Audio Horizons TB5.0n Tube Buffer review

Audio Horizons TB5.0n Tube Buffer


  • Frequency Response: 20 Hz to 100kHz
  • Total Harmonic Distortion THD): 0.05% @-20dBV Dynamic Range: Better than 110 dB
  • Signal to Noise Ratio: 117 dBv
  • Channel Separation: 90 dB @ 1 kHz
  • 65 dB @ 10 kHz
  • Gain -1 dB Price: $725

“Tube buffer or not tube buffer? That is the question”

Audio Horizons is the brainchild of Joseph Chow, an engineer specializing in small-signal processing, with 25+ years of experience working with Kenwood, Proton and MIT Cables among others who has decided to use his network of contacts in Asia to help him produce a range of audio components that offer high quality at real-world prices. Selling online, the company has developed a strong and loyal customer base, and had particular success, from my reading of reviews, with his 2.1 stereo preamp. The company also offers a phono stage and DAC, cables and power cords, upgrades to classic products, and has plans for further products in development, all built around Joseph Chow’s belief in zero-feedback designs which aim to provide the reliability and low noise of solid state with the body and warmth of tubes. Those given to reading component specs will note the impressive figures accompanying each product (see

The Audio Horizons Tube Buffer 5.0n is one of a number of add-on components that promise owners an easy entry to the world of tubes without the cost or hassle of dealing with tube amps. The general pitch for such products is the promise of sweeter, warmer sound that only tubes, supposedly, can provide. This is usually presented as a natural complement to the power, convenience but ultimately colder sound of solid state gear. I’ve been aware of such products since Musical Fidelity launched its X-10 tube buffer a decade or more ago, which received many positive reviews (and no few dismissals as a gimmick) but reportedly worked by adding what some deemed certain ‘inaccuracies’ to the signal, albeit pleasant sounding inaccuracies to most people’s ears, taking us up the familiar path of measurement versus listening preferences. Mark, our editor, recently reviewed the Grant Fidelity B-283 tube processor and found it a pleasant addition to a solid-state system, and now comes a costlier, full-size buffer from Audio Horizons, the TB5.0n, a two tube, XLR and RCA enabled version with single on/off switch. In my case it came with the optional upgraded lownoise Siemens NOS E88CC tubes with an 8000-10,000 hour life expectancy, a $975 version. Audio Horizons also offers a fully balanced version which modifies the circuit for another $125 (the XLR version I used was not fully balanced internally) so you can see the potential here. Fit and finish is acceptable but this product will not win any awards for looks, the casing feels slight, evidence of where the money, hopefully, is spent. Audio Horizons offers a 30-day home trial with full return rights so you can learn how this works in your own system, which is very important for most serious listeners.

Insertion of the TB5.0n into a system is simple, either place it between pre and power amp or between a component and a pre-amp, but in all cases necessitating an extra run of cables, which will make some folks uncomfortable already. I noticed some extra noise from its installation, nothing serious, the kind I had to put my ears to the speaker to confirm but there nonetheless whenever I employed the TB5.0n. The TB5.0n also ships without a power cord, and Audio Horizons are pretty direct on this, stating that you should employ a high quality cable of your own choice to get the best out of the buffer, and of course, they offer their own as a perfect match (starting at $225). I employed a variety that I had to hand, including a MAC HD, Virtual Dynamics David and a PS Audio Prelude. Interconnects were either PS Audio Transcendents (XLR) or MIT Terminator 2s (RCA). I also used the TB5.0n in combination with three different set ups: between a PS Audio GCP 200 pre and BAT VK500, the same pre but now with Spectron Musician 3 Mk2 monoblocks, and finally between the Nuforce P8.5 pre and P8.5 stereo power amp, the latter also being used to power a bedroom system running KEF 103/2 speakers rather than my reference Von Schweikert VR5SEs in the main rig. In other words, I gave the TB5.0n a pretty full work out across several systems and the results varied accordingly, as outlined below.

