I have had a little bit of experience with hybrid amps from the Vali, Little Dot 3, and finally the Fournier HTA-2. What I have not had experience is with all in one tube-hybrid/DAC which yes I have seen them around from unknown chinese versions that cost less and High end audio gear that cost so much more. I will say for this Price I think many units will have a hard time beating out this DAC/Amp. Now that fact that you can travel with this and have it connected to your laptop and or tablet on a bus or train and being listening nise 96khz files from a great amp and DAC is just a hefty plus. Mainly because I actually preferred getting the Gateway which is the aftermarket powersupply, for a cleaner and or more solid power supply. The sound quality on this unit for the price you can find them at is what really is amazing, because this DAC is definitely on par with the ODAC/CDAC+ that I have used in the past, which many know from their own experiences is fantastic DAC for the value it brings to all types of audio hobbyists. Well, the PanAm is not a slouch in the DAC dept. and man does it sound clean and clear with great detail, which for this price it should be. Yet, all this is for not if the amp is lacking in qualifications....well do not fret, because the Amp is in many ways the star of the show being even better, from power(raw power this thing is seriously fronting with the ring of power or something) to versatility. This amp can drive them phones, and does it sound good? *a very satisfying hell yeah, Let us get into a few specifics
 
The Design/Build
 
 Honestly this feels and looks like a higher quality DAC/Amp from the small compact size to the sturdy construction and aesthetically pleasing chassis and ability to stack the PanAm with both the Gateway power supply( same size and color if one so chooses between black and silver) and the Passport( the battery pack that can charge and last up to 10 or so hours otg) which if buying both of the aftermarket accessories/extensions this product looks really cool and still is much smaller than many to any DAC/amp combo's I have seen. That amber to orange led light is non-obtrusive to the eye and gives a very nice pairing with the the orange tubes leds. It is heavier that it looks for it's size but that just adds to the solid feel it gives when first unboxing this gem. To myself this is easily a 10 out of 10 if they had decided to throw in the ability to use RCA out and have a stand alone DAC for those hobbyists, and I am happen to be one, that like to have more than one amp for a pairing with a particular headphone. I understand that was not in the design and new this going in, but I also know 500$ is nothing to scoff at so I give Design  and build an 8/10
 
Sound quality and performance
 
  If I could of a one word description, perhaps...beautiful. I can honestly say this unit with all the headphones from 35 ohm to 600ohms, from Dynamics to Orthos everyrthing is driven with authority. Not just authority though, with the RTC French 5654 tubes I am using everything has a spaciousness and detail that just knocks me to a music dream state. I have used 5 headphones with this unit the top 3 with it that I have given ample listening time are the T70p(35ohms), the HD600(300 ohms), and the ZMF X Vibro(Ortho not sure on Ohm)...each performed admirably but these exceeded that with performing remarkably. I have say as far as closed back headphones both the X Vibro and T70p are great for a pairing, one have heavier bass impact lush full midrange and smooth easy listening treble. Where the T70p has great extension on bottom and top, the bass being lighter but tight and quick, the midrange being the best I have heard from a Beyerdynamic, and treble though bright is very detailed and not as harsh as the lesser siblings of the DT line. The T70p's resolution and spaciousness for a closed headphone really helped it be an easy fit with the ALO PanAm especially pairing with the RTC tubes which has great detail and separation yet still has a musicality and intimacy that I happen to love ...with the T70p this feels like a very detailed yet musical pairing that many hobbyists would grow to love. I happen to Listen to all three of these headphones pretty regularly with the PanAm, but what I did not expect was how incredible this hybrid would sound with the pairing of lower sensitivity IEMs such as the ER4PT. I plugged them into the 3.5 audio jack turned gain to low setting and took a shot, fingers crossed, and was surprised with awesome satisfaction when I heard no hiss and or noise with the ER4PT and never have I heard them sound so good or large for that matter. Versatility is definitely a strong point with the PanAm, because it has torn through all the Headphones and IEMs(which are only a few) that I have put in it's path. I am hopefully getting the Cfte tubes from a member of this community( a very good one at that) and will be trying them on for size and when I do I will probably put down an edit list at the bottom where I place what tubes I felt  made the best impression along with what headphones. Granted all of this is subjective because everyone's ear and taste is different to some extent. Sound quality and performance I give a 10/10 especially for the price right now.
 
