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The Burson Buffer Amplifier
as reviewed by Max Dudious
Do I Have Your Complete Attention?
We've all heard of some guys who started making amps or speakers in their garages, training their wives or girlfriends as technicians to solder up circuits, who climbed the necessary steps up the ladder, and eventually wound up a giant in the field. Polk Audio comes to mind. I think the guys at Burson Audio, in Melbourne Australia, have been bitten by that bug and have already put a few products "out there" when they aren't surfing the big waves.
I'll now tell you about one of their products because I believe it's worthy, if a bit specialized. It is an aftermarket, discrete parts, on-board power supplied, buffer amplifier. Burson claims it can take an old or entry-level (say, $200) CD player, and get it to approach the sound of a much more expensive (say, $3000) CD player by inserting its Buffer Amplifier (base price $250 plus shipping) in series with the CD player. Similarly, they say, if you have an older piece of solid-state gear whose line-out section is driven by an 8-pin dual op-amp, like my old ADCOM pre-amp (PA 555), or my old ADCOM (GFT-555) tuner, you might revitalize it with their Buffer. They expect the performance would jump up to approximate some of the better pieces in the entry level tier of the "High End."
Do I have your attention now?
Op-Amps: Discrete and Indiscrete
Most audio hobbyists know there are 8-pin chip operational amplifiers all over everything electronic. They have different functions in audio, video, computers, microwave data transmission, and the chip designers come up with specialized types to suit the needs of client manufacturers: wide-band and not so wide band, fast and faster, etc. Sometimes a chip designed for video or computer purposes turns out to be a great audio chip (wide-band, flat frequency response, high slewing rate, good current handling capability) by luck, or accident. How they are made is something of a mystery to me. For a brief overall view see Wikipedia's Integrated Circuits article, under "Fabrication." In over-simplified terms they have small, I mean very miniaturized parts, with traces 65-90 microns thick (which might light up incandescently with a few more volts), and parts (capacitors, resistors, transistors, chokes) that are dope and heat-bonded onto spots on a silicon substrate that follow a schematic so they can work as a circuit a half-inch square.
The operational amplifiers are the ones we're interested in. They are very small, with short copper traces, which usually means fast, and when they are in a well designed circuit they can do amazing things. (The Intel 1361 series is a good example of this.) Op-amp chips began by mimicking and miniaturizing the analog computer circuits that were much larger when made with discrete parts, the difference being the equivalent of one half inch square for a chip, versus a small box of wooden matches (two actually for a dual op-amp) for a discrete circuit—about a sixty-four to one reduction in size, or something in that neighborhood. The earliest op-amp chips were good for functioning at frequencies higher than the audio band, and were designed to draw low current to keep cool. Audio, by its nature, calls for the ability to handle more current for musical peaks. So there's the rub: what was good for the average op-amp (high frequency, low current capability), was inadequate for an audio chip (lower frequencies, more current handling capability). And that may explain why, up ‘til recently, Hi-End audio designers eschewed op-amp chips. [Just now, I'm reminded of a graduate student who taught my writing seminar and who often marked in my marginalia, "Eschew obfuscation!"]
It seems about sixteen years ago the audio industry recognized the not-discrete, miniature, 8 pin-dip, op-amp chips had reached some outer limit of their performance where a discrete, if larger, op-amp could improve some audio circuits. The Marantz Corporation began making their version of a buffer amp in 1991, and in 1992 they named and registered it as the HDAM®, for "High Definition Amplification Module." A few years ago I'd spoken with John Curl about these things while preparing a review of some high-end Marantz gear that used HDAMs liberally, and I wanted to know what they did. From my notes of our conversation he said a few things that seemed very provocative to me.
Chips are sensitive to thermal problems that make them go non-linear. According to Curl (citing Barrie Gilbert), some chips are so sensitive there might be only a 10 nano-second window before the chip overheats and goes non-linear. So heat can be a very real problem inside most chips. According to a conversation I had with Ed Meitner (another of my gurus), "buffer stages could cause more harm than good." He goes on to point out that units which "already have low impedance will have problems with impedance matching." I reason that the buffer amplifier might be good for audio, but only if the buffer amp can run cool and drive the impedance of the particular gear it "sees" next down the line in a block diagram. Curl says there are many ways to set up an op-amp, so the idea of a "universal" buffer amp is very much a long shot. And this is why "each manufacturer that uses buffer amps makes its own," to match the various parameters of the circuitry in front of it, and the circuitry it expects to see downstream—usually designed in-house by the same crew. This seems to be true of Marantz, Marc Levinson, and Musical Fidelity. In addition to Burson, to my knowledge only Musical Fidelity makes an outboard ($400), stand-alone buffer-amplifier. Theirs is made with nuvistors, and may do best with tube gear.
From the above paragraph I draw the inference that getting the promised performance out of any manufacturer's equipment is always a matter of knowledgeable gear-matching, and the "universal" buffer amp might be an extreme example of a piece that requires very rigorous and careful gear-matching. Unless you know the circuit parameters of every type of circuit in question—say, an older CD player and the Burson Buffer Amplifier—you might get little or no improvement. (On Burson's website they specify the output of the Burson Buffer Amplifier as 15-30 ohms, an important thing to know.) In fact, as Ed Meitner suggested, things could sound worse.
I had that experience playing CDs through the "headphone out" jack of a portable walk-around CD player, which is probably the worst case I could have subjected the Burson Buffer Amplifier to (Mea culpa.), because the circuit is designed for headphones that are usually pretty low in impedance. There was an exaggerated amount of bloom on an album that had a lot of natural reverberation. Instead of cleaning up the sound, things became imprecise, too resonant. So I stumbled on the worst case first, which colored my perception of Burson's little gem. Ultimately, I figured out what a mistake I'd made, and things improved. Given two or three chances, I usually can get things right. My bad!
