I first encountered Ray Samuel’s SR-71B in prototype form at a Can-Jam event back in 2010, and was fascinated by the little amp from the start (even though it was just a naked circuit board at the time). The concept for the product struck me, then and now, as being amazingly ambitious, in that it called for a very high performance portable amp that would offer sophisticated, fully balanced circuitry from input to output, plus sufficient output to drive just about any headphone on the market (save for electrostatic ‘phones, of course). In order to give the preceding sentence its proper weight and context, it helps to carefully consider two facts. First, most headphone amps with fully balanced circuitry are relatively large and expensive (think four-figure price tags). Second, despite what their manufacturers may claim, most desktop amps fail to do a truly credible job of driving “just about any headphone on the market,” either because they are too noisy to drive high-sensitivity ‘phones well or insufficiently powerful to drive truly difficult loads. Is it possible, then, for a portable amp to succeed where many full-size desktop amps have failed?
The answer, in the case of the SR-71B ($650), is “Yes”, though with a few caveats, which we’ll discuss in this review. $650 is a lot of money to pay for a portable amp, but arguably a small price to pay for a headphone amp—regardless of configuration—that promises do as many things well as this one does. And speaking of small, let’s note that the SR-71B is truly tiny, as in about the size of a deck of playing cards. So, the key questions we need to answer in this review involve sound-quality (how good is it, really?) and the amp’s ability to deliver on the promise of being able to drive nearly any headphone on the market.
To answer both questions, we evaluated the SR-71B by using it with a variety of source components, some with balanced-outputs, and with a wide range of earphones and headphones. At the risk of getting ahead of ourselves, let us cut to the chase and tell you right up front that we think the SR-71B builds a very strong case for being one of the two finest portable headphone amplifiers currently available. To learn why that’s our assessment, read on.
- Fully-balanced, “quad mono” circuitry. The SR-71B was the first portable amplifier in the world to offer fully balanced circuitry.
Circuit implemented via extremely high quality balanced output op amps, supported by premium quality resistors, capacitors, etc. The amp features an ALPS volume control.
Switch selectable single-ended and balanced stereo inputs.
The single-ended inputs are implemented via a 3.5mm input jack, while the balanced inputs are implemented via a miniature, square-shaped, four-pin connector.
A number of specialty cable makers offer stereo XLR-to-miniature 4-pin adapter cables that make it easy to connect high-end home or pro-sound source components to the SR-71B.
A special phase-splitter circuit within the SR-71B ensures that, even when single-ended source components are, the fully balanced headphone outputs will still be properly driven.
- Switch selectable single-ended and balanced stereo inputs.
Switch selectable left and right-channel master gain switches, with settings form low, medium, and high gain.
- This feature lets users adjust the overall sensitivity of the amp to match the sensitivity of their earphones and headphones.
- For example, you might use the “Low” or “Medium” gain settings with high-sensitivity custom-fit in-ear monitors, but the “High” gain setting with very hard-to-drive full-size headphones.
- Single-ended and balanced stereo outputs (implemented, respectively, via a 3.5mm mini-jack and the aforementioned miniature 4-pin balanced connectors). Whenever the amplifier is powered up, both the single-ended and balanced outputs are live. By design the amp provides circuitry that converts single-ended input signals into balanced signals, ensuring that the full benefits of the amplifier circuit are always brought into play.
- Built-in quad Lithium-ion battery packs. The battery packs provide 18V peak-to-peak swings in single-ended mode and 32V peak-to-peak swings in double-ended mode. According to Ray Samuels, the SR-71B’s maximum voltage swing capabilities are roughly twice those of any other fully balanced portable amplifier.
- Wall wart-type battery charger with charging status lights (“red” means “charging”, while “green” means “fully charged.”
- Available in satin black and matte silver finishes.
Backgrounder: In our listening tests, we evaluated the SR-71B with a wide variety of source components including:
- Apple iPod Classic loaded exclusively with lossless CD-resolution files, with signals fed via high-quality line out dock (LOD) cable supplied by Ray Samuels Audio.
- Apple iPod Classic loaded exclusively with lossless CD-resolution files, with digital signal fed from the iPod to a Cypher Labs AlgoRhythm Solo portable DAC, with digital signals fed to the AlgoRhythm Solo and analog signals fed, respectively, through high-quality digital and analog cables from ALO Audio.
- Oppo BDP-95 universal/Blu-ray players, using the player’s balanced outputs with signals fed via high-quality balanced analog cables from Moon Audio.
Earphones and Custom-Fit In-Ear Monitors:
- ACS Custom T2 Classic
- Audeo by Phonak PFE 122 and PFE 232
- JH Audio JH16 PRO
- Monster Turbine Pro Copper Edition
- Westone TrueFit 4 and Elite Series ES5
- Ultimate Ears In-Ear Reference Monitors, UE18 PRO, and Personal Reference Monitors.
