extensive experience with the Promitheus dual-box EI-core TVC and the new double C-core dual-box Signature TVC in my SET audio system.
The Promitheus EI-core TVCs are an excellent value with very good sound quality, but Nicholas Chua has really raised the stakes with his new line of C-core based TVCs. The C-core TVCs have more fullness, weight and body to the music and they give you an uncanny sense of presence. If you want to see what a TVC can really do, I can heartily recommend the new C-core TVCs in the Promitheus line of products. The Signature TVC is a force to be reckoned with that, in my audio system, competes very effectively with high end active preamps.
Well, I certainly get the sense that the two brands are very competive with no clear cut winner, which is good as I can sort of decide on price, ergonomics, and aesthetics. I had the Placette RVC which was very clear, neutral and deatailed, but not "plump" enough in the mid bass and bass for me, it seem a bit reticent. Maybe the frequencies were there, but no in-room bloom like I get from my Joule LA 150 MKII, or for that matter the Placette Active which I had transitionig to the Joule. I love the Joule, but I also want a passive for kicks and to have a different sound signature to enjoy. I'm not sure what C-core means since I know nothing at all about electronics, but I take it they perform better that EI transformers - don't know. I hear alot about the S&B tranformers used in the Bent NOH, Tap, and others, are you saying the C-core is a superior technology? I'm not sure I am ever going to really understand this so I'll depend on rational consensus and try one or the other.
Pubul57, I am also challenged technically, but here is what I know (or, I should say, what I think I know...any of you EE types should feel free to correct me where I go astray): The type of core (EI vs. C in this case) simply describes the shape of the ferrous core in the transformer through which the music signal is effectively transfered from the primary windings (input) to the secondary windings (output) as the result of magnetic inductance. (The signal flowing around the core on the primary windings induces a magnetic flux in the core, which, in turn, induces an electrical signal on the secondary windings.)
With respect to the transformers that Promitheus is using in their TVCs, the EI-core transformer is rather small with comparatively thick core laminations (.35mm). The C-core transformer is much larger and heavier and uses finer laminations in the construction of the core (.05mm). The result is much better sound quality in the bigger and more expensive transformer. The flagship model TVC is the Signature model, which uses a pair of the C-cores in each transformer (one transformer per channel) and also uses more expensive Elma switches as the source selector and volume control. The sound quality of the flagship Signature TVC is significantly better than the EI-core models, which, in and of themselves are very good (and an excellent value).
Since everyones gear and ear is different trying both styles would be best. C-core has always been better to my mind. I want remote and have very well suited gear for a passive setup. I use Placette's w/ 3 inputs and a remote and 125 volume positions. With Vishay S-102 resistors, a logic circuit,relay controlled resistor ladder. No pot. Very nice. I tried a friends Promethius TVC and it was a bit more veiled in the HF and less dynamic.
The S&B transformers used by Bent seem to have a great reputation, is it possible that the Promtheus trasformers are as good, even with C-core?
ET, if you get a chance to try the Promitheus Signature TVC, I think you will find it worth your while. The new TVC has better top end frequency extension, dynamics, bass weight and overall refinement/finesse than the less expensive EI-core units. I would be very interested in how the new Signature TVC compares with a system such as yours, which sounds like a well-optimized Placette RVC implementation.
I think you have a great point...could a TVC REALLY sound better than a passive resistor attenuator set up with ideal source - amp connections? I use EVS attenuators with a Nuforce 9.02 and in conjunction with Harmonic Prosillway Plus short IC's (1.5 meters). It sounds really great. However the only problem... mabe not..is that sometimes I could use a little more volumme. I too would really like to try a Promethius TVC against? the EVS attenuators. HMMmmmmm....maybe I will have to go out and but the TVC's and try them against the EVS attenuators.
If I do that I will let all of you on Audiogon know what the comaparison revealed.
Charlie, I'm not sure I understand the volume issue with passives in most cases. My DAC put out 3Volts and my amp plays at full power with .839Mv, I'm not sure how volume can be compromised. The other issue I have with transformers is that they are bandwidth compromised to some extent, and my understanding (limited) is that my volume control is not. I would love to hear a demo with SOTA passive potentiometer, passive stepped attenuator, TVC, and tube pre. I know there is a gap between theory and hearing, and that sometimes we hear the theory, we hear what we expect. Anyway, it is all fun.
