December 2005

Raysonic SP-100 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, including graphical information displayed below, is the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

• Measurements were made at 120V AC line voltage with both channels driven and with volume control fully up unless otherwise noted.
• Input sensitivity for 1W output into 8 ohms: 177mV.
• Gain, output voltage divided by input voltage, volume at maximum: 16.0X, 24.1dB.
• Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination, volume control fully up (clockwise position, worst case): wideband 0.37mV, -77.7dBW; A weighted 0.15mV, -85.5dBW.
• Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination, volume control fully down (counterclockwise position): wideband 0.23mV, -81.8dBW; A weighted 0.08mV, -91.0dBW.
• AC line current draw at idle: 1.77A.
• Output impedance at 50Hz: 0.77 ohms.
• This integrated amplifier does not invert polarity.

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 40W
• 8-ohm load at 10% THD: 60W
  
  
• 4-ohm load at 1% THD: 28W
• 4-ohm load at 10% THD: 44W

General

The Raysonic SP-100 is a medium-power stereo push-pull tube integrated amplifier utilizing one pair of EL34 output tubes in each channel. This integrated amp has a digitally controlled volume control and selector switch ahead of the power amplifier.

Chart 1 shows the frequency response of the amp with varying loads. This amp has a nicely controlled high-frequency response with some way-out-of-band output-transformer aberrations above 100kHz. The output impedance, as judged by the closeness of spacing between the curves of open circuit, 8-ohm, and 4-ohm loading over most of the audio range is somewhat lower than typical for tube power amplifiers. The variation with the NHT dummy load in the audio range is about +/-0.7dB. Of academic interest with this design, the output impedance actually becomes 0 at 80kHz and becomes negative between 80kHz to about 160kHz where it becomes positive again.

Chart 2 illustrates how total harmonic distortion plus noise versus power varies for 1kHz and SMPTE IM test signals and amplifier output load. As is usual for most tube power amplifiers, the power at the onset of clipping is greatest for tap "matched" impedance, in this case, 8-ohm loading on the 8-ohm output.

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 admirably low in this design.

Damping factor versus frequency is shown in Chart 4 and is amazingly constant over the whole audio range.

A spectrum of the harmonic distortion and noise residue of a 10W 1kHz test signal is plotted in Chart 5. AC-line harmonics are numerous but decrease in magnitude as the harmonic number goes up. The 120Hz line harmonic does intermodulate quite noticeably with the nulled-out 1kHz signal fundamental frequency. Some further intermodulation can be seen on the skirts of the second- and third-signal harmonic also. The decay of the amplitude of the signal harmonics is quite uniform and is judged to be desirable in some quarters.

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

(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

8-ohm output loading
Cyan line: 30W
Blue line: 20W
Magenta line: 10W
Red line: 1W

Damping factor = output impedance divided into 8

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

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