Link: reviewed by Philip Beaudette on *SoundStage! Hi-Fi* on November 15, 2023

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The Rotel Michi X5 Series 2 was conditioned for one hour at 1/8th full rated power (~43W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The X5 Series 2 offers a multitude of inputs, both digital and analog, line-level analog pre-amp outputs, subwoofer line-level outputs and two pairs of speaker-level outputs (for biwiring). There is also a ¼″ TRS headphone output on the front panel. For the purposes of these measurements, unless otherwise stated, the following inputs were evaluated: digital coaxial 1 (RCA), analog balanced (XLR), as well as RCA phono, configured both for moving-magnet (MM) and moving-coil (MC) inputs. Comparisons were made between unbalanced (RCA) and balanced (XLR) line-level inputs, and no differences were seen in terms of THD+N (FFTs for both can be seen in this report); however, the balanced input offers 3.84dB less gain than the unbalanced inputs. Bluetooth is also offered; however, our APx555 does not currently have a Bluetooth board.

Most measurements were made with a 2Vrms line-level, 0dBFS digital input, 5mVrms MM-level, and 0.5mVrms MC-level analog input. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 350W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, but with a lower input voltage to achieve the same 350W output.

Based on the accuracy and random results of the left/right volume channel matching (see table below), the X5 Series 2 volume control is likely digitally controlled but operating in the analog domain. The X5 Series 2 offers 96 volume steps. Between steps 1 and 5, step increases are 2dB, steps 6 to 18 are 1.5dB, 19 to 66 are 1 dB, 66 to 86 are 0.5dB, and volume settings 87 to 96 are 0.25dB.

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

1 | 0.06dB |

10 | 0.073dB |

30 | 0.064dB |

50 | 0.064dB |

70 | 0.011dB |

80 | 0.015dB |

90 | 0.017dB |

96 | 0.019dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Rotel for the Michi X5 Series 2 compared directly against our own. The published specifications are sourced from Rotel’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth is set at its maximum (DC to 1MHz), assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Amplifier rated output power into 8 ohms (1% THD+N, unweighted) | 350W | 400W |

Amplifier rated output power into 4 ohms (1% THD+N, unweighted) | 600W | 659W |

THD (1kHz, 10W, 8ohms) | <0.009% | <0.007% |

IMD (60Hz:7kHz, 4:1) | <0.03% | <0.023% |

Frequency response (line-level) | 10Hz-100kHz (0, -0.6dB) | 10Hz-100kHz (-0.7, -0.5dB) |

Frequency response (phono, MM) | 20Hz-20kHz (0, -0.2dB) | 20Hz-20kHz (-0.25, -0.07dB) |

Frequency response (digital, 24/96) | 20Hz-20kHz (0, ±0.4dB) | 20Hz-20kHz (-0.2, -0.2dB) |

Damping factor (20Hz-20kHz, 8 ohms) | 350 | 493 |

Channel separation (1kHz) | >65dB | >78dB |

Input sensitivity (line level, RCA, maximum volume for rated power) | 380mVrms | 0.934Vrms |

Input sensitivity (line level, XLR, maximum volume for rated power) | 580mVrms | 1.46Vrms |

Input sensitivity (phono, MM) | 5.7mVrms | 5.72mVrms |

Input sensitivity (phono, MC) | 570uVrms | 521uVrms |

Input impedance (line level, RCA) | 100k ohms | 108k ohms |

Input impedance (line level, XLR) | 100k ohms | 50.6k ohms |

Input impedance (phono, MM) | 47k ohms | 46.1k ohms |

Input impedance (phono, MC) | 100 ohms | 141 ohms |

Input overload (line level, RCA) | 12.5Vrms | 13Vrms |

Input overload (line level, XLR) | 12.5Vrms | 12.7Vrms |

Input overload (phono, 1kHz, MM) | 197mVrms | 200mVrms |

Input overload (phono, 1kHz, MC) | 19mVrms | 19mVrms |

Output impedance (preout) | 470 ohms | 454 ohms |

SNR (line-level, A-weighted, rated output power) | 102dB | 103dB |

SNR (phono MM, A-weighted, rated output power) | 80dB | 88dB |

SNR (digital 24/96, A-weighted, rated output power) | 102dB | 103.5dB |

Tone controls | ±10dB at 100Hz/10kHz | ±8dB at 100Hz/10kHz |

Our primary measurements revealed the following using the balanced line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 400W | 400W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 659W | 659W |

