The Apex Teton – The Ultimate OTL?
by Dubstep Girl
The Apex Teton is a single-ended output transformer-less (OTL) pre-amplifier and headphone amplifier designed and made by Pete Millet and sold exclusively through Todd the Vinyl Junkie. At $5000, it is half the price of the flagship Apex Pinnacle headphone amplifier and is one of the more expensive OTL headphone amplifiers available right now. When I received the Apex Teton for review, I was excited, very excited. If you have seen my posts on Head-Fi and my tube reviews, you’ll know how much I enjoy the airy, detailed, yet coherent and natural sound of a well-designed OTL amplifier. In my opinion, they are some of the best amplifiers you can use for driving high impedance headphones from Sennheiser and Beyerdynamic. The Apex Teton has impressed me so much, I think it’s the best amplifier I have heard for the Sennheiser HD 800 to date; the pairing is absolutely sublime and out-of-this-world crazy good!
The Apex Teton design is based off the older Wheatfield audio HA-2 but with several improvements made including a power supply upgrade and newer high quality components. Like other OTL amplifiers, the Apex Teton uses some of my favorite tubes, a 5U4G rectifier, a 6SN7 input, and a 6080 output tube. With these three tube types, the tube rolling possibilities are endless and should keep tube addicts satisfied for however long they decide to own this amp. The Teton has three single-ended inputs and a single-ended preamp output which could be selected via the two knobs in the front. The Teton has one single-ended headphone jack that can drive headphones over 16 ohms and can deliver up to 340mA at 150 ohms. Power is more than adequate for high impedance headphones and most dynamic headphones. While I have not tested it myself, the Teton certainly feels capable enough for power hungry planar magnetic headphones. Additionally, there is an IEM output selection that will reduce the gain on the headphone output in order to better drive sensitive loads like IEMs without introducing noise.
The build quality of the Apex Teton is excellent and comparable to other amplifiers in this price range. The heavy black anodized aluminum chassis is thick, solid, and well put together. The large TKD potentiometer volume knob is very smooth and easy to turn. The bright LEDs on the input selector knobs and power knob change colors depending on your selection and add a nice touch to the amp. The aluminum heat sink on top of the amp works well to dissipate heat from the tubes. I was less impressed with the screwed-on rubber feet, plastic tube sockets, and DIY appearance of the transformers on top of the amplifier, which I feel could all be of higher quality given its cost. However, they function flawlessly and are of high enough quality that I have no concerns about their durability or long term performance. This is only a minor nitpick as other expensive amplifiers have been guilty of much worse (glued-on rubber feet, annoying ill-fitting tube sockets, and sheet-metal-plastic-oven- knob aesthetics are not uncommon in the world of high-end audio).
For this review, my primary headphone was the Sennheiser HD 800 as I am very familiar with its sound signature and it remains my reference headphone when comparing the sound of different tubes. I used Audioquest King Cobra interconnects as well as Audioquest Power and USB Cables. My source was lossless music files from my computer fed to my Mytek Stereo192 DSD DAC. As usual, my music choices varied and included just about everything. After several days of tube rolling with the Apex Teton, my final tubes of choice were the USAF 596, Tung Sol 5998, and metal base Sylvania 6SN7W.
The sound of the Apex Teton can best be described as fast, liquid, and immersive. Like other top-of-the-line amplifiers that I have heard, the Teton delivers its unique sound signature in a way that is pretty much flawless. This isn’t some warm tubey-sounding amplifier that as a result of its warmth ends up missing the last bit of detail or feeling slightly veiled. Nor is it a neutral amplifier that ends up being too flat and uninspiring or with a slight edge in the treble. No, the Teton is one of these special amplifiers that sound so good, it’s hard to find any flaws! Even with the stock tubes, the level of detail and transparency is as good as it gets and there is phenomenal synergy with the Sennheiser HD 800. With upgraded tubes, the Apex Teton is by a good margin, the best HD 800 amplifier I have heard to date.
As I am quite experienced with tube rolling 5U4G and 6080 tubes (at one point I owned just about every 5U4G and 6080 tube substitute available), I decided to cheat a bit (who wouldn’t?) and immediately plugged in the best tubes I had, the mighty USAF 596 rectifier, Tung Sol 5998 power tube, and metal base Sylvania 6SN7W drive tube. I was not disappointed. The sound quality from this combination was as perfect as I can imagine it to be, the Teton did everything right and it all was present in just the right amounts.
