Details

Parent Category: Products

Category: Amplifier Measurements

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

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

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

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

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

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

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

Stereo mode
Damping factor = output impedance divided into 8

Chart 4A

Mono mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

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

Details

Parent Category: Products

Category: Amplifier Measurements

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.

Note: Measurements were made at 120V AC line voltage and through the balanced input and with the 0dB gain switch position unless otherwise noted. All measurements made with Audio Precision AUX-0025 filter (AP filter) except where noted.

Power output with 120VAC

• Output power at 1% THD+N: 1130W @ 8 ohms, 2120W @ 4 ohms
• Output power at 10% THD+N: 1430W @ 8 ohms, 2210W @ 4 ohms

Power output with 240VAC

• Output power at 1% THD+N: 1130W @ 8 ohms, 2160W @ 4 ohms
• Output power at 10% THD+N: 1430W @ 8 ohms, 2850W @ 4 ohms

Additional data

• This amplifier does not invert polarity (XLR or RCA input).
• AC-line current draw at idle: 0.36A, 0.69PF, 29.8W
• Gain: output voltage divided by input voltage, 8-ohm load
  
  •      Unbalanced inputs: 28.5X, 29.1dB
  •      Balanced inputs: 27.7X, 28.4dB
• Input sensitivity for 1W output into 8 ohms
  •      Unbalanced inputs: 91.0mV
  •      Balanced inputs: 102.0mV
• Output impedance @ 50Hz: 0.0079 ohm
• Input impedance @ 1kHz
  •      Unbalanced inputs: 8.9k ohms
  •      Balanced inputs: 12.0k ohms
Output noise, 8-ohm load, unbalanced or balanced inputs (termination 1k ohm for unbalanced, 600 ohms for balanced)
•      Without Audio Precision AUX-0025 filter, wideband: 1.025V, -9.92dBW
•      With Audio Precision AUX-0025 filter, wideband: 1.93mv, -63.3dBW
•      With Audio Precision AUX-0025 filter, A weighted: 0.128mV, -83.4dBW

Measurements summary

The Anthem Statement M1 is a high-powered, solid-state, mono power amplifier designed in-house by Anthem.

Chart 1 shows the M1’s frequency response with varying loads. As can be seen, the high-frequency response is little affected by load. Without the Audio Precision filter, the -3dB point rose from about 38 to 48kHz. The output impedance is so low that the response with the NHT dummy speaker load didn’t show up at the chart resolution used.

Chart 2 illustrates how the M1’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE IM test signals and amplifier output load for 8- and 4-ohm loads. These data were taken with the normal 120V AC input. Since the M1 can also accept 240V, I also checked its THD+N vs. power output at that voltage. This is plotted in Chart 2A, along with a curve for 2-ohm loading. The 8-ohm power into clipping was unchanged, while the 4-ohm power was increased a bit. The M1’s power output into 2 ohms reached nearly 3kW before the amp’s 10A circuit breaker popped. With that load, there’s no question that it would have popped earlier if fed 120V. Still, 3kW without clipping is prodigious output!

THD+N as a function of frequency at several different power levels is plotted in Chart 3. The rise in distortion with increasing frequency is quite pronounced at all power levels, the amount above 10kHz being reduced by the AP filter.

The M1’s damping factor vs. frequency, shown in Chart 4, is typical of most solid-state analog power amplifiers: high at low frequencies, and, in this case, beginning to decrease above about 200Hz.

A spectrum of the M1’s harmonic distortion and noise when fed a 10W, 1kHz test signal is plotted in Chart 5. The magnitudes of the AC line harmonics are very low here, and the signal harmonics are predominantly second and third, with a number of higher harmonics at lower amplitudes.

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

Chart 2 - Distortion as a function of power output and output loading (120VAC)

(Line up at 10W 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 - Distortion as a function of power output and output loading (240VAC)

(Line up at 10W to determine lines)
Top line = 2-ohm THD+N
Second 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 = 10W
Magenta line = 30W
Blue line = 200W
Cyan line = 500W
Green line = 900W

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 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

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 through the balanced input 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: 133.7W @ 8 ohms, 212.2W @ 4 ohms
• Power output at 10% THD+N: 165.0W @ 8 ohms, 267.7W @ 4 ohms

Power output (mono mode)