As it stands there are other units for both DAC/Amp out there especially with the growing values out there in the audio world that compete with the PanAm, but I do not feel there is many that allow you to get this size, soundquality, versatility, and option to tube roll for the price that is on par with the PanAm, but granted this is my subjective opinion. Do I feel it warrants the money spent? Yes, I definitely do and it is incredible as far as audio performance in such a small package such as the PanAm. 
 
This was just the initial impressions and review after a couple weeks with this device, but after I try more headphones and some different tubes I will definite come back to edit what I feel needs to be.
Thanks for reading please leave comments and questions below. 

So the Pan Am from ALO Audio. This little guy is pretty dang impressive. An excellently-built, functioning desktop solution that is pretty easy on the eyes too! For the record, I've got the whole stack - Pan Am, Passport, and Gateway. Haven't done much comparison between the two power supplies yet.
 
As for the sound, the presentation is not glaringly tilted towards the bright or dark end of the spectrum. In a word: neutral. Now of course the tubes you pick can change that, but it's nice to know that with a conservative tube like the Yugo 6HM5 or RTC, you're starting pretty close to neutral.
 
I think that DAC implementation is equal to the ODAC. Very capable and revealing from the 256 MP3s I've tested all the way up to the 24 bit higher res stuff. No complaints here.
 
Now the amp. Power, power, and more power! Even with the ZMF V1s, high gain yields plenty of authoritative power with a dynamic punchy bass, lush mids, and nicely-detailed-but-never-sibilant treble. I also appreciate the versatility in that the Pan Am still plays well with lower impedance cans like my Grados and D2000s. I'm very impressed with it's synergy with the DT880 Pros as well. The tubes take the edge off their treble making them one of my favorites.
 
Tubes. Woohoo! I've got the Mullards, Siemens, RTCs, Voskhods, Yugo HM5s and Sylvania HM5s. So far the Mullards take the cake with the Yugos and Voskhods in at a close second. The Mullards rich lush bass and lower mids are unmatched out of this collection. Now the RTCs do treble better, but for me, I'll sacrifice a little extension for some thump.
 
Overall I'm very happy with this little setup. It's versatility, size, form factor, and tube-rolling options make it pretty dang satisfactory. Consider upgrade-itis cured... for now. 
 
Add: Unfortunately the Pan Am is being phased out by ALO. For anyone looking for a slightly tubey desktop solution that will power just about anything you throw at it, I'd seriously consider the Pan Am.
 

November 2013 Video Review​

 ​

 ​

Original review:​

A Tale of Two Tube Amps​

Woo Audio WA7 and ALO Audio PanAm​

 
My normal gear preference and choice for many years has been solid state. I have held a curiosity, however, in tube-based audio gear and the possibilities and presentation that comes from it. It might be considered ironic that considering how endlessly I have been fiddling with my main system for years now that I wouldn't consider an amp that would allow me to do this considerably more via tube rolling, but my indecisiveness has intervened more often than not, especially when presented with too many options. 
 
Likewise, many people, when seeking suitable audio equipment to buy, simply want an answer to seeking good sound, without the complexity and fuss that that us enthusiasts tend to dabble in. So given my interest in exploring tube amps and the recent interest in both the PanAm and the WA7, I arranged to have both sent to me. As an exercise in something a little different to the norm, I'm going to review them together.
 
I'd wager that if you asked the average Head-Fier whom they thought of when tube headphone amps are concerned, they'd say Woo Audio. Jack Woo and family's stable of amps, from the WA-2 through to WA-6 and variations have been the go-to for many seeking a well-built amp to fit their budget. The WA6 I'd say has pretty much become a standard for tube amps on Head-Fi. Lately, however, they have been expanding into new and interesting directions with a CD transport and DAC and the latest of their amps, the WA7 which, unusually, includes a USB input.
 
The story behind the WA7 is, basically, that Jack wanted to design something for the ordinary person, with a good aesthetic, compared to his usual offerings which come across more for enthusiasts. Seeking an appealing design, he asked the best person in the world for advice about the shape it should be: His wife.  "A cube" she replied and thus that is what the WA7 became. However, as the WA7 has transformers for the headphone outputs inside, taking up quite a bit of space, something was going to have to give and thus the power supply is external, connected via an umbilical. To complete the picture, the box itself has no visible screws, those having been banished to underneath the amp. Likewise, connections and controls other than the headphone sockets and volume are at the back. The result, for $999 is a unit with the simplicity and neatness of something I would more imagine seeing on the shelves of an up-market home-wares store than in my local hi-fi store.
 