After that, I tried the Burson Buffer Amp (BBA) with some older gear. I found that I could coax good performance from it with a ten-year old Sony CD player XA3ES. Their ES line was a notch above their mid-fi line, but not their ultimate CD player of 1995. Playing without the BBA, I found this CD player sterile and overly analytical, somewhat harsh and fatiguing, lacking the warmth associated with SACD recordings. Playing regular red-book CDs through the Burson Buffer Amp, and through various headphone amps (the SinglePower SLAM, the HeadRoom Millett amp, the Grado RA-1, Ray Samuel's Hornet), the BBA always made the Sony sound more like an SACD player to me; warmer, less harsh, more spacious, pretty much as advertised. On my stereo "Big Rig" I found the least improvement, probably because my Marantz 8260 SACD/CD player already had the benefits of their buffer amplifier on its output.
So this Burson Buffer Amplifier is a mixed bag. It improves the sound of some older gear a noticeable notch, in the ways described above. But it is not a panacea. It doesn't do well with pieces that have noticeably low impedance, such as Walkaround CD players, unless they have a "line-out" jack. Having said that, it does seem to do well feeding my tubed headphone amps, The SLAM and The Millett Hybrid. And while the difference is immediately noticeable to me, it is subtle and some folks might not think it worth the money—like the folks who disbelieve in SACD and automatic transmissions, saying "Regular CDs are good enough."
I did find that the BBA also does well with older pieces suffering from "digititis," that disease characterized by sound too harsh, too etched, lacking warmth and beautiful tone. It had a salubrious effect on a ten plus year old ADCOM GFT-555 tuner, from which I now get very loverly FM music. Not quite as loverly as my Marantz 10B gives me, but it provides at least a two notch improvement on my feel-good scale as compared to without the BBA in the playback system. If you listen to FM radio a lot, as I do, the Burson Buffer Amplifier could be a welcome addition to an older solid-state tuner.
In my rheumatic ruminations about this piece I've leapt to some tentative conclusions. Since you have to buy the Burson Buffer Amplifier directly from Burson through their website, you ought to get your "return privilege authorization" in an email note. This is not to suggest anything unethical about the boys from down under, quite the opposite: they were awarded some sort of certificate of excellence from eBay for having a gaudy 100% customer satisfaction record. So it seems they value their good reputation and they are O.K. to deal with. But you might find my enthusiasm exceeds yours and decide to return your Buffer Amp. A return privilege authorization statement will just make clear who pays for shipping to Australia, etc.
Though I have not conducted an exhaustive listening test of the BBA with every type of gear I could think of, I have listened to it through just about each of the six or eight pieces mentioned above, and through headphones to eliminate room nodes and echo. That's a far cry from the thousands it would require to make statistically significant statements. There was a Swiss developmental psychologist, Jean Piaget, who came up with his own, very highly acclaimed system for understanding childhood development with a sample of merely three: his own kids. So sometimes small samples can make large contributions if you know what you're doing.
I'm no wizard, but I've been at this a long time now and feel comfortable saying if you have a well-defined, if somewhat limiting, expectation of what the Burson Buffer Amplifier can do; and your needs fall within the cautionary warnings I've offered (don't expect miracles, don't use with low-impedance gear) you can expect very satisfactory outcomes from the BBA. It is a well-conceived and well-executed piece that can, in fact, bring a ten year old CD player more or less up to date while costing about 10% of a first class new one.
The Burson Buffer Amplifier is a stand-alone operational amplifier with its own very quiet, well designed, on-board power supply. It comes packaged in a 8.5" x 6" x 3" black aluminum case with appropriate care to fit and finish. It is a little longer than my HeadRoom Millett Hybrid Desktop Amplifier, that has an outboard wall-wart power supply. It has an IEC connector that allows you to voice the piece by selecting an AC cord most compatible with your system. The BBA is best used as a buffer stage in an attempt to match impedances between, say, a CD player and a pre-amp. It does this job most admirably when the output impedance of the CD player is higher than its own input impedance. Care must be taken to avoid a mismatch, where the output impedance of the CD player (FM tuner, Walkman, iPod) is lower than the BBA's input impedance. Low output to high input is the rule.
The most cost-effective use of this product is in getting optimum sound from an older CD player, or even a relatively young, inexpensive "universal" player whose stereo output section is driven by chips. Most likely the BBA will be able to bring the sound of such digital sources up to the level of gear costing much more. Used in this way, and with the proper matching, I recommend the Burson Buffer Amplifier as a very useful device with a real ability to improve the sound in entry level systems (low distortion, high signal to noise, and 6dB gain). I'd go so far as to recommend putting one in series with a reasonably good tuner, tapedeck, DVD player, etc., if you want to improve it, and the pre-conditions I've noted are met. In sum, a very useful "black box." But performance can vary, so get out your owner's manual and do your homework.
If you want to improve the performance of a piece of digititis-afflicted gear for a reasonable price, rather than buy a new and pricey replacement, the Burson Buffer Amplifier is a reasonable way to go. If that's you, boogie on down to your computer's Internet connection, point your browser at http://www.bursonaudio.com, and click-on so you can read more about the features of the BBA. You find the instructions for contacting Burson directly through email at their site.
Remember, if you negotiate a purchase, be sure to tell our Australian buddies that Max Dudious sent ya!