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Ah, Brazil...land of coffee, the samba, Pelé, Rio-by-the-sea-o, and tube amplifiers. All right, so perhaps the amplifier connection isn't quite as well-established. But one Brazilian amplifier designer, Eduardo de Lima, has published articles in Glass Audio magazine that are viewed by many as groundbreaking, and his evolving products have been seen at various specialist tube equipment shows. De Lima—president, founder, product designer, and principal owner of Audiopax Sistemas Eletroacusticos—is an electrical engineer who started out designing equipment for a telecommunications company, but…
Why is Timbre Lock important? This is where things get a bit complicated—and controversial. De Lima suggests that an amplifier of relatively high distortion, when combined with a given speaker, can actually produce less total system distortion than the same speaker driven by an amp of lower distortion. According to this view, a higher-distortion amp may sound superior to a lower-distortion one not just because low distortion in an amplifier is usually achieved through the use of greater negative feedback, tilting the distortion spectrum toward the more objectionable higher-order harmonics (…
I found the controls quite fiddly to operate, the LED display changing with the slightest turn of the knob. The bias levels indicated by the LEDs tended to drift after the nominal warmup period, so that while the bias levels may have been adjusted an hour after turn-on to read 11/3, a few hours later they could be at 11/2. Having tweaked the bias to read 11/3 near the end of a late-night listening session, it was not unusual for me to find the next day, after a half-hour warmup, that the bias levels were off by one or more LED indicators. I can't say that the sonic effect of the bias drift…
In the case of the Audiopax Model Eighty Eight, the answer to all these questions was a resounding "Yes." The music just seemed to be there, the amplifier (and the rest of the system) getting out of the way. The most striking aspect of the Model Eighty Eight's contribution to the system's sound was that it seemed to reduce much of the harshness and edgy quality that I'd assumed was simply a characteristic of certain recordings. Whether this was due to the claimed reduction of total system distortion or the effect of a kind of "harmonic enhancement," perhaps replacing what had been lost in…
Sidebar 1: Specifications
Description: Single-ended pentode monoblock power amplifier. Power output (at 1kHz): 30Wpc into 8 ohms (14.8dBW). Frequency response: 14Hz-90kHz, -3dB. S/N Ratio: >95dB unweighted ref. full output. Input impedance: 83k ohms. Output impedance: 3.5 ohms. Absolute polarity: inverting. Maximum power consumption: 110W.
Dimensions: 13.5" H by 9" W by 14.5" D. Weight: 42 lbs.
Finishes: Chromed brass, lacquered or unlacquered wood.
Serial numbers of samples reviewed: 22106 A/B (auditioning), 24105 A/B (measuring).
Price: $9970/pair. Approximate number of…
Sidebar 2: Associated Equipment
Analog source: Linn LP12 turntable (fully updated), Linn Ittok tonearm, AudioQuest AQ-7000nsx cartridge.
Digital source: PS Audio Lambda II CD transport, Perpetual Technologies P-1A, ModWright P-3A digital processors.
Preamplifier: Convergent Audio Technology SL-1 Ultimate.
Loudspeakers: Avantgarde Acoustic Uno 3.0.
Cables: I2S: Mystic Reference. Digital: Illuminati Orchid AES/EBU. Interconnect: Nordost Valhalla, Nirvana S-L. Speaker: Nordost Valhalla, PS Audio Lab Cable, Shunyata Research Taipan. AC: TARA Labs Decade.
Accessories: Duende…
Sidebar 3: Measurements
The Audiopax Model Eighty Eight's two Timbre controls make possible a large number of combinations. I decided, therefore, to simplify matters by looking at the drop-dead-gorgeous amplifier's measured performance with both controls set to their fully clockwise positions, which I assumed was maximum bias current, and set as Bob Deutsch preferred: the left control to "11," the right to "3."
The input impedance at 1kHz was a usefully high 229k ohms, and the amplifier inverted absolute polarity. The voltage gain into 8 ohms varied somewhat according to the…
Sidebar 4: Manufacturer's Comment
Editor: Finally! Six long years after Eduardo de Lima's first published papers in 1997, John Atkinson and Robert Deutsch have wonderfully proved the point that Eduardo's been making.
Let's face it, there's no real art or science involved in building an amp that'll drive a test-bench resistive load. It's easy to build an amp with "low distortion." The Crown DC-300 broke that ground over 30 years ago. But the test bench doesn't know what to do with the second-order distortion of single-ended amplifiers. Certainly, if it existed as audible…
Robert Deutsch wrote again about the Audiopax Eighty Eight in January 2006 (Vol.29 No.1):
The second power amp I had around for comparison with the $2795 PS Audio GCC-100 was the Audiopax Model Eighty Eight SE, a tubed single-ended pentode monoblock ($10,000/pair) that simulates the sound of single-ended triodes but with more power (see my review in the May 2003 Stereophile, Vol.26 No.5). The relationship between the sounds of the Audiopax and the Avantgarde Uno speakers is a particularly synergistic one—in fact, the Audiopax was originally imported by Avantgarde USA because of that…
One of the delights of being published by a multinational conglomerate that grows through acquisition, as Emap Petersen does, is that Stereophile finds itself in interesting company. Like La Nouvelle Revue du Son in France, for example, edited by the legendary Jean Hiraga, who turned me on to the sonic importance of wires and passive components almost 25 years ago. And Mojo, an English music magazine tightly targeted on baby boomers like me, who bought their first stereo systems in the '60s to better appreciate the progressive rock we lived and loved by. (I wonder if turn-of-the-millennium…