Quite often in audio, the question of what to buy next is ultimately an exercise in problem solving. There is a huge sea of options out there, but NY-based Woo Audio appears to take immense effort in providing products that form a perfect fit for a given solution, even for an extremely niche audience. This is likely the reason for the company’s newest headphone amp called the TUBE mini ($499 shipped U.S. and $549 shipped worldwide). Simply put, it is the first amplifier/DAC that uses tube amplification in a dongle-sized form factor.
Woo Audio is probably best known for their tube amplification. While they do make a few digital only products, flagship tube amplifiers for electrostatic and dynamic headphones are likely the first thing that comes to mind for many when they think of the brand. It seems only fitting then, that they would parley that know-how into a modern form factor like the dongle.
There are quite a few caveats to getting the TUBE mini up and running properly, but as with most analog listening the labor of love is usually part of the fun of the ritual – but I’ll get into those details later.
In the hand the TUBE mini feels as well built as the rest of Woo’s tank-like casework. The outer shell is solid metal, and a peek-a-boo window graces both the top and bottom sides of the old school stick-of-gum sized device. Woo chose the full sized USB-A connection due to its durability and strength. Many other USB-C sized connections in mobile devices (especially cameras) have been known to deteriorate with some regularity over time – and not something you really want to hang your hat on (metaphorically and literally). Some cables are specifically recommended by Woo for the best performance, with one terminating in USB-C (included in the box) and the other in Apple’s Lighting (optional, sold separately, $35) form factor. Even though the amplifier does incorporate glass tubes, the overall weight is fairly minimum, and certainly light enough to dangle slightly from a phone or computer. Also utilized in the name of strength and durability is a 4.4mm balanced jack (replacing the previous 2.5mm older balanced connector options). The TUBE mini offers both this balanced connection and the more traditional 3.5mm single-ended option, along with a physical switch to change between the two options. Both sockets cannot be used at the same time. Along the opposite side you can find some basic volume control buttons. All buttons click firmly and jacks grip tightly on the TUBE mini.
Some of those cavates for analog playback come to rest squarely with the “old school” tube technology. Tubes are inherently microphonic. Tap directly on the glass of any vacuum tube amplifier and there is a chance you will hear it ping through the speakers as well. And while you can’t physically touch the tubes through the sealed enclosure, if you bang around the TUBE mini hard enough, you might start to hear some outside noise make its way through the audio signal. My actual experience with this was quite limited. I was very interested in the performance with the latest iPhone as a truly portable option, and I found those results quite satisfactory. Even dangling from my phone, the playback was relatively free of microphonics and outside interference. Woo also recommends keeping the device away from too much WiFi or cell traffic. In my use case, I did run into some minimal circumstances where I could pick up some external EMI noise – usually when I laid it down beside the big iMac rig in the main office. Laptop usage was pretty clean, as was the surprising cell phone usage that I already mentioned. As with the microphonics, if you really set the unit down you might hear something on occasion, but sitting on a desk or table never proved to be a problem in the long haul.
Power delivery from the two glowing tubes inside the TUBE mini was sufficient for driving every headphone I threw at it, including several 300 Ohm options. DCA Ether Flow 2 and ZMF Headphones Atrium both proved to be a good pairing, with the Atrium allowing for a little more synergy with the smooth articulation of the amp/dac combo. Compared to the headphone jack on the latest Macbook Air, the volume was easily halved for the necessary power to get to reasonable listening levels. That being said, the device is not really fine tuned for sensitive IEM listening, again playing into the idea that this isn’t a device for everyone, but rather the perfect device for a select group. What is that group ultimately? I would say its someone who is looking to add a little of that tube sound to a pair of full sized headphones on a desktop. It is a micro package of Woo Audio’s more classic offerings.
I would also recommend investing in a 4.4mm balanced connector or cable for use with the TUBE mini. It feels like there is a little extra shove on that side of the amplifier along with a slight bump to resolving power.
As for the exact sound, one of the best ways to sum up the grand total of its influence over the signal is to say that it sort of acts like a good corn starch to any soy-based sauce, that is, it’s a great thickening agent. Vocals appear more full and characteristically more human to my ears. Strings and guitar sounds remind me more of standing next to them rather than sitting at my desk pretending with a pair of headphones. That being said, some might think there is a slight ding to resolution in the same areas, but at its core, the sound is quintessential tube in my mind. The funny thing is that I’ve heard so many tube amplifiers that actually sound distinctly solid state (including a few of Woo’s models) that at times I wonder what is the point of tubes if it doesn’t sound like something – at a bare minimum. If you want your tubes to sound like solid state, then just stick with the lower cost, higher reliability/longer lasting technology. Tubes should sound like analog, and that’s what the TUBE mini feels like at its core. Sure, the whole thing is 1 degree more of a hassle than an Audioquest Dragonfly, but I don’t think many would argue that the TUBE mini sounds nearly the same by comparison.
There is also the longevity of the product to consider. As of this publishing, the tubes are not replaceable in the dongle. That leaves a bit of a timestamp on the lifespan if you plan to beat the heck out of the playback, however, Woo Audio does provide a 3-yr warranty on the product. I feel confident that any user would get their money’s worth out of it before they would see any real quality degradation, but I feel like it was worth mentioning within the context of this review.
Overall, the TUBE mini by Woo Audio is a really good solution for a question perhaps just a few were asking. That is, How do I inject a tube sound into a truly portable package? Woo does make other products for dragging tube sound from home to office, or office to cafe, but the cost and the weight is significantly higher than the TUBE mini is capable of bragging about. What this device does is extremely unique, and something that its target clientele is certain to appreciate. The output power is surprisingly strong, the sound is just “tuby” enough and the portability is at a maximum. Once you navigate yourself around the physical technicalities inherently involved with tube design playback, I think most purchasers will be pleasantly surprised by the unique proposition involved here. A very fun listen for almost any full-size headphone.
More info: Woo Audio TUBE mini