RAAL-requisite SR1a Earfield Headphone Monitor &
HSA-1b Headphone & Speaker Amplifier Review
Part 1 of 2: Introduction, Setup, and Initial Impressions
Part 2: Optimizations, Competitive Comparisons, and Conclusions (link)
My interest in the RAAL-requisite SR1a was first piqued at CanJam RMAF 2018, where I noticed a booth with perennially long lines, demoing what looked from afar like an electrotherapy device. We headphone nuts know that looks are deceiving, and what look like medieval instruments of torture can in fact be world-class headphones! I never did get a chance to have a listen to the SR1a, so it went on the mental list of “things to check out in the future.”
I didn’t run into the SR1a at any of the shows I went to in 2019, so it wasn’t until early last year, when Chris @The Computer Audiophile published his review, that my attention was revived. After Chris’ review, I was determined to get my hands on them and hear them for myself. But since I didn’t have high-end speaker amps lying about — I am, after all, a headphone guy — I decided I would do a combined review of the SR1a with the then-forthcoming RAAL-requisite HSA-1b amplifier. Arrangements were made, but with pandemic disruptions, delays were inevitable. Finally, earlier this spring, a handsome Pelican case containing the SR1a and HSA-1b showed up at my doorstep.
About the SR1a Headphones
There are several attributes that make the SR1a “earfield monitors” ($3500 MSRP) interesting, even unique, in the headphone space. Unlike the more common dynamic, planar magnetic, or electrostatic drivers, these drivers are true ribbons that are claimed to reproduce 30Hz to 30kHz. The ribbons are engineered to fit in a cartridge that easily slides into (and out of) baffles that are mounted like wings on a headband. The baffles are designed to pivot, so their angle and position relative to the ears can be changed, allowing one to tune the sound. The modular ribbons are easy to replace, making for excellent serviceability.
Another interesting attribute of the ribbon drivers is their extraordinarily low impedance of 0.2Ω (ohms), which means they cannot be driven directly by conventional headphone amps. RAAL-requisite offers two paths to achieve this. The first is to use a so-called direct-drive amp, like the Schiit Jotunheim-R (MSRP $799 amp only, $999 with internal Multibit DAC), or RAAL-requisite’s own HSA-1b ($4500 MSRP, reviewed here). These amps are designed to deliver high current with extremely low output impedance via the headphone output directly to the SR1a.
The second path is to use RAAL-requisite’s amp/ribbon interface, driven by a conventional speaker power amp rated at 100Wpc or above. This interface box presents an impedance of 5.6Ω to the power amp, while supplying high current/low impedance output to the SR1a. Using this interface box opens up a universe of possibilities, and I know of audiophiles who have experimented with truly TOTL boutique power amps. I’m sure these sound wonderful, but this is a rabbit hole I was not equipped to explore!
About the HSA-1b Headphone & Speaker Amplifier
The RAAL-requisite HSA-1b ($4500 MSRP) is a real Swiss Army knife of an amp because of all the things it can do! Direct-drive the SR1a? Check. Drive conventional dynamic and planar magnetic headphones? Check. Drive speakers? Check. It even has a gorgeous red (though not Swiss Army red!) precision stepped volume attenuator. Both single-ended and balanced inputs are provided.
I found the fascia design and red accents very attractive. At 8.58” wide, this amp is narrower than it is deep, but it has a substantial heft to it, and looks and feels like it means business. It weighs in at 11.6 lbs, almost the same as my reference Cavalli Liquid Gold amp (at 12.1 lbs).
Much is demanded of headphone amps at this price point, and ultimately, the proof of its quality will be in the listening.
You can read the full specifications at this link.
My Listening Setup
The RAAL-requisite combo arrived at a very serendipitous time as, after many years of intense tweaking, I had reached a fairly stable system topology that was sounding as good as it has ever done. When this happens, the itchy audiophile often turns to transducers for the next leap forward, so this was a dangerous time for my wallet to bring a highly acclaimed, and potentially game-changing, set of headphones into my system! Of course, from the review perspective, it meant the RAAL-requisite combo would be driven by a high-quality chain that would fully showcase what they were all about.