- Audeze LCD 2 with rev2 drivers and LCD 3
- Audio-Technica “Grandioso”
- HiFiMAN HE-400 and HE-6
- Shure SRH840
- Sennheiser HD800
The Sound: Frankly, the SR-71B really doesn’t fit most peoples’ preconceived notions of how a portable amp will sound, because it in fact delivers a sound that would do most full-sized desktop headphone amps proud. In practice, this means several things—all of them good.
First, the SR-71B sounds punchy and authoritative with rock-solid bass extension, a lively and articulate midrange, and lovely, delicate, silvery highs. Some writers have commented about the amp having a touch of treble roll-off way up high (remarks that might, in an absolute sense, contain a small grain of truth), though I personally think the SR-71B’s perceived treble extension and linearity are more a function of the headphones and headphone signal cables chosen than of the amp itself. Over the last year, I’ve mentioned in various Playback earphone reviews that certain earphones need “a really good portable amplifier to sound their best,” and frankly, I made most of those comments specifically with the SR-71B mind. This amp, along with ALO Audio’s fully balanced Rx-MK3B portable amp, is the portable power plant of choice for tapping the full sonic potential of today’s best earphones and custom-fit in-ear monitors, etc.
Second, note that the SR-71B is extremely low in noise, a factor that becomes critically important when listening to high-sensitivity earphones and custom-fit in-ear monitors where even trace amounts of noise would be obnoxious and annoying. If you look around, you’ll discover that many amp makers have resorted to building separate models for different applications—building low-noise (but relatively low powered) amps for use with high-sensitivity ‘phones and then making high-powered (but relatively noisy) amps for use with low-sensitivity ‘phones. With the SR-71B, however, you have more of a true, one-amp-fits-all solution, which is a major part of the SR-71B’s appeal. As you might expect, the 71B’s three-level master gain switches prove very useful in terms of helping you find the just-right combination of adequate gain and low noise, not matter what type of ‘phones you use.
Third, the SR-71B is quite powerful and offers enough power and gain to drive most headphones to satisfying volume levels, which is saying a mouthful (although I can think of one ultra hard-to-drive headphone that might be an exception, as we’ll discuss in a moment). The practical reality, though, is that the SR-71B is essentially as powerful as many desktop amps at its price, and is—believe it or not—actually more capable and versatile than most. What’s hard for most listeners to process is the fact that this little, tiny, pocket-sized amp readily and eagerly delivers the sort of dynamic muscle and moxie typically associated with much bigger amps.
Is there such a thing as a Ray Samuels “house sound?” I think there is and that if you tried to summarize it in a few words those words would be: punchy, powerful, energetic, and detailed. There’s an overall vividness of presentation here that’s very hard for most portable amps to match. Interestingly, that sound can be heard not only in the SR-71B, but also in Ray Samuel’s less expensive and less elaborately full-featured models such as The Protector ($475), The Hornet ($370), etc. This is a roundabout way of saying that, if you don’t need all the I/O flexibility and power the SR-71B has on offer, you may well be able to find an equaling pleasing RSA portable that sounds similar, yet costs much less.
What can’t the SR-71B do? Well, I would say that it successfully drove every headphone I through at it to more than satisfying volume levels, save for one; namely, the brutally difficult-to-drive, ultra low-sensitivity (83.5 dB) HiFiMAN HE-6. While the SR-71B successfully drove the HE-6 to levels I found satisfying almost all of the time, I ran across a few recordings with low signal levels and/or extremely wider dynamic where the SR-71B had difficulty getting the HE-6 to play loudly enough.
I asked Ray Samuels about this and his response was illuminating. He pointed out that, since the SR-71B has very high voltage swing capabilities (see comments on the quad battery pack, above), the amp’s power output capabilities are to some extent governed by available signal levels from various source components. “With an iPod, which is a single-ended source component and that has roughly 0.5V output, you may need to turn the SR-71’s gain almost all the way up in order to get sufficient output level for the HE-6,” said Samuels. “But, with balanced-output source components, where output voltage is much higher, the SR-71B can easily drive the HE-6 to louder levels than anyone would need.”
Samuels went on to point out that selecting master gain level settings for a multi-purpose amp such as the SR-71B is always a balancing act. On one hand, there needs to be a setting with low enough gain to ensure low noise when driving ultra-sensitive in-ear monitors, but on the other hand there also needs to be a setting with high enough gain to ensure adequate power output when driving ultra-low-sensitivity full-size headphones. Happily, I found the SR-71B is sufficiently quiet that you can—in a pinch—get away with a practice you would probably never dare to try with most headphone amps; namely, setting the amp’s gain switch in the “High” position and then listening with the volume control turned all the way up. (Caution: You can try this with the HE-6 if you feel the need, but I would not advise trying it with easier-to-drive headphones unless you plan on listening at dangerous, “ear bleed” volume levels.).
