One of the things that distinguishes expensive power amplifiers from the rest is that they rarely break or shut down on the test bench, even when driving 2 ohm loads at high levels at high frequencies. Such was the case with the No.23.5, which proved a powerhouse. With one channel driven, it comfortably exceeded its 23dBW power specification, the 1% distortion point being reached at 305W into 8 ohms (24.8dBW), 505W into 4 ohms (24dBW), and 750W into 2 ohms (22.7dBW), this behavior shown graphically in fig.1. With both channels driven, these figures dropped…
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Brian Tucker, the US Quad importer, introduced me to the Woodside MA50 tube amplifiers and their manufacturer, John Widgery, during the 1992 Summer CES. Tucker's combination of Woodside MA50 tube amplifiers and Quad ESL-63 USA Monitors sounded unusually neutral, dynamic, and detailed. This was good news; back in 1987, Dick Olsher (Vol.10 No.6, pp.104–5) was unable to recommend an earlier Woodside-manufactured amplifier, the Radford STA 25 Renaissance. Brian mentioned that the MA50's design is a much-improved version of that earlier Radford model. Time for another review.
Some history…
Unscrewing four Phillips-head fasteners allows the cover to be lifted. From the front, the toroidal AC transformer and printed circuit board (pcb) are positioned at chassis right, while the output tubes and large E-I audio output transformer are on the left. Both transformers employ solder tags, rather than flying leads. This means Woodside can choose better wire; in this case, silver. The tube sockets are not attached to the circuit board. This prevents tube-generated heat from aging the solid-state components, but point-to-point wiring is needed to connect the pcb with the tube sockets.…
Sidebar 1: Specifications
Description: Tubed monoblock amplifier using four EL34 tubes in the output stage. Rated output power: 50W minimum continuous sinewave power into 8 ohms at 1kHz (17dBW), with no more than 0.2% THD; 75W minimum continuous sinewave power into 4 ohms at 1kHz (15.75dBW), with no more than 0.2% THD. Dynamic headroom: 1.6dB. Peak output current: 15A. Frequency range: 8Hz–56kHz. Input impedance: 100k ohms. Sensitivity: 750mV (equivalent to a voltage gain of 28.5dB). Slew rate: 15V/µs. Power consumption: not given.
Dimensions: 9" (220mm) H by 16.8" (420mm) W by 10.8…
Sidebar 2: System & Setup
My listening room measures 26' long, 13' wide, with a 12' semi-cathedral ceiling. An 8' high by 4' wide doorway at the back of the room opens into a kitchen, adding an additional 25' by 15' area. I also used a second listening room, 17' by 10', to audition the MA50s.
I compared the Woodsides with a Mark Levinson No.27.5. Additional gain-matched listening tests were conducted with a Krell KSA-250. Because its power ratings are twice that of the Woodsides, sonic comparisons with the Mark Levinson focused on low-frequency extension, imaging, soundstage…
Sidebar 3: Measurements
The Woodside MA50's chassis was hot over the output tubes following the 60-minute, 1/3-power preconditioning, but no more so than the typical tube amplifier. Its input impedance measured just over 92k ohms, its voltage gain into 8 ohms, 29.7dB. The Woodside is non-inverting; a positive-going input results in a positive-going output. S/N ratio measured an excellent 110dB (unweighted, 22Hz–22kHz referenced to 1W output into 8 ohms). The amplifier's DC offset was unmeasurable, as is almost always the case with transformer-coupled designs.
The Woodside's output…
I had been sent a sample of the Woodside SC26 tube preamplifier during my June 1994 review of Woodside's MA50 monoblock amplifier (Vol.17 No.6). Although I used a number of preamplifiers during that review, I was most impressed with the MA50s' spacious, three-dimensional soundstage when driven by the SC26. At the time, I had an impression that the SC26's sonics combined a midrange richness with a good dynamic range. Although I had to return the Woodside MA50s to the importer after I reviewed them, I continued listening to the SC26.
Description
The SC26 looks functional and slim. The…
Each plate of the dual-triode cathode follower tube is fed by a separate 300V regulated supply. The filament supplies are unusual in that rather than power the tubes from a 12V source, the SC26 drives one side of the filaments from 60V and the other from 72V. By raising the filament voltages closer to the operating point of the cathode, the tube is said to run quieter.
Sound
I traced the SC26's initial hum problems to a faulty ECC83, which Woodside replaced with a Golden Dragon 12AX7. The SC26 was then as quiet as my solid-state preamplifiers—at least on casual listen. I detected…
Sidebar 1: Specifications
Description: Tube preamplifier with built-in/optional internal moving-coil transformer stage. Unit can be ordered as a line model (L) or a phono model (P) set up for either moving-coil or moving-magnet cartridges. Inputs: five single-ended line level, one phono (either MC or MM), Tuner, Video, Tape 1, Tape 2, CD. Outputs: single-ended main out, buffered tape out. Frequency response: 5Hz–50kHz, ±1dB, line; ±0.25dB, phono. RIAA accuracy: ±0.25dB. S/N Ratio (A-weighted): 85dB (line), 80dB (phono). Distortion (THD): !x0.1%. Input impedance: 47k ohms, line; 47k ohms…
Sidebar 2: Setup
My large listening room is 26' long by 13' wide, and has a 12' semi-cathedral ceiling. An 8' by 4' doorway at the back of the room opens onto my 25' by 15' kitchen. I also used my second, 17' by 10' listening room.
CDs were played on a Krell MD-1 turntable driving a Krell SBP-32X D/A converter; either a Rotel RHT-10 or a Day-Sequerra FM Reference tuner provided music from New York classical station WQXR; and LPs were played on a Linn Sondek LP12/Lingo turntable, an Ittok arm, and a Spectral MC cartridge.
I compared the SC26 with a Krell KBL preamplifier,…