Rotel RA-1572MKII Integrated Amplifier-DAC Measurements

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

General Information

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

The RA-1572MKII was conditioned for one hour at 1/8th full rated power (~15W 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 RA-1572MKII offers a multitude of inputs, both digital and analog, line-level analog preamp outputs, subwoofer line-level outputs, and two pairs of speaker level outputs (A and B). For the purposes of these measurements, the following inputs were evaluated: digital coaxial 1 (RCA) and optical 1 (TosLink) S/PDIF, analog balanced line-level (XLR), and phono (moving magnet, MM). Comparisons were made between unbalanced (RCA) and balanced line-level inputs, and no differences were seen in terms of THD+N; however, the balanced input offers 4dB less gain than the unbalanced inputs. The RA-1572MKII also offers a USB input, however, I was unable to successfully recognize the RA-1572MKII using Rotel’s USB driver for Windows. Bluetooth is also offered, but our APx555 does not currently have a Bluetooth board, so that could not be tested.

Most measurements, with the exception of signal-to-noise (SNR) or otherwise stated, for the balanced line-level analog input were made with the volume set to unity gain (0dB) on the volume control (position 92) with respect to the preamp outputs (which offers 1dB of gain with the unbalanced input, and -3dB with the balanced input). At this volume position, to achieve 10W into 8 ohms, 660mVrms was required at the balanced line-level input. For the digital inputs, a volume position of 53 yielded 10W into 8 ohms with a 0dBFS input. For the phono input, a volume position of 77 yielded 10W into 8 ohms with a 1kHz 5mVrms input. The SNR measurements were made with the volume control set to maximum.

Based on the high accuracy of the left-right volume channel matching (see table below), the RA-1572MKII volume control is likely in the analog domain but digitally controlled. The RA-1572MKII offers 100 volume steps. Between steps 1 and 10, step increases range from 7dB to 2dB. Steps 10 and 11 offer 1.5dB volume increments, steps 11 through 20 offer 1dB, then from 21 to 100 each volume step is 0.5dB.

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 RA-1572MKII 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 channels.

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

For the continuous dynamic power test, the RA-1572MKII was able to sustain 230W into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (23W) 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 top of the RA-1572MKII was warm to the touch, but did not cause discomfort to the touch.

Our primary measurements revealed the following using the phono-level inputs (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 RA-1572MKII is nearly flat within the audioband (20Hz to 20kHz). At the extremes the RA-1572MKII is 0.5dB down at 10Hz and 0.3dB up at 100kHz. These data corroborate Rotel’s claim of 10Hz to 100kHz (+/-0.5dB). The RA-1572MKII 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.

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 RA-1572MKII will provide a maximum gain or cut of approximately 12dB at 20Hz, and a maximum gain or cut of approximately 9dB at 20kHz.

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

The chart above shows the RA-1572MKII’s frequency response as a function of input type. The green trace is the same analog input data from the previous chart. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and pink is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same for the digital input for all sampling frequencies: -0.5dB at 20Hz. The behavior at high frequencies for all three digital sample frequencies is as expected, offering sharp filtering around 22k, 48k, and 96kHz (half the respective sample rate). It is also obvious from the plots above that the 44.1kHz sampled input signal offers the most “brick-wall”-type behavior, while the attenuation of the 96kHz and 192kHz sampled input signals approaching the corner frequencies (48kHz and 96kHz) is more gentle.

Frequency response (8-ohm loading, phono input)

What’s displayed in the chart above is the RA-1572MKII’s frequency-response deviation from the standard RIAA curve frequency response. To display that, the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision. Therefore, zero deviation would yield a flat line at 0dB. The plots above show a very small maximum deviation of about -0.2dB (200Hz) from 20Hz to 20kHz, which is typical of many high-quality phono stages we have measured.

Phase response (phono input)

Above is the phase response plot from 20Hz to 20kHz for the phono input, 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 plot 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 RA-1572MKII. 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 is a straight flat line at 0dB (i.e., the amplitude of the digital input perfectly matches the amplitude of the measured analog output). Both digital input types performed similarly, approaching the ideal 0dB relative level at -100 dBFS, then yielding perfect results to 0dBFS. At -120dBFS, both channels at 16/44.1 overshot the ideal output signal amplitude by 1dB (right channel) and 2.5dB (left channel), while the left and right channels at 24/96 overshot by 1dB (left channel) and just above 0dB (right channel).

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

The graph above shows the impulse responses for a -20dBFS 16/44.1 (blue/red) and 24/96 (purple/green) dithered input stimulus, measured at the line level output of the RA-1572MKII. We see symmetrical pre and post ringing that is typical of “fast” or “sharp” linear-phase reconstruction filters.

J-Test (coaxial input)

The plot above shows the results of the J-Test test for the coaxial digital input, measured at the line-level output of the RA-1572MKII. The J-Test was developed by Julian Dunn in the 1990s. It is a test signal comprised of, specifically, a -3dBFS, 24-bit, undithered 12kHz square wave sampled (in this case) at 48kHz. 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 RA-1572MKII input shows obvious peaks in the audioband from -95dBrA to just below -120dBrA. This is an indication that the RA-1572MKII’s DAC section may be susceptible to jitter, which the jitter-injected tests on the coaxial input below demonstrate.

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 RA-1572MKII. The results here are very similar to the coaxial input, but slightly worse, with the highest peaks nearing -90dBrA, indicating that the optical input may be slightly more susceptible to jitter.

