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Equipment Measurements

January 2006

Rogue Audio Metis 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, including graphical information displayed below, is 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.
  • Gain:
    • Line section, Lch/Rch = 4.62X, 13.3dB / 4.36X, 12.8dB
    • Phono section (at 1kHz) = 76X, 37.6dB
  • Output noise versus bandwidth and volume-control position, wideband/A weighted:
    • Volume control turned CCW, wideband, Lch/Rch = 0.23mV / 0.24mV
    • Volume control turned CCW, A weighted, Lch/Rch = 0.032mV / 0.060mV
    • Volume control at reference (unity gain), wideband, Lch/Rch = 0.24mV / 0.27mV
    • Volume control at reference (unity gain), A weighted, Lch/Rch = 0.037mV / 0.058mV
    • Volume control turned CW, wideband, Lch/Rch = 0.74mV / 0.75mV
    • Volume control turned CW, A weighted, Lch/Rch = 0.057mV / 0.058mV
  • Phono referred input noise, 1k-ohm source impedance:
    • Wideband, Lch/Rch = 11.4V / 3.0V
    • A weighted, Lch/Rch = 3.7V / 0.91V
  • AC line current draw at idle: 0.27A
  • Output impedance at 1kHz:
    • Line section = 720 ohms
    • Phono section (at fixed outputs) = 39 ohms
  • Input impedance at 1kHz:
    • Line section = 150k ohms
    • Phono section (paralleled with 150pF) = 47k ohms
  • Phono overload at 1kHz = 106mV
  • This preamplifier line section inverts polarity; the phono preamp section does not invert polarity.
Measurements Summary

General

The Rogue Audio Metis preamplifier utilizes two octal-based 6SN7 tubes in its line-section signal circuitry. The phono circuitry is implemented with a dual op-amp.

Chart 1 shows the frequency response of the Metis for both channels with the volume control set for unity gain and with instrument and IHF loading. With the IHF load, the high-frequency response is unaffected, but the low-frequency response starts to roll off due to the size of the output coupling capacitors and the relation to the 10k IHF loading. Generally, this preamp’s high-frequency response is at its worst at full volume and gets better as the volume is turned down.

At full gain with the volume fully up, Chart 2A shows the most high-frequency roll-off. With the volume control set at an attenuation of about –30dB, which is where the volume would likely be set for typical listening, the response is much flatter, as shown in chart 2B. Volume-control tracking between channels was within 0.8dB down to –60dB attenuation. Note that in chart 2B tracking between channels is particularly close.

Chart 3 shows how THD+N (total harmonic distortion plus noise) varies as a function of preamp output level. The volume control is set for unity gain. In this particular case, the curves were only a little different for the three test frequencies of 20Hz, 1kHz, and 20kHz, and for instrument and IHF loading. This is good for the distortion to be essentially independent of frequency and loading. The curve shown in Chart 3 is typical for the various frequencies and loading.

With the volume control again set for unity gain, a plot of the 1kHz distortion at 0.5V output is shown in Chart 4. Results for this test were about the same for instrument or IHF loading.

Because this preamp has no tone controls, there is no Chart 5 to display the tone-control characteristics.

RIAA equalization error for the phono preamp is plotted in Chart 6. The two channels differ above 1kHz, but the overall error is quite acceptable.

Phono THD+N versus output voltage and frequency is shown in Chart 7 for instrument loading. With the IHF load, instability set in between 2-3V, which prevented getting the curve data for that condition.

Chart 1 - Frequency Response at Unity Gain with IHF and Instrument Loading


IHF loading
Blue line = left channel
Cyan line = right channel

Instrument loading
Red line = left channel
Magenta line = right channel

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

Chart 2A - volume at maximum (0dB)

Instrument loading
Red line = left channel
Magenta line = right channel

Chart 2B - volume at -31dB

Instrument loading
Red line = left channel
Magenta line = right channel

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


Instrument loading

Red line = 20Hz, 1kHz, 20kHz

Chart 4 - Distortion and Noise Spectrum


Red line = spectrum of 1kHz test-signal distortion and AC-line harmonics at 0.5V input and output

Chart 6 - Phono-Stage RIAA Equalization Error


Instrument loading

Red line = left channel
Magenta line = right channel

Chart 7 - Phono-Stage Distortion vs. Frequency and Output


Instrument loading

Red line = 1kHz
Magenta line = 20Hz
Blue line = 20kHz

 

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