Arcam Radia SA45 Streaming Integrated Amplifier Measurements

Link: reviewed by Dennis Burger on SoundStage! Simplifi on March 15, 2026

General Information

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

The SA45 was conditioned for 1 hour at 1/8th full rated power (~20W 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 SA45 offers four sets of line-level analog inputs (three single-ended RCA, one balanced XLR), two phono inputs (MM and MC over RCA), two digital coaxial inputs (RCA), two digital optical inputs (TosLink), left/right pre-outs and sub-outs (RCA and XLR), one set of speaker-level outputs, and one headphone output over 1/8″ TRS connector. Bluetooth, HDMI and streaming inputs are also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (XLR) line-level and phono (MM and MC), as well as the headphone output.

Most measurements were made with a 4Vrms line-level balanced analog input and 0dBFS digital input. The phono inputs were 5mVrms (MM) and 0.5mVrms (MC). The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the achievable output power of 177W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum. The SA45 offers four digital filters for the digital inputs, labelled as follows in this report:

• Filter 1: Linear phase apodising (default)
• Filter 2: Linear phase slow roll-off
• Filter 3: Minimum phase slow roll-off
• Filter 4: Minimum phase

The SA45 also offers Dirac Live room correction. If no subwoofers are enabled and Dirac Live is off, the SA45 does not digitize incoming analog signals. For comparisons, frequency response and FFTs of analog inputs (line-level and phono) are shown in this report with the subwoofer setting toggled on and off (which engages and disengages the ADC at the input).

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the SA45 volume control is digitally controlled but operating in the analog domain. The SA45 overall volume range is from -81dB to +35dB (line-level input, speaker output). It offers 3dB increments from position 0 to 10, 2dB increments from positions 11 to 20, 1dB from 21 to 50, 0.5dB from 51 to 85, and 0.25dB from 86 to 100. 

Our typical input bandwidth filter setting of 10Hz-22.4kHz was used for all measurements except FFTs and THD versus frequency, where a bandwidth of 10Hz-90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.

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 Arcam for the SA45 compared directly against our own. The published specifications are sourced from Arcam’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 was extended 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.

Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 4Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the SA45 was able to sustain 290W into 4 ohms (~4% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (29W) for 5 seconds, for 5 continuous minutes without inducing a fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the SA45 was slightly warm to the touch.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sinewave 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 sinewave 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 sinewave, 2Vrms input/output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

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

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the SA45 is essentially perfectly flat within the audioband (20Hz to 20kHz, 0/-0.1dB). The -3dB point is at roughly 80kHz, and 0dB at 5Hz. The SA45 appears to be DC-coupled. 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-ohms loading, line-level analog input, ADC on)

Above are the frequency response plots (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, with the ADC at the input on. The main difference here versus the plot above with an analog signal chain is the sharp high-frequency attenuation around 30kHz. The -3dB point is at roughly 46kHz.The ADC appears to be sampling at 96kHz.

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 SA45 yielded only about -30 degrees of phase shift at 20kHz.

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

The chart above shows the frequency response (relative to 1kHz) for the MM phono input. The red/blue plots are with the ADC off, purple/green with the ADC on. We see a very flat response from 100Hz to 20kHz (up to 10kHz when the ADC is on), and essentially no channel-to-channel deviations. Below 100Hz, there is steep attenuation (-3dB at roughly 17Hz), as Arcam appears to have implemented an anti-rumble filter on their phono input. 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).

Phase response (MM input)

Above is the phase response plot from 20Hz to 20kHz for the MM phono input, measured across the speaker outputs at 10W into 8 ohms. The SA45 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 +20 degrees at 20Hz and -100 degrees at 20kHz.

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

The chart above shows the frequency response (relative to 1kHz) for the MC phono input. The red/blue plots are with the ADC off, purple/green with the ADC on. We see essentially the same result as with the MM input.

Phase response (MC input)

Above is the phase response plot from 20Hz to 20kHz for the MC phono input, measured across the speaker outputs at 10W into 8 ohms. We see essentially the same result as with the MM input.