 
ALO Audio's PanAm too was the result of a particular idea -- customer requests for a desktop amp under $1k, though in this case, considerably below it with the basic configuration starting at $499. While in the past Ken has been associated mostly with cables, more recently he has entered very solidly into the portable amp market with the RX, National, Continental and now International amps. The PanAm resembles a larger version of the Continental with regular tubes as opposed to the small "hearing aid" tubes in the portable. Like the WA7, it has a separate power supply, but this is where things get interesting. The basic amp comes with a regular wall wart but can optionally be paired with two different power supplies, each in a box the same size as the amp itself. The first is The Gateway, a wall-powered unit containing a better power supply than the wall wart, improving the sound. The second is The Passport, which contains a battery. Three lengths of neat, right-angle-plug umbilical cords come with either so you can arrange them neatly beside or atop each other.
This gives the PanAm an unusual calling: As well as being able to act as a desktop amp, it is also a light-weight battery-powered transportable amp. It too contains a USB input and, thus, DAC, cased in well-made, somewhat industrial-looking brushed aluminium. It is attractive more so being small and neat, the amp itself sitting neatly atop the Passport and/or Gateway. The amp comes with stick-on feet but my feeling is to also add a couple of small pieces of velcro on top and under the various units as required to help them stay together, such is their lightness. Large rubber bands will do this too, though that doesn't look as neat. Bought together with either the Gateway or Passport the PanAm becomes $569 and $639 respectively or $749 for the full kit (before extra tubes).
 
The WA7 in comparison is heavy, not only sporting two custom transformers between the tube output and the headphones but a block of glass -- yes, that really is glass around the tubes. Jack Woo took the aesthetic angle even further and went to a huge amount of trouble to get the blocks made. Opening the box, which was quite heavy with the power supply, one of the first items I spotted was a polishing cloth.  The manual cautions about placing the glass on carefully -- straight down around the tubes and not at any angles in any direction. With good rubber feet underneath, the amp doesn't move anywhere when headphones are inserted or removed.
 
The PanAm is deceptively small. For some reason, whenever I saw the pictures, I imagined it to be larger than it really is. The 1/4" headphone socket on the front and RCA sockets give it away though. So too are the Gateway and Passport. While the weight adds up with all three units together, any two together aren't particularly heavy and I could very realistically consider taking them with me when travelling. In fact, the whole kit would fit nicely into my Reddox Gator, along with my 11" MacBook Air with room for a good-sized pair of headphones and other gear. For this purpose ALO Audio will include a special carrying case.
 
 
Bringing our attention to the rear of both amps reveals a similar set of connections, with a couple of small, but significant differences. The PanAm has a mini-plug input, not a surprise considering it is intended to be (trans)portable and a mini-to-mini (or mini to dock connector) is the most convenient cable to use with an iDevice or DAP when out and about. However, while the PanAm's RCA connections are only for input, the WA7's can be used as either an input or a line output from the DAC.
 
Indeed, that is one of the neat features of the WA7: The USB DAC works even when the amp is switched off. It powers, unlike the amp, from USB directly and the output does not go through the tube amp at all. The positive of this is that, say, one could use it with powered speakers during the day, then switch on the amp at night for use with headphones. I can readily do this with my ADAM ARTist 3 speakers, as they have a linked volume control feature this is perfect for.
 
I could readily use the PanAm as a pre-amp, but that requires use of the front headphone sockets. Conveniently my ARTist 3s have a front input, so I tried it with a mini-to-mini cable with good results.  The WA7, likewise sounds good as a DAC.  Being USB-powered, the WA7's DAC can be improved upon to a degree with a better USB power supply system (such as an Aurorasound USB Bus Power Pro, Vaunix USB hub or the like). While I'm usually fairly picky about the quality of digital components, I feel satisfied enough with the quality of the DACs in both the WA7 and PanAm that I don't feel the need to dissect the sound of each nor felt a desire to use one of my high-end external DACs with either. More notable for the PanAm considering its transportable pretensions, the DACs in both amps fare far better than I've experienced in portable amps with the exception of the most expensive ones, such as the Fostex HP-P1 and CLAS. 
 
