All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Unless otherwise noted, these measurements were taken at the left-channel unbalanced analog inputs of the Exogal Ion PowerDAC at 120V AC line voltage, both channels driven. I used the old IHF standard for integrated amplifiers, in which the volume control is set so that a 500mV analog input signal produces a nominal output of 5W into 8 ohms. Unless stated otherwise, I used Audio Precision’s Aux-0025 external filter.

Power output

  • Power output at 1% THD+N: 80.0W @ 8 ohms, >100.0W @ 4 ohms
  • Power output at 10% THD+N: 100.0W @ 8 ohms, >100.0W @ 4 ohms

Additional data

  • Input/output polarity
    • Analog input: inverting
    • Digital input: noninverting
  • AC-line current draw
    • Standby: 9.0W, 0.17A, 0.44PF
    • Operating: 25.0W, 0.31A, 0.68PF
  • Gain: output voltage divided by input voltage, 8-ohm load (Lch/Rch)
    • Unbalanced inputs: 36.70X, 37.7dB / 36.18X, 37.7dB
  • Input sensitivity for 1W output into 8 ohms (Lch/Rch)
    • Unbalanced inputs: 77.1mV / 78.3mV
  • Output impedance @ 50Hz: 0.065 ohm
  • Input impedance @ 1kHz
    • Unbalanced inputs: 1.87k ohms
  • Output noise at reference conditions, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
    • Wideband: 0.352mV/0.350mV, -78.1dBW/-78.2dBW
    • A weighted: 0.142mV/0.142mV, -86.0dBW/-86.0dBW
  • Output noise with volume at maxium, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
    • Wideband: 127.2mV/128.3V, -26.9dBW/-26.8dBW
    • A weighted: 1.95mV/1.89mV, -63.2dBW/-63.5dBW
  • Output noise with volume at minimum, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
    • Wideband: 0.352V/0.350V, -78.1dBW/-78.2dBW
    • A weighted: 0.142mV/0.142mV, -86.0dBW/-86.0dBW

Measurements summary

Exogal’s Ion PowerDAC is an unusual combination of a DAC and line stage (the Comet) coupled to a DAC and switching power amp (the Ion). I used the unbalanced analog inputs of the Comet to test the combination as an integrated amplifier.

It was difficult to measure some things on the Ion PowerDAC, including its maximum power and damping factor. The Exogal’s very sensitive protection circuit frequently shut it down, requiring a restart, and the damping factor was affected by some interference from the untested right channel.

Chart 1A shows the frequency response of the Ion PowerDAC with varying loads and with my usual vertical scale. The FR is strongly dependent on the load, as is typical of switching-amp designs. With resistive loading, the -3dB bandwidth for an 8-ohm load extends slightly higher than 20kHz; with a 4-ohm load, the bandwidth is 11-12kHz. Chart 1B shows the Exogal’s high-frequency response out to 30kHz: It rolls off pretty quickly and, with the open circuit loading, peaks at over +10dB. This will probably not be a problem with non-inductive tweeters, but with a typical moving-coil tweeter, the Ion PowerDAC may produce a high-frequency rise in the top octave of the audioband: 10-20kHz.

To test the tracking of the Exogal’s volume control, I used a 1kHz test tone; the reference volume was the 5W output with a 500mV input signal. The volume-control tracking was within a few tenths of a dB down to -60dB.

Chart 2 illustrates how the Ion PowerDAC’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE intermodulation (IM) test signals and amplifier output for 8- and 4-ohm loads. As mentioned above, it was not possible to get full distortion data because of the behavior of the Exogal’s protection circuit. The THD+N of the 1kHz test signal was pretty good, but the IM distortion was unusually high throughout the range I was able to measure.

The Ion PowerDAC’s THD+N as a function of frequency at different power levels is plotted in Chart 3. To reduce the out-of-band noise, I had to use the regular Audio Precision low-pass filter set to 30kHz instead of the usual 80kHz, and a 40kHz sharp cutoff filter to keep the distortion measurement uncontaminated by noise throughout most of the audioband. Any rise in high-frequency distortion is therefore masked above about 10kHz. At the 70W level, the amount of distortion rises precipitously below 100Hz and above about 15kHz.

It wasn’t possible to take my usual measurements of damping factor vs. frequency. What can be deduced from Chart 1A is that the damping factor is reasonably high at low frequencies, at around 123, and decreases rapidly above about 1kHz -- as can be seen in the divergence of the curves above that frequency.

Chart 5 plots the spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal sent through the Exogal. The magnitudes of the AC line harmonics are not visible in what is a relatively high level of background noise throughout the audioband. The signal harmonics are mainly the third, fifth, and seventh, with lower-level, higher-order harmonics above 10kHz.

Chart 1 - Frequency response of output voltage as a function of output loading



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


Chart 1B

Red line = open circuit
Magenta 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

Chart 2

(Line up at 20W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 4-ohm THD+N
Bottom line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency


(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 70W

Chart 5 - Distortion and noise spectrum

Chart 5

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