Description: Single-play CD transport. Outputs: one AES/EBU on XLR jack (110 ohms), one S/PDIF on RCA jack (75 ohms), one HP ST-Type optical (AT&T–compatible), one EIAJ (Toslink) optical. Additional inputs and outputs: slave in and slave out (for communication with other Mark Levinson digital products).
Dimensions: 19.375" W by 5.56" H by 13.726" D (14.426" H with lid open). Shipping weight: 62 lbs.
Price: $8495 (1993); no longer available (2008). Approximate number of dealers: 65.
Manufacturer: Madrigal Audio Laboratories, Middletown, CT 06457 (…
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Sidebar 2: Specifications
To high-end audiophiles, the Boulder 500 amplifier and its less expensive derivative, the 500AE (Audiophile Edition), would not seem to be "high-end" designs. They are designed around op-amps (felt by many to be generally poor-sounding), they have scads of negative feedback (which is perhaps why op-amps sound bad), and they have only a moderately hefty power supply. Why, then, is Stereophile publishing a review of an op-amp–based power amplifier? Read on...
The op-amp (for operational amplifier) circuit module was originally intended to perform simple mathematical operations in…
I borrowed two 500AEs for my review, which allowed me to audition one amp in straight stereo or both in strapped mono. The fact that both amps worked flawlessly right out of the box and have continued to work for several months was my second clue that they might not be what most of us think of as "high-end" audio products. My first clue was when Boulder prez Jeff Nelson assured me that the 500AE requires no warmup prior to listening. I beg to disagree. To me, the amplifier sounds veiled, edgy, and flat on turn-on. It starts to show promise after 30 minutes, but is still nothing to do…
For some reason or other, it seems that 40Hz is the effective low-end limit of 90% of the big loudspeakers on the market today. Some go deeper, but most do not do it well, and few do it with authority. This, I believe, is why audiophiles who do a lot of listening to what is reputedly very good equipment seem astonished when they hear stuff that sounds substantially deeper coming out of the updated Sound-Labs. With the 500AEs, the A-3's apparent low-end range is a good half-octave lower than it was with my previous reference standard, the VTL 300. The main difference is that, since there is…
Sidebar 1: Specifications
Description: Solid-state stereo power amplifier. Power output (continuous): 150W into 8 ohms (21.8dBW), 250W into 4 ohms (21dBW), 325W into 2 ohms (19.1dBW), 500W mono into 8 ohms (27dBW). THD at rated power: 0.0015% up to 2kHz, 0.005% at 20kHz. Slew rate: 35V/µs stereo, 70V/µs mono. Voltage gain: 26dB stereo, 32dB mono (no load specified). Frequency response: 20Hz–20kHz, +0.0, –0.04dB; –3dB at 0.015Hz and 200kHz. Peak current: 50A. Damping factor: 800 below 1kHz (equivalent to an output impedance of 0.01 ohms). Input impedance: 33k ohms unbalanced, 12k ohms…
Sidebar 2: Transient Intermodulation Distortion
TID is due to the active devices being unable to slew the voltages they are asked to handle sufficiently fast to keep up with the demands of the signal. Slew rate, expressed in V/µs, is the speed with which the output voltage of an active device is able to change and is a critical factor in the behavior of a negative feedback circuit: if slewing can't keep up with the changes in input level, the fed-back signal will not be able to properly attenuate the input signal, which will then increase to the point of amplifying-device overload.
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Sidebar 3: Complementary Symmetry
The complementary-symmetry circuit is sometimes called complementary push-pull, but strictly speaking, push-pull operation always means two identical output devices handling the same audio signal in relative inverted polarity. The output from these devices is their difference signal, which means out-of-phase signals—the music—produce maximum output while in-phase signals—even-order distortion and common-mode noise—cancel to produce zilch. Fig.1 shows how this works (in theory).
Fig.1 Simplified circuit of a push-pull transistor output…
Sidebar 4: Measurements
The Boulder's input impedance measured 11k ohms into its balanced inputs (the only type of input furnished on our sample). This is a fairly low figure; care should be taken to insure that the source fed into the 500AE has a low output impedance. The output impedance of the Boulder itself varied between 0.07 ohms and 0.11 ohms, depending on load and frequency, indicating that its frequency response should not vary with the load to any significant extent. Gain into 8 ohms measured 25.97dB at 1kHz, and the S/N ratio was 85dB referenced to 1W into 8 ohms. The DC…
Robert Harley wrote about the Boulder 500AE in April 1992 (Vol.15 No.4):
I was taken aback when I read J. Gordon Holt's rave review of the Boulder 500AE power amplifier last October. In comparing the 500AE with other high-end amplifiers (specifically Levinson, Krell, and Audio Research), JGH suggested that "...the Boulder 500AE will make acoustically produced music sound more realistic than any of these can." He continued: "After having lived with the 500AE for several months now, and attending symphony concerts locally from time to time, I contend that the 500AE has more of the ring of…
Lewis Lipnick reviewed the Boulder 500AE in June 1992 (Vol.15 No.6):
As JGH suggested in his glowing review of the $3999 Boulder 500AE, this manufacturer has not (until now) been considered a serious contender in the high-end audio marketplace. I've seen scads of Boulder amps in studios while playing on recording sessions, but never took the time to really listen. So when I ran into the people from Boulder at last January's CES in Las Vegas, they were quick to accommodate my request to sample their wares in my own system. A pair of 500AEs arrived while I was preparing a review of the…