Power output with 1kHz test signal
- 8-ohm load at 1% THD: 142W
- 4-ohm load at 1% THD: 158W
The darTZeel NHB-108 is a medium-power solid-state design
with typically wide bandwidth and output impedance a bit higher than is usual for
solid-state amplifiers. Some of its measured characteristics are similar to those of a
tube amplifier, such as relatively high measured distortion and a modest damping factor.
Both are suggestive of little or no overall negative feedback in the design.
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 +/-0.25 dB.
Chart 2 illustrates how total harmonic distortion plus
noise vs. power varies for 1kHz 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. Amount of distortion is relatively high for solid-state designs, but the way
the amp goes into clipping is more like a typical solid-state amplifier.
Total harmonic distortion plus noise as a function of
frequency at several different power levels is plotted in Chart 3. Interestingly, the
distortion amount vs. frequency for the lower powers is virtually constant, whereas at
higher powers the distortion does rise a bit at the high end of the audio band.
Damping factor vs. frequency is shown in Chart 4, and is
moderate but reasonably constant with frequency, again not usual for solid-state designs.
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 is
quite numerous and intermodulation components of line harmonics with signal harmonics are
also just visible near the noise floor. The test signal harmonics are both even and odd
and don't decline or tail-off with frequency very fast.