Technics Grand Class SU-G700M2 Integrated Amplifier Measurements

Link: reviewed by Dennis Burger on SoundStage! Access on December 1, 2022

General Information

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

The Technics SU-RG700M2 was conditioned for 1 hour at 1/8th full rated power (~9W 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 SU-RG700M2 offers two line-level analog inputs (RCA); one pair of phono RCA inputs, configurable for moving-magnet (MM) or moving-coil (MC) operation, RCA pre-amp outputs, RCA main-in inputs, two coaxial (RCA) and two optical (TosLink) S/PDIF inputs, one USB digital input, two pair of speaker-level outputs, and one headphone output over a 1/4″ TRS connector. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level, as well as phono (MM and MC). Unless otherwise stated, Direct In mode was used with Attenuation and LAPC both off.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, 0.5mVrms MC input, and 0dBFS digital input. The volume control is variable from -88dB to 0dB. The following volume settings yielded approximately 10W into 8 ohms: -29dB for analog line-level and digital, -14dB for MM and MC. 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 70W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, where only 0.188Vrms was required to achieve 70W into 8ohms.

Based on the accuracy and repeatability of the left/right volume channel matching (see table below), the SU-RG700M2 volume control operates in the digital domain. The SU-RG700M2 offers 5dB volume steps ranging from -88dB to -78dB, 4dB steps from -78dB to -70dB, 3dB steps from -70dB to -64dB, 2dB steps from -64dB to -56dB, 1dB steps from -56dB to -19dB, and 0.5dB steps from -19dB to 0dB. Overall range is -45.7dB to +42dB (line-level input, speaker output).

Because the SU-RG700M2 is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted-bandwidth setting.

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 Technics for the SU-RG700M2 compared directly against our own. The published specifications are sourced from Technics’ 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 was extended to 250kHz, 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.

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

For the continuous dynamic power test, the SU-G700M2 was able to sustain 164W into 4 ohms (~4% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (16.4W) 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 top of the SU-G700M2 was only slightly warm to the touch.

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

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

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sine wave, 2Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

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

In our frequency response plots above, measured across the speaker outputs at 10W into 8 ohms, the SU-G700M2 is nearly flat within the audioband (20Hz to 20kHz). The SU-G700M2 is -0.2dB at 20Hz and +0.1dB at 20kHz. At the extremes, we are at -3.5dB at 5Hz and -1dB at 80kHz. These data essentially corroborate Technics’ claim of 5Hz to 80kHz (-3dB). There’s a rise in the frequency response above 20kHz, where we see +0.5dB at 50kHz, which is a result of the digital amplifier and its high output impedance at high frequencies. Into a 4-ohm load (see RMS level vs. frequency vs load impedance graph below), instead of a rise there is a significant dip at and above 20kHz. 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.

Frequency response (8-ohm loading, line-level input, bass and treble controls)

Above is a frequency-response plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/-7dB of gain/cut is available.

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

Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the midrange control set to maximum (blue/red plots) and minimum (purple/green plots). We see that there is roughly +/-8dB of gain/cut available centered around 1kHz.

Frequency response (8-ohm loading, line-level input, bass and treble and midrange controls)

Above is a frequency-response plot measured at the speaker-level outputs into 8 ohms, with the bass, treble, and midrange controls set to maximum (blue/red plots) and minimum (purple/green plots). The levels are relative to 3kHz. We see that with all controls set to either minimum or maximum, there is a maximum deviation of no more than +/-5dB. When all the tone controls are at their maximum, there are two dips in the frequency response at roughly 300Hz and 3kHz. When the tone controls are at their minimum, we see troughs at 300Hz and 3kHz.

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

Above are the phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The SU-G700M2 does not invert polarity and exhibits, at worst, 40 degrees (at 20kHz) of phase shift within the audioband.

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

The chart above shows the SU-G700M2’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same 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, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 data exhibits brickwall-type filtering, with a -3dB point at 21.1kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 46.5kHz and 91.9kHz respectively. The analog data looks nearly identical to the 24/192 digital data, which is evidence for the SU-G700M2 sampling incoming analog signals at 192kHz.

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

The chart above shows the frequency response for the phono input (MM configuration) without (blue/red) and with (purple/green) the subsonic filter enabled. What is shown is the deviation 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). We see a maximum deviation of about +0.2/-0.5dB (30Hz/10kHz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 24Hz.

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

The chart above shows the frequency response for the phono input (MC configuration) without (blue/red) and with (purple/green) the subsonic filter enabled. What is shown is the deviation 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). We see a maximum deviation of about +0.2/-1dB (30Hz/20kHz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 24Hz.

Phase response (MM input)

Above is the phase response plot from 20Hz to 20kHz for the phono input (MM configuration), measured across the speaker outputs at 10W into 8 ohms. The SU-G700M2 does not invert polarity. 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.

Phase response (MC input)

Above is the phase response plot from 20Hz to 20kHz for the phono input (MC configuration), measured across the speaker outputs at 10W into 8 ohms. The SU-G700M2 does not invert polarity. 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 for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line level output of the SU-G700M2. 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 data were essentially perfect as of -90dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were about 7dB above reference, while the 24/96 data were at +6dBFS. This is a mediocre linearity test result.