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

The chart above shows the SA45’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency-response graph above. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, the digital signals yielded a flat response down to 5Hz, same as the analog response. The -3dB points are: 21kHz for the 16/44.1 data, 46kHz for the 24/96, 70kHz for the 24/192 data, and 80kHz for the analog input.

Frequency response vs. filter type (16/44.1, left channel only)

The chart above shows the SA45’s frequency response (relative to 1kHz) as a function of filter type measured across the speaker outputs at 10W into 8 ohms for a 16/44.1 digital input (left channel only). The blue plot is the default linear phase apodizing filter (#1), the red is the linear phase slow roll-off filter (#2), green is minimum phase slow roll-off (#3), and pink is the minimum phase filter (#4). We can see how filters 1 and 4 are brickwall filters showing only 0.2dB of attenuation at 20kHz, while the other two filters (2 and 3) are at -4dB 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 for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outputs of the SA45, where 0dBFS was set to yield 2Vrms. For this test, 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 -100dBFS up to 0dBFS. The 24/96 data were flat down to about -115dBFS below which a muting circuit appears to engage, while the 16/44.1 data were +2/+4dB at -120dBFS.

Intersample headroom (+3dB 11.025kHz sinewave at 24/44.1 at -3/-1.5/0dBFS) — PASS

The chart above shows the results of an intersample headroom test for the coaxial digital input, measured at the line-level pre-outputs of the SA25, where a standard 0dBFS sinewave was set to yield 2Vrms (2.83Vp or 5.66Vpp). For this test, the DAC is fed a test file consisting of a 11.025kHz sinewave sampled at 24/44.1 at +3.01dB. This is achieved without digital clipping by using a sinewave at exactly one quarter the sample rate, completely avoiding sampling at the peaks and troughs of the waveform. The test file is then run through the DAC at -3, -1.5, and 0dBFS (purple/green/orange plots). A DAC with built-in headroom will be able to reconstruct all three sinewaves cleanly with no distortion, with the highest amplitude sinewave at 4Vp (3.01dB above the standard 2.83Vp for a 0dBFS input signal). A DAC without built-in headroom will show significant clipping (up to ~10% THD) when the test file is fed at -1.5 and 0dBFS. The DAC in the SA45 passed this test.

Impulse response (24/44.1 data, Filter 1)

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 SA45, for Filter 1 (linear phase apoziding). We find a standard symmetrical sinc function response.

Impulse response (24/44.1 data, Filter 2)

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 SA45, for Filter 2 (linear phase slow roll-off). We find a standard symmetrical sinc function response with less ringing than Filter 1.

Impulse response (24/44.1 data, Filter 3)

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 SA45, for Filter 3 (minimum phase slow roll-off). We find a response with minimal pre-ringing and some post-ringing.

Impulse response (24/44.1 data, Filter 4)

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 SA45, for Filter 4 (minimum phase slow roll-off). We find a response with no pre-ringing and significant post-ringing.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outputs of the SA45 where 0dBFS is set to 2Vrms. 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.

Here we see a strong J-Test result, with only a few very low-level peaks in the audioband, ranging from -145dBFS down to -160dBFS. This is an indication that the SA45 DAC should have strong 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 pre-outputs of the SA45. The optical input yielded very similar results compared to the coaxial input.

J-Test (coaxial, 10ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SA45, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz can be seen but at a very low -145dBFS. The optical input behaved similarly.