I have the EVS attenuators and compared them to the K&K TVC that I also have (with S&B MkI transformers and Seiden switches). The TVC was better in regards to micro dynamics and overall sound stage presentation. The EVS presented a sound stage that was somewhat less 3 dimensional. Both are quite transparent though and for the price the EVS is a great value.
Not sure if you have seen this, but some good information on S&B transformers:
Clio09, I've been listening to the K&K TVC for three hours now -- WOW! Works great with the CAT. Thanks for "breaking it in". Love it.
I thought you would enjoy it. The MkI transformers with copper windings have that warmth factor that make them special. It was sitting idle for about a month so over another 50 or so hours it will gradually get even better.
I take it you don't notice any limited bandwidth ;)
I'm too enthusiastic at the moment to be beleiveable. I'm going to spend a few weeks with this and my Joule 150 MKII to get a fair measure of both. I have the sense I will keep both, as they both make recording sound wonderful, though different, and both they and the rest of my system sound different than live. Nevertheless, they both reproduce music that is very, very enjoyable in the home. At the price points of the passives, even the "expensive" ones, they seem to be a no-brainer to at least audition. I also get the sense they will last for many, many trouble free years - not much to wear out (except maybe the switches at some point).
Well, I'm still impressed and I find that it is actually a better match with my Music Reference RM9 MKIIs which are running EL34s, while I slightly prefer CAT JL2 with the Joule pre - the CAT is ultra transaparent on its own. I think the "musicality" of EL34s are better matched with the TVC - a great combination. Don't get me wrong, I'm splitting hairs to some extent as all these pieces sound good in any combination.
Very cool! glad to see you enjoying the TVC.Have you tried putting the pot in a box back in the system yet?
I tried it with the CAT and thought it worked extremely well; the fact that it cost $135 has to make you scratch your head. I order a aluminum case version which I beleive is locked in my mail room at the moment, but will be comparing soon.
Pubul57, I noticed that you have the K & K for sale now. Can you tell why you're selling and what you've kept? I have a Music Reference RM-9 and have been considering a TVC to run between my Shanling CDP so I can eliminate the digital volume control of the Shanling. I'm leaning toward the Promitheus Dual Box system. Thanks.
I'm going to be using the Joule 150 MKII which works especially well with my Merlins (and I like the way it looks) and Roger's Pot-in-a-Box for back up should a tube blow. I'm selling because I feel stupid with too much equipment on my hands. I was considering selling the Joule instead of the K&K, but I know how I am with equipment and I expect I may make a move down the road to a non-passive friendly system and regret having gotten rid of a great tube active.
Thanks for responding to my query so quickly; I don't know what a K & K TVC is so a little more info please. Also I want to try a really good tube preamp in place of the EVS attenuators. ( I have to admit I really like their tranparency) Have you really enjoyed the Joule or do you plan to replace it with something else? An acquaintance of mine at the Cable Company suggested that I try a First Sound preamp and/or a Suprateck Chardonay preamp. AS an aside I have been listening to a pair of the Nuforce 9.v'2s SE's fed direct with a monarchy DAC 24 into the EVS attenuators and the sound is absolutlely WONDERFUL!
I came to the Joule after having a CAT SL1 Ultimate MKII, a LAMM LL2, and a Placette Active. All are fantastic, but I felt the Joule added just a touch more "body" that works especially well with my CAT amp and Merlin speakers. What I find is that most of this stuff does sound fantastic in its own right, until you compare it to something else. I have had several amps in the past 1-2 years and they were all great, terribly enjoyable and then I would use the CAT and realize it was superior, without the CAT I could easily have lived with many of them, Quicksilver V4 and Pass XA30.5 most recently. Transparency is addictive, and so is organic presence (hard to describe, but you know it when you hear it)finding something that can share in both qualities, in good measure is the trick, and part of what makes the hobby side of this fun.
I have the Bent Audio TVC and find that the transparency that this offers is remarkable. It is feeding an Atmasphere S30 Mkiii OTL which works fine as a combination for me as my speakers are very effiecient (Duo's 108 dB/w). I have tried various active pre's including the Atmaspere MP1 and in my view the TVC wins hands-down.
I can recommend the Bent Audio without hesitation (if you can find one now) - they are really well made.
I have to confess that I've not tried the Promitheus but I reckon it would offer very similar performance. Good luck.
New Bent TAPs are on the way using custom Intact Audio autoformers. According to John he's finishing up the first few production units and then needs a few weeks to stock up on parts.
What are the theoretical beneifts/disadvantages between autoformers and transformers?
From what I've read,the one advantage of the TVC is that it provides galvanic isolation, an autoformer cannot.
Will this make a difference is sound for better or worse..I have no idea.
Autoformers have been available for some time, John Chapman (BENT) and other premier passive TVC cos chose to use the S&B transformers; I have to believe there was a reason for that. Not saying the autoformers won't make great product, but it seems they were not the first choice when S&Bs were avaiable to the open market.
I will agree the S&Bs are classics. However, the Slagle autoformers by Intact Audio enjoy a pretty good if not somewhat cult like following. I learned recently that Jeffrey Jackson at Experience Music utilizes them and I have seen a couple other boutique manufacturers using them in their demo set ups at audio shows. Are they going to be as good as the S&B. Not sure, but I'd like to find out. John Chapman mentioned on his forum that if he couldn't get the new TAP to sound as good as the S&B version he wouldn't bother with it. Seems the custom wound autoformers (and John used custom S&Bs as well) are stacking up just fine.
Wired up my own TVC, using S&B mkIII's. They can be set up as autoformers, using only one side and I did try that after reading that method was better, espescially for lows. I didn't notice much difference but I can understand how it might help if impedances and voltages are less than ideal. I preferred to have the isolation and balanced input/output. You need two autoformers per channel for balanced operation. I'm pretty sure that's how the Django does it.
TVC's: It's fun to scare somebody by unplugging the ic's while music is playing. Don't try that at home, kids.
Has anyobe heard the new autoformer TAP yet? I just bought one, but I'm sure it is not the first one out there...or is it?
i own a bent tvc-based preamp. it is my reference. i have also heard the promitheus with the silver wire and silver rcas..
i prefer the bent wired with continuous cast copper and vampire wire copper female rcas over the prometheus with silver wire.
I was fortunate to have been able to audition John's Slagle Autoformer prototype during it's development into the final "new" TAP. I had it in my system for months while John was finalizing the production aspects of the final version. As soon as the first full production version was available I exchanged (ie. purchased) it and returned the prototype. There was another person in Seattle (I think - is that you Clio09?) that had use of the prototype as well. I think the two of us got the first full production units.
I never had the chance to compare the Slagle 'formers with S&B's, however the "new" TAP sounds great to me. It replaced the Modwright SWL 9.0SE and Wyetech Labs Coral in my system. Since I had plenty of gain in my setup (high gain SET mono's with Zu Druid's) the gain of the active pre's was redundant and the TVC gave up nothing (except excess gain) in comparison.
I've had no problems with impedance matching and the Slagle modules are very transparent, dynamic and extended in the frequency extremes. The "new" TAP functions flawlessly with a remote controlled optically encoded volume control that provides 1db graduations for very fine loudness adjustments. The autoformer windings are switched in and out of the signal path through reed relays which are mounted on the same pc boards that accommodate the autoformers. Makes for a neat and complete "module" with very short signal path.
This TAP version also features an "active" gain circuit that can be switched into the main signal path to help in situations where additional gain and matching impedance buffering are required. Active circuit sounds quite good as well.
Once again, I cannot offer sonic comparos to S & B's (or other TVC modules) but I can say that John's (Bent Audio) engineering and implementation of TVC modules is amongst the best in the industry.
I guess you can say that I'm pleased with my "new" TAP and John is a great guy to deal with - always available for questions and comments.
Just a note for those adventurous soles - the laminations on the Slagle autoformers can be stacked in various configurations that will have a noticeable influence on the sound. Visit the Intact Audio website for lots of info.
Unfortunately that was not me who was able to play with a prototype. I actually live in Las Vegas.
I have been in touch with John about building the TAP with a K&K or some other phono stage so it would be full function. It will most likely require a two-box solution, but John was very helpful in explaining the options and how he could accommodate my request.
I'm in a bit of a transition and for the time being am using a VAC Avatar SE integrated with phono to conserve space. Ultimately I think I want to go fully balanced and may wait for John to put out the balanced version of the TAP.
Mrtennis, can you clarify which Promitheus TVC it was that you compared to the Bent TVC? Was it one of the budget (i.e., under $1k) TVC models that is built around EI-core Rev. 3 transformers? Or was it one of the newer Reference C-Core or Signature (Double C-core) models?
