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, 8ohm load, unbalanced input, 1kohm input
termination: wideband 0.429mV, 76.4dBW; A weighted 0.108mV, 88.4dBW.
 Output noise, 8ohm load, balanced input, 600ohm 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
 8ohm load at 1% THD: 142W
 4ohm load at 1% THD: 246W
General
The Coda Model 12 is a highpower solidstate design with
very low output impedance and a relatively high outputstage idling current. As far as the
frontpanel designation of "Class A," this is most decidedly not the case. A
true classic standard definition classA amplifier at this power level would draw some 10A
off the AC line to be class A up to clipping with 8ohm 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, 8ohm, and 4ohm 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 4ohm 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
AClinehum 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 higherorder products disappear rapidly.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
Magenta line: open circuit
Red line: 8ohm load
Blue line: 4ohm load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
(line up at 10W to determine lines)
Top line: 4ohm SMPTE IM
Second line: 8ohm SMPTE IM
Third line: 4ohm THD+N
Bottom line: 8ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
4ohm output loading
Red line: 2W
Magenta line: 20W
Blue line: 120W
Cyan line: 220W
Chart 4  Damping Factor
as a Function of Frequency 
Damping factor = output impedance divided into 8
Chart 5  Distortion and
Noise Spectrum 
1kHz signal at 10W into an 8ohm load