Do balanced inputs and outputs make a difference? Let’s look at this question in two parts. On the input end of things, I found there could be small but audible benefits to using the SR-71B’s balanced inputs, most notably in terms of transparency, openness, and inner detail. With that said, however, let me concede that I don’t really know for sure if those differences are attributable to the SR-71B’s fully balanced input circuitry or to the fact that—with some source components such as the Oppo BDP-95—the source’s balanced outputs just plain sound better than its single-ended outputs do. Yet another possibility is that the cables you would typically use to feed the SR-71B’s balanced inputs have to be custom made, and thus are likely to use much better materials and workmanship than the mass-market cables you might normally use for the single-ended inputs. Either way, the good news is that the SR-71B supports both and lets you choose which you want to use at the flick of a mini-toggle switch.
On the output end of things, I found that using balanced outputs made little difference with some headphones, but a much more significant difference with others, where the benefits tended to be a purer, more open, and somewhat more dynamically expressive sound. Examples of ‘phones I tried where I felt the benefits of balanced outputs were audible and beneficial included the Audeze LCD3, the HiFiMAN HE-6, and the Sennheiser HD800. To be clear, all of these ‘phones sound good when driven via single-ended outputs, but sound a small yet worthwhile bit better with balanced drive engaged. My thought is that, if you’re interested in top-tier headphones like these, then taking small but noticeable sonic steps forward will likely seem like a worthwhile endeavor to you. Again, since the SR-71B’s single-ended and balanced outputs are both live whenever the amp is powered up, the choice is yours.
How does the SR-71B stack up vs. full-size desktop amps? In an absolute sense, I found the SR-71B could hold its own with or even surpass the sound quality of most desktop amps near its price, which is most impressive. But, if you are willing to spend a little more than the price of an SR-71B on a desktop amp, your extra expenditure can buy you noticeable improvements in low level detail, resolution, and top-end “air”—factors that together make for a more multidimensional sonic presentation. An example would be Burson Audio’s new $960 Soloist amp, which—even though it does not offer the SR-71B’s balanced inputs and outputs—can outperform the little RSA portable amp in terms of pure sound quality. Even so, dollar-for-dollar, we know of no amp more flexible than the SR-71B (although ALO Audio’s $649 Rx-MK3B portable amp matches the SR-71B feature for feature and is entirely competitive in terms of sound quality).
Given its terrific sound, brilliant versatility, and incredibly compact size, the SR-71B can easily stake its claim as one of the top two portable amps on the planet (the other is the ALO Rx-MK3B which we’ll cover in a separate Playback review).
One of the primary reasons to look at the SR-71B is to enjoy subtleties that other amps miss, and to hear what this can potentially mean listen carefully to Jennifer Warnes’ performance of the Leonard Cohen song “If It Be Your Will” from Famous Blue Raincoat [Impex]. Part of the beauty of Warnes’ voice centers on its soaring purity and uncanny ability to add emphasis through the most delicate of swells or unexpected decrescendos, coupled with crystal clear enunciation. In short, Warnes shows how less can be more through deliberate and, I think, carefully calculated touches of understatement—paradoxically achieving a more captivating and powerful presentation through not trying to sound powerful. Listen to the profound sounds of reverent submission, sadness, and longing as Warnes sings (or prays aloud) these lines, “If it be your will/that I speak no more/and my voice be still/as it was before/I will speak no more/I shall abide until/I am spoken for/ if it be your will…” Emotion, here, is conveyed not through vocal pyrotechnics, but through vanishingly brief moments of vibrato, small changes in inflection, and very carefully controlled swells in volume—especially on the brave “I shall abide until…” line, which I take to be a quiet but profound statement of faith. On tracks like this one, the SR-71B proves its worth by digging out the wealth of musical details at hand, yet without pressing them with more forcefulness than is appropriate. Few portable amps can match this level of subtlety and detail.