• Power output at 1% THD+N: 477.7W @ 8 ohms, 687.9W @ 4 ohms
• Power output at 10% THD+N: 610.0W @ 8 ohms, 900.0W @ 4 ohms

Additional data

• This amplifier does not invert polarity.
• AC-line current draw at idle: 0.29A, 0.52PF, 17.7W
• Gain (stereo mode): output voltage divided by input voltage, 8-ohm load
  •      Unbalanced inputs: 26.5X, 28.5dB
  •      Balanced inputs: 13.1X, 22.4dB
• Gain (mono mode): output voltage divided by input voltage, 8-ohm load
  •      Unbalanced inputs: 52.6X, 34.4dB
  •      Balanced inputs: 26.2X, 28.4dB
• Input sensitivity (stereo mode) for 1W output into 8 ohms
  •      Unbalanced inputs: 107.0mV
  •      Balanced inputs: 216.0mV
• Input sensitivity (mono mode) for 1W output into 8 ohms
  •      Unbalanced inputs: 54.0mV
  •      Balanced inputs: 108.0mV
• Output impedance @ 50Hz
  •      Stereo mode: 0.026 ohm
  •      Mono mode: 0.032 ohm
• Input impedance @ 1kHz (stereo and mono modes)
  
  •      Unbalanced and balanced inputs: >700k ohms
• Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
  
  •      Wideband (no AUX-0025 filter): 1.08V/1.10V, -8.4dBW/-8.2dBW
  •      Wideband: 1.5mV/1.25mV, -65.5BW/-67.1dBW
  •      A weighted: 0.22mV/0.23mV, -82.2dBW/-83.0dBW
• Output noise (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
  
  •      Wideband (no AUX-0025 filter): 1.08V/1.09V, -8.4dBW/-8.3dBW
  •      Wideband: 1.48mV/1.23mV, -65.6dBW/-67.2dBW
  •      A weighted: 0.22mV/0.22mV, -82.2dBW/-82.2dBW
• Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
  
  •      Wideband (no AUX-0025 filter): 1.56V, -5.2dBW
  •      Wideband: 1.68mV, -64.5dBW
  •      A weighted: 0.14mV, -86.1dBW
• Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms
  
  •      Wideband (no AUX-0025 filter): 1.76V, -4.1dBW
  •      Wideband: 1.72mV, -64.3dBW
  •      A weighted: 0.11mV, -88.2dBW

Measurements summary

The Eximus S1 is a moderately powerful amplifier that uses a custom input buffer and input-switching circuit board, followed by a bridgeable ICEpower 250ASX2 switching amplifier.

Because the S1 can be switched between stereo and bridged-mono operation, measurements were taken of its performance in both modes. In each of the charts of the measurements, the suffix “A” indicates the mono-mode measurements.

Charts 1 and 1A show the frequency response of the S1 with varying loads. The amount of switching carrier noise in mono mode prevented getting a good measurable response without the Audio Precision AUX-0025 external filter, so the filter was used in both cases to provide comparable responses for stereo and mono operation. There is a bit more noticeable deviation of high-frequency response in mono mode, but of more interest is the rise in the low-frequency response. Apparently, the designers felt this would give more weight to the S1’s low-end sound.

Charts 2 and 2A illustrate how the S1’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation (IM) test signals and amplifier output load for 8- and 4-ohm loads. Testing into a 4-ohm load in mono mode caused the AC line fuse to blow. I was able to get a reading of THD+N once before the fuse blew, but couldn’t measure the SMPTE IM distortion because this test takes longer to run; the fuse blew before the test could be completed.

THD+N as a function of frequency at several different power levels is plotted in Charts 3 and 3A. High-frequency distortion rises considerably with increasing frequency; to keep the S1 from shutting down, the high-frequency limit was lowered to 6kHz at higher power levels.

The S1’s damping factor vs. frequency, shown in Charts 4 and 4A, is of a value and nature typical of many solid-state amplifiers: high up to about 1-2kHz, then rolling off with frequency.

A spectrum of the S1’s harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Charts 5 and 5A. The magnitude of the AC-line harmonics is relatively low, with some 60Hz showing in stereo mode but not in mono mode, the latter probably due to cancellation. The signal harmonics are low in amplitude and noticeably simpler, with a cleaner baseline, in mono mode.

