I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Acora SRB's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield and in-room responses. My initial measurements were performed on one of the original samples auditioned by Julie Mullins, serial number TIB0010. After Acora found out that the first samples had been incorrectly assembled with the tweeters wired in the wrong polarity, which resulted in a massive suckout in the crossover region, they submitted new samples. I performed a complete set of…
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Talk about a Scarlet Letter. The term class-D amplification, which describes PS Audio's new M1200 monoblocks, exists only because another amplifier innovation had already parked in the "C" space. Soon after appearing in high-performance audio gear, class-D became synonymous with "digital amplification" in part because, like early CDs, many listeners found the sound glary, hard, and unpleasant. Besides, class-D is related to "pulse width modulation" and requires a low-pass filter to block high-frequency pulses—that sure sounds digital. But they're not (see sidebar).
To this day, many audio…
"Punchy" doesn't begin to describe the M1200's low-end solidity, extension, rhythmic swagger, and complete freedom from overhang. I played a plain American pressing of David Bowie's Station to Station (RCA APL 1-1327); following the train drive-by, George Murray's bass line kicks in, followed by a single Dennis Davis drum "thwack" that felt as if the woofer cones might have broken free of the baskets if I had played it much louder, taking the surrounds with them! The energy concentration on and around individual notes was one of the M1200's most memorable characteristics.
The middle and…
Sidebar 1: Is Class-D Digital?
When I first read Mikey's introduction to this review, I was struck by his matter-of-fact statement that class-D isn't digital. Really? Are you sure?
Yes, I know the D in class-D doesn't stand for digital, but that doesn't mean the technology isn't digital. After all, in a class-D amplifier, the signal fluctuates rapidly between two levels, just as it does in DSD—what could be more digital than that?
Fact is, I've always thought of class-D as digital, and of class-D–isn't-digital claims as marketing propaganda propagated by people who want…
Sidebar 2: Specifications
Description: Hybrid class-D monoblock power amplifier. One 12AU7 vacuum tube, ICEedge ouput module. Inputs: 1 balanced (XLR), 1 single-ended (RCA), DC trigger. Outputs: 2 pair five-way binding posts. Output power (1kHz, 1% THD): 600W into 8 ohms, 1200W into 4 ohms (both 27.8dBW). Frequency response (2.8V RMS into 4 ohms): 10Hz–45kHz, ±3dB. Voltage gain: 30.5dB, ±0.5dB. Sensitivity: 2.08V for rated output power. Input impedance: single-ended, 50k ohms; balanced, 100k ohms. Damping factor (50Hz, 2.8V RMS), 8 ohms: >1100; 4 ohms: >550. THD: <0.005% (1kHz,…
Sidebar 3: Associated Equipment
Analog sources: Continuum Audio Labs Caliburn & Castellon turntable & stand; SAT XD1 direct-drive turntable, OMA K3 direct-drive turntable, SAT CF1-09, CF1Ti-09, Schroeder OMA, and Kuzma 4Point tonearms; Lyra Atlas Lambda SL, Ortofon MC Century, Anna Diamond, A95, A90, Grado Epoch3, Miyajima Labs Infinity (mono), Grado Epoch (mono), Aidas Audio Gala Gold LE cartridges.
Digital sources: dCS Vivaldi One SACD player DAC; Lynx Hilo A/D-D/A converter; Roon Nucleus server; Pure Vinyl and Vinyl Studio software.
Preamplification: darTZeel NHB-18S,…
Sidebar 4: Measurements
I performed a full suite of measurements on one of the PS Audio Stellar M1200s (serial no. 12-A1-0G0033), using my Audio Precision SYS2722 system (see the January 2008 "As We See It"). Because the Stellar M1200 features a class-D output stage, all the measurements other than the frequency response tests and one of the squarewave tests were taken with Audio Precision's AUX-0025 auxiliary passive low-pass filter, which eliminates much of the ultrasonic noise that might otherwise drive the analyzer's input into slew-rate limiting. Without the filter, 373mV of…
During my tenure as a Stereophile writer, I've reviewed a lot of integrated amplifiers. The mostly moderately priced integrated machines I've reviewed have included the Heed Audio Elixir ($1195), Luxman SQ-N150 ($2795) and L-509X ($9495), NAD C 328 Hybrid Digital ($549), Octave Audio V 80 SE ($10,500), Rega Brio ($995), and Schiit Ragnarok 2 ($1799 as equipped). Regardless of price, all these integrated amplifiers engaged my senses and made engaging, dynamic, colorful music from LP grooves and ones and zeros.
Decades ago, integrated amplifiers were full-featured beasts—and then there was…
Listening
As Stereophile's Recommended Components list attests, just because a product is built to a $1200 price point doesn't mean it won't pack a wallop. This held true for the CXA81, which consistently impressed me with its ability to challenge competing amplifiers in a similar price range and by how good it sounded with different speakers. The CXA81 had me uttering "wow" (several times) at its transparency to the sound of upstream electronics and recordings. When I switched between my Thorens and Kuzma turntables, for example, the difference was clear, immediate, and profound, as if…
As Stereophile's Recommended Components list attests, just because a product is built to a $1200 price point doesn't mean it won't pack a wallop. This held true for the CXA81, which consistently impressed me with its ability to challenge competing amplifiers in a similar price range and by how good it sounded with different speakers. The CXA81 had me uttering "wow" (several times) at its transparency to the sound of upstream electronics and recordings. When I switched between my Thorens and Kuzma turntables, for example, the difference was clear, immediate, and profound, as if…
Sidebar 1: Specifications
Description: Two-channel, class-AB integrated amplifier with DAC, Bluetooth. Analog inputs: 4 pair unbalanced (RCA), 1 pair balanced (XLR). Outputs: 2 sets custom speaker posts, 3.5mm headphone, 1 pair unbalanced (RCA) preamp out, unbalanced (RCA) subwoofer out. Power output: 80Wpc into 8 ohms (19dBW); 120Wpc into 4 ohms (17.8dBW). Frequency response: 5Hz–60kHz, ±1dB. THD (unweighted, at 80% of rated power): <0.002% 1kHz; <0.02% 20Hz–20kHz. S/N ratio (ref. 1W into 8 ohms): >93dB, (ref. full power): >105dB. Input sensitivity: Input A1–A4 (unbalanced…