Monday, September 25, 2017

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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.

Notes: Measurements were made at 120V AC line voltage with both channels being driven (stereo mode). Measurements were made on the left channel unless otherwise noted. The Audio Precision AUX-0025 measurement filter was used unless otherwise noted.

Power output (stereo mode)

  • Power output at 1% THD+N: 63.6W @ 8 ohms, 106.7W @ 4 ohms
  • Power output at 10% THD+N: 84.7W @ 8 ohms, 137.8W @ 4 ohms

Power output (mono mode)

  • Power output at 1% THD+N: 231.3W @ 8 ohms, 366.7W @ 4 ohms
  • Power output at 10% THD+N: 289.0W @ 8 ohms, 476.0W @ 4 ohms

Additional data

  • This amplifier does not invert polarity.
  • AC-line current draw at idle: 0.17A, 0.42PF, 8.6W
  • Gain: output voltage divided by input voltage, 8-ohm load
    •      Stereo mode: 17.2X, 24.7dB
    •      Mono mode: 34.7X, 30.8dB
  • Input sensitivity for 1W output into 8 ohms
    •      Stereo mode: 164.4mV
    •      Mono mode: 81.5mV
  • Output impedance @ 50Hz
    •      Stereo mode: 0.012 ohm
    •      Mono mode: 0.027 ohm
  • Input impedance @ 1kHz
    •      Stereo mode, Lch/Rch: 8.2k ohms, 46.3k ohms
    •      Biwire mode, Lch/Rch: 8.2k ohms, 8.2k ohms
    •      Mono mode: 8.2k ohms
  • Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
    •      Wideband (no AUX-0025 filter): 1.08V/0.88V, -8.9dBW/-10.1dBW
    •      Wideband: 1.54mV/1.40mV, -65.3dBW/-66.1dBW
    •      A weighted: 0.058mV/0.072mV, -93.8dBW/-99.1dBW
  • Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
    •      Wideband (no AUX-0025 filter): 1.76V, -4.1dBW
    •      Wideband: 1.72mV, -64.3dBW
    •      A weighted: 0.086mV, -90.3dBW

Measurements summary

The Calyx Femti is a stereo power amplifier of moderate output that uses a bridgeable ICEpower 125ASX2 switching amp preceded by a custom input buffer and input-switching circuit board. The switching amp is the lowest-powered of the three available ICEpower models.

Because the Femti can be switched from stereo to bridged-mono mode, measurements were taken in both modes. In the accompanying charts, the suffix “A” denotes a measurement of bridged mode. In the third mode, biwiring, in which the two stereo channels are both fed the same input signal, is no different from the performance in stereo mode, except for a peculiarity of the input impedance (see data above).

Charts 1 and 1A show the frequency response of the Femti with varying loads. The amount of switching carrier noise in bridged mode prevented getting a good measurable response without the Audio Precision AUX-0025’s external filter, so to get compatible responses in the stereo and bridged modes, the filter was used in both cases. There is a bit more noticeable deviation of high-frequency response in bridged mode, with an earlier high-frequency rolloff and a bit more out-of-band high-frequency peaking.

Charts 2 and 2A illustrate how total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output load for 8- and 4-ohm loads.

THD+N as a function of frequency at several different power levels is plotted in Charts 3 and 3A. High-frequency distortion rise with increasing frequency is considerable, and there is also a rise in low-frequency distortion with power. As can be seen, the apparent noise floor is somewhat lower in bridged mode, as the amount of distortion is lower in the midband.

The Femti’s damping factor vs. frequency, shown in Chart 4, is of a value and nature typical of many solid-state amplifiers: high up to about 1-2kHz, then rolling off with rising frequency.

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal in stereo mode is plotted in Chart 5. The magnitudes of the AC-line harmonics are reasonably low, and the signal harmonics are low in amplitude. The 10W/4-ohm spectrum for the bridged mode (not shown) looked about the same as in Chart 5.

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

Chart 1

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

Chart 1A

Chart 1A

Mono mode
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 

Stereo mode
(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 2A

Chart 2A 

Mono mode
(Line up at 10W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Second line = 4-ohm THD+N
Third line = 8-ohm THD+N

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

Chart 3

Stereo mode
(4-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 20W
Cyan line = 70W
Green line = 100W

Chart 3A

Chart 3A

Mono mode
(4-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 50W
Cyan line = 200W
Green line = 400W

Chart 4 - Damping factor as a function of frequency

Chart 4

Stereo mode
Damping factor = output impedance divided into 8

Chart 4A

Chart 4A

Mono mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Chart 5

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

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