The SR-71B takes the concept of portable balanced amplification that was first introduced in the Protector and upped it even more. Reading the product information on RSA’s website will leave you drooling. Quad mono amplifier sections to handle each of the four section balanced signals separately and an addition of quad output buffers for increased current capability. Single ended signals go through two phase splitter chips to create a fully balanced signal out of them. RSA claims the best in terms of PCB quality, opamps, capacitors, and resistors. Compared to the earlier, legendary portable SR-71a, the SR-71B have higher power output, fully balanced drive, rechargeable batteries (one of the big shortcomings of the SR-71A), AND a thinner and shorter case.
And to top everything off is a quote from Ray’s website:
There is no headphone ever made that SR-71B can’t drive with great authority & control. It will stand toe to toe with best balanced home amps out there.
I am going to skip through the formalities and go straight to the comparisons.
RSA SR-71B vs RSA Protector
If you currently own the RSA Protector, then moving to the SR-71B will give obvious improvements in sound quality while retaining pretty much a similar signature. I don’t know if the improvements are due to the quad mono topology, or if Ray had implemented some other design changes in the amplifier. With the HD650 headphone in balanced, I am hearing a wider soundstage, much improved instrument separation, and a more open sound. On the HD800, the difference becomes even more pronounced. While the RSA Protector’s soundstage feels like a small blob, the SR-71B’s extend very wide, filling the whole space of the HD800’s huge earcups. Instruments very clearly projected from the black background. This, of course, is aside from the improvements in power output ratings, which again you get with the SR-71B. If you own a Protector, definitely go for an upgrade!
RSA SR-71B vs RSA SR-71A
A more interesting comparison is with the SR-71A amplifier, which is the best single ended portable amp you can find on Ray’s line up. Both carries the SR-71 “Blackbird” code, indicating serious level of performance. While generations apart, both amps are still well within the RSA house sound that is warm, dark, and bottom heavy. However, the 71B and the 71A has a lot of differences when it comes to A-Bing between the two of them.
With the SR-71B’s balanced drive, you get a better pace and ultimately a better PRaT, especially for driving a laid-back headphone like the HD650. Where the SR-71A is very graceful and smooth, it does not add anything in terms of PRaT. The SR-71B also has a more forward presentation compared to the relatively laid-back SR-71A. In short, the SR-71B makes music more lively, where the SR-71A is more mellow and more refined.
Aside from advantages of having rechargeable batteries on the SR-71B, and a line in port in the back (which I prefer over having both in and out jacks in the front), the SR-71A is actually more preferable for my music. Here is why: I listen to a lot of live recordings, and so soundstage portrayal is more important to me than pace or PRaT. Besides, most of my music are relatively moderate in pace. On the SR-71B, you get a wider soundstage due to the balanced drive. Although this gives an impression of a bigger soundstage on short listens, longer listens reveals that the soundstage is less coherent as the presentation is panned hard to the left and right sides.
On the SR-71A, the soundstage is slightly narrower, but is actually bigger overall due to the much better depth. The width is still very wide, and quite wide to fill in the huge HD800 soundstage. With the SR-71A, I also get better coherence in the soundstage imaging, better center focus, and better ambiance than on the SR-71B. Now that last part is very important for live recordings, though studio recorded music are less critical of those factors.
My experience with balanced amplifiers tell me that the more the parts count on an amplifier, the more variances on transistors, resistors, chips, and the harder it is to get a coherent imaging (which you get by perfect symmetry between the left and right channel). In this sense the simpler amplifier would do better, as there are less variances in the parts. There arguments are equally strong for both sides, but I just want to brought this up to show how the SR-71A and the SR-71B demonstrates this fact very well, but still within the same RSA house sound signature. Very interesting indeed, and I am most fortunate to have both amps in my possession to be able to switch back and forth between the two.
BALANCED vs UNBALANCED SOURCE
The SR-71B comes with two inputs: Balanced and Unbalanced. Selecting the input can be done through the toggle switch in the back. Make sure that you toggle the switch to the correct position, otherwise you may run a risk of damaging the amp. This happened to me once, luckily I was quick to turn of the amp at the moment and nothing was damaged (Sorry, Ray). I don’t quite know the schematic, but I suspect this may have something to do with balanced signals being routed to the phase splitter chip which is designed to take single ended signals and create a balanced signal out of it.
