The Fifth Element

The recording project I've mentioned before in this column, that of documenting the historical and significant pipe organs of Rhode Island, is finally (!) in the can. (Except that today, of course, we no longer use cans. Or tape, for that matter.) It has been a learning and growing experience for us all—more than a dozen remote-location recording dates, spread over eight months.

But before sending any PMCD master files off to the pressing plant, it's necessary to give them a few very careful listens. Some tools for doing so are the subjects of the first part of this column: a high-performance headphone amplifier and two pairs of headphones. I then briefly profile some enviable microphones I got to use in the wrapping-up.

RudiStor RPX-33 mk2 headphone amplifier
RudiStor, a name new to me, is a boutique electronics manufacturer in Italy. In addition to the very impressive headphone amplifier their US representatives lent me, RudiStor makes integrated and power amplifiers, and other models of headphone amplifiers, including a portable. RudiStor's designs variously employ solid-state devices or tubes, in a range of implementations. The RPX-33 mk2 ($1900) appears to slot in the middle of RudiStor's line of headphone amps; above it are balanced versions and a high-end tube model, and below are more affordable, non-dual-mono versions, and the portable.

I didn't set out to borrow a headphone amp, much less a somewhat exotic one from a true-believer company I'd never heard of. I was discussing the upcoming mastering of the organ project with my music and engineering mentor, Jerry Bruck of Posthorn Recordings. Jerry mentioned to me that although he hadn't yet heard them, some of his engineering colleagues were very impressed with headphones from the German company Ultrasone. Indeed, at least one peer had said that they were the best he'd heard. My usual reaction to such a claim is at least to form the thought "How many others has he heard?" (if not speak it outright, for good manners' sake). However, when the declarant is from Jerry's circle, I assume it is an observation of more than average validity.

I called Ultrasone USA, which is based near Nashville, in Franklin, Tennessee. History buffs will remember the town as the site of the Battle of Franklin, by the end of which no fewer than six Confederate generals were laid out dead. Science-fiction buffs may recall the Battle of Franklin as central to the class-leading military/alternate-history/time-travel novella The Chronicle of the 656th, by George Byram. But I digress.

Ultrasone USA's Cathy Kelly fairly radiates enthusiasm for Ultrasone headphones. If her professions of their superiority are insincere, she deserves an Oscar. Her advocacy also encompasses RudiStor headphone amps, which, she tells me, Ultrasone USA began handling simply because they sound so good, and mate so well with Ultrasone's cost-no-object Edition 9s.

Okay then. Please ship me a RudiStor headphone amp, Ultrasone's cost-no-object headphone model, and something more affordable.

The box arrived promptly, but the RudiStor amp was DOA, owing to its front-panel power switch, a miniature toggle, having been completely bashed in. The toggle itself stands proud of the front panel, with nothing to shield it. In view of the fact that there's an identical toggle on the rear panel for ground lift, I was reluctant to risk more shipping damage by sending it back for repair.

With John Atkinson's and RudiStor's permission, I opened the unit and bypassed the power switch by soldering together the wires leading to and from it. I not only matched up the right wires, my self-inflicted burns were limited to one solder splatter. It seems that whenever I unsolder something, at least one wire is under tension—spring-loaded, so to speak. As soon as the solder melts, the wire acts as a tiny catapult, launching a tiny sphere of molten metal my way. That's why I leave the DIY stuff to my soul brother, Art Dudley.

I did suggest to Ultrasone USA tech Evan Doyle that RudiStor replace their vulnerable spindly toggles with the kind of milspec (MS25224-1) guarded arming switch Tom Cruise had to lift in Top Gun before firing a missile. Doyle probably thinks I was kidding. At least, get a righteous hardshell case for the press loaner (Hardigg is my fave) and rethink the packaging for the civilian units.

The RPX-33 mk2 is a dual-mono class-A headphone amplifier that also has a pair of RCA preamp outs. There are also "repeater" output jacks directly under the RCA line-level inputs, if you need to run the input somewhere else at the same time—such as to your main system. Clever.

The design is dual-mono from the IEC power-cord inlet on. There are two hefty (for such an application) toroidal power transformers. Most of the components are on a single large PCB. The internal layout is cleanly symmetrical.

The RPX-33's case construction is a bit unusual. Its faceplate is taller than its chassis, overlapping it top, bottom, and sides. The casework itself is 13" wide, 1.6" high, and 11.25" deep. The front panel is 13.75" wide, 2.4" high, and the usual 3/8" thick. Stick-on rubber feet add half an inch to the unit's height. Weight is a substantial 9 lbs.

The front panel is covered with a thin veneer of black plastic. This is not glued, but held on by four Allen bolts and the headphone jacks. My unit had black casework; I imagine that the available silver-casework option dispenses with the plastic veneer.

Left to right, the front panel holds the toggle switch for power (the one that arrived smashed in); a very small pilot light; a large, round, shiny, centrally located volume knob with a very small, uncolored position-indicating dimple (the volume control has very smooth action, and obviously is a high-quality part); and two ¼" headphone jacks marked H and L—for output level, not impedance.

I used the RPX-33 mk2 with Ultrasone's Edition 9 and PROline 2500 headphones, listening not only to raw and mastered takes from the organ project, but also to all the recordings I recommended in my February column. And others, to be sure.

Listening through the combination of RPX-33 mk2 and Edition 9 to Eric Whitacre's Cloudburst, and Secret and Divine Signs, tenor Michael Slattery's disc of the music of Craig Urquhart, brought me very deeply, hauntedly into the music, and put me at risk of concluding that I hadn't praised those recordings fervently enough. (I'm not going to worry about the Hyperion Arvo Pärt SACD I praised—it's just won a Grammy.) But, rereading what I wrote in February, the moment passed. To put it in as few words as possible: The RudiStor RPX-33 mk2 is a phenomenal headphone amp. Paired with the Ultrasone Edition 9, it's extraordinary.

The RPX-33 mk2 is a noticeable step up in dynamics, bass drive, and resolving power from both the Benchmark DAC 1 and Grace m902 D/A headphone amps, as well as the headphone amp on the Sound Devices 722 digital recorder. There was more of a sense of "thereness" to the ambient sound of live recordings—by which I mean the sound before the music starts. I attribute this to the RudiStor's very robust bass performance, dynamic reserves, and dual-mono design.

After all, that's the way it should be. The RudiStor is a single-purpose design that costs more than the Benchmark and Grace "Swiss Army knife" DAC-headphone amp-line-stage models. Although I suppose that if you had only one source, or didn't mind swapping out cables, you could use the RudiStor as your system's preamp (I didn't try this). It's also a bit sobering to note that the RudiStor costs not all that much less than Sound Devices' 722, which records at up to 24-bit/192kHz and has an internal 40GB hard drive. And has all kind of cool lights.

The RPX-33's internal layout is impressive. But, on the whole, its design and build quality are utilitarian rather than elegant—only a couple of steps above average DIY. This is not "audio jewelry." However, people aren't going to part with $1900 based on the way it looks, but the way it sounds. Which in my book is excellent.

I don't do all that much headphone listening. Nonetheless, I was sad to see it go. Conclusion: RudiStor's RPX-33 mk2 is a luxury item, but if headphones are your principal means of listening, I recommend it highly.