Maximum burst output power (IHF, 8 ohms) | 469.5W | 469.5W |

Maximum burst output power (IHF, 4 ohms) | 846.7W | 846.7W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -74.1dB | -87.4dB |

Damping factor | 501 | 493 |

Clipping no-load output voltage | 66.2Vrms | 66.2Vrms |

DC offset | <0.2mV | <-0.06mV |

Gain (pre-out, RCA line-level in) | 6.58dB | 6.57dB |

Gain (pre-out, XLR line-level in) | 2.74dB | 2.74dB |

Gain (maximum volume, RCA line-level in) | 35.1dB | 35.1dB |

Gain (maximum volume, XLR line-level in) | 31.2dB | 31.2dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-81dB | <-81dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-74dB | <-72dB |

Input impedance (line input, XLR) | 50.7k ohms | 50.6k ohms |

Input impedance (line input, RCA) | 108k ohms | 106k ohms |

Input sensitivity (maximum volume, RCA) | 0.934Vrms | 0.933Vrms |

Input sensitivity (maximum volume, XLR) | 1.46Vrms | 1.45Vrms |

Noise level (with signal, A-weighted) | <380uVrms | <350uVrms |

Noise level (with signal, 20Hz to 20kHz) | <570uVrms | <540uVrms |

Noise level (no signal, A-weighted, volume min) | <97uVrms | <51uVrms |

Noise level (no signal, 20Hz to 20kHz, volume min) | <110uVrms | <64uVrms |

Output impedance (pre-out) | 454 ohms | 453 ohms |

Output impedance (sub-out) | 201 ohms | 201 ohms |

Signal-to-noise ratio (350W, A-weighted, 2Vrms in) | 103.0dB | 103.1dB |

Signal-to-noise ratio (350W, 20Hz to 20kHz, 2Vrms in) | 100.6dB | 100.7dB |

Signal-to-noise ratio (350W, A-weighted, max volume) | 102.5dB | 102.6dB |

Dynamic range (350W, A-weighted, digital 24/96) | 104.3dB | 104.4dB |

Dynamic range (350W, A-weighted, digital 16/44.1) | 95.6dB | 95.4dB |

THD ratio (unweighted) | <0.0057% | <0.0070% |

THD ratio (unweighted, digital 24/96) | <0.0056% | <0.0070% |

THD ratio (unweighted, digital 16/44.1) | <0.0056% | <0.0070% |

THD+N ratio (A-weighted) | <0.0078% | <0.0089% |

THD+N ratio (A-weighted, digital 24/96) | <0.0083% | <0.0092% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.0085% | <0.0095% |

THD+N ratio (unweighted) | <0.0089% | <0.0094% |

Minimum observed line AC voltage | 119.6 VAC | 119.6 VAC |

For the continuous dynamic power test, the X5 Series 2 was able to sustain 700W into 4 ohms (3.6% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (70W) for five seconds, for five continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the sides of the X5 Series 2 were warm to the touch, but not enough to cause discomfort.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz sinewave at 5mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -60.5dB | -65.7dB |

DC offset | <-2.8mV | <-0.3mV |

Gain (default phono preamplifier) | 36.2dB | 36.2dB |

IMD ratio (18kHz and 19 kHz stimulus tones) | <-80dB | <-79dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-78dB | <-78dB |

