Backgrounder: In our listening tests, we evaluated the SR-71B with a wide variety of source components including:
Earphones and Custom-Fit In-Ear Monitors:
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.