So what’s the deal with buffers? I confess to being wary of adding extra stages with associated cables and figure if you need to add this, presumably something is not quite right in your system to start with, but then, isn’t this the natural condition for any audiophile? Without giving the conclusions away, I will tell you that if you expect night and day differences because of the addition of a tube circuit in your system, you might be in for a surprise with the Audio Horizons TB5.0n. In all of the set-ups where I employed the TB5.0n, the effects were subtle. Second, I found the best test of the TB5.0n’s effects required me to leave the buffer in place for several days, giving the tubes ample time to warm up (30-60 mins is recommended, and I don’t disagree), then taking the buffer out. It was usually easier to learn what the buffer did when it was removed from a familiar system than when it was immediately added, but that might just be me. Since I had the buffer in my home during a time of unusual plenty in the amplification department, what is a reviewer to do but try multiple comparisons, which is what I did here, so let’s take the comparisons system by system.

Between the PS Audio Preamp and BAT VK500 power amp

Audio Horizons TB5.0n Tube Buffer back

This amplification coupling is my long-term reference and I know its sound with my Von Schweikerts like the back of my hand; light and airy on top, rich and clean in the middle and with a firm but not super-tight, slightly rolled off lower end. The addition of the TB5.0n did little to the overall sonic character of the mids and upper that I could easily determine, that is to say, the music continued to flow, if perhaps with a slighty less detailed top end, but the buffer did add some weight to the bass. This new quality of bass worked on some recordings but on others made the reproduction a little bottom heavy. Note, this was not a boom but a transient quality dependent on the tune and the recording. Over time I became used to it and it is possible that some listeners might prefer that reproduction but to my ears this combo veered a little too far to the warm side in places, and in so doing caused transients to blur slightly and the overall sound to lose some of the sparkle that can make the BAT so seductive. Case in point, the Haden & Metheny collaboration Under a Missouri Sky, one of my reference recordings, can sound flat or congested in some systems but opens up beautifully when reproduced well. I felt the TB5.0n took some of the edge off this album when played through the BAT and Charlie Haden’s bass lost some defini- tion and separation from Pat Metheny’s harmonized guitar lines. This was a distraction to my enjoyment of the album. Similarly, with Holly Cole’s Temptation, an album with no shortage of bass, the addition of the buffer seemed to give me a touch too much of bass richness on some tracks which shifted the overall balance of the recording. I can imagine that for some listeners with lean systems this would be a preferred sound but I suppose having lived with the alternative for so long and rejected other options that I’ve compared, it would be hard to convince me this was a step forward. I had to go back and forth on this set up several times to get a real handle on the TB5.0n’s effects here and this fact alone is indicative of the Audio Horizon’s sonic signature, it is not a blanket sonic fix, but a subtle adjuster. When sitting between the PS Audio and BAT however, the adjustment was not entirely to my liking.

Between the Nuforce pre/power combo

Having this pair in for review (forthcoming), I wanted to get a quick impression of how the TB5.0n might work with these little wonders. At first, in the exact opposite to the interaction with the BAT, the TB5.0n seemed to totally deprive the Nuforce of it’s commanding and ultra tight bass reproduction. This turned out to be temporary however, a function of the combined units warming up as it passed within the playing time of a CD, thereafter allowing the Nuforce to deliver some of what it does best. Given the lack of XLR inputs on the Nuforce power amp, I was forced to use lower quality MIT single-ended cables here which may have also been contributory, but over time I came to enjoy this combination of Nuforce amplification, In fact, when used as a system with my Kef 103/2s and an older Rotel 945 CD player attached to a Parasound DAC 2000 Ultra, the resulting sound was undoubtedly the best I’d ever heard from these speakers. Yes, the Nuforce components are largely responsible but the TB5.0n took a very decent sounding smaller system (small in size, not in sonics) made up of older and current components, and gave it that little extra musicality that made me listen again and again. Music seemed to flow more easily, the bass reproduction now seemed more natural and there seemed to be a lessening of the need to turn the music up to make the speakers breath. Taking the TB5.0n out of this loop was immediately noticeable, the music just hardened perceptibly and became less compelling. Adding the TB5.0n provided just that little bit of softness which rounded the presentation out most pleasantly. Here, with the KEFs, Haden&Metheny grooved effortlessly, the sound seemingly now coming from larger speakers, with a pleasing roundness that had me viewing the TB5.0n as providing a significant step up in the overal reproduction. If this were my set-up, I’d likely keep the TB5.0n in place and be satisfied that I was getting the best from all components.

