March 2004

Odyssey Audio 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 driven.
• 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

General

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.

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

(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

4-ohm output loading
Cyan line: 150W
Blue line: 80W
Magenta line: 20W
Red line: 2W

Damping factor = output impedance divided into 8

1kHz signal at 10W into a 4-ohm load

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