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.
The PanAm stack next to a Leckerton UHA-6MKII.
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 PanAm with Mullard tubes.
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:
- Small, attractive form factor that doesn't take up much desk space.
- All-in-one DAC and amp.
- Dedicated IEM port.
- Drives most all headphones, no worrying about matching your headphones or IEMs to the amp.
- Good USB DAC that works with the amp switched off.
- Dead silent background.
- 192k high-res USB input.
- Small and attractive design.
- Light and transportable.
- Flexible with a choice of power supplies.
- Good USB DAC.
- Drives full-size headphones reasonably well, even orthos.
- Tube rolling options are cheap.
- Power usage is low.
- 96k USB input.
- Not transportable. Firmly for your desktop.
- No tube rolling unless you want to pay extortionate prices from eBay sellers.
- Glass cover invites OCD-like polishing.
- Not so great with IEMs.
- Stock tubes are a bit lack-luster (though an upgrade is only $9).
- Ultimate power is limited.
Thanks to Ken Ball and Jack Woo for lending me these amps for review.
MB Quart QP 400 (bright, high impedance headphones)
September 2013 update: Here's a video review: