Audio Alchemy HPA v1.0 headphone amplifier

For headphone listeners, this is truly a golden age—we have multiple choices at many different price levels. During the course of this review, I had as many as five headphone amplifiers (and, in several cases, multiple power supplies) set up for comparison. Yet many people don't understand why we might want a headphone amp in the first place.

Here's a reason: I live with an intelligent, dynamic, astoundingly tolerant woman, who doesn't seem to mind (much) that I've turned every room of our house into a mad scientist's maze of wires, boxes, and speakers. Yet, having gone that far, she unreasonably refuses to be forced to share my job with me 24 hours a day. Sometimes she insists on sleeping. So I need to use headphones at certain times of the day (and night, of course)—even though I have access to some of the finest preamps on earth. None of which, I might add, sport a headphone jack. That's the most basic reason one might desire a headphone amp: simply to have a place to plug in your headphones.

But portable cassette and CD players, mass-market receivers, and VCRs, laserdisc players, and A/V receivers all typically boast headphone connections, so people who own those components don't need a headphone amplifier, right? True, you can plug a pair of 'phones straight in to those components, but their headphone sections are vestigial at best. The amplifying circuits aren't particularly powerful—or clean, for that matter. They lack clarity and cohesion, and they wash out a lot of tonal color—listen for any length of time and you'll be reaching for the analgesic bottle. Besides, a lot of us connect our laserdisc players to D/A converters for better sound, and you lose the benefits of that when you employ the player's 'phone jack.

But the main reason you should consider using a headphone amplifier is the complexity of the task of driving headphones in the first place. Think about what conventional headphones are: moving-coil transducers with impedances that vary from 32 ohms to 600 ohms, with sensitivities that vary by as much as 27dB. That's a lot to ask a 27-cent op-amp chip to cope with.

Audio Alchemy's solution to this problem is, like all of their products, compact and well-thought-out. At $259, the HPA v1.0 is the least expensive amp in this survey—and at 5.5" by 4" by 1.5", it's for darn skippy the smallest. It can fit in an audiophile's shirt pocket—if we take the pocket-protector out first. It comes with an outboard power supply, the Power Station One, but it can be used with AA's Power Station Three, which almost triples the PS1's 250mA output—and at $259, also doubles the price. If you wish to use the HPA on the road, it runs off AA's Robyn I DC battery power supply, but—since the HPA runs in class-A—not for long (about two hours).

Connections are minimal; the rear panel has a mini-jack power supply connection and two pair of RCA jacks: source input and pass-through output (not affected by the volume control). This last is a thoughtful addition for those who must plug the HPA into their only tape-loop; it means they still have the use of the loop for a tape deck. The front panel has a ¼" stereo phone jack in the middle, a fluted volume control knob to its left, and a button engaging HeadRoom's Audio Image Processor to its right. That's it.

Need I mention that, in a unit the size of a cigarette pack, the HPA v1.0's circuit paths are extremely short? The small chassis is packed with amazingly high-quality parts, given its list price. Voltage gain is via Analog Devices OP-275 op-amps running in pure class-A, while complementary pairs of Toshiba output transistors (also running in class-A) handle the current gain for the discrete output stage. (These Toshibas are also used in AA's OM-150 and OM-50A power amplifiers as pre-driver transistors.) The volume control is a precision-matched, conductive-plastic Dale potentiometer that has a seriously sensuous, silky feel—and is billed as having superlative tracking over its entire range.

I asked Audio Alchemy's Richard Liddell how they could afford to pack all of that into a product that was going to hit the street for $200. "We tend to use as many of the same parts as possible—that way we know what they can do and we can buy them in enormous quantities, which makes them affordable." Not that I'm complaining, mind you.

You've noticed, of course, that the HPA has HeadRoom's Audio Image Processor; Audio Alchemy is one of only three companies licensing this technology. (The other two, Sonic Frontiers and Counterpoint have not yet sent us products to review.) We've written at some length about HeadRoom's own units (Vol.17, Nos.1 & 2), paying specific attention to the effects of the AIP. For a detailed discussion of that process, refer to my review of the Home HeadRoom (Vol.18 No.1). Essentially, what the AIP does is spread the sound, giving a more realistic sense of lateral cohesion, avoiding that annoying left ear/center-of-head/right ear headphone signature. It adds a sense of depth as well. I find this circuit addicting and miss it when it's not there or not engaged. I think that all high-end manufacturers should consider it essential in a headphone amplifier, so I'm particularly pleased to see that several of them are beginning to use it—especially at this price point, where most companies would be looking for stuff to leave out.

Tota in minimis existit natura
The first thing I noticed when listening to the HPA v1.0, was the control that the amp manifested over the headphones. Its 6.5V output immediately asserted itself. The sound was big, dynamic, and warm—with lots of low-level information. Listening to the Paniagua Group's disc, I clearly heard great amounts of spatial detail (even more with HeadRoom's AIP engaged). I did find the HPA's warmth and that of the Grado RS1s combined to be far too much of a good thing, however. Ironically, this excess of richness served to leach liquidity from the sonic picture—things sounded just too darn warm'n'fuzzy to be believable. That big bass drum's attack was aggressive, but I could not hear the rattles clearly. Switching over to the HD580 Jubilees, I realized that the HPA/RS1 combo was obscuring detail, especially in the round fullness of the oud's string tone. The leaner midrange of the Jubilees (not necessarily their most endearing trait) and their superior bass tautness restored musical and low-level ambient information.

"Third Uncle" had drive and slam galore with both headsets, but sounded much more muscular with the Sennheisers.

Then I switched power supplies, having finally gotten my Power Station Three up and running. (Originally, I had been sent a PS3 with a ¼A fuse, which proved to be incredibly persnickety driving my Audio Alchemy Digital Line Control preamp. I discovered, after blowing four fuses trying to drive the HPA, that this is the wrong value—it should have been ½A all along.) Switching to the Power Station Three, things just got better. The difference in bass was profound: tighter, more controlled, with better pitch definition. The highs also sounded sweeter, with less graininess and much better clarity in the differentiation of adjacent tones (and of similar consonant attacks like p, b and t). Now we were talking!

HeadRoom's own $399 HeadRoom Supreme headphone amplifier seemed the logical comparison to the HPA v1.0/PS3. The portable HeadRoom can run off either a small wall-wart, or an external four-D-cell power pack. I prefer its sound with the battery pack, so I used that for my comparisons.

They were both very good, but the Audio Alchemy sounded just a shade coarser, with a bit of grit in the upper octaves. On the Eno track, this added an edge that was not out of keeping with the music—an effect that I enjoyed, even as I questioned its faithfulness to the signal. The Audio Alchemy controlled the headphones with greater authority, however, and propelled Brian Turrington's bass-line along like crazy.

The Paniagua track, of course, did not benefit in the same way from the Alchemy's edginess. There the leading edge of the plucked oud just sounded coarsened and somewhat fuzzy. The frame drum had greater body and slam, but its reverberation in the room sounded diminished. The HeadRoom was, to my ears, slightly but significantly better.

However, you need to consider a few things before deciding which you want. If you travel, the HeadRoom can play off of its battery pack for over 20 hours—which will get you pretty far around the world before you have to recharge. The Audio Alchemy, run by the Robyn power supply, will only play for a couple of hours. On the other hand, if you're going to add headphone capacity to an existing preamplifier, the HPA's pass-through is a real boon. I fed the signal from the AA's outputs into the SHA-Gold, compared them to the signal coming into the SHA-Gold straight out of the CD1, and heard virtually no difference. (I'm hedging here, because I don't want you to lose all respect for me—the fact is I was hard-pressed to detect any change.) This is another feature that I think every headphone amp should have and it may well be enough to convince many of you to test-drive an HPA v1.0.

I also approve of the upgradability of the power supply. It's true that it can double the price of the unit, but you get to choose what level of performance you desire (or can afford).

All in all, Audio Alchemy's HPA v1.0 is well-thought-out and implemented. I found a lot to like in its sound and found several of its features indispensable. It's an impressive product at an affordable price.

Audio Alchemy
no longer trading (2006)