Between PS Audio and Spectron Monos

Definitely the most expensive combo to hand during the trial period. The complete class D set up might, on paper, appear to be the perfect vehicle for a little tube smoothness but this is again where assumptions don’t always match reality. First, the Spectrons are not like any other class D I’ve heard. When I first installed them they had far warmer and rounder bass, more like the BAT but still seemed to have that steely upper register that I’ve heard with lesser class D amps. Over time this smoothed out and I’m left with a sense that these just aren’t like other amps I’ve heard. Regardless, with the TB5.0n in place between the preamp and these monos, the music seemed just a little muted, not unpleasantly so by any means but in direct comparison, in or out, I noticed this effect. Take Chris Smither’s live album, Live as I’ll Ever Be, an engaging and intimate recording of one man singing with a guitar, his own foot tapping in rhythm, and a live audience laughing and cheering him along. With the TB5.0n in place I felt the live nature of the space was lost slightly, the sonics more focused on the man on the stage, less on the man and the ambient space in which he was playing. This was very subtle however, and likely to be one of preference as the TB5.0n version gave the guitar a little more central solidity, the vocals a more natural body but the crowd a more background feel. Any muting of the soundspace was dwarfed though by the more noticeable alteration I experienced with bass reproduction. When I put the TB5.0n into the loop, I scratched my head and wondered again, as I had with the Nuforce, just where it all went. Only this time, it never really came back. The Spectrons alone offer no shortage of bass, it’s there and you cannot help hear it, full, defined, and deep. The TB5.0n seemed to haul it back in and reduce the sonic window accordingly, offering as a result, less of match here than with any of the other combos on some music. This was most noticeable on recordings with strong electric bass, such as Ronnie Earl, or SRV where the sonic window seemed to be shortened. On mostly acoustic music it offered what I can best describe as a more rounded off sonic presentation that seemed to shrink the soundstage width while polishing the midrange. Haden & Metheny seemed a little further back in presentation, and Haden’s bass was noticeably reduced in size and presence but what remained had a little more fluidity perhaps, a tad more smoothness in key areas. This makes the value of the buffer with this combo a little harder to call. The best analogy I can give is to think of an image file that you try to zoom in on. If the resolution is right, zooming can expand your image well, giving you a larger and more intimate picture, but if not, the image breaks up at some point and is best viewed at reduced, lower resolution. The Spectrons seek to reproduce all images, warts and all. The TB5.0n seemed to take CDs and offer a reduced but smoothed out final sonic image great for ordinary recordings but not fully exploiting the potential of better ones. For me, the slight compromises in bass and presence outweighed the slight gain in midrange ease, but you might feel differently.

Audio Horizons TB5.0n Tube Buffer

Shifting places: using the buffer to feed the preamp in these systems

While thus far I’d employed the buffer between the pre and power amps, as seemed most logical to me with my rig, I was not entirely happy with what I was hearing so I moved the buffer forward in the chain to take the signal from my SACD player directly then feeding it on to the preamp. Note that using the TB5.0n in this manner means it can work on the signal from one component only, the one feeding it, not all components that feed the preamp, a compromise for those of us with more than one source component. Again, let’s take this system by system.