Impulse response (24/44.1 data)

The graph above shows the impulse response for the SU-G700M2, fed to the coaxial digital input, measured at the line level output, 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. We find a typical, symmetrical sinc function reconstruction filter.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line level output of the SU-G700M2. 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 (24 bits). 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 sine wave (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 input exhibits low-level peaks in the audioband, at -115dBrA and below, at 2kHz and below. This is a good J-test result, indicating that SU-G700M2 DAC should yield good jitter immunity.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the line level output of the SU-G700M2. The optical input exhibits low-level peaks in the audioband, at -115dBrA and below, at 2kHz and below. This result is essentially identical compared to the coaxial input.

J-Test with 100ns of injected jitter (coaxial)

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine-wave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved exceptional—with essentially identical results for both inputs, so only the coaxial is shown—with no visible sidebands at the 100ns jitter level.

J-Test with 500ns of injected jitter (coaxial)

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial jitter sine-wave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved exceptional, with no visible sidebands at a very high 500ns of injected jitter. The results were the same for both inputs, so only the coaxial is shown. Above this level of jitter, the SU-G700M2 DAC lost sync with the signal with both inputs.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)

The chart above shows a fast Fourier transform (FFT) of the SU-G700M2’s line-level output with white noise at -4dBFS (blue/red) and a 19.1 kHz sine wave 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 the behavior of the SU-G700M2’s reconstruction filter. There are no aliased image peaks within the audioband. The primary aliasing signal at 25kHz is at -95dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -80 and -70dBrA.

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 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. Here we find that at low frequencies (i.e., around 20Hz), the deviations between no load and 4 ohms are at their lowest at 0.3dB, but at high frequencies, the differences are significant, at about 1.5dB at 20kHz. This is a result of the digital amplifier technology used, which exhibits a high damping factor at low frequencies, but a low damping factor at high frequencies (see the damping-factor chart at the end). When a real speaker is used, the major deviations appear once again at high frequencies, with a 0.45dB deviation between 5kHz and 20kHz.

RMS level vs. frequency (1W, left channel only, real speaker, LPAC on and off)

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 analog line-level input swept from 20Hz to 20kHz. Both plots are for the Focal Chora 806 speaker, with (blue) and without (purple) LAPC enbaled. The SU-G700M2 provides a feature called Load Adaptive Phase Calibration (LAPC). This feature measures the outputs of the amplifier while the speakers are connected by using test tones to establish a correction curve to deal with the amplifier’s inherently high output impedance at high frequencies. The theoretical goal is to achieve a flat frequency response for the user’s speakers when LAPC is enabled. We can see here that the blue trace is not flat, but closer to ideal compared to when LAPC is disabled. When LAPC is disabled, we are at -0.3dB at 200kHz and 20kHz, compared to the -0.2dB with LAPC enabled.

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 analog 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 63W. The power was varied using the volume control. At 1W, the right channel outperformed the left by about 5dB, and hovered around 0.01% throughout the measured audioband. At 10W, the THD ratios were constant around 0.06% for both channels.  The 63W THD values were slightly higher, between 0.1% and 0.07%.

THD ratio (unweighted) vs. frequency at 10W (MM and MC phono inputs)

The chart above shows THD ratio as a function of frequency plots for the phono input measured across an 8-ohm 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. All THD ratios were fairly constant from 20Hz to 6kHz, hovering between 0.06 and 0.07%. The exception is at very low frequencies for the MC configuration, where THD ratios were as high as 0.15% at 30Hz.

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 SU-G700M2 as a function of output power for the analog 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). Both data sets track relatively closely, except for maximum power. There is a dip in THD, from 0.02% down to 0.005% in both data sets that occurs when the output voltage is around 1Vrms (0.1W into 8 ohms, 0.3W into 4 ohms). The “knees” occur at around 70W (8-ohm) and 120W (4-ohm), below which THD values range as low as 0.004% (below 1W) to 0.05% (above 10W). We find that the 8- and 4-ohm data reach the 1% THD mark at 85W and 156W.

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 SU-G700M2 as a function of output power for the analog 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 both loads were similar up to 50W, ranging from 0.5%, down to 0.02%, then up to 0.05%.

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 SU-G700M2 as a function of frequency into three different loads (8/4/2 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 analog 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 roughly the same constant THD values of just above and below 0.05% for the 8- and 4-ohm data, respectively. The 2-ohm data yielded higher THD ratios, hovering around 0.2% across the measured audioband.

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 SU-G700M2 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). In general, the measured THD ratios for the real speakers were close to the 8-ohm resistive load. The worst-case diffrences were around 25dB at 20Hz (between the Focal and dummy load), and then about 10dB between 100Hz and 200Hz (between the Paradigm and dummy load). Above 500Hz, THD ratios were either very close, or lower with the real speakers compared to the dummy resistive load, hovering around the 0.02% mark.