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

Stereo mode
Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 1A

Mono mode
Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 2 - Distortion as a function of power output and output loading

Stereo mode
(Line up at 10W 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

Mono mode
(Line up at 10W to determine lines)
Top 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

Stereo mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 60W
Cyan line = 100W

Chart 3A

Mono mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 100W
Cyan line = 300W
Green line = 400W

Chart 4 - Damping factor as a function of frequency

Stereo mode
Damping factor = output impedance divided into 8

Chart 4A

Mono mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

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

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

Details

Parent Category: Products

Category: Amplifier Measurements

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.

Note: Measurements were made at 120V AC line voltage with both channels being driven. Measurements made on left channel through the balanced inputs and 8-ohm outputs unless otherwise noted.

Power output

• Output power at 1% THD+N: 26.0W @ 8 ohms, 15.0W @ 4 ohms
• Output power at 10% THD+N: 40.0W @ 8 ohms, 32.0W @ 4 ohms

Additional data

• This amplifier does not invert polarity.
• AC-line current draw at idle: 1.42A, 0.89PF, 151W
• Gain: output voltage divided by input voltage, volume at maximum, Lch/Rch: 18.61X, 25.4dB:
  •      Balanced inputs: 39.75X, 32.0dB / 40.31X, 32.1dB
  •      Unbalanced inputs: 50.32X, 34.0dB / 52.18X, 34.4dB
• Input sensitivity for 1W output into 8 ohms, volume at maximum, Lch/Rch:
  •      Balanced inputs: 0.071mV / 0.70mV
  •      Unbalanced inputs: 0.56mV / 0.54mV
• Output impedance @ 50Hz: 2.15 ohms
• Input impedance @ 1kHz: 50k ohms
• Output noise, 8-ohm load, balanced inputs, termination 600 ohms, Lch/Rch
  •      Volume control at reference position
              Wideband: 0.89 mV, -70.0dBW / 4.88mV, -55.3dBW
              A weighted: 0.21 mV, -82.6dBW / 0.70 mV, -72.1dBW
  •      Volume control full clockwise
              Wideband: 1.11mV, -68.2dBW / 5.08mV, -54.9dBW
              A weighted: 0.28mV, -80.1dBW / 0.71mV, -72.0dBW
  •      Volume control full counterclockwise
              Wideband: 0.89mV, -70.0dBW / 4.89 mV, -55.2 dBW
              A weighted: 0.18mV, -83.9dBW / 0.68 mV, -72.4 dBW
• Output noise, 8-ohm load, unbalanced inputs, termination 1k ohm, Lch/Rch
  •      Volume control at reference position
              Wideband: 1.12mV, -68.1dBW / 5.09mV, -54.9dBW
              A weighted: 0.20mV, -83.0dBW / 0.74mV, -71.6dBW
  •      Volume control full clockwise
              Wideband: 1.59mV, -65.0dBW / 4.97mV, -55.1dBW
              A weighted: 0.25mV, -81.1dBW / 0.73mV, -71.8dBW
  •      Volume control full counterclockwise
              Wideband: 0.95mV, -69.5dBW / 5.32mV, -54.5dBW
              A weighted: 0.19 mV, -83.5 dBW / 0.72 mV, -71.9 dBW

Measurements summary

The JE Audio VS70.1 is a medium-power tubed power amplifier with a front-panel volume control. Its overall gain is 6-7dB over the "nominal" power gain of 26dB. However, the extra gain would be useful for low-output CDs, such as Reference Recordings’ HRx discs.

Chart 1 shows the VS70.1’s frequency response with varying loads. This was made at the usual 1W/8-ohm level, with the volume control turned fully clockwise. The frequency-response variation with the NHT dummy load is of the order of ±1.5dB. The high-frequency rolloff is nicely controlled in that its shape is quite independent of load.

With the reference condition set up for measuring integrated amplifiers -- i.e., volume control set for 5W output into 8 ohms for 500mV input -- another response was run, and is shown in Chart 1A. Here we see that the HF response is a little more extended, and the very low-frequency level is starting to roll off because of output-transformer limitations. Channel tracking as a function of volume-control position down from this reference condition was generally within ±1dB down to 50dB of attenuation, below which hum, noise, and capacitive coupling altered the response and the channel separation.

Chart 2 illustrates how total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. It is apparent that the power is maximized for the 8-ohm load, whereas the power for a 4-ohm load is lower at higher distortion. Further, the amounts of intermodulation distortion are rather excessive at the higher power levels.