TB5.0n before PS Audio and Spectrons

With the system wired up with the Spectrons, I reconnected the front end to have the TB5.0n before my PS Audio. Used this way the buffer produced another sonic shift, and this one much more to my liking monos. Bass returned, perhaps not as clearly or as powerfully as with the Spectrons alone, but definitely at a more balanced level that gave the music a better presentation and soundstage. More than this, treble response was greatly enhanced. Without the TB5.0n, the complete class D amplification set up could present cymbals in a slightly steely manner, the rise and decay noticeably stilted, the shimmer of struck metal vibrating in space coming over as artificial and frankly, not too pleasant. This is a reference point of mine in the Tord Gustavson Trio’s work, particularly The Ground. With the buffer in or out of the link between the pre and the power amps, the effect was minimal here, but when placed before the preamp, taking the signal directly from my Marantz SA11-1 player and feeding the PS Audio’s inputs, the glory of the cymbals obviously returned almost to the levels I am used to with the BAT VK500 which does a marvellous job in this regard. Everything I played with the TB5.0n before the preamp sounded better than it had with the TB5.0n between the pre and power amps. Haden &Matheny came back as a real duo, the guitar and bass separated but intertwined in musical lines and Patricia Barber’s Companion live recording came through with renewed palpability. The acoustic guitar on ‘Let it Rain’ is always a good test. Yes, it sounds like acoustic guitar on any set up but with the best, you can almost sense the wood body and bent strings in real space between your speakers, the notes floating through air, the small finger slides and scuffs on the strings giving the track real presence. WIth the TB5.0n feeding the preamp, this quality came through as never before. And all this without any apparent loss of important midrange or upper frequency detail, as far as I could tell. On Ronnie Earl’s Grateful Heart, another long term reference, the music had a such a pleasant smoothness that I had to the leave the album on entirely, so seductive and well balanced was the resulting soundscape of mellow guitar, saxaphone, organ, bass and drums. The Emerson Quartet playing Bach’s Art of the Fugue similarly captivated, the music flowing richly forth in a manner that just makes listening easy (not to be confused with coming across as easy listening!). Whether it is some interaction with the power amps or the preamp, I cannot say with any certainty, but used in this location, I feel the Audio Horizons tube buffer really delivers on its promise.

TB5.0n before PS Audio and BAT VK500

On the basis of it’s clear benefits feeding the preamp with the Spectrons I went back an tried it this way with the BAT to determine if my views of it’s value in the long-term reference rig might shift if positioned differently in the chain. The answer is not really. The softening of bass definition I’d perceived with the buffer between the PS Audio and the BAT was perhaps not so obvious now and the music had the typical qualities I know this pre and power set up to possess. However, the benefits I’d found from feeding the preamp this way with the Spectrons was not so apparent with the PS Audio/BAT combo, a finding I can only imagine might reflect the BAT’s own somewhat tubey sounding qualities which dwarfed any effects of the TB5.0n. Tord Gustavson’s The Ground sounded a little bass heavier than usual, as did Ronnie Earl’s Grateful Heart, fine for those who like that but not for me, after years of familiarity with both the music and the amp, the added bass weight seemed too much to my ears. The Emerson Quartet seemed to lose a little of their spatial spread, and lines seemed less distinctive though remaining timbrally real. Differences can be better or not, and this was different, as outlined before. So I conclude from this that the BAT VK500 does not really require the extra elements that the TB5.0n brings to the party, regardless of location in the system chain.

TB5.0n before Nuforce pre/power combo

Feeding the Nuforce pre/power combo, the TB5.0n provided a pleasant refinement over the combo on its own, and, as far as I could tell, no real shift from using the TB5.0n between these amplification stages. I should emphasize that this is not a criticism of the Nuforces, they are really good but as noted above, the TB5.0n and Nuforce combination offers sweet sound, full range but balanced, with a smooth, unfatiguing presentation that just draws you in. Some will hear this as detail reduction, others will call it as tube refinement, and we can compromise by calling this a matter of taste, only I don’t fully concur. I found the TB5.0n to offer that little something extra which took a fine sound and refined it further. Sure, the bass was a little rolled off, but the effect was subtle on many recordings. Certainly, the common problem of Class D amps being a little steely at the top end is never true of the Nuforces partnered with the TB5.0n. Ronnie Earl and co sounded sweet, spacious and smooth, the guitar and sax reproduced in a manner that, if somewhat less detailed, left little to be desired timbrally. I could hear Newman’s breath as he played the intro to ‘Drown in my own tears’ as if he was close to me in the room. Tord Gustavson’s The Ground had the full glory of the cymbals reproduced in a way the has defied many other class D designs I’ve auditioned. Analogies are always a little misleading but I felt the TB5.0n gave these units just a touch of midrange focus that seemed to take a very slight edginess off the sound. Once I became used to this, I missed what the buffer brought to the show. The exception was on driving rock,
where I felt the combo lost some of the bass authority that was so obvious without the buffer in the loop. Switching it in and out confirmed this, bass was altered. Time limits prevented me giving this combo the full auditioning time I’d like to be sure, but what I heard lets me think the TB5.0n brings something complementary to the Nuforces. Regardless of placement, this combo provided an enjoyable listening experience.