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

The plot above shows the results of the J-Test test for the coaxial digital input, measured at the line-level output of the RA-1572MKII, 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 -70dBrA. This is a clear indication that the DAC in the RA-1572MKII has poor jitter immunity. For this test, the optical input yielded effectively the same results, so we chose to show only the coaxial result.

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 RA-1572MKII, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are very clear again, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/-2kHz jitter signal) manifest at -50dBrA—the RA-1572MKII’s digital section degrades further as more jitter is introduced. For this test, the optical input yielded effectively the same results, so, again, we chose to only show the coaxial input result.

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

The chart above shows a fast Fourier transform (FFT) of the RA-1572MKII’s line-level output with white noise at -4dBFS (blue/red) and a 19.1kHz sinewave at 0dBFS fed to the coaxial digital input, dithered and sampled at 16/44.1. The sharp roll-off above 20kHz in the white noise spectrum shows the implementation of a brick-wall type reconstruction filter. There are obvious aliased images (or resultant intermodulated signals between either the alias or signal harmonics) within the audioband reaching -85dBrA around 10kHz. The primary aliasing signal at 25kHz is at -60dBrA, while the second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are much higher in amplitude, lying between -60 and -35dBrA.

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

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the 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 0.05dB (at 20kHz) from 4 ohms to no load, 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 as a load is smaller still, deviating by a little less than 0.04dB within the flat portion of the curve (100Hz to 20kHz), 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 2kHz.

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 sinewave 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 120W. The power output was varied using the volume control. The 10W data exhibited the lowest THD values (but very close to the 1W data), from just above 0.001% to 0.01%. At the full rated power of 120W, THD values track the 1 and 10W data below 300Hz, however, above this frequency, THD values steadily increase from around 0.002% to about 0.04%.

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

Above are THD ratio plots as a function of frequency for the phono input measured across an 8-ohm load at 10W output. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from just above 0.001% (500Hz to 1kHz) to 0.01% (20Hz and 20kHz).

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 RA-1572MKII 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 only 2-3dB and range from 0.005/0.01% at 50mW, respectively (8/4 ohms), down to just above 0.001% between 50W and 100W for both loads. The “knee” in the 8-ohm data occurs just past 100W, hitting the 1% THD mark at 143W. For the 4-ohm data, the “knee” occurs around 150W, hitting 1% THD around 226W.

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 RA-1572MKII 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). Overall, THD+N values for the 8-ohm load before the “knee” ranged from around 0.1% (50mW) down to about 0.003%. The 4-ohm data was similar, but 2-3 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 RA-1572MKII as a function of load (8, 4, and 2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W 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 8 and 4 ohms, and as much as 20dB worse from 4 ohms to 2 ohms above 5kHz. Overall, even with a 2-ohm load at roughly 40W, THD values ranged from as low as 0.001% at around 500Hz to 0.04% at 20kHz.

FFT spectrum – 1kHz (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 very low at -110/-120dBrA (left/right), or 0.0003/0.0001%, and around -105dBrA, or 0.0005%, at the odd third (3kHz) and fifth (5kHz) harmonics. Below 1kHz, we see peaks from power supply noise artifacts at 60Hz (just below -110dBrA, or 0.0003%), 180Hz (just above -110dBrA), with the subsequent harmonics falling below this level.

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 resolution. We see signal harmonics at higher levels compared to the analog input, reaching -90/-100dBrA, or 0.003/0.001% (left/right), at 2kHz, and exceeding -90dBrA at 3kHz.

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-harmonic profile as with the 16/44.1 sampled input. The noise floor, however, is reduced by a small margin compared to the 16/44.1 sampled FFT above.

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 only see the 1kHz primary signal peak, at the correct amplitude, along with the 60Hz power-supply peak (-110dBrA, or 0.0003%) with subsequent lower-level harmonics (i.e., 120/180Hz) visible.

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. As with the 16/44.1 chart above, we only see the 1kHz primary signal peak, again at the correct amplitude, and the 60Hz power-supply peak (-110dBrA, or 0.0003%) with the subsequent lower-level harmonics (i.e., 120/180Hz) visible.

FFT spectrum – 1kHz (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. We see the signal harmonic profile is similar to the line-level balanced input–the second, third, and fifth harmonics are all below -100dBrA, or 0.001%.

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 40Hz 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 -110dBrA, or 0.0003%, and the second power-supply-related noise harmonic (120Hz) at just above -110dBrA.

FFT spectrum – 50Hz (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. The most predominant (non-signal) peaks are that of the primary (60Hz) and third (180Hz) power-supply-related noise harmonics at or near -90dBrA, or 0.003%. The second signal harmonic (100Hz) cannot be seen above the 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 -110dBrA, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are higher, at just above and below -100dBrA, or 0.001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 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. Here we find close to the same result as with the balanced line-level analog input. The second-order 1kHz peak is at -100dBrA, or 0.001%, while the third-order peaks are the same as with the balanced line-level input above.

Square-wave response (10kHz)

Above is the 10kHz square-wave response using the balanced 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 RA-1572MKII’s slew-rate performance. Rather, it should be seen as a qualitative representation of its extended bandwidth. An ideal square wave 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 RA-1572MKII’s reproduction of the 10kHz squarewave is very clean, with only very mild overshoot and undershoot in the edges.

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

The final chart shown above is the RA-1572MKII’s damping factor as a function of frequency. Both channels show relatively constant damping factors across the audioband, with the left channel slightly outperforming the right channel. The right channel measured from around 250 to 260, while the left measured from about 280 to 295.

Diego Estan
Electronics Measurement Specialist