Link: reviewed by Dennis Burger on *SoundStage! Access* on August 15, 2022

**General Information**

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

The Marantz 40n 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 40n offers three line-level analog inputs (RCA), one pair (left/right) of moving-magnet (MM) phono inputs (RCA), one pair of fixed line-level outputs (RCA), one variable sub-out (RCA), a pair of main-in inputs (RCA), one digital coaxial (RCA) input, one optical (TosLink) input, one digital HDMI input, two speaker-level outputs and one headphone output over a 1/4″ TRS connector. The 40n also offers a Bluetooth input and streaming via ethernet or WiFi. The 40n also features two digital filters, labelled Filter 1 and Filter 2, as well as a Lock Range (Narrow/Medium/Wide) for digital inputs to minimize the effects of jitter. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level, and phono. Unless otherwise stated, Source Direct mode was engaged, which bypasses the balance and tone controls. Filter 1 and the default Wide Lock Range were used for the digital-input measurements, unless otherwise specified.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, and 0dBFS digital input. The volume control is variable from 0 to 100. The following volume settings yielded approximately 10W into 8 ohms: 45 for analog line-level and digital inputs, and 64 for MM input. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 70W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, where only 0.219Vrms was required to achieve 70W into 8 ohms.

Based on the accuracy and variability of the left/right volume channel matching (see table below), the 40n volume control is likely digitally controlled but operates in the analog domain. The 40n offers 4dB volume steps ranging from volume levels 1 to 6, 2dB steps from 6 to 17, 1dB steps from 17 to 46, and 0.5dB steps from 46 to 100. Overall range is -57.1dB to +40.7dB (line-level input, speaker output).

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

Volume position | Channel deviation |

1 | 0.007dB |

10 | 0.000dB |

30 | 0.017dB |

40 | 0.015dB |

50 | 0.006dB |

70 | 0.005dB |

80 | 0.013dB |

100 | 0.050dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Marantz for the 40n compared directly against our own. The published specifications are sourced from Marantz’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 500kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Amplifier rated output power into 8 ohms (0.5% THD) | 70W | 77W |

Amplifier rated output power into 4 ohms (0.5% THD) | 100W | 122W |

Frequency response | 5Hz-50kHz | 5Hz-50kHz (-0.1/-0.05dB) |

THD (20Hz-20kHz, 8 ohms, 66W) | 0.02% | 0.002-0.03% |

Damping Factor (1kHz) | 100 | 227 |

Input sensitivity (phono) | 2mVrms | 1.65mVrms |

Input impedance (phono) | 47k ohms | 52.6k ohms |

Input sensivity (line-level) | 220mVrms | 218mVrms |

Input impedance (phono) | 20k ohms | 18.0k ohms |

Signal-to-noise ratio (phono, A-weighted, 5mVrms in) | 87dB | 87.4dB |

Signal-to-noise ratio (line-level, A-weighted, 2Vrms in) | 106dB | 112.4dB |

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 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 78W | 78W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 127W | 127W |

Maximum burst output power (IHF, 8 ohms) | 85.3W | 85.3W |

Maximum burst output power (IHF, 4 ohms) | 149.7W | 149.7W |

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

Crosstalk, one channel driven (10kHz) | -83.6dB | -85.6dB |

Damping factor | 237 | 227 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 28.6Vrms | 28.7Vrms |

DC offset | <-2mV | <-2mV |

Gain (sub-out) | 14.7dB | N/A |

Gain (maximum volume) | 40.7dB | 40.7dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-98dB | <-96dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-91dB | <-91dB |

Input impedance (line input) | 18.0k ohms | 18.1k ohms |

Input sensitivity (for rated power, maximum volume) | 218mVrms | 219mVrms |

Noise level (A-weighted) | <55uVrms | <55uVrms |

Noise level (unweighted) | <148uVrms | <148uVrms |

Output impedance (line-out) | 559 ohms | 556 ohms |

Output impedance (sub-out, 20Hz) | 1155 ohms | N/A |

Signal-to-noise ratio (full power, A-weighted, 2Vrms in) | 112.5dB | 112.4dB |

Signal-to-noise ratio (full power, unweighted, 2Vrms in) | 104.2dB | 104.2dB |

Signal-to-noise ratio (full power, A-weighted, max volume) | 102.6dB | 102.6dB |

Dynamic range (full power, A-weighted, digital 24/96) | 111.4dB | 111.3dB |

Dynamic range (full power, A-weighted, digital 16/44.1) | 96.1dB | 96.2dB |

THD ratio (unweighted) | <0.0009% | <0.0008% |

THD ratio (unweighted, digital 24/96) | <0.001% | <0.001% |

THD ratio (unweighted, digital 16/44.1) | <0.001% | <0.001% |

THD+N ratio (A-weighted) | <0.0011% | <0.0011% |

THD+N ratio (A-weighted, digital 24/96) | <0.0013% | <0.0014% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.0023% | <0.0024% |