Anyway, for those of you who’ve read my Ibasso PB-2 review, you know that I had overlooked the fact of testing the amp with a balanced source, and so I’ll make up for it on this article.
The source that I use is a top-loading CEC TL51XZ CD Player that offers both unbalanced and balanced analog outputs. I used my reference copper interconnect cables to create identical cables to compare both the unbalanced and balanced inputs of the SR-71B: An RCA to 3.5mm, and an XLR to 4-pin Protector connector. For maximum transparency, the headphone used is the HD800 with Whiplash TWAg recable.
Depending on the source being used, the difference between unbalanced and balanced outputs are quite minimal. In some cases like on the Cambridge DacMagic, the unbalanced output is theoretically less transparent due to one extra stage that the unbalanced signal have to go through compared to the balanced signal. On my CEC TL51XZ, the only difference is some slight figures in THD and Noise. On the SR-71B’s side, the unbalanced input theoretically should be less pure since it goes through a phase splitter chip which many claims won’t be as good as a true balanced signal right out of the D/A chip. While I do believe that the simpler and shorter signal path will yield ultimate transparency, depending on the system being used to make the evaluation, often that difference is too little to be noticeable.
Now, going back to my little test rig with the CEC TL51XZ to the SR-71B to the Whiplash TWAg recabled HD800. A-Bing between balanced and unbalanced input signals to the SR-71B, the only difference that I can hear is a slightly wider soundstage with a balanced input, and a slightly thicker bottom frequency. The difference is there, but they’re so slight that a difference in source quality is bound to make a bigger impact than a lesser source boasting fully balanced outputs. It’s quite interesting that my observations on the Balanced Beta22 also reveals similar differences (though at a higher level of resolution): more bottom end body and a wider soundstage when being fed from a balanced source.
I forgot to mention that with a balanced source, you get twice of the amplitude of the original signal, hence the loudness (dB) gets doubled. In case you’re feeling that the amp is not pushing your headphones loud enough, then going to a balanced source would help to get things louder.
BALANCED vs UNBALANCED OUTPUT
Going between the unbalanced and balanced drive with the same headphone, mostly the improvements are similar to moving from an unbalanced source to a balanced source. Wider soundstage that fills in the whole cups of the HD800, where an unbalanced drive only gives me a noticeably smaller soundstage that cannot fill up the entire space of the HD800. You also get slightly fuller body on the low end, but more importantly is bass impact and slam factor has been improved. The amplifier feels much more energetic than if driving on single ended at the same volume level. I think this is the effect of the increased slew rate from four different amplifiers working simultaneously.
Single ended drive does have its own merits though. If you think that your headphone’s soundstage is wide enough, and that your music doesn’t require the added bass impact, then I want to mention that I did get a more coherent soundstage with better center focus than from the balanced drive.
Finally, like when using a balanced source, loudness level also gets doubled. This is not an effect of the quad amplifiers, but rather because of the phase splitter chip on the input side that effectively doubles the amplitude of the signal.
RSA SR-71B vs Ibasso PB-2
This time, I think Ibasso has done pretty well to steal the thunder from RSA. The PB-2 was also recently released, and it boasts an uncanny resemblance on features and specs. Quad opamps? Check. Quad buffers? Check. Rechargeable batteries? Check. Build quality? Check. Balanced signal generator from single ended inputs? Check. And to top everything off, Ibasso also boasts a higher voltage swing, a rollable opamp and buffer, and a pricetag that will make everyone thinks twice before ordering the SR-71B ($650 for the SR-71B vs $325 for the PB-2).
In audio, experienced readers would know that the price to performance curve is not linear. Actually, this also applies to computers (dollar versus clock speed, dollar versus memory capacity, etc), and automobiles (dollar versus 0-60 times, etc). Hence, experienced readers would know that it’s quite a long shot to expect the SR-71B at twice the price to offer twice the performance of the PB-2. Or looking from the other point of view, the PB-2 is probably going to be better than if you take the SR-71B and degrade its performance by 50%.
