Opera Audio is a Chinese producer of high-end audio gear, their most popular items being the Consonance line of tube-based amplifiers and preamplifiers, although they also produce tube CD players and even a tuner. The M100 Plus, an integrated amplifier represents the most successful of Opera’s budget, or M-Value series. The M100 model in particular has been through several generations in the past eight years from the original to the Mark II, the SE, and now the Plus, which features remote volume control.
The M100 Plus delivers 40Wpc with user-selectable output of 4 or 8 ohms. It is a class-AB, push-pull design, which is said to be the sweet spot between efficiency and distortion. The class-AB operation keeps current flowing through the tubes even when idle, but only a small amount. Push-pull configuration is said to minimize second-order harmonic distortion, which, although it is typically perceived as a more benign kind, is nonetheless an amplification artifact.
The M100 Plus accepts three input sources via RCA connectors only. There is no tape output, preamplifier output, or phono stage. One set of five-way binding posts for each channel are topped with thick metal lugs that are easy to grip and clamp down even onto thick spades. The unit accepts an IEC-style detachable power cord, measures 17 1/2" wide x 10 1/2" deep x 6" high (not counting the tubes), and weighs 45 pounds. It is flanked by wood-grain side pieces and has a brushed-steel base. Rising from the steel base, the tubes and power transformers stand up like silos on a busy farm. An included black steel cage can be positioned over the tubes for protection from curious meddlers such as, say, cats.
The face is a model of minimalism, with only an on/off toggle, a blue power-indicator LED, and two identical-looking black rotary knobs -- one for input selection, the other for volume. The volume can also be controlled using the included remote, which is a small, square, and surprisingly heavy sculptural piece that consists only of a large circular button to raise and lower the volume. The volume knob on the unit’s face is not lighted, so you can’t see the relative volume position from a distance.
The M100 Plus utilizes one pair of EL34 output tubes per channel. The four EL34 tubes are run in ultralinear mode, which drives the tubes with only a part of the output signal and claims to lower distortion. In addition, a pair each of 12AX7 and 6SN7 dual-triode tubes drive the input and driver stages respectively. The M100 Plus does not possess automatic or manual bias regulation, although the product manual takes pains to explain that small voltage differences between tubes do not cause any problems in the unit.
Control Functions: Volume, Input, Power On/Off
Power Output: 40 watt,RMS 1KHz
Total Harmonic Distortion: less than 1%(10watt, 1kHz)
Frequency Response: (-3dB points at 10 watt) 6Hz-60kHz
Input Sensitivity: 290mV
Input Impedance: 100k ohms
Output Impedance: 4, 8 ohms. (User selectable.)
Input Interfaces: 3 groups (RCA) ---(1,2 , 3 on the rear panel)
Overall Negative Feedback: Little (-6dB)
Vacuum Tube: EL34 x 4, 12AT7 x 2, 6SN7 x 2
Dimensions: 446(L) x 264(W) x 155(H) mm