The first gen Promitheus that I owned couldn't be beat for $300. It had all the transparency and detail you could ask for, but the bottom end was lacking compared to a Sonic Euphoria and a Bent TVC. The Promitheus also suffered from ground issues. It has a common ground for all the inputs and outputs. I got hum if any of the inputs weren't connected to a component. Maybe Nick has fixed this with newer versions, but it was a significant problem for me. The Sonic Euphoria has an identical wiring scheme (common ground bus), but it has a wire that can be connected to an outlet to stem the problem. It still has a little hum, but not as bad as the Promitheus. The Bent, on the other hand, is dead silent when it comes to grounding issues. There are two things different about its design. The inputs don't share a common ground -- hot and ground are independently switched through the source selector. There's also a switch that lets you toggle between floating and grounding the output to the source. All in all, the Bent is very well designed and sounds superb. John Chapman is one of the most helpful and courteous fellows I've ever dealt with.
I haven't heard Nick's new C-core TVC, but I've read that it's a big improvement. I only wish he would redesign the chassis. It's one of the most unattractive cases I've ever seen. I affectionately called it the Duckling.
Mingles, Nick is now including a grounding lug on the rear of each chassis to allow the transformers to be grounded. It sounds like the same wiring scheme that you described for the Sonic Euphoria. Nonetheless, I have never encountered the hum problem that you mentioned with any of the three Promitheus TVCs I have owned. (I have owned the Reference Dual-Box rev. 3 EI-core TVC, the Reference C-core TVC, and the Signature Double C-core TVC.) They have all been dead silent in all three of my audio systems where I have experimented with them. This makes me wonder whether Nick has done something to improve on his wiring configuration beyond the addition of the ground lug.
The new Promitheus TVCs that are built around either a single or double C-core transformer improve significantly on bass frequency extension. These TVCs have a much fuller, weightier sound than that of the TVCs built around the rev. 3 EI-core transformer. In addition, the Signature (double C-core) TVC provides uncanny presence, palpability and image saturation. If you get a chance to audition the new top model (i.e., the Signature TVC), I think you will be very pleased.
I agree that the chassis for the Promitheus TVCs could certainly be more attractive. However, the looks have never bothered me much because of the way the dark color of the TVCs has tended to make them disappear in my equipment racks.
i can't comment on that , but i did audition one, during 2008. i think one of the considerations for me is internal wiring. i generally don't like silver. also, i prefer copper rcas, especially vampire wire.
i would conjecture that my bent would be softer sounding than any promitheus preamp, and therefore, more forgiving of questionable discs.
Wow! The new Bent TAP-X using the Slagle autoformers arrived. Why John does not call it the TAP-AVC I don't know. I did not have the previous generation Bent TVC, but I did have a K&K passive using the S&B MKI transformer and I tried it with my CAT JL2 (now gone) and the Music Reference RM9SE. For some reason the K&K did not float my boat - of course it was good, but I much prefered my Joule LA-150MKII and the Music Reference Pot-in-a-Box (resistor attentuator. This is a different creature, I love it and the Joule is gone. I can't A/B for precise comparisons, but overall the S&B did wow me, this Slagle-based unit does. I have a feeling John is going to succeed with this unit like he did with his NOH and TAP till S&B pulled thr rug out from under him. His new product is his best revenge. Certainly worth a try if your experience ends up being anything like mine.
I meant to say the S&B unit did NOT wow me.
Pubul57, thanks for the news. A lot of people have been waiting for this unit. How is the warmth factor? Particularly in the mid bass? Have you done a back-to-back comparison with an active?
If by midbass you mean cello or standup bass, I would say both the Joule and the K&K were warmer (I found the K&K to be warmer than I expected from a passive). The Bent TAP-X is certainly balanced in that I feel (in my set up)I don't feel anyone part of the spectrum is highlighted or supressed - I get a satisfactory sense of the whole from top to bottom and very realistic sense of both cello on classical pieces and bass on jazz - and fantastic trumpet and sax. That being said, I think it is more neutral that the Joule in the sense of being a bit tighter and defined, and not quite is "loose" and bloomy - to me it seems like well controlled bass with presence and scale, but not in the overtly warm camp. That is with a Music Reference RM9SE amp that while it uses EL34s, remains a very neutral tube amp. Compared with the K&K, I feel a much better sense of soundstage presence and image specificity based on my memory, not a direct A/B.