Chart 3 plots THD+N as a function of frequency for 8-ohm loading at several different power levels. The rise in distortion at higher frequencies is reasonably low. Because of output-transformer characteristics, low-frequency distortion gets progressively worse as the bass frequency rises and the power level increases.

The VS70.1’s damping factor vs. frequency (Chart 4) is fairly low, but not unusually so for a tubed power amplifier. What is good is that it is quite flat with frequency.

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal into 8 ohms is plotted in Chart 5. The magnitudes of the AC-line harmonics are quite high and complex, as are the signal harmonics. Intermodulation components of line harmonics with signal harmonics are numerous, and can be seen at the baseline of the signal harmonics.

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

(Volume control fully clockwise)
Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load
Cyan line = NHT dummy load

Chart 1A (Additional Measurement) - Frequency response with volume control at reference position (8-ohm load)

Red line = left channel
Blue line = right channel

Chart 2 - Distortion as a function of power output and output loading

(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 = 5W
Blue line = 15W
Cyan line = 30W
Green line = 35W

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 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

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.

Note: Measurements were made at 120V AC line voltage with both channels being driven. Measurements made on left channel through the balanced inputs unless otherwise noted.

Power output

• Output power at 1% THD+N: 224.8W @ 8 ohms, 372.2W @ 4 ohms
• Output power at 10% THD+N (est., see text): 250W @ 8 ohms, 400W @ 4 ohms

Additional data

• This amplifier does not invert polarity.
• AC-line current draw at idle: 1.52A, 0.75PF, 137W
• AC-line current draw at standby: 0.4A, 0.77PF, 37W
• Gain: output voltage divided by input voltage for balanced inputs: 18.61X, 25.4dB 
• Input sensitivity for 1W output into 8 ohms, balanced inputs: 152.0mV
• Output impedance @ 50Hz: 0.15 ohm
• Input impedance @ 1kHz: 1M ohm
• Output noise, 8-ohm load, balanced inputs, termination 600 ohms, Lch/Rch
  •      Wideband: 0.369mV/0.363mV, -77.7 dBW/-77.8dBW
  •      A weighted: 0.078mV/0.076mV, -91.2dBW/-91.4dBW

Measurements summary

The VX-R, one of Ayre Acoustics’ newest models, is a medium-power solid-state stereo power amplifier. Though of relatively small size, this dual-mono design, milled from a solid block of aluminum, is one heavy beast of an amp: It weighs almost 80 pounds.

Chart 1 shows the VX-R’s frequency response with varying loads. The high-frequency response is quite wide, with an approximate 3dB down point in excess of 200kHz.

The frequency response varies a small amount with load; therefore, the VX-R’s output impedance is reasonably low. The effect of the NHT dummy load is hard to see at the resolution at which this chart is usually shown; it amounts to a frequency-response deviation of about ±0.2dB.

Chart 2A illustrates how the VX-R’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals and amplifier output for 8- and 4-ohm loads. The protection fuses in the “front end” of the VX-R blew repeatedly when I attempted to drive it to 10% THD+N, so the values listed in the Additional Data are estimates. The amount of distortion is reasonable for what is claimed to be a no-overall-feedback design.

Chart 3 plots the THD+N as a function of frequency at several different power levels. The amount of increase in distortion at high frequencies is admirably low up to 150W. Attempts to get data at the 200W level blew the front-end fuses.

The VX-R’s plot of damping factor vs. frequency (Chart 4) is unusually flat. I have seen only a few amps with this characteristic. This usually goes along with flat distortion amount with changing frequency, as is the case with this design.

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Chart 5. The magnitudes of the AC-line harmonics are very low, and the signal harmonics are predominantly the second and third; all higher harmonics are an order of magnitude lower.

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 load

Chart 2 - Distortion as a function of power output and output loading

(Line up at 10W 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 = 70W
Cyan line = 150W

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 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

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. Measurements were made on the left channel through the balanced input unless otherwise noted. The Audio Precision AUX-0025 measurement filter was used unless otherwise noted.

