Khartago Stereo 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 and graphical
information displayed below are the property of SoundStage! and Schneider
Publishing Inc. Reproduction in any format is not permitted.
- Measurements were made with 120V AC line voltage.
- Power output and distortion plotted with both channels
- Gain: 37.0x, 31.4dB.
- Output noise, 8-ohm load, unbalanced input, 1k-ohm input
termination: wideband 0.527mV, -74.6dBW; A weighted 0.105mV, -88.6dBW.
- AC line current draw at idle (warmed up): 0.6A.
- Output impedance at 50Hz: 0.1 ohms.
- This amplifier does not invert polarity.
Power output with 1kHz test signal
- 8-ohm load at 1% THD: 114W
- 4-ohm load at 1% THD: 187W
The Odyssey Audio Khartago is a medium-power solid-state
design with typically wide bandwidth and low output impedance.
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 is about +/-0.1 dB, not of great consequence. Chart 2 illustrates
how total harmonic distortion plus noise versus power varies for a 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. When the amount of distortion is fairly
constant over a wide range of power, as is the case here, it is usually indicative of a
dominance of even harmonic distortion. 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 relatively low, a desirable characteristic. Note how the
amount of distortion here is fairly constant with power level over much of the frequency
range. There is a beat frequency phenomenon in this amplifier between the 120Hz
power-supply ripple frequency and the signal-frequency distortion components as evidenced
by the peak/dip/peak in the chart in this frequency range. Damping factor versus frequency
is shown in Chart 4. Unusual here is the falloff in the damping factor at low frequencies.
A spectrum of the harmonic distortion and noise residue is plotted in Chart 5. The AC-line
harmonics are quite prominent in this chart. Note that the even harmonics of the 1kHz test
frequency, the second (2kHz), fourth (4kHz), and sixth (6kHz), are dominant as expected
from the earlier comments on Chart 2.
- Frequency Response of Output Voltage as a Function of Output Loading
Magenta line: open circuit
Red line: 8-ohm load
Blue line: 4-ohm load
Cyan line = NHT dummy-speaker load
|Chart 2 - Distortion as a Function
of Power Output and Output Loading
(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
|Chart 3 - Distortion
as a Function of Power Output and Frequency
4-ohm output loading
Cyan line: 150W
Blue line: 80W
Magenta line: 20W
Red line: 2W
|Chart 4 - Damping Factor
as a Function of Frequency
Damping factor = output impedance divided into 8
|Chart 5 - Distortion and
1kHz signal at 10W into a 4-ohm load