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 SU-G700M2 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 balanced analog line-level input. Here the CCIF IMD method is 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). At high frequerncies, there is a 5-8dB difference between the dummy load (-75dB) and real speaker (-70dB) IMD values. Between 2.5 and 7kHz, IMD ratios were either very close, or lower with the real speakers comapred to the dummy resistive load, hovering around the -80 to -75dB (0.01-0.02%) mark.

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 SU-G700M2 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 balanced analog line-level input. Here, the SMPTE IMD method is 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 plots yielded roughly the same IMD values, between 0.05% to 0.1% up to 500Hz, then a drop to 0.01%.

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 analog line-level input. We see that the signal’s second harmonic, at 2kHz, is at -100/-70dBrA (left/right), or 0.001/0.03%, while the odd harmonics at 3 and 5kHz dominate at -65 and -75dBrA, or 0.06% and 0.03%. There are no power-supply related noise peaks to speak right of the signal peak. There is a rise in the noise above 20kHz, characteristic of digital amplifiers.

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. Signal harmonics are very similar to the analog input FFT above. Here again, there are no power-supply related noise peaks to speak of.

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. Signal harmonics are very similar to the analog input FFT above. Here again, there are no power-supply related noise peaks to speak of.

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 see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -110dBrA.

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 see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -110dBrA.

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 even and odd signal harmonics up to 20kHz, at -65dBrA, or 0.06%, and below. The most significant signal harmonic peak is at 3kHz. The most significant power-supply-related noise peaks can be seen at 60Hz at -80dBrA, or 0.01%. The second (120Hz) and third (180Hz) noise-related harmonics can also be seen at -105 and -95dBrA, or 0.0006% and 0.002%.

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. We see even and odd signal harmonics up to 20kHz, at -65dBrA, or 0.06%, and below. The most significant signal harmonic peak is at 3kHz. The most significant power-supply-related noise peaks can be seen at 60Hz at -60dBrA, or 0.1%. The second (120Hz), third (180Hz), fourth (240Hz), fifth (300Hz), seventh (420Hz), and ninth (540Hz) noise-related harmonics can also be seen at –70dBrA to -100dBrA, or 0.03% to 0.001%.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the analog 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. Even (e.g., 100Hz, 200Hz, etc.) and odd (e.g., 150Hz, 250Hz, etc.) signal harmonics can be seen throughout, at -65dBrA (150Hz), or 0.06%, and below. There are no power-supply noise-related harmonics to be seen.

FFT spectrum – 50Hz (MM phono input)

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MM configuration). 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 signal-related harmonic is at 150Hz at -65dBrA, or 0.06%. Higher-order signal harmonics can also be seen at lower amplitudes. The most predominant power-supply noise-related peak is at the 60Hz fundamental at -80dBrA, or 0.01%.

FFT spectrum – 50Hz (MC phono input)

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). 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 signal-related harmonic is at 100Hz at -65dBrA, or 0.06%. Higher-order signal harmonics can also be seen at lower amplitudes. The most predominant power-supply noise-related peak is at the 60Hz fundamental at -60dBrA, or 0.1%.

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 sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the analog 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 -80dBRa, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are slightly higher at around -75dBrA, or 0.02%.

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 -80dBRa, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are slightly higher at around -75dBrA, or 0.02%.

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 sine-wave 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 -80dBRa, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are slightly higher at around -75dBrA, or 0.02%.

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. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -80dBRa, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are slightly higher at around -75dBrA, or 0.02%.

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 sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MC. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -85dBRa, or 0.006%, while the third-order modulation products, at 17kHz and 20kHz, are higher at around -75dBrA, or 0.02%.

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 SU-G700M2’s slew-rate performance. Rather, it should be seen as a qualitative representation of the SU-G700M2’s mid-tier bandwidth. An ideal squarewave 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. In this case, because of the digital nature of the amplifier, we see a 768kHz switching frequency (see 1MHz FFT below) riding on top of the squarewave.

Square-wave response (10kHz, restricted 500kHz bandwidth)

Above is the same 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 500kHz input bandwidth on the analyzer to filter out the 768kHz switching frequency. We can see significant over/undershoot in the corners of the squarewave, a consequence of the SU-G700M2’s mid-tier bandwidth.

FFT spectrum (1MHz bandwidth)

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 analog line-level input, with an extended 1MHz input bandwidth. This enables us to see the high-frequency noise above 20kHz reaching almost -75dBrA at 300kHz. We also see a clear peak at 768kHz, reaching just past -35dBrA. The peak, as well as the noise, are a result of the digital amplifier technology used in the SU-G700M2, however, they are far above the audioband—and are therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final graph above is the damping factor as a function of frequency. We can see here the clear trend of a higher damping factor at low frequencies—around 32 from 20Hz to 2000Hz—and then the steep decline down to 12 at 20kHz. This is a limitation of the digital amplifier technology used in the SU-G700M2, and the reason Technics has incorporated their clever Load Adaptive Phase Calibration (LAPC) feature, to compensate for losses into low impedances at high frequencies.

Diego Estan
Electronics Measurement Specialist