My system hardware is shown in the picture above. It consists of a chain of audiophile switches, feeding my music server, the Taiko SGM Extreme, equipped with the Taiko USB card upgrade. Audio data is output over USB to an Audiowise SRC-DX bridge, which presents it to the Chord DAVE DAC via its dual BNC S/PDIF inputs. My reference headphones are the Meze Empyrean, the Abyss AB-1266 Phi CC, and a modded Sennheiser HD-800 (SD mod). The switches are powered by independent DC rails supplied by a Paul Hynes SR7MR3DRXLFC10 power supply. AC power is delivered via a 6AWG dedicated circuit to a Sound Application TT-7 Reference power conditioner, to which the amps, the Extreme, and the Paul Hynes PSU are directly connected.
The bulk of my listening is through the Empyrean, driven directly from the single-ended 6.3mm jack on the DAVE. Those who know the DAVE know that the sheer transparency of this direct path is incredible, and hard to beat using conventional amps. Not pictured, but included in my system, is a Cavalli Liquid Gold headphone amp. These days, its primary role is to drive the Abyss headphones, as these relatively insensitive ‘phones really benefit from more power than the DAVE can directly provide.
The software stack plays a vital role in maximizing the sound quality delivered by the hardware. The foundation is the highly optimized Windows 10 LTSC OS in the Taiko SGM Extreme. Second is the music player. Taiko addressed growing concerns about Roon’s lagging sound quality (SQ) by developing their own player, Taiko Audio Server (TAS), and its SQ is head and shoulders above Roon’s. Finally, I used PGGB, a remastering tool, to upsample my music files offline, so the DAVE only ever sees 24-bit, 16FS (705.6/768kHz) music streams.
To enable you to listen to the same tracks that I did, I have created a public playlist on Qobuz USA. This playlist includes the tracks mentioned in this review, as well as some of the others I listened to in the course of this evaluation. Please note that in some cases, the Qobuz track will not match the mastering I listened to, especially since all my listening was with PGGB-upsampled files. Still, this gives you a sense for the music I listened to for evaluation.
Since PGGB remastering only applies to local files, and since the resulting SQ of a native file PGGBed offline is head and shoulders greater than the SQ of the same native file streamed from Qobuz and real-time upsampled with something like HQPlayer, all my critical listening for this review was done with remastered PGGB files stored locally on the Extreme.
SR1a Listening Impressions (with HSA-1b Amp)
Before any serious listening, I followed my usual practice of letting both the headphones and the amp burn in for a couple of weeks of continuous music. How much burn-in is actually necessary I couldn’t say; certainly, by the time I started listening, there were no further changes in the sonic characteristics that I could discern.
My initial reaction to the SR1a was somewhat mixed. I quickly realized these sound very different from the other headphones in my stable, and I couldn’t just do quick A/B’s between them and the SR1a. I found I had to wean myself off of my existing headphones’ sound signatures, and allow myself time to acclimate to the SR1a. This isn’t particularly unusual, as I’ve done this with other headphones, but in the case of the SR1a, it proved absolutely vital. It took a few days of exclusively listening on the SR1a, and strictly abstaining from the others, before I felt my brain was truly dialed-in to these headphones!
The SR1a are fast. As in blazingly fast. The transient response and accuracy is just off the charts compared to anything else I’ve heard. Leading edges of percussive notes, like plucked strings, piano, cymbals and drums are perfectly rendered, and the resolution and detail impart a sense of realism that just takes your breath away. Consistent with this speed, music seems to flow effortlessly, and the level of rhythmic articulation, especially in the upper bass is simply superb.
Another attribute that grabs you immediately is the soundstage. It is vast and holographic. Instruments are placed with pinpoint precision in three-dimensional space. This becomes even more impressive in dense passages in large orchestral pieces like Mahler’s 8th symphony. Rather than sounding congested and muddy, the SR1a takes these passages in its stride and maintains a coherent soundstage.
