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.