The Apex Teton and HD 800 with these tubes presented some of the best treble I have ever heard out of any system. The treble was dreamy and beautiful, extending infinitely to the highest frequencies. Every little nuance and itty bit of detail, like stars in the night sky, shined brilliantly through the many layers of sound. The excellent detail retrieval and pitch-black background make the Teton extremely revealing and transparent, there is zero grain and the clarity is unreal. However, it is also musical, rich in tone, and completely non-fatiguing; you really can have the best of both worlds! Similar to other OTL amplifiers I’ve heard, the Teton has a crystalline treble that is lifelike and interconnected with the midrange and bass. As a result, the Teton is very coherent and natural sounding, much more than most amplifiers. High-res albums like Melody Gardot’s The Absence and Chick Corea’s Light as a Feather allowed me to see what the HD 800 were capable of with the Teton. Instruments seemed to come alive with plenty of spatial cues and tiny details being effortless reproduced over the silent background.
The HD 800 is known for having a huge soundstage and precise imaging. With the Apex Teton, the HD 800 is able to effortlessly reproduce the soundstage of the recording with holographic imaging and 3D layers of sound, resulting in an extremely immersive experience. Movies and video games suddenly came to life as the “you are there” feeling was more present than ever before. Nox Arcana’s dark ambient album Phantoms of the High Seas was one of my favorites to listen to with this combination. I was able to close my eyes and feel like I was on a ghost pirate ship with its crew looking for buried treasure. Creepy bells, cannonball blasts, and eerie drumbeats sent a chill down my spine as they could easily have been mistaken for the real thing. I later ended up going through some of their other albums including Shadow of the Raven and Winter’s Knight, all of which I highly recommend if you ever get a chance to listen to this combo, the experience is exhilarating!
The Teton’s midrange is as equally impressive as its treble; it is flat line neutral but possesses the inherent warmth and sonic characteristics of an OTL amplifier. The midrange is neither recessed nor forward in any way and due to the speed and resolving capabilities of the amplifier, is able to contrast and separate sounds vividly while remaining coherent and balanced. The effortless way in which the Teton renders detail in the midrange is extremely noticeable on Alison Krauss’ Forget About It. Tracks such as “Stay” and “Empty Hearts” were pure bliss as Alison’s angelic voice seemed to just jump out from the recording and touch my soul, I could feel the emotion behind her every breath. The instruments though layered and spaced in the background, were just as palpable. The acoustic versions of “Salt in our Wounds”, “Heartache Every Moment”, “Pretending”, and “In Joy and Sorrow” from HIM’s album, Deep Shadows and Brilliant Highlights, have incredible vocals from Ville Valo which where greatly enhanced by the Teton’s euphonic yet uncolored midrange. I could feel and understand the maelstrom of love that Ville sings about better than ever, the Teton just took everything to the next level. The Teton and HD 800 created midrange magic that seemed to work for just about every genre of music. If you were listening to rock, pop, or electronic, the forgiving nature of the Teton allowed for long listening sessions and the dynamic realism kept your toes tapping the whole time. If you chose jazz or classical, the Teton quickly reminded you of the intrinsic beauty of analog music as it effortless reproduced sound in that euphonic, sweet, goose bump-inducing way that is only found in the very best tube amplifiers.
The bass performance of the HD 800 with the Teton is second to none and amongst the best I’ve heard; it is engaging, deep, visceral, and has incredible control. The amount of bass is what I would consider “tube neutral”, having a decent amount of punch and slam for a tube amplifier, yet would probably be considered slightly lean if it was a solid-state amplifier. It was enough for just about every genre of music and always felt “just right”. The bass blends very well with the midrange and the quick decay allows the bass to always keep up with the rest of the music. Bass notes are layered and have a great deal of depth and detail to them, filling the void many other amplifiers leave behind. Though a lot of amplifiers are able to give the HD 800 good bass or texture or speed, none have brought it all together like the Teton. “Hope There’s Someone” from Avicii’s True is one of my favorite test tracks, the deep bass in the song is tricky to reproduce accurately and can easily show me how good an amp can handle deep bass extension and details. The Teton and HD 800 had no problems here. Heavier rap bass in Yo Gotti’s “Act Right” is generally something the HD 800 tends to have problems with. However, the bass still hit hard enough to please most bassheads and the amount of detail in the bass was almost unbelievable. Usually bass in rap music lacks depth and sounds boomy, but just like with the midrange and treble, the Teton just seems to upscale the resolution on everything and enhance it, constantly reminding you that it is truly a top-of-the-line product.
Though most of my listening on the Teton was with the Sennheser HD 800, I did briefly audition my Master & Dynamic MH30 headphones on the Teton and I was blown away, Though obviously not as good as the HD 800, the MH30 scaled up tremendously in a way that reminded me a lot of the Sennheiser HD 650; they just keep getting better and better even on amplifiers that cost many times more what the headphones do. The warmth of the MH30 became a layer of rich syrupy awesomeness which just seemed to do wonders with rock and acoustic music and the transparency was almost planar-magnetic good, this is still a $350 headphone right? One headphone I really wish I could have auditioned with the Teton is the Beyerdynamic T1, a headphone that just loves OTL amplifiers. I believe the Teton would pair excellently with the T1 just as it did with the HD 800.