Being in the right place at the right time!

What I can conclude from all this auditioning is that the value of this buffer is system and location dependent. The TB5.0n is not the type of component that imposes one sound without discrimination on all other components. It is far too subtle for such effects. Instead, the TB5.0n seems to interact with components depending on their specific design and sonic qualities in clearly audible ways. I wish it were simply a matter of saying the buffer worked with digital but not solid state, or that it worked a treat with older gear rather than newer designs but audio reality is not so clear cut. With two class D set ups I experienced somewhat different results, one which would cause me to avoid the use of a buffer between pre and power, the other which would have me laying down the cash for it now. The most powerful case for the TB5.0n in my home is to use it after the source but before the preamp where it provided very positive results with my PS Audio/Spectron combo, at odds with the sonic experience I had when using it between these amplifiers. With the Nuforces, I enjoyed what the TB5.0n brought to the party, regardless of where I positioned it in the chain. With the BAT, I would not be inclined to add the buffer anywhere, the trade-offs that resulted gave too few rewards overall.

Given the basic similarities of the TB5.0n and the full Audio Horizon preamp, any interested purchaser faces a serious decision. Stepping up to the preamp does cost more initially but it requires one less run of cables and one less power cord, while surely providing the sonic charms of the buffer’s tube stage (and I confess to a preference for keeping the system simple wherever possible). If you’re happy with your preamp then it’s a non-issue, but if you are looking for what the TB5.0n can provide without having to worry about extra cable runs, you might want to think about going as far as the Audio Horizons preamp where you get the simpler set up and the ability to connect multiple sources. At the asking price, there are cheaper alternatives out there but the AH TB5.0n offers simple design, easy connectibility and fuss-free operation. You also get the opportunity to tube roll should your heart desire. The claims for no loss of detail seem true, in part, with the above caveats on system and use. While it’s dangerous to rely on sonic memories, I’d really like to hear this with the Wyred4Sound amp I reviewed last year because if it provided the sort of extra life I heard in some of the Class D set ups here, then it could have added necessary finesse to the affordable muscle that amp provided, a potentially excellent combination of strengths that would be worth trying. If I was in the market for just a buffer stage, I’d stop my search right here. Since I am not, I will conclude that Audio Horizons offers a product that might just take your system that little bit closer to where you want to be at a reasonable price. You have to try it to know if it’s right for you but be prepared to play with location, cabling and cords to get the best of what it can offer.

Manufacturer’s Comment:

We’d like to thank A$$A for taking the time to review our TB 5.0n tube buffer. The reviewer notes that “the value of this buffer is system and location dependent.” He found it to be more location dependent than we have but since the TB 5.0n is so system dependent that may be true in his experience. It has not been true in ours. He also writes that “the TB5.0n is not the type of component that imposes one sound without discrimination on all other components. It is far too subtle for such effects. Instead, the TB5.0n seems to interact with components depending on their specific design and sonic qualities in clearly audible ways.” We whole-heartedly agree, and that is why we offer to qualified customers a free, freight prepaid home audition. We urge interested customers to visit our website, for details.

The TB 5.0 was designed for owners of solid-state equipment who are in the main satisfied with the sonic signature of their system but wish to add a little warmth, textural richness, and musical flow to it. We did not want to design a component that would add so much of its own tube-like coloration that it altered that signature. We assumed that if an owner were really unhappy with his system he would simply replace one of his components with a piece of tube gear, for example, our TP 2.1 preamplifier where the sonic differences will be greater and we hope deliver the desired blend of solid state detail and tube warmth and richness. Again our thanks to Patrick Dillon for a thorough, thoughtful, and fair review.

  • Audio Horizons
    8188 Belvedere Ave.
    Suite D
    Sacramento, CA 95826, USA

from affordableaudio, by Patrick Dillon