J-Test (coaxial, 100ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SA45, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz can be seen but are still low in amplitude at -125dBFS. The optical input behaved similarly.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Filter 1, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the SA45’s line-level pre-outputs 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 using Filter 1 (linear phase apodizing). The steep roll-off around 20kHz in the white-noise spectrum shows brickwall-type attenuation. There are no low-level aliased image peaks within the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is highly suppressed at -120dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near the same level.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Filter 2, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the SA45’s line-level pre-outputs 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 using Filter 2 (linear phase slow roll-off). The slow roll-off around 20kHz in the white-noise spectrum is as expected and advertised. There are two low-level aliased image peaks within the audioband at -120dBrA and below. The primary aliasing signal at 25kHz is barely suppressed at -15dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are around the -110 to -120dBrA level.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Filter 3, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the SA45’s line-level pre-outputs 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 using Filter 3 (minimum phase slow roll-off). The slow roll-off around 20kHz in the white-noise spectrum is as expected and advertised. There are two low-level aliased image peaks within the audioband at -120dBrA and below. The primary aliasing signal at 25kHz is barely suppressed at -15dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are around the -110 to -120dBrA level.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Filter 3, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the SA45’s line-level pre-outputs 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 using Filter 4 (minimum phase). The roll-off around 20kHz in the white-noise spectrum is steep but not as sharp as Filter 1. There are no low-level aliased image peaks within the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is highly suppressed at -105dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near the same level.

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 50kHz. 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 see that the deviations between no load and 4 ohms are very small at roughly 0.04dB. This is a strong result and an indication of a very low output impedance, or high damping factor. With a real speaker load, deviations measured lower at roughly 0.03dB.

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

The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave 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 137W. The power was varied using the SA45’s volume control. The 10W THD ratios were the lowest (right channel), ranging from 0.00015% from 30Hz to 2kHz, then up to 0.0008% at 20kHz. The rest of the 1 and 10W data were close to these levels (within 5dB). At 137W, THD ratios ranged from 0.0005% from 30Hz to 1kHz, then up to 0.01% at 20kHz.

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

The chart above shows THD ratios as a function of frequency plots for the MM (blue/red) and MC (purple/green) phono inputs measured across an 8-ohm load at 10W. For this test, the input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM input vary from around 0.01% (20Hz) down to 0.0005% at 2kHz, then up to 0.002/0.001% (left/right) at 20kHz. The THD values for the MC input vary from around 0.05% (20Hz) down to 0.001% at 2 to 8kHz, then up to 0.0025% at 20kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the SA45 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right), with the volume at maximum. THD ratios into 4 and 8 ohms are close (within 5dB). The 8-ohm data range from 0.002% at 50mW, down to 0.0003% in the 5 to 30W range. The “knee” into 8 ohms can be found right around 140W, while the 4-ohm “knee” can be seen around 210W. The 1% THD marks were hit at 177W and 275W into 8 and 4 ohms.

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

The chart above shows THD+N ratios measured at the speaker-level outputs of the SA45 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right). THD+N ratios into 4 and 8 ohms are remarkably close (with 2-3dB). The 8-ohm data range from 0.03% at 50mW, down to 0.0007% at the “knee.”

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 SA45 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 20W at the output into 8 ohms (and roughly 40W into 4 ohms, and 80W 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 a roughly 5dB increase in THD from 8 to 4 to 2 ohms across the sweep (a strong result). These ranged from 0.00025% to 0.002% for the 8-ohm load and 0.001% to 0.005% for the 2-ohm load.

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 SA45 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 higher than those measured across the resistive dummy load. The differences ranged from 0.03% at 20Hz for the two-way speaker versus 0.00025% for the resistive load, and 0.006% at 20kHz into the three-way speaker versus 0.001% for the resistive load. Between the important frequencies of 500Hz to 4kHz, all three THD traces were very close, around the 0.0002-0.0005% level.

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 SA45 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, IMD ratios into the real speakers were higher than those measured across the resistive dummy load, with the three-way speaker yielding the highest results at 0.001 to 0.003%. The two-way speaker yielded results between 0.0004 and 0.002%, while the resistive load yielded more constant results at roughly 0.0003% across the sweep.

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 SA45 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). We find very similar IMD ratios into all three loads, a constant  0.002% across the sweep.

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 analog line-level XLR input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at a very low -115dBrA, or 0.0002%, and -125dBrA, or 0.00006% . There are subsequent signal harmonics visible at and below the extremely low -140dBrA, or 0.00001%, level. On the right side of the signal peak, we find power-supply-related noise peaks, but only at and below -130dBrA, or 0.00003%. Overall, this is a very clean FFT.