In practical terms, however, if you are like me and some of your music is higher-than-CD-quality from Linn Records, HDTracks and other places and you'll be using a computer as a digital source for either amp, some attention to the capabilities of the USB inputs will need to be paid. The PanAm's Tenor chip will accept 44.1 (CD quality), 48 and 96 kHz input, but not 88.2.  The WA7's CMedia USB higher and accepts 44.1, 48, 96 and 192 but not 176 kHz. [Note: Jack informed me 176k was supposed to be available and is investigating why it isn't.] If you have high-res music with a variety of bit rates, you'd do well to have software that can match the output bit rate suitable as well as re-sample on the fly if required.
 
Also worth noting is, while the PanAm shows up in my Mac's Sound preferences as "ALO Audio" the WA7 showed up as a bunch of inputs and outputs. The "Speaker" output is the correct one to select, the others having no function. However, I imagine many people choosing the PanAm will be using it like I did with the Passport and a portable source such as an iPhone where this isn't an issue.
 

The Amp Sections

I wanted to get into describing the sound of each amp but to do that requires some understanding of how each amp is set up to drive headphones.  
 
The WA7's blurb states that no semiconductors are used in the signal path, though this refers to the amplification section, not the DAC. As the output of tubes alone isn't entirely suited to driving a wide variety of headphones, custom made transformers are used instead. A switch on the back is included allowing selection of "High-Z" or "Low-Z" headphones -- high for 70 Ohms and above and low for any headphones, but especially IEMs. The WA7 is the first desktop amp I've encountered with a socket specifically for IEMs and is designed electronically to match. Jack emphasised this point and that the amp is completely silent. Indeed, plugging in a pair of RE-ZEROs which are fairly sensitive and turning the volume all the way up (without music playing)  there was not the slightest noise to be heard.
 
The PanAm on the other hand is a hybrid amp, the ultimate output via a solid state circuit. It too has two output sockets with a gain switch next to the volume control. Again, testing with the RE-ZEROs I was presented a dead silent background, even on high gain. The only sound I could hear was the result of noise passed through the tubes as a result of touching the amp.
 
While Woo Audio's usual offerings facilitate using a selection of tubes, allowing the enthusiast considerable entertainment in attuning the amp to one's headphones and tastes (and the possibility of spending considerable money on new-old-stock tubes) the WA7 is unique in that the stock tube is pretty much the only one available in its type. On offer is a single, $100 upgrade by way of a pair of Electro Harmonix Gold Pin tubes in limited quantity.  The PanAm on the other hand uses tubes for which there are many and varied varieties available, very often for cheap, both from ALO and elsewhere. Thus while the WA7 is focussed on plug-it-in, listen and enjoy, the PanAm facilitates the enthusiast's enjoyment of tweaking.
 
One might ask here: Why tubes at all? Especially so with the PanAm, which, with the tubes sticking out perpendicular to the lay of its container, ends up interfering with its own portable pretensions. The answer is: Why not? The reasons for using tubes in an amp range from the preferences of their harmonics to certain benefits they have over solid state components and, not to mention, the almost limitless tweaking. They also look cool and their aesthetic is only emphasised by the design of both amps.
 
However, while the WA7's limitation is that it is not a tube-roller's amp, the less expensive PanAm, with its option of battery power has something of a limitation when it comes to power and headphone drive. While with my LCD-3s I can turn the WA7 up to ear-bleeding levels without them distorting, try such a thing on high gain with the PanAm and the amp distorts. That loud I didn't try with the headphones on my head, of course, and I doubt anyone could listen at that level without their hearing being rapidly destroy. Regardless, it emphasises the difference between both amps.
 
In real listening terms, at the levels I listen at (70-90dB before peaks) it only becomes a potential issue with the PanAm if I break out big orchestral works listening with LCD-3s and turn the volume right up, at which point there is some audible compression (ie: the sounds start to blur altogether). For most listening I did the PanAm surprised me by capably delivering a lively and good rendition of all that I usually listen to, despite its physically insubstantial size and I very much enjoyed listening with it. Even with the PanAm on battery power, for most of the music I like, it still sounded great and didn't fail to deliver. The tubes only get moderately warm in the PanAm -- I could still touch them after it had been on an hour with the Gateway. Using the Passport as the power supply instead they were yet less warm, suggesting they are drawing less power.
 
That being said, the PanAm's stock tubes, while they sound good out of the box, have some shortcomings. Especially with my 300 Ohm MB Quarts the bass was wooly and the treble a little harsh. Thankfully it is possible to upgrade to better tubes for as little as $9/pair for the Russian Voshkods.  Given how much tighter the bass was and how much better the soundstage, mids and treble are with some of the tubes I'm going to consider a tube upgrade as part of the kit in the same way the Gateway is if you want the best results from it.
 