The Teton is able to tap deep into the essence of the tubes, the sound profile of each tube being able to greatly influence the overall sound signature and quality of the sound. Switching over to the stock Sylvania 7236 power tube, Sylvania 5U4GB rectifier, and modern production Tung Sol 6SN7 drive tube, I was surprised at how not bad the Apex Teton sounded. The Sylvania 5U4GB tends to be a little too solid-state sounding for my tastes and I generally find the new Tung-Sols to be quite inferior to the NOS tubes of old. The Teton however, seemed to be happy with the tube combination and delivered excellent clarity, a huge soundstage, and well-controlled bass that I wouldn’t have expected these tubes to be capable of. Unfortunately, the treble did have a slight edge that became annoying after several hours, most cheap tubes do this. Upgrading the stock rectifier to the 596 seemed to clean up the slight hardness in the treble and increased overall sound quality and transparency as well as improving bass extension. I briefly tried the Mullard CV593 rectifier in the Teton, however, this resulted in a lusher sound and there was slightly less detail as a result, so back to the 596 it was. When I compared the Tung-Sol 5998 power tube to the Sylvania 7236 on the Teton, I found that the 5998 was a much better pairing with the Teton as the 7236 made the midrange and treble too forward and aggressive for my tastes. Upgrading the newer Tung Sol 6SN7 to the NOS Tung Sol 6F8G improved the resolution of the amplifier and made the sound much more 3D and layered. However, I found the 6F8G to be a little too lush and polite sounding for the Teton. The metal base Sylvania 6SN7W was a much better pairing as it was just as resolving but was faster and had better bass. I did not spend too much time tube rolling the cheaper tubes provided as I felt that they took away from the potential of the Teton and I believe most people who will buy this amplifier will want to use the best tubes anyways to get the most out of it.
The first amplifier I compared the Apex Teton to my Woo Audio 5 (WA5), my reference 300B SET amplifier. The Woo Audio 5 is an amazing amplifier, however, it is quite different from the Apex Teton in sound. With the EML 300B power tubes, Tung Sol 6F8G drive tubes, and Mullard CV593 rectifiers, the WA5 is quite a bit warmer than the Teton, having more lushness and smoothness to its sound. The bass, although excellent on the WA5, is still not as controlled as the Teton’s. The WA5 exhibits a slower decay and lacks the dynamic punch of the Teton; bass quantity was quite similar however. The WA5 has a more rounded midrange and as a result, is slightly less detailed and defined than the Teton. The Teton separates more, has more fluidity and speed, and a more refined treble overall. Transparency is top-level on both amplifiers as there is no grain or unnaturalness anywhere in the sound. After hours of listening, I switched the Mullard CV593 for the 596 rectifier that narrowed the differences between the two amps. Transparency and detail were almost identical and it was difficult to tell which amplifier was better in this regard. The WA5’s bass became tighter and faster, though it was still tubier and fuller sounding than the Teton’s. Treble extension improved with the 596 but the Teton seemed to still have the better treble, even if it was by only a small amount. Though these differences seem big at first, they really aren’t as both amplifiers are close to being perfect. However, the Teton had better synergy with the HD 800 and was the better pairing overall.
I later compared the Apex Teton to my Headamp GSX MK2, which is my reference solid-state amplifier. The GSX though half the cost of the Teton, held it own quite well as it matched the Teton in speed, liquidity, and detail. However, its neutral character simply made it less enjoyable than the Teton, as I felt that it lacked the euphonic warmth and musicality of the Teton. The GSX is also more unforgiving of poor recordings and lacks the 3-D layering of a tube amplifier, which was easily noticeable on most tracks. The GSX being a solid-state amplifier, has more bass punch, presence, and control than the Teton however, the differences are still small. Overall, the Teton is more lifelike and natural sounding whereas the GSX is more precise and accurate sounding; the HD 800 seems to prefer the former by a good margin.
The Apex Teton is one of the best amplifiers I have ever heard with the Sennheiser HD 800, period, and should be strongly considered if you are looking for an end-game amplifier for this particular headphone. Due to its high price of $5000 and its second-place standing in the Apex line of amplifiers, I feel that it is often overlooked, especially if one is seeking more power or balanced outputs. However, the Apex Teton is worth every penny and is the last 5% you crave. Discriminatory ears will be quick to notice the improvements over lesser amplifiers, especially with upgraded tubes. If I could afford the Teton right now, I would buy it. The Teton has set the benchmark for all future OTL amplifier reviews.