REVIEW: Ray Samuels Audio SR-71B balanced portable headphone amp
Is it really possible that there is yet another level of performance to be squeezed out of a portable headphone amp? Apparently so. I would not have believed it, but two amps recently have changed my mind. One was the Meier Audio Stepdance, which changed my mind about what was possible from a headphone amp, and at a relatively affordable price.
And now there is the SR-71B, a relatively small but massively powerful balanced portable amp. The mere existence of this product was unthinkable a couple short years ago. I’m glad there are people like Ray Samuels and Jan Meier around to push the performance envelope!
Ray offered to send me a loaner of the SR-71B for evaluation, and of course I took him up on his offer.
The SR-71B sure is nice looking:
I began the evaluation by running the balanced outs (using Moon Audio Blue Dragon cable) of my Yulong D100 DAC into the SR-71B, driving the Hifiman HE-6 via my balanced cable from A Pure Sound (using a short adapter provided by Ray).
Listening to Open by Cowboy Junkies, the sound was absolutely ridiculous. I wasn't quite prepared for how good it was. While at $600 this amp is far from cheap, it does an astonishing job driving the HE-6. I was genuinely impressed as to how powerful, detailed, and yet smooth the sound was. There is a tiny bit of congestion during very intense crescendos versus my Decware Mini-Torri, but overall it was really, really good sounding, and it was hard to imagine that there could bethis much power available from such a small, batter operated amp.
The bass was really impressive. Ray’s amps have always had excellent bass, I thought, but the SR-71B has some incredibly deep, powerful bass, and it managed that even with the HE-6. The bass from Dave Matthews Band’s “Two Step” was reproduced in all its explosive and subterranean glory. Same with the bass notes on Cowboy Junkies’ “Beneath the Gate”. The bass was very well defined as well as being very deep and powerful . That the SR-71B can accomplish this with the HE-6 is nothing short of astonishing.
The mids are incredibly open and transparent. They have a little of that RSA warmth, but I’s say they are the most neutral mids of any RSA amp yet, and that’s saying something. The HE-6 are supremely transparent in the mids, and will reveal almost anything, and the SR-71B acquitted itself amazingly well here. Margo Timmins’ layered vocals on “Small Swift Birds” were very cleanly reproduced. Same with Alison Krauss’s wonderful but delicate signing on “Maybe”. And on the acoustic version of Porcupine Tree’s “Time Flies”, which features only Steven Wilson’s vocals and acoustic guitar and John Wesley’s vocals and electric guitar – essentially ALL midrange – things stayed clean and well sorted out and delineated, which in that track is no easy trick if the mids are not up to snuff. The transparency of the SR-71B allowed these songs to really deliver emotionally. I could also hear distortion on CD’s with brickwall compression, too, unfortunately. Such is life.
Soundstaging was excellent, but here was an area where I felt it was not quite on par with the Concerto. Even with the Concerto’s crossfeed off, the Meier amp had more soundstage width and depth. But this was only slightly noticeable. In the highly atmospheric “2-1” from Imogen Heap’s new “Ellipse” LP, I did feel that the SR-71B was slightly shrinking the soundstage, but this was only noticeable on direct comparison. This track also showed the SR-71B’s excellent deep bass capabilities, as well as its treble extension, ability to sort out details, have explosive dynamic swings and reproduce female vocals and strings well. This song is a one-track hi-fi demo, and puts maximum stress on an amp – and the SR-71B sailed through the test very, very well.
If there was an Achilles heel to the SR-71B at all, it was that I felt there was a very slight lack of top end extension and air compared to the very best portable headphone amps, or home amps. This was offset by just a tiny bit of extra energy in the treble presence region. I consider this to be the hallmark of the RSA “house sound”, to the extent that there is one. The treble was very clean, transparent, and grainless, but it is just short of dead neutral, and I would have preferred personally to have the presence region lessened and the top end extension just a bit more noticeable. But this was just a very, very subtle shading that came to light only in very careful, level-matched comparisons.
Configurations and Comparisons
I compared the SR-71B to some of my home amps that can drive the HE-6, and it seems to me that the SR71B can indeed drive the HE-6 adequately. I spent a short amount of time listening FAR louder than I normally would, and far louder than anyone actually should. There was still no audible clipping or distortion, and the sound was clean and unstressed. I still hear just a little congestion during very loud and busy passages, but I have heard that from home amps trying to drive the HE-6 as well. The HE-6 had no problem driving the HE-6 to crazy loud levels, with only the very slightest hint it’s breaking a sweat. That’s pretty impressive.
The SR-71B uses a phase splitter to take the single ended input and run it through the amp balanced. Either of its inputs uses the entire amp, and can feed the balanced output. But a balanced source is very likely to be stronger than a SE one. The only practical implication of this will be what is the maximum amount the amp will be able to amplify the lower voltage input.
