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Equipment Measurements

March 2008

Oracle Audio SI 1000 Integrated Amplifier: Measurements

All  amplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test 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 driven; measurements made on left channel with unbalanced input unless otherwise noted.
  • This integrated amplifier does not invert polarity.
  • AC line current draw:
    • at idle: 0.72A
    • in standby: 0.32A
  • Input sensitivity for 1W output into 8 ohms, volume at maximum: 49.2mV
  • Input impedance @ 1kHz:
    • balanced inputs: 47.0k ohms
    • unbalanced inputs: 24.0k ohms
  • Output impedance at 50Hz: 0.4 ohms
  • Gain, output voltage divided by input voltage, volume at maximum: 57.2X, 35.2dB
  • Output noise, 8-ohm load, 1k-ohm input termination, Lch/Rch
    • Volume control at reference position
      • wideband: 0.65mV, -72.8dBW / 0.68mV, -72.4dBW
      • A weighted: 0.28mV, -80.1dBW / 0.35mV, -78.2dBW
    • Volume control full clockwise
      • wideband: 1.39mV, -66.2dBW / 1.37mV, -66.3dBW
      • A weighted: 0.59mV, -73.6dBW / 0.62mV, -73.2dBW
    • Volume control full counterclockwise
      • wideband: 0.60mV, -73.5dBW / 0.66mV, -72.6dBW
      • A weighted: 0.27mV, -80.4dBW / 0.34mV, -78.4dBW
Measurements Summary

Power output with 1kHz test signal

  • 8-ohm load at 1% THD: 141.3W
  • 8-ohm load at 10% THD: 173.1W

  • 4-ohm load at 1% THD: 213.4W
  • 4-ohm load at 10% THD: 266.6W

General

The Oracle SI 1000 is a remote-controlled, medium-power solid-state integrated amplifier. Overall gain of this unit is about right for a modern integrated amplifier -- a bit higher than average power-amp-only gain.

Chart 1 shows the frequency response of the amp with varying loads. This plot was made with the reference volume-control position as set for 0.5V input to produce 5W output into an 8-ohm load. The high-frequency response is moderately wide, with an approximate 3dB-down point of about 60kHz. Output impedance as judged by the closeness of spacing between the curves of open-circuit, 8-ohm and 4-ohm loading is somewhat high for solid-state power amplifiers. Still, the variation with the NHT dummy speaker load is only of the order of +/- 0.25dB -- it’s not going to make much of an audible difference with most speakers. Of note, the high-frequency roll-off shape is nicely independent of loading. The frequency response of this unit was quite independent of volume-control setting. Tracking between channels was within about 0.1dB from full up to -70dB of attenuation.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. Not typical of most solid-state amplifiers, distortion maximizes right in the typical listening range of power output, in the 1-5W range.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3 for 4-ohm loading. The amount of rise in distortion at high frequencies is quite pronounced, with some rise at the very low frequencies at 200W output.

Damping factor vs. frequency is shown in Chart 4 and is of a value and nature not typical of most power amplifiers -- being relatively low and uniform over most of the audio range. As mentioned earlier, the output impedance is relatively high for a solid-state power amplifier, yielding a damping factor of about 20.

A spectrum of the harmonic distortion and noise residue of a 10W 1kHz test signal into 8 ohms is plotted in Chart 5. The magnitudes of the AC-line harmonics are moderately high and complex in nature. However, intermodulation components of line harmonics with signal harmonics are low. Signal harmonics consist of a tapering off spectrum of even and odd 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 10W 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


4-ohm output loading
Green line: 200W
Cyan line: 160W
Blue line: 120W
Magenta line: 10W
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 an 8-ohm load

 

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