Power output

• Power output at 1% THD+N: 187.5W @ 8 ohms, 348.8W @ 4 ohms
• Power output at 10% THD+N: 272.7W @ 8 ohms, 448.8W @ 4 ohms

Additional data

• This amplifier does not invert polarity.
• AC-line current draw at idle: 0.14A, 0.63PF, 10.0W
• AC-line current draw in operation: 0.59A, 0.67PF, 48.8W
• Gain: output voltage divided by input voltage, 8-ohm load
  •      Unbalanced inputs: 39.5X, 31.9dB
  •      Balanced inputs: 39.5X, 31.9dB
• Input sensitivity for 1W output into 8 ohms
  •      Unbalanced inputs: 71.6mV
  •      Balanced inputs: 71.6mV
• Output impedance @ 50Hz: 0.018 ohm
• Input impedance @ 1kHz
  •      Unbalanced inputs: 135k ohms
  •      Balanced inputs: 135k ohms
• Output noise, 8-ohm load, balanced inputs terminated with 600 ohms and unbalanced inputs terminated with 1k ohms, without AUX-0025 filter, Lch/Rch
  
  •      Wideband: 471mV/477mV, -15.6dBW/-15.5dBW
• Output noise, 8-ohm load, balanced inputs terminated with 600 ohms and unbalanced inputs terminated with 1k ohms, with AUX-0025 filter, Lch/Rch
  
  •      Wideband: 0.87mV/0.91mV, -70.2dBW/-69.9dBW
  •      A weighted: 0.29mV/0.34mV, -79.8dBW/-78.4dBW

Measurements summary

The Rogue Audio Medusa is a high-power hybrid stereo power amplifier with a vacuum-tubed front end coupled to a pair of Hypex switching-amplifier modules.

Chart 1 shows the Medusa’s frequency response with varying loads. The amp’s high-frequency response is rolled off before the cutoff frequency of the Audio Precision AUX-0025 measuring filter used for measuring switching amplifiers. As a result, the high-frequency response remained virtually unchanged, regardless of whether or not it was sent through the filter. The -3dB point is about 26kHz. Further, the -3dB down point at 26kHz is independent of load -- a feature of the Hypex modules.

As can be seen, the Medusa’s output impedance is so low that the variations with the NHT dummy speaker load don’t show up on the response plot.

Chart 2 illustrates how the Medusa’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load for loads of 8 and 4 ohms. The amount of distortion, and how it rises with output level, are similar to those of tube power amplifiers, and are no doubt caused by the Medusa’s tubed front end.

THD+N as a function of frequency at several different power levels is plotted in Chart 3. The degree of increase in distortion at high frequencies is admirably low.

Damping factor vs. frequency, shown in Chart 4, is of a value and nature typical of many solid-state amplifiers: high up to about 1kHz, then rolling off with increasing frequency.

Chart 5 plots the spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal. The magnitude of the AC line harmonics is relatively complex, with 120Hz being the dominant one. Not surprisingly, the dominant signal harmonic is the second, coming from the tube circuitry. All higher harmonics quickly disappear into the noise level.

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

Chart 2 - Distortion as a function of power output and output loading

(Line up at 100W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 4-ohm SMPTE IM distortion
Third line = 8-ohm THD+N
Bottom line = 4-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 = 70W
Cyan line = 200W

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 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

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.

Note: Measurements were made at 120V AC line voltage and through the balanced input unless otherwise noted.

Power output

• Output power at 1% THD+N: 355.2W @ 8 ohms, 520.7W @ 4 ohms
• Output power at 10% THD+N: 447.2W @ 8 ohms, 663.1W @ 4 ohms

Additional data

• This amplifier does not invert polarity.
• AC-line current draw at idle: 1.39A, 0.64PF, 105W
• Gain: output voltage divided by input voltage, 8-ohm load
  
  •      Unbalanced inputs: 31.4X, 29.9dB
  •      Balanced inputs: 30.4X, 29.7dB
• Input sensitivity for 1W output into 8 ohms
  •      Unbalanced inputs: 91.1mV
  •      Balanced inputs: 93.0mV
• Output impedance @ 50Hz: 0.026 ohm
• Input impedance @ 1kHz
  •      Unbalanced inputs: 10.8k ohms
  •      Balanced inputs: 50.5k ohms
• Output noise, 8-ohm load, unbalanced inputs, termination 1k ohm
  •      Wideband: 0.175mV, -84.2dBW
  •      A weighted: 0.042mV, -96.6dBW
• Output noise, 8-ohm load, balanced inputs, termination 600 ohms
  •      Wideband: 0.991mV, -69.1dBW
  •      A weighted: 0.188mV, -83.6dBW

Measurements summary

The Jones Audio PA-M300 Series 2 is a high-powered, solid-state, monoblock power amplifier.