Input impedance | 46.1k ohms | 46.6k ohms |

Input sensitivity | 5.72mVrms | 5.72mVrms |

Noise level (A-weighted) | <0.95mVrms | <0.91mVrms |

Noise level (unweighted) | <2.3mVrms | <2.1mVrms |

Overload margin (relative 5mVrms input, 1kHz) | 32dB | 32dB |

Signal-to-noise ratio (full rated power, A-weighted) | 88.0dB | 88.7dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 81.1dB | 82.6dB |

THD (unweighted) | <0.007% | <0.008% |

THD+N (A-weighted) | <0.013% | <0.013% |

THD+N (unweighted) | <0.027% | <0.025% |

Our primary measurements revealed the following using the phono-level input, MC configuration (unless specified, assume a 1kHz sinewave at 0.5mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -46.0dB | -62.3dB |

DC offset | <-6mV | <-6mV |

Gain (default phono preamplifier) | 64.9dB | 64.6dB |

IMD ratio (18kHz and 19 kHz stimulus tones) | <-72dB | <-72dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-70dB | <-70dB |

Input impedance | 141 ohms | 141 ohms |

Input sensitivity | 521uVrms | 552uVrms |

Noise level (with signal, A-weighted) | <10mVrms | <7.7mVrms |

Noise level (with signal, 20Hz to 20kHz) | <27mVrms | <20mVrms |

Overload margin (relative 0.5mVrms input, 1kHz) | 31.6dB | 31.6dB |

Signal-to-noise ratio (full rated power, A-weighted) | 67.2dB | 69.1dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 61.1dB | 61.2dB |

THD (unweighted) | <0.011% | <0.016% |

THD+N (A-weighted) | <0.11% | <0.08% |

THD+N (unweighted) | <0.29% | <0.22% |

Our primary measurements revealed the following using the balanced line-level inputs at the headphone output (unless specified, assume a 1kHz sinewave 2Vrms input, 2Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left and right channel |

Maximum gain | 20.55dB |

Maximum output power into 600 ohms (1% THD, unweighted) | 101mW |

Maximum output power into 300 ohms (1% THD, unweighted) | 138mW |

Maximum output power into 32 ohms (1% THD, unweighted) | 76mW |

Output impedance | 151 ohms |

Noise level (with signal, A-weighted) | <60uVrms |

Noise level (with signal, 20Hz to 20kHz) | <85uVrms |

Noise level (no signal, A-weighted, volume min) | <60uVrms |

Noise level (no signal, 20Hz to 20kHz, volume min) | <83uVrms |

Signal-to-noise ratio (A-weighted, 1% THD, 6.5Vrms out) | 99.5dB |

Signal-to-noise ratio (20Hz - 20kHz, 1% THD, 6.5Vrms out) | 97.0dB |

THD ratio (unweighted) | <0.00095% |

THD+N ratio (A-weighted) | <0.0033% |

THD+N ratio (unweighted) | <0.0048% |

**Frequency response (8-ohm loading, line-level input)**

In our measured frequency response (relative to 1kHz) plot above, the X5 Series 2 is nearly flat within the audioband (-0.2dB at 20Hz, -0.05dB at 20kHz). At the extremes the X5 Series 2 is -0.7dB at 10Hz, and -0.5dB at 100kHz. These data only half corroborate Rotel’s claim of 10Hz to 100kHz (0/-0.6dB). The X5 Series 2 can be considered a high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Phase response (8-ohm loading, line-level input)**

Above is the phase-response plot from 20Hz to 20kHz for the balanced line-level input, measured across the speakers outputs at 10W into 8 ohms. The X5 Series 2 does not invert polarity and exhibits, at worst, +20 degrees (at 20Hz) of phase shift within the audioband.

**Frequency response (treble/bass at minimum and maximum settings, 8-ohm loading, line-level input)**

Above are two frequency response plots (relative to 1kHz) for the balanced line-level input, measured at 10W (8-ohms) at the speaker outputs, with the treble/balance controls set at both minimum and maximum. They show that the X5 Series 2 will provide a maximum gain/cut of approximately 12dB at 20Hz, and a maximum gain/cut of approximately 9dB at 20kHz.

