October 2003

Coda Technologies 12.0 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, including graphical information displayed below, is the property of SoundStage!. Reproduction in any format is not permitted.

• Measurements were made with 120V AC line voltage.
• Power output and distortion plotted with both channels driven.
• Test signal applied to unbalanced inputs unless otherwise noted.
• Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination: wideband 0.429mV, -76.4dBW; A weighted 0.108mV, -88.4dBW.
• Output noise, 8-ohm load, balanced input, 600-ohm input termination: wideband 0.239mV, -81.5dBW; A weighted 0.113mV, -88.0dBW.
• AC line current draw at idle: 3.7A cold, 1.8A warmed up.
• Output impedance at 50Hz: 0.052 ohms.
• This amplifier does not invert polarity.

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 142W
  
  
• 4-ohm load at 1% THD: 246W

General

The Coda Model 12 is a high-power solid-state design with very low output impedance and a relatively high output-stage idling current. As far as the front-panel designation of "Class A," this is most decidedly not the case. A true classic standard definition class-A amplifier at this power level would draw some 10A off the AC line to be class A up to clipping with 8-ohm loads. Unusually, the low output impedance extends way up into the ultrasonic frequency measurement limit of my Audio Precision measurement system.

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 very low. The variation with the NHT dummy load would be about a neglible +/-0.05dB. Note that the curves track each other above the audio range, indicating the output impedance is low in this region also. Chart 2 illustrates how total harmonic distortion plus noise versus 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. Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. This amp is one of a very few in my experience that has the desirable characteristic of approximately constant amount of distortion versus frequency. Damping factor versus frequency is shown in Chart 4. Note how this is quite constant over the audio range. A spectrum of the harmonic distortion and noise residue is plotted in Chart 5. As seems to be the case with many amplifiers measured, this one has a rich series of AC-line-hum harmonics with some sidebands of these harmonics about the nulled fundamental frequency and the signal harmonics. Of note: the amount of signal harmonics are low and the higher-order products disappear rapidly.

Magenta line: open circuit
Red line: 8-ohm load
Blue line: 4-ohm 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
Red line: 2W
Magenta line: 20W
Blue line: 120W
Cyan line: 220W

Damping factor = output impedance divided into 8

1kHz signal at 10W into an 8-ohm load

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