Chart 1 shows the frequency response of the PA-M300 with varying loads. The response is quite wideband, with a -3dB point of over 200kHz. Although the NHT dummy load shows no appreciable variation in the audioband, it does have some visible effect above 50kHz.

Chart 2 illustrates how total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals and amplifier output for 8- and 4-ohm loads. The amount of distortion and how it rises with output level is typical of most solid-state power amplifiers, except that the IM distortion is not materially higher than the harmonic distortion. Also of note: The low-power THD+N with the unbalanced input (not shown) is quite a bit lower due to that input’s lower noise.

Chart 3 plots THD+N as a function of frequency at several different power levels. The amount of increase in distortion at high frequencies is very pronounced as the power level rises.

Damping factor vs. frequency, shown in Chart 4, is of a value and nature typical of many solid-state amplifiers: high up to about 1kHz, then rolling off with increasing frequency.

Chart 5 plots the spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal. The magnitude of the AC-line harmonics is relatively complex, with mostly odd harmonics of 60Hz extending way up into the midrange. Signal harmonics are low, with the second, third, and fifth harmonics being visible in the spectrum.

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

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

Chart 2 - Distortion as a function of power output and output loading

(Line up at 100W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 4-ohm THD+N
Third line = 8-ohm SMPTE IM distortion
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 = 150W
Cyan line = 300W

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 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

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.

Note: Measurements were made at 120V AC line voltage with both channels being driven. Measurements made on right channel digitally fed via the AES/EBU input at a 24/96 sample rate. Unless otherwise noted, the Audio Precision Aux 0025 external low-pass filter was used to keep high-frequency spuria from contaminating the Audio Precision SYS 2722 measuring instrument.

Power output

See "Additional data" section (these are manufacturer-supplied specs)

• Output power: 190W @ 8 ohms, 240W @ 6 ohms

Additional data

• This amplifier does not invert polarity through the digital or analog inputs.
• AC-line current draw at idle:
  •      Gain set +20 & 0, AES/EBU input, 96k Fs: 59W, 0.96PF, 0.5A
  •      Gain set -20 & below, AES/EBU input, 96k Fs: 30W, 0.94PF, 0.27A
• Gain: output voltage divided by input voltage, analog line input, gain set to 0dB: 13.0X, 22.3dB
• Input sensitivity:
  •      For 1W output into 8 ohms, analog line input, gain set to +30dB (max): 6.9mV
  •      For 1W output into 8 ohms, digital input, gain set to +30dB (max): -52.2 dBFS
• Output impedance @ 50Hz: 0.0024 ohm
• Input impedance @ 1kHz: 14.2k ohms
• Output noise, digital input, digital input level at 0, 8-ohm load, Lch/Rch:
  •      Gain at -30dB, wideband: 123/130uV, -87.2/-86.7dBW
  •      Gain at -30dB, A weighted: 40/40uV, -97.0/-97.0dBW
  •      Gain at 0dB, wideband: 137/143uV, -86.3/-85.9dBW
  •      Gain at 0dB, A weighted: 42/39uV, -96.6/-97.2dBW
  •      Gain at +30dB, wideband: 174/180uV, -94.2/-83.9dBW
  •      Gain at +30dB, A weighted: 74/71 uV, -91.6/-92.0dBW
• Output noise, analog input, input termination 1k ohm, 8-ohm load, Lch/Rch:
  •      Gain at -30dB, wideband: 124/118uV, -87.2/-87.6dBW
  •      Gain at -30dB, A weighted: 40/45uV, -97.0/-96.0dBW
  •      Gain at 0dB, wideband: 296/298uV, -79.6/-79.6dBW
  •      Gain at 0dB, A weighted: 154/160uV, -85.3/-85.0dBW
  •      Gain at +30dB, wideband (note: values in mV): 8.4/8.6mV, -50.5/-50.3dBW
  •      Gain at +30dB, A weighted (note: values in mV): 4.6/5.0mV, -55.8/-55.0dBW

Measurements summary

The Devialet D-Premier is unique -- a volume-controlled power DAC that accepts both digital and analog inputs. Its uniqueness is in how it generates its output, being a combination of a low-powered, class-A analog output stage and a digital-switching section. The class-A stage controls the output voltage, and the switching section adds the necessary current to supply the output power. Also of note is the power-factor-corrected power supply, which measures close to unity. This is a good thing, as it makes the incoming AC line current sinusoidal rather than the usual 120Hz, 2-3ms rectifier-charging pulses of conventional capacitor input power supplies. The result is less crap on one’s AC power line, and less messing up of the sound of the other connected gear.

