In Playback 41 I reviewed the terrific Burson Audio HA-160 headphone amplifier (click here to read the review), finding it to be “a superb sounding and incredibly well made headphone amplifier that is more than reasonably priced at $695.” But one point I mentioned only in passing in the review is that I often listened to the HA-160 headphone amp with another important piece of Burson gear inserted in the signal path; namely, the firm’s AB-160 RCA audio buffer stage ($549). Frankly, Burson’s audio buffer and headphone amp fit together like hand and glove, together creating an overall sound that is greater than the sum of the parts. This, of course, raises two important questions: what exactly is an “audio buffer stage” and why would listeners want to use one? Let me try to provide a brief explanation.
Burson Audio contends that one of the main reasons why audio systems sometimes fail to live up to our expectations is that there are impedance mismatches between the output stages of our chosen source components and the input stages of our preferred amplifiers. The result of these mismatches, says Burson, is both “signal loss and distortion,” most often perceived as a loss of low-level sonic detail and an apparent blunting or dulling of transient sounds—as if some of the expected life and vividness of the music has been drained away. In simple terms, Burson’s audio buffer can be thought of as a figurative “black box” whose purpose is to “remove any impedance mismatch by acting as an isolation platform between any of the source components … and downstream amplification.”
Let’s speak candidly. The whole idea of adding a buffer stage to improve system performance seems to run contrary to the established beliefs of audio purists whose working assumption is that simpler and less cluttered signal paths always sound better than complex ones. In short, many purists would argue that it is simply a fool’s quest to try to realize sonic gains by adding more circuitry to the system—in this case the circuitry found in the AB-160 audio buffer. Even so, Burson’s fundamental claim is an interesting one, since their point is that source components can only give of their best when presented with optimal and easy loads to drive (otherwise, all sonic bets are off).
The AB-160 provides what Burson terms a “high sensitivity input buffer (HSIB)” which is a very high impedance (and thus high-sensitivity) FET-based input stage that is extremely easy to drive and that, Burson claims, “effectively allows our buffer stage to match up to any input or output signal drains.” The AB-160 also provides a modest 3 – 6 dB of gain, thus making good on Burson’s promise that its audio buffer “will increase signal transmission efficiency between all components, unlocking the potential of any system.” As you’ll learn in this review, these statements on Burson’s part are not mere hollow marketing claims; they’re actually a pretty accurate synopsis of what the AB-160 is and does.
For a really in-depth discussion of the technologies used in the Burson AB-160 (and the design philosophies behind them), you’ll want to visit the Burson web site: www.bursonaudio.com. Here, though, I’ll provide just a few highlight that listeners will want to know about.
• Dual mono circuit design with extremely short (“less than 6 cm” or 2.36”) signal paths.
• Features high sensitivity input buffer (HSIB), which is a very high impedance, high-sensitivity, FET-based input stage that is extremely easy to drive. The circuit is fully balanced and operates in pure class A mode.
• In keeping with Burson tradition, no integrated circuits (ICs) are used anywhere in the AB-160, since Burson passionately believes that ICs sound inferior to discrete high-quality semiconductor devices.
• Low noise, regulated power supply featuring, again, discrete (not IC-based) regulator devices.
• Resonance free aluminum (RFA) enclosure is precision milled from 6mm slabs of aluminum. By design, the case panels each have different resonant frequencies and together form a rigid enclosure that doubles as the heat-sink for the AB-160. The entire component offers exquisite, camera-like fit and finish (though the AB-160 is far more physically robust than any modern-era camera we have seen).
• High quality parts and construction methods are used throughout, including a “high quality PCB” and “Elna Audio graded caps, carefully matched high quality audio transistors, DALE military graded resistors ...” All components are hand-soldered.
• Wide bandwidth design: Burson quotes a frequency response specification of 0 – 220kHz (-3dB).
• Low noise design: Burson quotes a signal-to-noise ratio of -120 dB.
• Dual, switch selectable inputs (RCA version).