**Frequency response vs. input type (8-ohm loading, left channel only)**

The chart above shows the X5 Series 2’s frequency response (relative to 1kHz) as a function of input type. The green trace is the same (but limited to 80kHz) analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally pink is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same for all the digital sample rates, as well as the analog input: -0.25dB at 20Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering filtering around 22, 48, and 96kHz (half the respective sample rate). The 44.1kHz sampled input signal exhibits typical “brick-wall”-type behavior, with a -3dB point at 21kHz. The -3dB point for the 96kHz sampled data is at 46kHz, and 68kHz for the 192kHz sampled data.

**Frequency response (8-ohm loading, MM input)**

What is shown above is the moving-magnet (MM) phono stage’s deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision. No deviation would yield a flat line at 0dB. So the chart above shows the frequency response (relative to 1 kHz), which displays very small maximum deviations of about -0.25/-0.04dB (20Hz/20kHz) and +0.1dB (100Hz) from 20Hz to 20kHz.

**Frequency response (8-ohm loading, MC input)**

The chart above shows the frequency response for the phono input (MC configuration). We see essentially the same result as with the MM configuration, with the exception of the left channel deviating by +0.08dB at 4kHz.

**Phase response (MM and MC phono inputs)**

Above is the phase response plot from 20Hz to 20kHz for the MM phono input (MM and MC configurations behaved identically), measured across the speakers outputs at 10W into 8 ohms. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about +60 degrees at 20Hz and +40 degrees at 20kHz.

**Digital linearity (16/44.1 and 24/96 data)**

The chart above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outs of the X5 Series 2. For this test, the digital input was swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output was analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both digital input types performed similarly, approaching the ideal 0dB relative level at -100dBFS, then yielding perfect results to 0dBFS. At or near -120dBFS, both sample rates overshot by 3 to 5dB.

**Impulse response (24/48 data)**

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line level pre-outs of the X5 Series 2. We can see that the X5 Series 2 utilizes a reconstruction filter that favors no pre-ringing and significant post-ringing. Since the initial pulse/peak shows a negative voltage, it's likely that the digital input inverts polarity.

**J-Test (coaxial input)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the X5 Series 2. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24bit). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g.*, 250Hz, 750Hz, 1250Hz, etc). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial SPDIF X5 Series 2 input shows obvious peaks in the audioband from -95dBrA to -140dBrA. This is a poor J-Test result and an indication that the X5 Series 2’s DAC may be susceptible to jitter.

**J-Test (optical input)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the X5 Series 2. The results here are similar but slightly better than the coaxial input, with the highest peaks just below -100dBrA.

**J-Test (coaxial, 2kHz sinewave jitter at 10ns)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the X5 Series 2, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The results are very clear, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/-2kHz jitter signal) manifest at near -70dBrA. This is a clear indication that the DAC in the X5 Series 2 has poor jitter immunity. For this test, the optical input yielded effectively the same results.

**J-Test (coaxial, 2kHz sinewave jitter at 100ns)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the X5 s2, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are very clear, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/-2kHz jitter signal) manifest at near -50dBrA. This is further indication that the DAC in the X5 Series 2 has poor jitter immunity. For this test, the optical input yielded effectively the same results.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the X5 Series 2’s line-level output with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The steep roll-off around 20kHz in the white-noise spectrum shows that the X5 Series 2 uses a brick-wall-type reconstruction filter. There are no obvious aliased images within the audioband, with the exception of a small peak at -115dBrA at 15kHz. The primary aliasing signal at 25kHz is highly suppressed at -100dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -85 and -75dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the balanced analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Zoomed in, we can see a maximum deviation within the audioband of only about 0.15dB (at 20kHz) from 4 ohms to no load, and much less (0.05dB) within the flatter portion of the curve, which is an indication of a high damping factor, or low output impedance. The maximum variation in RMS level when a real speaker was about the same, deviating by about 0.04dB within the flat portion of the curve (100Hz to 5kHz), with the lowest RMS level, which would correspond to the lowest impedance point for the load, exhibited around 200Hz, and the highest RMS level, which would correspond to the highest impedance point for the load, at around 3-5kHz. The more significant deviations in RMS level between loads at 10kHz and 20kHz is an indication of a dip in damping factor in this frequency range. This can be seen in our damping factor graph (see last graph in the report).