Tonality is where things get a little interesting. Let’s start with the excellent. The upper-mids and highs are just exemplary, with no harshness or edge to speak of. The mids provide what I would characterize as a front-row presentation. Relaxed, these headphones are not! I’m sure some of this perception just comes from the extreme speed and resolution of the transducers, but the SR1a is not forgiving of subpar recordings or upstream electronics. That said, the only time I heard grunge was when I played it! Which was almost never. Luckily my tastes run to more refined genres.
Which brings us to bass. I’ve already waxed lyrical about the articulation of the upper bass. However, there is no getting around the fact that the SR1a is light in the lower and sub-bass. I’ll explore to what extent this can be mitigated with cables, EQ, etc, but as shipped, the SR1a are definitely bass-light. Obviously, the degree to which this matters depends on your sensitivity to this frequency region and personal preference. It’s tempting to say this affects some genres more than others, but I disagree. Accurate bass response is vital to all music genres, whether it is a capella, solo piano, or a massive orchestra.
Coming soon in Part 2 (link) of this review, the rubber finally meets the road. I’ll describe various adjustments and tweaks I made to see how much more the SQ of the SR-1a and HSA-1b could be improved. Following that, we get to the part I love most: comparisons with the competition! Finally, I’ll wrap up with my conclusions and overall assessment of the SR1a and HSA-1b.
SR1a, Case: $3200
SR1a, Interface, Case: $3500
SR1a, HAS-1b, Case: $8000
SR1a, HSA-1b, Interface, Case: $8500
Music Computer: Taiko Audio SGM Extreme Music Server, Taiko USB upgrade
Headphone Amplifier: Cavalli Liquid Gold
Headphones: Meze Empyrean, Abyss AB-1266 CC
DAC: Chord DAVE
USB to dual-SPDIF: Audiowise SRC-DX bridge
Ethernet Switches: SOtM sNH-10G, Uptone EtherREGEN,
Buffalo BS-GS2016 (modded for LPS)
Power supplies: Paul Hynes SR7 MR 3DSXL (dual regulation, 3-rail) for switches
Sean Jacobs DC-3 for DAVE
Power Details: Dedicated 30A 6 AWG AC circuit,
Sound Application TT-7 Reference Power Conditioner
Power Cables: Sablon King (wall to TT-7), Sablon Prince (Extreme),
Cardas Clear Beyond (DC-3, SR-7),
Cardas Clear for all other components
USB cables: Sablon Reserva 2020 USB
BNC cables: High Fidelity Cables CT-2
Ethernet cables: Sablon 2020, SOtM dCBL-Cat7, Supra Cat 8
DC cables: Neotech OCC (DC-3), Paul Hynes fine silver (SR-7)
Interconnects: Cardas Clear XLR balanced
Headphone cables: Transparent Ultra cable system
Accessories: Synergistic Research Tranquility Base XL UEF with Galileo MPC
Synergistic Research MiG 2.0 footers
Taiko Audio Daiza Isolation Platforms
Many thanks to the following companies for supplying cables and accessories to aid in this evaluation:
Cardas Audio, for a full loom of Cardas Clear cables.
Transparent Audio, for the Transparent Ultra headphone cable with a full complement of headphones leads and source terminators.
About the Author
Rajiv Arora — a.k.a. @austinpop — is both a computer geek and a lifelong audiophile. He doesn’t work much, but when he does, it’s as a consultant in the computer industry. Having retired from a corporate career as a researcher, technologist and executive, he now combines his passion for music and audio gear with his computer skills and his love of writing to author reviews and articles about high-end audio.
He has "a special set of skills" that help him bring technical perspective to the audio hobby. No, they do not involve kicking criminal ass in exotic foreign locales! Starting with his Ph.D. research on computer networks, and extending over his professional career, his area of expertise is the performance and scalability of distributed computing systems. Tuning and optimization are in his blood. He is guided by the scientific method and robust experimental design. That said, he trusts his ears, and how a system or component sounds is always the final determinant in his findings. He does not need every audio effect to be measurable, as long as it is consistently audible.
Finally, he believes in integrity, honesty, civility and community, and this is what he strives to bring to every interaction, both as an author and as a forum contributor.