And indeed, this was my expereicne. Using my iPad as a source, via the dock connector with an ALO LOD cable, feeding the SE input of the HE-6, and using somewhat soft source material but with wide dynamic range ("Aja" from Steely Dan), I could get to full rotation on the SR-71B and I would classify the volume as only "loud", not crazy loud. The sound was still excellent, louder than I would normally listen (by a good margin), and there is still zero clipping or distortion. And on songs that have a higher average level, the HE-6 can still be driven to clean but stupid-loud levels.But I have no idea what the output voltage of the iPad's line out via dock connector actually is. My guess it's below the standard 2V.
Using my trust Rat Shack SPL meter, I measured the output of the HE-6 using the SR-71B in high gain, and with the volume maxed, with the iPad serving as the source, into the SE input of the SR-71B. Using a song I consider to be somewhat quietly recorded ("Solid Ground" by The Radiators from Total Evaporation), I was able to get 94 dBA peaks. On a recording at a hotter level ("Good Times Bad Times" from Led Zeppelin 1), I was able to get 100 dBA peaks. At that level (which I will only listen to for a few seconds, lest I risk hearing damage), I could detect no audible distortion. I really cannot say if the sound was "good" or not, as sound that loud bothers my ears. But I can say it was "clean".
Given that the HE-6 is one of the least sensitive/efficient headphones on the market, however, I would say that this "torture test" satisfies me that the SR-71B will be able to drive the HE-6 balanced even from in's SE input in the vast majority of cases, for all but the volume- craziest of you – and you people should reform, before you’re deaf!
I think the SR-71B drives the HE-6 slightly better than the Meier Concerto does, but the HE-6 is a stretch for the Concerto (and note here I am talking about the home Concerto, not the portable Stepdance!). My big tube amps (all but one of which can drive speakers) do sound a bit better with the HE-6 than the SR-71B...but they are all at least 2x the price, and 50 times the weight...
The next torture test was to drive the Beyer T1 single-ended. My T1 are not balanced, so there was no way to try them in this mode. The SR-71B still has to be used in high-gain mode to power the T1 to stupid-loud levels, but my normal listening levels were attainable at 2:00 on the volume control in medium gain. Not too shabby.
However, I slightly preferred the sound of the Meier Stepdance driving the T1 than the SR-71B. The preference was only slight, but I felt that the T1 sounded just a little thin on the SR-71B. I’m not sure if this is due to their being used single ended, or if it’s just the sound signature of the amp, but it was for repeatable – when I would switch from the Stepdance to the SR-71B (having carefully matched levels with my SPL meter), the Stepdance was just a little more transparent, and a little more open sounding in the treble. The Stepdance is an absolutely outstanding amp, though, and drains battery pretty fast in its effort to deliver maximum sound quality. And the SR-71B still sounded outstanding powering the T1’s – and really driving 600 ohm cans well is something very few portable amps can really do.
Same story with the LCD-2 and Edition 8, which again I do not have balanced cables for. Used just single-ended across the board, the SR-71B is very good indeed, but I marginally preferred the Meier Stepdance with these single ended headphones, although I really wished I had had a balanced cable for the LCD-2 to use with the SR-71B.
The SR-71B is really kind of a hard product for me to review in some respects. It delivers truly incredible performance, in an almost astounding manner, in an application that I don’t personally have any real use for. I tested it balanced source – balanced amp – balanced headphone, and in that application it was really amazing. I tested it SE source – balanced amp – balanced headphone, and again, amazingly good performance. In these two modes, it’s a special amplifier. I couldn’t believe what it was able to deliver with the very-hard-to-drive HifiMan HE-6.
But used single-ended across the board, the amp is merely excellent. Unless you plan to use it balanced, either now or in the future, I’d save money and buy the Meier Stepdance, or RSA’s own P-51 Mustang if you don’t need huge amounts of power.
As such, for me personally, as good as I feel the SR-71B can be when used balanced, I will not be buying the review loaner. I don't think it's better than the Meier Stepdance when it's used purely single ended, and I personally have no need for a balanced portable amp. My main portable headphones are the supremely easy to drive Beyer t50p, which sound great with the Stepdance and the RSA P-51 Mustang. My only balanced headphones are the HE-6, and while the SR-71B is very impressive with the HE-6, but it's not as good as my big home tube amps like the Leben or Decware, and as such I personally don't really have any reason to buy it.
But for anyone needed, or just wanting, a very powerful portable amp, or if you are looking for a powerful balanced amp for both home and portable use, and either don’t want or cannot afford to have multiple different amps, the SR-71B is really an astounding product, and it’s hard to believe what it’s capable of doing. It certainly is in the very top echelon on portable amp performance, and in fact, in its shining application, actually redefines what portable amp performance means. Ray’s delivered the unthinkable. I wonder what he will think of next!