**THD ratio (unweighted) vs. frequency vs. output power**

The graph above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the balanced line-level input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the full rated power of 350W. The power was varied using the volume control. The 10W and 1W data exhibited effectively the same THD values, and remained commendably flat with the entire audioband, between 0.006% and 0.01%. At the full rated power of 350W, THD values were remarkably close to the 1/10W data, ranging from 0.006% to 0.01% up to 10kHz, then up to 0.2% at 20kHz.

**THD ratio (unweighted) vs. frequency at 10W (phono input)**

The graph above shows THD ratio as a function of frequency plot for the phono input measured across an 8 ohms load at 10W. The MM configuration is shown in blue/red (left/right channels) and MC in purple/green (left/right channel). The input sweep was EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.02% (20Hz) down to just above and below 0.005% (1kHz to 10kHz). The MC THD values were higher, ranging from 0.3/0.2% (20Hz, left/right channel), down to 0.005% (2kHz, left channel). Between 1kHz and 3kHz, the left channel outperformed the right channel for the MC configuration by as much as 10dB.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the X5 Series 2 as a function of output power for the balanced line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data outperformed the 4-ohm data by about 5-6dB, and both data sets show fairly constant THD values across measured output power levels until the “knees” at just past 300W (8 ohms) and 500W (4 ohms). THD levels for the 8-ohm data are around 0.005-0.007%, and 0.01-0.015% for the 4-ohm data. The 1% THD mark for the 8-ohm data is at 400W, and 659W for the 4-ohm data.

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the X5 Series 2 as a function of output power for the balanced line-level-input for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Overall, THD+N values for the 8-ohm load before the “knee” ranged from around 0.1% (50mW) down to about 0.007%. The 4-ohm results were similar, but 2-4 dB worse.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)**

The chart above shows THD ratios measured at the output of the X5 Series 2 as a function of load (8/4/2 ohms) for a constant input voltage that yields 40W at the output into 8 ohms (and roughly 80W into 4 ohms, and 160W into 2 ohms) for the balanced line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing levels of THD from 8 to 4 to 2 ohms, with about a 5dB increase between each halving of the load, but nearly 20dB difference at 20kHz between the 8- and 2-ohm data. Overall, even with a 2-ohm load at roughly 160W, THD values ranged from as low as 0.02% through most of the audioband to 0.07% at 20kHz.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows THD ratios measured at the output of the X5 Series 2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Generally, THD ratios into the real speakers were similar to the resistive dummy load, which hovered between 0.01 and 0.005%. THD ratios were higher (5-10dB) at 20Hz for the two-way speaker and at 20kHz for the three-way speaker, but also lower (5-10dB) than the resistive load between 800Hz and 6kHz. This is a strong result, and shows that the X5 Series 2 will yield consistently low THD results into real-world speaker loads.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the X5 Series 2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Generally, THD ratios into the real spakers were similar to the resistive dummy load, which hovered around 0.005%. At lower frequencies, both speakers yielded lower IMD results (0.002-0.003%), and at higher frequencies, the 3-way speaker yielded higher IMD results than the resistive load, 0.01% at 20kHz.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows IMD ratios measured at the output of the X5 Series 2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are similar enough to be judged identical, hovering around 0.02%.

