Rotel Michi X5 Integrated Amplifier-DAC Measurements

Link: reviewed by Roger Kanno on SoundStage! Hi-Fi on August 1, 2021

General Information

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

The Michi X5 was conditioned for 1 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 offers a multitude of inputs, both digital and analog, line-level analog preamp outputs, subwoofer line-level outputs, two pairs of speaker-level outputs (A and B), and a 1/8" TRS headphone output. For the purposes of these measurements, the following inputs were evaluated: digital coaxial 1 (RCA), optical 1 (TosLink), USB, analog balanced (XLR) and unbalanced (RCA) line-level, and moving-magnet (MM) as well as moving-coil (MC) phono. Comparisons were made between unbalanced (RCA) and balanced (XLR) line-level inputs, and no differences were seen in terms of THD+N; however, the balanced inputs offer 3.85dB less gain than the unbalanced inputs. Comparisons were made between digital coaxial, optical, and USB inputs, and no differences were seen in terms of THD+N. Bluetooth is also offered, but our APx555 does not currently have a Bluetooth board installed.

Most measurements, with the exception of signal-to-noise ratio (SNR) or otherwise stated, for the line-level analog inputs, were made with the volume set to unity gain (0dB) on the volume control (position 86 for the balanced XLR input, and 78 for single-ended RCA) with respect to the preamp outputs (which offers 6.6dB of gain with the unbalanced input, 2.75dB with the balanced input). At the unity-gain volume position, to achieve 10W into 8 ohms, 325mVrms was required at the balanced line-level input. For the digital inputs, a volume position of 55 yielded 10W into 8 ohms with a 0dBFS input. For the phono input, configured for MM, a volume position of 78 yielded 10W into 8 ohms with a 1kHz 5.1mVrms input. Configured for MC, a volume position of 78 yielded 10W into 8 ohms with a 1kHz 0.48mVrms input. The SNR and dynamic range measurements were made with the volume control set to maximum.

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

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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Rotel for the Michi X5 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 8ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst case measured result between the left and right channel.

Our primary measurements revealed the following using the balanced line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 325mVrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

For the continuous dynamic power test, the X5 was able to sustain 630W into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (63W) for 5 seconds, for 5 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 were quite warm to the touch, causing discomfort and pain after about 10 seconds.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz sinewave, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Our primary measurements revealed the following using the phono-level input, MC configuration (unless specified, assume a 1kHz sinewave, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Our primary measurements revealed the following using the balanced line-level inputs at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth):

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

In our measured frequency response plot above, the X5 is nearly flat within the audioband (20Hz to 20kHz). At the extremes the X5 is -0.5dB down at 10Hz and at 100kHz. These data only half corroborate Rotel’s claim of 10Hz to 100kHz (0/-0.6dB). The X5 can be considered a high-bandwidth audio device. In the chart above and most of the charts 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 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 for the balanced line-level input, measured at 10W (8-ohm) at the speaker outputs, with the treble and bass controls set at both minimum and maximum. They show that the X5 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’s frequency response as a function of input type. The green trace is the same analog input data from the previous graph. The blue trace is for a 16bit/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: -0.6dB at 20Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering filtering around 22kHz, 48kHz, and 96kHz (half the respective sample rate). The 44.1kHz sampled input signal does not exhibit the typical “brick-wall”-type behavior found in most DACs, with a -3dB point at 18kHz. The -3dB point for the 96kHz sampled data is at 38kHz, and 71kHz for the 192kHz sampled data.

Frequency response (8-ohm loading, MM and MC phono inputs)

The chart above shows the frequency responses for the MM and MC phono inputs. The responses represent deviations from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). The MC and MM inputs perform almost identically, and, as you can see, adhere very closely to the ideal RIAA curve. Both traces show very small maximum deviations of about -0.2/-0.15dB (20Hz/20kHz) and +0.1dB (100Hz) from 20Hz to 20kHz.

Phase response (MM and MC phono inputs)

Above is the phase response plot from 20Hz to 20kHz for the phono input for both the MM and MC configuration—they behaved identically—measured across the speaker 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 200Hz and 5kHz.

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 output of the X5. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is 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, the 16/44.1 data overshot by 4dB (left) and undershot by 2dB (right) the ideal output signal amplitude, while the left/right channels at 24/96 overshot by 2dB (left) and 1dB (right).

Impulse response (16/44.1 and 24/96 data)

The graph above shows the impulse responses for a -20dBFS 16/44.1 dithered input stimulus (red), and -20dBFS 24/96 dithered input stimulus (green), measured at the line-level output of the X5. The shape is similar to that of a typical sinc function filter, although with less pre-ringing.

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. The J-Test was developed by Julian Dunn the 1990s. It is a test signal, specifically a -3dBFS, undithered 12kHz square wave sampled (in this case) at 48kHz (24 bit). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz square wave 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 sine-wave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial S/PDIF X5 input shows obvious peaks in the audioband from -110dBrA to -140dBrA. This is an indication that the X5’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. The results here are worse than the coaxial input, with the highest peaks above -100dBrA, so this input is likely more susceptible to jitter.

