March 2006

Vincent SP-T100 Mono Amplifiers: 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.

• Measurements were made at 120V AC line voltage with one channel being driven (this is a mono amplifier).
• Gain: 26.3x, 28.4dB.
• Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination: wideband 0.158mV, -85.1dBW; A weighted 0.051mV, -95.0dBW.
• AC line current draw at idle: 1.2A.
• Output impedance at 50Hz: 0.11 ohms.
• This amplifier does not invert polarity.

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 107W
• 8-ohm load at 10% THD: 129W
  
  
• 4-ohm load at 1% THD: 189W
• 4-ohm load at 10% THD: 225W

General

The Vincent SP-T100 is a medium-power solid-state design with typically wide bandwidth, low output impedance typical of solid-state power amplifiers. It is of a hybrid design with vacuum tubes used for the front-end circuitry and solid-state devices used for the output stage. A vacuum tube rectifier is used for the tube circuitry supply.

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 open circuit, 8-ohm, and 4-ohm loading, is quite low. The variation with the NHT dummy load in the audio range is of the order of +/-0.1dB.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1 kHz and SMPTE IM test signals and amplifier output load. As can be seen, attainable power is greater for the 4-ohm load, as is usual for most power amplifiers. Furthermore, the way that the distortion increases as power nears maximum is a much softer curve than is typical for a solid-state amplifier. This indicates the possibility of low amounts of overall feedback in the design. In fact, the manual says the output stage doesn’t have any feedback taken around it.

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 high frequencies is non-existent in this design, although there is some distortion increase at low frequencies at the 180W level.

Damping factor vs. frequency is shown in Chart 4 and is reasonably constant with frequency.

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 low as are intermodulation components of line harmonics with signal harmonics. The signal harmonics above the second and third are admirably low in number and magnitude for the 8-ohm loading shown. For the 4-ohm loading case, the higher harmonics do increase but are still all below 0.005%.

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

(line up at 20W 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

4-ohm output loading
Cyan line: 180W
Blue line: 60W
Magenta line: 20W
Red line: 2W

Damping factor = output impedance divided into 8

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

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