**FFT spectrum – 1kHz (XLR line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the balanced line-level input. We see that the signal’s second harmonic, at 2kHz, is at -85dBrA or 0.005%, and around -100dBrA, or 0.001%, at the fourth (4kHz). The sixth (6kHz) and eighth (8kHz) harmonics follow at -110 and -120dBrA, or 0.0003 and 0.0001%. Below 1kHz, we see peaks from power-supply noise artifacts at 60Hz (around -100dBrA or 0.001%), and then the odd harmonics (180Hz, 300Hz, 420Hz) dominating at between -90dBrA, or 0.003%, and -100dBrA, or 0.001%.

**FFT spectrum – 1kHz (RCA line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the unbalanced line-level input. We see effectively the same results as with the XLR balanced input FFT above.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. We see effectively the same results as with the analog balanced input FFT above.

**FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. We see essentially the same signal and noise harmonic profile within the audioband as with the 16/44.1 sampled input.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, along with the 60Hz power-supply peak (-110dBrA) with a multitude of subsequent harmonics at and below -95dBrA.

**FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, along with the 60Hz power-supply peak (-110dBrA) with a multitude of subsequent harmonics at and below -95dBrA.

**FFT spectrum – 1kHz (MM phono input)**

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MM. We see the signal harmonic profile is similar to the line-level balanced input, with the second harmonic dominating at -85dBrA, or 0.005%. The noise-related peaks are at and below the -80dBrA level, or 0.01%.

**FFT spectrum – 1kHz (MC phono input)**

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MC. The main signal harmonic is again the second harmonic (2 kHz) at around -80dBrA or 0.01%. What dominates the FFT are the noise peaks, which is due to the very high gain required for an MC cartridge, and are as high as almost -55dBrA, or around 0.2% at 60, 180, and 300Hz.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the balanced line-level input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are that of the signal’s second (100Hz) harmonic at -85dBrA, or 0.005%, and the fifth power-supply noise harmonic (300Hz) at -90dBrA, or 0.003%.

**FFT spectrum – 50Hz (MM phono input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input configured for MM. The most predominant (non-signal) peaks are that of the signal’s second (100Hz) harmonic at -85dBrA, or 0.005%, and the primary (60Hz), third (180Hz), and fifth (300Hz) power-supply noise harmonics at nearly the same level.

**FFT spectrum – 50Hz (MC phono input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input configured for MC. The most predominant (non-signal) peaks are the primary (60Hz), third (180Hz), and fifth (300Hz) power-supply noise harmonics at around -60dBrA, or 0.1%. The second (2kHz) signal harmonic is just below -80dBrA, or 0.01%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8 ohm load at 10W for the balanced line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90dBRA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are lower, at -100dBrA, or 0.001%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90dBRA, or about 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -105dBrA.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90dBRA, or about 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MM. Here we find close to the same result as with the balanced line-level analog input. The second order 1kHz peak is at -90dBrA, or 0.003%, while the third-order peaks are at -100dBrA, or 0.001%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MC phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MC. The second order 1kHz peak is at -80dBrA, or 0.01%, while the third-order peaks are at -100dBrA, or 0.001%.

**Intermodulation distortion FFT (line-level input, APx 32 tone)**

Shown above is the FFT of the speaker-level output of the X5 Series 2 with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—*i.e.*, the “grass” between the test tones—are distortion products from the amplifier and below the -110dBrA, or 0.0003%, level. The peaks at lower frequencies that reach the -90dBrA level are not IMD products but power-supply-related noise peaks.

**Square-wave response (10kHz)**

Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the X5 Series 2’s slew-rate performance. Rather, it should be seen as a qualitative representation its extended bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. The X5 Series 2’s reproduction of the 10kHz square wave is very clean, with only very mild softening in the edges.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels show a relatively steady decline in damping factors from low to high frequencies, and track very closely to one another. From 20Hz to 2kHz, damping factors ranged from 600 to just shy of 500, then a decline to 125 at 20kHz. These are strong damping factor results.

*Diego Estan*

Electronics Measurement Specialist