This D-Premier is extremely well protected against various things that might damage it or the load. As a consequence, it was difficult, if not impossible, to produce curves of power output vs. distortion that went into clipping below loads of 8 ohms, as is usual with other, more conventional amps that have been measured. Therefore, the usual measured output powers at 1% and 10% distortion are not shown in the additional data. A Devialet publication, "Advanced Practical Information," indicates that the D-Premier’s short-term RMS power output is doubled each time the load is halved, to a maximum total power of 600Wpc.

Another observation was that the D-Premier’s distortion and noise floor was pretty much the same at the 192kHz sample rate, so we used a 96kHz sample rate for most of the measurements. The output noise, measured without the Aux-0025 filter, varied from 5 to 12mV over the gain range of ±30 for the digital and analog inputs.

Chart 1 shows the frequency response of the D-Premier with varying loads. The Devialet’s output impedance is so low that no difference can be seen at the scale we usually use in testing analog amplifiers. Also of great significance is that the D-Premier lacks an output low-pass filter, as is necessary in almost all other switching amplifiers; as a consequence, the high-frequency response is not load dependent -- an interesting plus among many of this design.

Chart 1A is a plot of the D-Premier’s frequency response as a function of the incoming sample rate, at 44.1, 96, and 192kHz. (Note: This plot is exactly what one sees for regular D/A converters used to decode signals from the digital outputs of CD transports and other digital sources to produce analog outputs.) The frequency response for analog inputs is similar to that shown in Chart 1, as the sampling rate for the analog input is also 96kHz. Not shown is the low-frequency response, which was flat to below 10Hz at all sample rates. The pulse and squarewave response shape, with its symmetrical ringing, is indicative of FIR filters being used. This plot is done without the Aux-0025 low-pass filter, to allow the full bandwidth of the D-Premier to be measured.

Chart 2 illustrates how the D-Premier’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load for 8- and 4-ohm loads. Amount of distortion is noise dominated up to perhaps 10-20W and then rises as distortion, per se, at higher power up to the power outputs shown on the chart. The amount of THD+N with the analog inputs was roughly twice as much. Looking at the D-Premier as a high-voltage-output D/A converter, I plotted the THD+N amplitude not as a percentage of reading, but as dB down from full scale as a function of decreasing input level below 0dBFS. I and others commonly do this to reveal any glitches in distortion level at various input levels, and also to easily illustrate the noise floor of the device when its input levels get way below where distortion, per se, occurs. This is shown in Chart 2A. A major aspect of this curve is that the noise floor is at about -115dBFS -- one of the lowest I have measured for a D/A converter over the years. However, the analog inputs were not so quiet, with a noise floor closer to -105dBFS.

Chart 3 shows the D-Premier’s THD+N as a function of frequency for 4-ohm loading at several different power levels. The apparent increase in distortion at high frequencies is reasonably low. Again, the Devialet’s protection circuitry prevented the taking of any measurements near the maximum amount of power the amp can deliver with music signals.

The damping factor vs. frequency, shown in Chart 4, is very high, and remains high to a far higher frequency than is typical of analog power amplifiers.

Chart 5 plots a spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal. The magnitude of the AC-line harmonics is relatively low, except for a prominent output at 120Hz. Signal harmonics are low in amplitude, the second, third, and fifth harmonics being the most significant.

I listened to this amplifier in my system quite a bit, and found it to be most revealing, clear, and musical. I wish I owned it!

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
(Note that the curves are so close together, it is not possible to see the different colors.)

Additional: Chart 1A

Red: 44.1kHz
Magenta: 96kHz
Blue: 192kHz

Chart 2 - Distortion as a function of power output and output loading

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

Additional: Chart 2A

THD+N vs. decreasing input level in dB down from full scale; 0 dBFS = 35.8V output

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

(4-ohm loading)
Red line = 2W
Magenta line = 20W
Blue line = 60W
Cyan line = 150W

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 a 4-ohm load