THD+N ratio (unweighted) | <0.0019% | <0.0019% |

Minimum observed line AC voltage | 123.6VAC | 123.6VAC |

For the continuous dynamic power test, the 40n was able to sustain 129W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (12.9W) 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 40n was warm to the touch, but did not cause discomfort.

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 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -82.0dB | -70.4dB |

DC offset | <-3mV | <3mV |

Gain (default phono preamplifier) | 42.3dB | 42.4dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-92dB | <-92dB |

IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-95dB | <-95dB |

Input impedance | 52.6k ohms | 52.6k ohms |

Input sensitivity (to max power with max volume) | 1.65mVrms | 1.65mVrms |

Noise level (A-weighted) | <350uVrms | <350uVrms |

Noise level (unweighted) | <1000uVrms | <1000uVrms |

Overload margin (relative 5mVrms input, 1kHz) | 24.5dB | 24.4dB |

Signal-to-noise ratio (full rated power, A-weighted) | 87.5dB | 87.4dB |

Signal-to-noise ratio (full rated power, unweighted) | 78.1dB | 78.9dB |

THD (unweighted) | <0.0008% | <0.0008% |

THD+N (A-weighted) | <0.004% | <0.004% |

THD+N (unweighted) | <0.012% | <0.012% |

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 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 530mW | 530mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 580mW | 580mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 168mW | 168mW |

Gain | 40.7dB | 40.7dB |

Output impedance | 324.5 ohms | 326.5 ohms |

Noise level (A-weighted) | <24uVrms | <24uVrms |

Noise level (unweighted) | <63uVrms | <63uVrms |

Signal-to-noise ratio (A-weighted, ref. max output voltage) | 113.4dB | 113.5dB |

Signal-to-noise ratio (unweighted, ref. max output voltage) | 105.4dB | 105.3dB |

THD ratio (unweighted) | <0.00065% | <0.00065% |

THD+N ratio (A-weighted) | <0.0013% | <0.0013% |

THD+N ratio (unweighted) | <0.003% | <0.003% |

**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 40n is perfectly flat within the audio band (20Hz to 20kHz). At the extremes the 40n is -0.1dB at 5Hz and -0.2dB at 100kHz, making “wide bandwidth audio amplifier,” as Marantz calls it, an apt descriptor for the 40n. 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 +/- 9.5dB of gain/cut is available, centered at 50Hz and 15kHz.

**Frequency response (8-ohm loading, variable subwoofer output)**

Above is a frequency response plot measured at the line-level sub-out, relative to 20Hz. We see that the corner frequency (-3dB) is at 80Hz, with a second-order (12dB/octave) slope, which are the default settings. The crossover frequency can also be set to 40, 60, 100, and 120Hz.

**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 40n does not invert polarity and exhibits, at worst, about 30 degrees (at 20kHz) of phase shift within the audio band.

**Frequency response vs. input type (analog and 16/44.1, 24/96, and 24/192 inputs with 8-ohm loading, left channel only)**

The chart above shows the 40n’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 (but limited to 80kHz). 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. For all digital signals, Filter 1 was used. The 16/44.1 data exhibits steeper filtering, with a -3dB point at 18.8kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 38.4kHz and 60.5kHz, respectively.

**Frequency response vs. filter type (16/44.1 input with 8-ohm loading, left channel only)**

The chart above shows the 40n’s frequency response as a function of filter type, measured across the speaker outputs at 10W into 8 ohms, for a 16/44.1 signal at the coaxial input. The blue trace is Filter 1, and the purple trace is Filter 2. We see that Filter 2 offers a more brick-wall type behavior than Filter 1. At 20 kHz, Filter 1 is at -4dB, while Filter 2 is at -1dB.

