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
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 doesnt 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%.