Of the upgrade tubes for the PanAm, my feeling was the Voshkod 6HZ1V-EPs are the most lively and spacious, the Siemens similar but with a bit flatter and less dynamic sound and the Mullards CV4010s the best balance between the sweetness of tubes and the detail and liveliness of the Voshkods. 
 
 
The WA7 gave me an initial impression of being somewhat mellow, the stock tubes emphasising the bass and de-emphasising the treble while delivering enjoyably syrupy vocals and instruments through the mid-range. The analogy that came to mind was of listening to music while relaxing in front of the fireplace (or maybe it should be relaxing in front of the pretty glowing tubes). It gives vocals the kind of warmth that wants to seduce you with the music more than point out every little detail and makes listening very relaxing. For example, the saxophone, harmonica and piano on Jean-Pierre Mas' (H)ombre seemed to be brought forward, yet at the same time given some warmth.  It did this while keeping a believable soundstage to the music. The presentation was so enjoyable that I had to stop writing to listen to Solamente Dos Veces in its entirety. If there is a downside to this, it's that the focus on the vocals and main instruments sacrifices the micro-detail, more of which I wish was audible. For that upgrading to the Electro Harmonix Gold Pin tubes will be necessary.
 
Though to some degree I adapted to the sound, I felt that the WA7 lost a little of its wooly-ness after having been run for a few days, the bass becoming less boomy than I felt it was at first. I left it on during the day to speed up any changes that might come about from use. Level matched with pink noise to the PanAm, the difference in drive felt like the difference from switching from a 2-litre hatchback to a big V8 sedan, the power being more effortless and my feeling moving more towards wanting to just listen to the music (and so it should, given that, depending on configuration it costs almost double the price). In fact, the degree to which both amps succeed in bringing enjoyment to the music was such that I didn't switch my main system on for some days but just used both amps to listen instead.
 
Appreciable about the WA7 was that whatever headphones or IEMs I used with it, the performance was consistent. Even with the Sony XBA-3s which, due to their wacky impedance, which goes as high as 90 Ohms in the treble which can trip up many amps, there were no issues, the music delivered cleanly and clearly.
 
Switching to the Electro Harmonix Gold Pin tubes and the WA7 becomes less "tube" like with the treble more open. This matched well for me with my LCD-3s but owners of brighter headphones might prefer the sound with the stock tubes. What wasn't lost was the lovely presentation through the mid-range and the sheer enjoyment of listening.
 
Likewise the PanAm. What struck me about the Continental the first time I tried it was how pleasant it was to listen to music through it, even with my iPod or iPhone as a source. The PanAm expands on that while optionally being transportable when purchased with the Passport power supply. It's main benefit is more power than a portable amp for driving full-sized headphones. With my tricky Sony XBA-3s it wasn't so happy, resulting in a bright and thin sound. However, relatively inexpensive IEMs are not what the PanAm is for. As I was writing this review, Anakchan suggested to me that what I needed was a pair of Ultrasone Signature Pros, as they are closed-back but good-quality headphones that are easy to drive. These would likely be spot on with the PanAm for a "bag rig" to take to a cafe or library.
 

In the end...

 
Both amps take up little desk space and don't require much to get started beyond a USB cable, (or a cable to connect your existing iDevice, CD player or the like) and some good music. If you're after a simple buying decision for a desktop amp and it's within your budget, get the WA7 at $999 (or $1099 with the EH Gold Pin tubes) and consider yourself done. If you want to be able to take the amp to and from work (or the library!) with a pair of full-sized headphones then get a PanAm kit ($499-749 depending on options selected, plus extra tubes). Both will work well with all full-sized headphones (possibly excepting the HE-6) and for a few hundred dollars extra (or close to double the price depending on the configuration) the WA7 gives you plenty of power for almost all headphones, 192k USB input and is great with IEMs too, if not transportability. 
 
Should I buy this amp? Here is a summary of the pros and cons of each:
 

 
 
Thanks to Ken Ball and Jack Woo for lending me these amps for review.

Headphones used:
Audeze LCD-3
Symphones Magnums
MB Quart QP 400 (bright, high impedance headphones)
Sony XBA-3
JVC HA-FXZ200