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, 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 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’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 shallow roll-off around 20kHz in the white-noise spectrum shows that the X5 does not use a brick-wall-type reconstruction filter. As a result, there are obvious aliased images (and/or resultant inter-modulated signals between either the alias or signal harmonics) within the audioband, reaching -90dBrA around 13kHz. The primary aliasing signal at 25kHz is just below -10dBrA, while the second- and third-distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -90 and -80dBrA.

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 used was about the same, deviating by about 0.05dB 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 significant deviation in RMS at 10kHz to 20kHz between no load and 4 ohms is an indication of a strong dip in damping factor in this frequency range. This can be seen in our damping factor graph (see the last chart in this report).

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sine-wave stimulus at the balanced line-level input. The blue and red plots are for left and right 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 0.005% and 0.01%. At the full rated power of 350W, THD values were the lowest at 20Hz (0.007%), then increase to near 0.05% from 100Hz to 2kHz, then up again to 0.1% at 10kHz-20kHz.

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

The graph above shows THD ratios as a function of frequency plots for the phono input measured across an 8 ohms load at 10W. The MM configuration is shown in blue/red (left/right), and MC in purple/green (left/right). The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.01% (20Hz and 20kHz) down to just above and below 0.005% (150Hz to 10kHz).  The MC THD values were higher, ranging from 0.3% (20Hz, left channel), down to 0.004% (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 as a function of output power for the balanced line-level input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right). 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 250W (8 ohm loading) and near 500W (4 ohm loading). 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 390W, and 646W 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 as a function of output power for the balanced line-level-input, for an 8 ohms load (blue/red for left/right) and a 4 ohms load (purple/green for left/right). Overall, THD+N values for the 8-ohm load before the “knee” ranged from around 0.1% (50mW) down to about 0.006%. The 4-ohm data was 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 as a function of load (8/4/2 ohms) for a constant input voltage that yielded 20W at the output into 8 ohms (and roughly 40W into 4 ohms, and 80W 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. Overall, even with a 2-ohm load at roughly 80W, THD values ranged from as low as 0.02% through most of the audioband to 0.03% at 20kHz.

FFT spectrum – 1kHz (line-level input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave 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 -110dBrA, or 0.0003%, at the odd third harmonic (3kHz); and -100dBrA, or 0.001%, for the fifth harmonic (5kHz). 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 (digital input, 16/44.1 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Both the signal and noise harmonic peaks are very similar or identical to the analog input FFT above. The notable exception is the third signal harmonic (3kHz), here at -100dBrA, or 0.001%, which is 10dB higher than for the analog input.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave 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 sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We only see the 1kHz primary signal peak, at the correct amplitude, along with the 60Hz power supply peak (-100dBrA) with a multitude of subsequent harmonics.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We only see the 1kHz primary signal peak, at the correct amplitude, along with the 60Hz power-supply peak (-100dBrA) with a multitude of subsequent harmonics.

FFT spectrum – 1kHz (MM phono input)

Shown above is the FFT for a 1kHz input sine-wave 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 peaks also follow the same pattern, with the odd harmonics dominating, but at higher levels (up to -85dBrA, or 0.005%, at 180Hz) due to the increased gain.

FFT spectrum – 1kHz (MC phono input)

Shown above is the FFT for a 1kHz input sine-wave 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 (2kHz) at around -80dBrA, or 0.01%. What dominates the FFT are the noise peaks, which due to the very high gain required for an MC cartridge, are as high as almost -55dBrA, or around 0.2% at 180Hz 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 third power-supply-noise harmonic (180Hz) at just below -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 and third power-supply-noise harmonics (60Hz, 180Hz) at 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 that of primary, third and fifth power supply noise harmonic (60, 180Hz, 300Hz) at just above (left) and below (right) -60dBrA or 0.1%. There are no clear signal harmonics above the higher noise floor.

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 just below -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 sine-wave 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 -95dBRA, or about 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are just below -100dBrA, or 0.001%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -20dBrA and their IMD products.

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 -95dBrA, or 0.002%.

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 sine-wave 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 -105dBrA, or 0.0006%.

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

Shown above is an FFT of the intermodulation (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 -90/85dBrA (left/right), or 0.003%/0.006%, while the third-order peaks are at -95/105dBrA (left/right), or 0.002%/0.0006%.

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’s slew-rate performance; rather, it should be seen as a qualitative representation its extended bandwidth. An ideal square wave can be represented as the sum of a sine wave 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’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 relatively steady decline in damping factors from low to high frequencies, with the right channel slightly outperforming the left. The right channel measured from around 590 down to 128, while the left measured from about 570 down to 118.

Diego Estan
Electronics Measurement Specialist