I think we all have to acknowledge Ibasso for the amount of improvements they’ve made to their portable amps. In the old days, nobody would have thought of comparing an Ibasso to an RSA amp, the latter universally acknowledged as the premium brand while the former is a cheap portable alternative from China. Ibasso surely have improved their build quality over time. Comparing the two amps side by side, it would really be unfair if I had said that one amp has a better build quality than the other. Somehow, I am still leaning a bit toward the SR-71B’s build and design, but I really don’t think it’s significant enough and it may just be my personal preference. I do want to give the SR-71B a plus point in terms of enclosure dimension. The slimmer and wider enclosure of the SR-71B makes for a better pairing together with the average Ipod, while the PB-2’s taller and longer dimension is not very friendly on the jeans pockets. The pulverization finish looks very slick, and although RSA’s anodized finish is a tad better in my eyes, I think they are just a matter of personal preferences. I have seen a number of cases where the silkscreen printing started to chip off on RSA amps, and though I have yet to see one Ibasso amp with the printing chipping off, though I’m not saying it won’t happen.
Other things that may matter to the user is the placement of gain switch and the ability of rolling opamps. If I am the type of person who loves tweaking, then the op-amp rolling capability of the PB-2 would be a strong point. Otherwise, the SR-71B works better as it’s more “plug-and-play”, and the placement of the gain switch at the rear panel is a big plus compared to the PB-2 where you need to open the enclosure everytime you want to change gain levels.
Now, what about the sound? The primary difference between the two amps is the sound signature, where the SR-71B maintains a warmer, darker, and heavier bottom end sound, the PB-2 less heavy on the bottom though not light and more low treble presence. Of course, while rolling opamps, you can “EQ” the PB-2 to be more trebly or more bassy, depending on what you’re using on the opamps and buffers. But even at the “darkest” and fullest bottom end setting with the stock opamp kits, the SR-71B still has a more solid bottom end body that I couldn’t find on the PB-2. On the other hand, if you are more into trebles, then the PB-2 will probably be a better suit for you.
I’ve been listening to both amps with the HD650 and the HD800, and I can say that I equally like them both. The added bottom end of the RSA can be nice in giving a more weighty and authoritative sound, but the Ibasso’s slightly lighter tone is better for picking up the pace of the music. Sometimes I like the added bottom end weight that the SR-71B gives me, even with the HD650. And at other times, I like the more neutral sound with the added treble of the PB-2. Of course you can equally nitpick the “faults” of both amps, if you want to. Some people would prefer a more relaxed treble than what the PB-2 offers, while others would prefer a less dark presentation than what you get with the SR-71B.
Technicalities wise, both amps are very similar. The PB-2 of course has a higher voltage swing, which would be useful if you ever attempt to drive the HE-6 with portable amps. But for standard 300 Ohm dynamic headphones like the Sennheisers, both the RSA and the Ibasso are equally good. Pairing them with my JH16 in balanced, the same thing pretty much applies, just in a much lower volume level.
Ray Samuels has always made great portable amps, and I am glad to see that the list of innovations continues to grow. When the RSA Protector was released, I remembered how revolutionary it was, being the first portable amp that offers balanced drive. With the SR-71B, that concept has been further improved, not only in power output but also in sonic qualities. This amp is a definite upgrade for Protector users. Compared to the SR-71A, I think both amps are great in their own regards. I personally am leaning more towards the SR-71A, but that’s just due to my music preference (and perhaps, age too!). However, when compared to the Ibasso PB-2, I think the pricing will be a very strong leverage for the Ibasso. Personally, I think the RSA SR-71B has the nicer built quality (if only slightly), and the overall packaging and features makes it the amp that I want more if pricing was not an issue.
Thanks for Mr. Ray Samuels and to my friend Peter Ong for the loaner units used in this review.
System used for review:
Headphones: JHAudio JH16Pro, Sennheiser HD650, HD800, Hifiman HE-6
Amplifiers: RSA SR-71B, SR-71A, Protector, Ibasso PB-2
Source: Hifiman HM-601, HM-602, Ipod Classic, CEC TL51XZ