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 analog line-level RCA input. The main difference between this FFT and the FFT above using the XLR input is slightly higher power-supply-related noise peaks, reaching -120dBrA, or 0.0001%, at the primary peak of 60Hz.

FFT spectrum – 1kHz (XLR line-level input, ADC on)

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 analog line-level XLR input, with the ADC sampling the incoming signal for the purposes of internal DSP. The main difference between this FFT and the FFT using the XLR input without any digitization is a few more higher order signal harmonics here. For example, the fifth (5kHz) and seventh (7kHz) harmonics can be seen here around the -120dBrA, or 0.0001%, level. What can also be seen are peaks at 95kHz and 97kHz, which is evidence of 96kHz sampling (the two IMD peaks between the signal and the sampling frequency).

FFT spectrum – 1kHz (MM phono 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 phono MM input. The signal harmonics are difficult to detect amongst the power-supply-related noise peaks, but the second (2kHz) and third (3kHz) harmonics are there just below -110dBrA, or 0.0003%. Power-supply-related noise peaks can be seen throughout the FFT ranging from -95dBrA, or 0.002%, down to -120dBrA, or 0.0001%.

FFT spectrum – 1kHz (MC phono 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 phono MC input. The signal harmonics are difficult to detect amongst the power-supply-related noise peaks, but the second (2kHz) and third (3kHz) harmonics are there just below -105dBrA, or 0.0006%. Power-supply-related noise peaks can be seen throughout the FFT ranging from -70dBrA, or 0.03%, down to -110dBrA, or 0.0003%.

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 that the signal’s second (2kHz) and third (3kHz) harmonics dominate at a very low -115dBrA, or 0.0002%, and -125dBrA, or 0.00006%, same as the analog FFT. Noise peaks are essentially the same as with the analog FFT above (at and below -130dBrA).

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 result as with the 16/44.1 FFT above, but with a lower noise floor due to the increased bit depth.

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, with no signal harmonics above the -135dBrA noise floor.

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, no signal harmonics above the -145dBrA noise floor, and power-supply-related noise peaks at and below -135dBrA, or 0.00002%.

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 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. The most predominant (non-signal) peak is the second (100Hz) signal harmonic at a low -115dBrA, or 0.0002%, followed by the third (150Hz) signal harmonic at -120dBrA, or 0.0001%. Other peaks (both signal harmonics and power-supply noise-related harmonics) can be seen at -130dBrA and below.

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 MM phono 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 the signal’s second (100Hz) harmonic and the 60Hz fundamental power-supply noise peak and its second (120Hz left channel) and fifth (300Hz left channel) harmonics, all at roughly -95dBrA, or 0.002%.

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 MC phono 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) peak is the 180Hz power-supply third-harmonic noise peak at -75dBrA, or 0.02%. Other power-supply-related noise peaks can be seen at -80dBrA, or 0.01%, and below. The highest signal harmonic is at 100Hz, at -90dBrA, or 0.003%.

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 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 -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are at -115dBrA, or 0.0002%. This is a very clean IMD result.

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

Shown above is the FFT of the speaker-level output of the SA45 with the APx 32-tone signal applied to the analog 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 are at and below the very low -140dBrA, or 0.00001%, level.

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 (0dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120/130dBrA (left/right), or 0.0001/0.00003%, while the third-order modulation products, at 17kHz and 20kHz, are very low at just under -120dBrA, or 0.0001%.

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 (0dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120/130dBrA (left/right), or 0.0001/0.00003%, while the third-order modulation products, at 17kHz and 20kHz, are very low at just under -120dBrA, or 0.0001%.

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 MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -95dBrA, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are lower at -110dBrA, or 0.0003%.

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 MC phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -90dBrA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are lower at -110dBrA, or 0.0003%.

Squarewave 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 SA45’s slew-rate performance. Rather, it should be seen as a qualitative representation of the SA45’s mid-to-high 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. In this case, we find relatively clean corners, with some softening and overshoot.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor just around 400 from 20Hz to 2kHz, then a decline to just under 200 at 20kHz. This is a strong result for a medium-powered solid-state integrated amplifier.

Diego Estan
Electronics Measurement Specialist