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April 2005

Opera Audio Consonance Cyber-10 Signature Integrated Amplifier: Measurements

All integrated-amplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test integrated amplifiers there. All measurement data and graphical information displayed below are the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

Additional Data
  • Measurements were made at 120V AC line voltage with both channels being driven.
  • Measurements made on the left channel with volume control set for 5W/8 ohm on the 8-ohm output for 500mV input signal level and taken on the 8-ohm output unless otherwise noted.
  • Input sensitivity, Lch/Rch: 54.4mV/51.7mV
  • Gain, Lch/Rch: 52.0X, 34.3dB/54.7X, 34.8dB
  • Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination, Lch/Rch: wideband, 0.27mV, -80.4dBW/1.1mV, -68.2dBW; A-weighted, 0.11mV, -88.2dBW/0.12mV, -87.5dBw.
  • AC line current draw at idle: 1.2A.
  • Output impedance at 50Hz: 2.2 ohms.
  • This integrated amplifier does not invert polarity.
Measurements Summary

Power output with 1kHz test signal

  • 8-ohm load at 1% THD: 4.5W
  • 8-ohm load at 10% THD: 11.8W

  • 4-ohm load at 1% THD: 2.2W
  • 4-ohm load at 10% THD: 9.9W

General

The Opera Consonance Cyber-10 Signature is a low-power integrated tube amplifier utilizing a great complement of tubes, including a 12AX7 first tube, a 6SN7 phase-inverter driver, and most interesting of all, a pair of 2A3 directly heated triodes operated in push-pull for output. These 2A3s are of the single-plate variety and made in Russia. I, being interested in tubes for a long time, was more familiar with the more common, dual-plate variety of 2A3s.

When I received the amp for measurement, one of the four output tubes had an open filament. Being determined to listen to this amp, I dug into my old bag of tubes dating back to my high school days and found, to my amazement and relief, exactly one pair of ancient 2A3 tubes. The old tubes worked just fine, and the amp sounded quite musical in my setup. Replacement tubes were obtained from the importer and the measurements were made with the intended tubes installed.

Directly heated triode output tubes frequently have hum balance controls. In the case of the Cyber-10 Signature, I had adjusted these for minimum hum, and the right channel had somewhat more hum, reflected in the wideband number. Normally, if the channels are more or less similar, only one channel's data is shown.

Chart 1 shows the frequency response of the amp with varying loads. As can be seen, the output impedance, as judged by the closeness of spacing between the curves of the open circuit as well as 8-ohm and 4-ohm loading, is of a typical value for tube amplifiers. The variation with the NHT dummy load in the audio range is of the order of +1/-1.5dB. Frequency response as a function of volume control setting was plotted over a range of 0dB down to -60dB, and the response was found to be quite constant over this range. The level tracking of the two channels stayed within about 1.5dB over this range, with the right channel usually being the higher output of the two.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. The amp is well matched to produce the best result with tap loading -- meaning with an 8-ohm load on the 8-ohm output and a 4-ohm load on the 4-ohm output. However, power and distortion are still reasonable with loads of half and double the output-tap value.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. Amount of rise in distortion at low and high frequencies is very respectable for a low-power integrated amplifier.

Damping factor vs. frequency is shown in Chart 4 and is of a value typical of many tube amplifiers.

A spectrum of the harmonic distortion and noise residue of a 10W 1kHz test signal is plotted in Chart 5. The magnitude of the AC-line harmonics are quite numerous, and intermodulation components of line harmonics with the signal fundamental and harmonics are also very numerous and visible. The standard test level normally used of 10W is into clipping for this amp. Lower-power spectrum results showed a nice, quickly decaying spectrum of harmonics.

Chart 1 - Frequency Response of Output Voltage as a Function of Output Loading


Red line: open circuit
Magenta line: 8-ohm load
Blue line: 4-ohm load
Cyan line: NHT dummy-speaker load

Chart 2 - Distortion as a Function of Power Output and Output Loading


(line up at 2W to determine lines)
Top line: 4-ohm SMPTE IM
Second line: 8-ohm SMPTE IM
Third line: 4-ohm THD+N
Bottom line: 8-ohm THD+N

Chart 3 - Distortion as a Function of Power Output and Frequency


8-ohm output loading
Cyan line: 10W
Blue line: 6W
Magenta line: 3W
Red line: 1W

Chart 4 - Damping Factor as a Function of Frequency


Damping factor = output impedance divided into 8

Chart 5 - Distortion and Noise Spectrum


1kHz signal at 10W into a 8-ohm load

 

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