Instruction manual

92
Australian
LAB REPORT
Modwright KWI 200 Integrated Amplifier
the 1dB downpoints at 2.2Hz and 180kHz,
and the 3dB downpoints at 190Hz. Channel
balance was excellent, at 0.02dB. Channel
separation was good at low and midrange
frequencies, as you can see from the tabbed
results, but diminished to just 42dB at 20kHz.
Output distortion levels were moderately
high, as you can see from the spectrum
analysis that’s shown in Graphs 1 through
4. At an output of 1-watt (Graphs 1 and 2)
you can see that into 8 ohm loads, the 2
nd
,
3
rd
and 4
th
harmonics were at levels of –48dB,
–50dB and –60dB respectively, equating to
percentage distortions of 0.39%, 0.31% and
0.1% for each of the distortion components.
Low-order distortion is perceived by the
human ear as being euphonious, and most
experts say that low-order distortion levels
of less than 3.0% are not audible in any
case. With this in mind, you can see that
the overall one-watt/8Ω THD+N level was
measured at 0.4%, as shown in the tabulated
results. As you can also see, distortion
increased further when the amplifier was
driving 4Ω loads, with the second and third
harmonics sitting just below –40dB (1.0%)
distortion and the fifth, sixth and seventh-
order harmonics all above –70dB (0.03%).
Distortion levels increased again when
the amplifier was operating at rated output,
as you can see in Graphs 3 and 4. This time,
harmonic distortion components are spread
right across the audio spectrum, with the
odd-order harmonics generally 10dB higher
than the even-order harmonics, but with all
harmonics generally constrained to between
–60dB (0.1%) and –80dB (0.01%). You can
see from the ‘grass’ on the noise floor around
the individual harmonics that the KWI
200’s power supply is operating right at its
limits. You can also see that the noise floor
is right down at around –130dB for the most
part, though increasing to –100dB at very
low frequencies. The overall signal-to-noise
ratio of the KWI 200 was measured at 80dB
unweighted and 84dB A-weighted referred to
one-watt, and 98dB unweighted and 106dB
A-weighted referred to rated output.
The frequency response of the Modwright
KWI 200 across the audio band is shown in
Figure 5 both into a standard laboratory 8Ω
‘dummy’ load (a high-power non-inductive
resistor) and when the amplifier is driving
a simulated loudspeaker load (Newport Test
Labs uses the circuit developed by Ken
Kantor as modified by John Atkinson, of
Stereophile). You can see the response into
the 8Ω load is essentially ruler-flat, being
just 0.1dB down at 20Hz and 0.2dB down at
20kHz. Note, however, that the response is
shown to be rising above 20kHz. There was
far more variation in the response when the
amplifier was driving the simulated load, so
that the response was 20Hz–20kHz ±0.4dB,
again with a rising output at high frequency.
This result suggests the KWI 200’s output
impedance was quite high, and indeed it was
measured at 0.7Ω, for a damping factor of 11.
CCIF-IMD was high, with high-
level intermodulation
components clustered
around the two high-
level test frequencies
(at 19kHz and 20kHz)
and a regenerated 1kHz
signal at –55dB (0.17%).
Interestingly, this graph
looks as though it could
have come direct from
a valve amplifier, rather
than a solid-state design—
particularly as regards the
regenerated 1kHz signal.
The square wave
oscillograms indicate that
although the frequency
response across the audio
band is flat, and that
the amplifier can easily
accommodate highly
reactive loudspeaker loads,
its frequency response rises
at ultrasonic frequencies.
The Modwright KWI 200
integrated amplifier proved
to be fairly power-hungry
when it’s operating and
will draw around 100-watts
from your mains power
supply in day-to-day use—
even when it’s on but not
being used—but potentially
can pull 664-watts. In
standby mode, the draw
is less than 2-watts, but
I would still recommend
you leave the amplifier
switched off when you are
not using it.
Steve Holding
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Newport Test Labs
Graph 2: Total harmonic distortion (THD) at 1kHz at an output of 1-watt into a 4-ohm non-inductive
load, referenced to 0dB. [Modwright KWI-200]
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Graph 3: Total harmonic distortion (THD) at 1kHz at rated output (200-watts) into an 8-ohm
non-inductive load, referenced to 0dB. [Modwright KWI-200]
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Graph 1: Total harmonic distortion (THD) at 1kHz at an output of 1-watt into an 8-ohm
non-inductive load, referenced to 0dB. [Modwright KWI-200]
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Newport Test Labs
Graph 6: Intermodulation distortion (CCIF-IMD) using test signals at 19kHz and 20kHz,
at an output of 1-watt into an 8-ohm non-inductive load, referenced to 0dB. [KWI-200]
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Newport Test Labs
Graph 5: Frequency response of line input at an output of 1-watt into an 8-ohm non-inductive load
(black trace) and into a combination resistive/inductive/capacitive load representative of a typical
two-way loudspeaker system (red trace). [Modwright KWI-200]
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Graph 4: Total harmonic distortion (THD) at 1kHz at rated output (400-watts) into a 4-ohm
non-inductive load, referenced to 0dB. [Modwright KWI-200]