Can the SR-71B rock? It most definitely can. Every since I was a young man (many moons ago), one of my favorite forms of rock music has been traditional, down’n’dirty electric blues, a perfect example of which would be “Satori in Chicago” from Noah Wotherspoon & the Stratocats’ Buzz Me [APO]. This extremely well recorded blues track can flat out burn when played through the SR-71B and a top-shelf pair of headphones (I happened to use the Sennheiser HD800’s for my most recent listening session, but many other ‘phones would also work well with the RSA amp). What I found was that the electric guitar had a just right ability to cut, cry, and carve its way through the mix with a delicious combination of bravado, sheer dynamic force, and finesse—with notes showing just the right amounts of what some guitarists might call “spank” (where the notes seem almost to erupt out of the guitar amp). Many portable amps can play loudly, per se, but few can equal the SR-71B’s ability to capture the variegated tonal colors of the guitar or its at times explosive dynamic character. Of course the anchor (or perhaps keel, if you will) for many great electric blues tracks is the electric bass, and this is precisely the case with “Satori in Chicago”. The bass has rock-solid weight and punch, yet is—when the situation warrants—supple, agile, and lithe-sounding, too. It’s hard to reconcile the diminutive size of the SR-71B with the big, forceful sound it can produce, which is why I think the little amp takes so many listeners by surprise. It may be tiny, but it has the heart of a lion.
To understand both the SR-71B’s strengths and limitations, let me suggest that you listen to excerpt of John Tavener’s Icons of Eros, performed by the Minnesota Orchestra and Chorale as conducted by Paul Goodwin, from the Reference Recordings 30th Anniversary Sampler [Reference Recordings, HDCD]. This unusual composition at once sound modern and yet almost medieval, with some passages that are driven forward by a percussion ensemble captured in the highly reverberant interior of the Cathedral of Saint Paul in Minnesota. What I’ve always found fascinating about this particular track is that its beauty and complexity derive not only from the sound of the instruments at play, but also from the way their sound lingers on the air, reverberating in the Cathedral long after they have stopped playing (by design, the composition features a number of short, interleaved musical passages with carefully spaced pauses in between).
The SR-71B sounds very, very sophisticated on this track—better by far than most competing portable amps. In particular, neatly delineates the complex instrumental voices and reveals the reverberant qualities of the recording space. However, if you do a side-by-side comparison between the Ray Samuels amp and a really first-rate mid-priced desktop amp (e.g., the Burson Soloist), it becomes apparent that some can potentially provide better resolution of low-level details, even more nuanced handling of transient sounds, and thus greater realism overall. On Icons of Eros, one hears these differences as an increase in overall three-dimensionality and especially as a heightened sense of the “air” surrounding the instruments and filling the interior of the cathedral. While the SR-71B can and does hold its own in comparison with like-priced desktop units (arguably surpassing many of them), those willing to invest a bit more will discover an even higher level of performance can be had. This comment, however, in no way diminishes what Ray Samuels has achieved with the SR-71B; for its size and price, this tiny Titan is flat-out amazing.
Consider this portable headphone amp:
- You want one of the two most versatile and best sounding portable amplifiers being made today—amps that truly re-define what portables can be and do.
- You own a number of different high-performance headphones and earphones, some easy to drive and others not, and need one amplifier that can do justice to them all.
- You love precision craftsmanship; the SR-71B is beautifully made and very finely finished.
Look further if:
- A $650 portable amp is too rich for your blood; but note, Rays Samuels Audio offers a complete range of less full-featured models that are very similarly voiced, one of which might work perfectly for you.
- Down deep, you want those little sonic extras that only one of today’s better desktop amps can provide. Note, though, that to get discernably better sound than the SR-71B provides, you will likely need to spend hundreds more.
Ratings (relative to comparably priced portable headphone amps):
- Design and Features: 9.5
- Tonal Balance: 10
- Timbral Purity: 9.5
- Detail & Resolution: 9.5
- Imaging/Soundstaging: 9.5
- Dynamics: 9.5 - 10
- Value: 9.5 - 10
Given the veritable explosion of high-performance, high-end earphones and headphones we’ve seen over the past few years (some of which are quite challenging to drive), the Ray Samuels Audio SR-71B fully balanced portable headphone amp is plainly an idea whose time has come. What we have here is a beautifully made little portable amp that, in terms of I/O features and sound quality, seems more like a sophisticated desktop amp than a typical portable. If you want one of the two best portables ever made, consider this a must-hear option.
Ray Samuels Audio SR-71B Blackbird Fully Balanced Portable Headphone Amp
Type: Compact, battery powered headphone amplifier with fully balanced circuitry from input to output.
Accessories: As noted under “FEATURES”, above.
Inputs: Two switch selectable stereo analog inputs (one single-ended input via 3.5mm min-jack, one fully balanced input via miniature, square 4-pin connector).
Outputs: Two headphone outputs (one single-ended output via 3.5mm mini-jack, one fully balanced output via miniature, square 4-pin connector).
Other controls: dual (left/right) three-position master gain switches with setting for “Low”, “Medium”, and “High” gain; on/off switch; rotary volume control.
Power output: not specified.
Dimensions (H x W x D): .79” x 2.6” x 4.09” (includes depth of control knobs, switches, etc.).
Weight: Not specified.
Warranty: Li-ion batter pack, 3 years; amplifier, lifetime warranty.
Ray Samuels Audio