SoundStage! Measurements - Esoteric C-03 Preamplifier (12/2008)

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December 2008

Esoteric C-03 Preamplifier: Measurements

All preamplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test preamplifiers 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.

Additional Data

Measurements were made at 120V AC line voltage and on the left channel unless otherwise noted.
This preamplifier does not invert polarity. It has selectable line-level gain: 12dB and unity gain.
AC-line current draw: 0.2A.
Input impedance at 1kHz, balanced/unbalanced inputs, unity/12dB gains
- Unity gain = 35k ohms.
- 12dB gain = 38k ohms
Output impedance at 1kHz
- Unbalanced output = 79 ohms.
- Balanced output = 158 ohms
Gain, volume at maximum, instrument loading
- Unity gain; range of gain, both channels, unbalanced and balanced I/O = 0.962X / -0.34dB > 0.977X / -0.2dB
- 12dB gain; range of gain, both channels, unbalanced and balanced I/O = 3.83X / 11.7dB > 3.88X / 11.8dB
IHF Sensitivity, input volts for standard IHF output of 0.5V, IHF loading, Lch/Rch
- Unity gain
  - Unbalanced I/O = 578.4mV / 515.8mV
  - Balanced I/O = 519.8mV / 517.2mV
- 12dB gain
  - Unbalanced I/O = 130.4mV / 129.8mV
  - Balanced I/O = 130.7mV / 130.4mV
Output noise versus bandwidth and volume-control position, wideband/A weighted in µV, input termination 1kHz, Lch | Rch
- Unity gain
  - Unbalanced I/O
    - Volume at maximum = 121µV / 11µV | 104µV / 11µV
    - Volume at -20dB & -90dB = 119µV / 8µV | 102µV / 8µV
    - Volume at minimum (mute) = 7µV / <1µV | 6µV / <1µV
  - Balanced I/O
    - Volume at maximum = 89µV / 19µV | 87µV / 18µV
    - Volume at -20dB & -90dB = 89µV / 17µV | 86µV / 17µV
    - Volume at minimum (mute) = 4µV / <1µV | 4µV / <1µV
- 12dB gain
  - Unbalanced I/O
    - Volume at maximum = 239µV / 43µV | 226µV / 45µV
    - Volume at -32dB & -90dB = 119µV / 8µV | 103µV / 8µV
    - Volume at minimum (mute) = 7µV / <1µV | 7µV / <1µV
  - Balanced I/O
    - Volume at maximum = 178µV / 44µV | 176µV / 44µV
    - Volume at -32dB & -90dB = 89µV / 17µV | 86µV / 17µV
    - Volume at minimum (mute) = 4µV / <1µV | 4µV / <1µV

Measurements Summary

General

The Esoteric C-03 line-level preamp is a elegantly crafted minimalist design utilizing discreet-device amplifier circuitry and a TI PGA2320 digitally controlled volume control. It has selectable line-level gain: 12dB and unity gain.

Chart 1A shows the frequency response in the unbalanced I/O mode with the volume control set for unity gain for 0.5V input with instrument and IHF loading. As set for unity gain, the volume is fully up. Chart 1B is for the balanced I/O mode of connection. There was no appreciable difference with the gain set for 12dB. The balanced I/O mode exhibits more roll-off at the frequency extremes. The bass roll-off is caused by the size of output coupling capacitors against the 10k ohms of the IHF load. Volume-control tracking, as usual when utilizing the PGA2320, was extremely close being with a tenth of a dB down to -70dB attenuation. Further, the high-frequency response was constant as a function of attenuation, a good measurement result.

Chart 3A shows how total harmonic distortion varies with input level and frequency for both IHF loading in the unbalanced I/O mode, and for either unity or 12dB gains. Chart 3B shows the same things for the balanced I/O mode. In both cases, there was little discernable difference with IHF or instrument loading.

A spectrum of the distortion and noise residual of a 1kHz test tone at 0.5V output with IHF loading is plotted in chart 4 for the unbalanced I/O mode. AC-line hum harmonics here are very low. A few of the lower-order odd harmonics are visible up from the noise level.

Chart 1 - Frequency Response

Chart 1A

Unbalanced I/O mode, instrument and IHF loading
Red = instrument loading
Magenta = IHF loading

Chart 1B

Balanced I/O mode, instrument and IHF loading
Red = instrument loading
Magenta = IHF loading

Chart 2 - Frequency Response as a Function of Volume Control Setting

N/A

Chart 3 - Distortion as a Function of Output Voltage and Frequency

Chart 3A

Unbalanced I/O mode
Red = 20Hz
Magenta - 1kHz
Blue = 20kHz

Chart 3B

Balanced I/O mode
Red = 20Hz
Magenta - 1kHz
Blue = 20kHz

Chart 4 - Distortion and Noise Spectrum

Unbalanced I/O

IHF loading
Red line = spectrum of 1kHz test-signal distortion and AC-line harmonics at 0.5V input and output at unity gain.

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