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

The chart above shows the frequency response for the phono input (MM). 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). For the 40n, we see a maximum deviation within the audio band of about +0.4dB between 100Hz and 200Hz.

**Phase response (MM input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MM), measured across the speaker outputs at 10W into 8 ohms. The 40n 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.

**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 40n. 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 -110dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were only +3dB above reference, while the 24/96 data remained perfect, so we investigated down to . . .

. . . -140dBFS, where the 24/96 data were within +/-1dB of the 0dB reference. This is an exceptional digital linearity test result.

**Impulse response (24/44.1 data)**

The graph above shows the impulse responses for the 40n, 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. Filter 1 is in blue and displays a symmetrical function with minimal pre- and post-ringing, while Filter 2, in purple, which Marantz describes as having an “asymmetrical impulse response,” shows less pre-ringing and more post-ringing.

**J-Test (coaxial) with Lock Range set to Wide**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the 40n. J-Test was developed by Julian Dunn in the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz square wave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz square wave is removed by the bandwidth limitation of the sampling frequency, we are left with a 12kHz sine wave (the main peak). In addition, an undithered 250Hz square wave 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 effectively zero low-level peaks in the audio band above the -150 dBrA noise floor. This is a very good J-Test result, indicating that 40n DAC should yield strong jitter immunity.

**J-Test (optical) with Lock Range set to Wide**

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the 40n. Interestingly, the optical input yielded a worse J-test result than the coaxial input, with peaks within the audio band reaching -110dBrA near the main 12kHz peak.

**J-Test (optical) with Lock Range set to Medium**

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the 40n, with the Lock Range changed to Medium (Lock Range set to Narrow yielded the same result). Here we see the same ideal J-Test result as with the coaxial input with the Lock Range set to the default Wide position.

**J-Test with 100ns of injected jitter (coaxial) with Lock Range set to Wide**

Since the coaxial input performed very well on the above J-Test test, it was 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 very good, with visible sidebands at the 100ns jitter level at a very low -130dBrA.

**J-Test with 100ns of injected jitter (optical) with Lock Range set to Wide**

The optical input was 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 predictably worse than with the coaxial input, with visible sidebands at the 100ns jitter level at a much higher -85dBrA.

**J-Test with 100ns of injected jitter (optical) with Lock Range set to Medium**

The optical input was further 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. Here the test was conducted with the Lock Range set to Medium and the same 100ns jitter level, and predictably, jitter rejection improved substantially. Sidebands are at a very low -140dBrA, barely visible above the noise floor.

**J-Test with 500ns of injected jitter (coaxial) with Lock Range set to Wide**

The coaxial input was further 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, at a much higher 500ns level. Jitter immunity proved very good yet again, with sidebands down at a very low -120dBrA. Above this level of jitter, the 40n DAC lost sync with the signal. Obviously, the coaxial input offers better performance than the optical input. With the optical input, the 40n DAC could not sync up with the signal with high jittter levels of 500ns, regardless of the Lock Range setting.

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

The chart above shows a fast Fourier transform (FFT) of the 40n’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 for Filter 1. The fairly gentle roll-off around 20kHz in the white-noise spectrum shows the behavior of the 40n’s reconstruction filter. There are two low-level aliased image peaks within the audio band, at around 6kHz at -120dBrA, and 13kHz at -115dBrA. The primary aliasing signal at 25kHz is at -15dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone, and other IMD products, are at -40dBrA and below. Ultrasonic noise levels rise above 50kHz and peak just over 65kHz, before decreasing into to the lowest levels at about 80kHz.

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

The chart above shows a fast Fourier transform (FFT) of the 40n’s line-level output with white noise at -4dBFS (blue/red) and a 19.1kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 for Filter 2. The steep roll-off around 20kHz in the white-noise spectrum shows the behavior of the 40n’s reconstruction filter. Unlike Filter 1, there are no aliased image peaks within the audio band. The primary aliasing signal at 25kHz is at -75dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -110dBrA and below. With this filter, there is a sharp rise in ultrasonic noise beginning at about 65kHz that peaks at just below 70kHz, but then steadily decreases, yet still extends past 95kHz, our measurement limit for this test.

**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 maximum deviation between no load and a 4-ohm load is quite small, at 0.08dB. This is an indication of a relatively high damping factor, or low output impedance. With a real speaker, maximum deviations in RMS level were smaller, at about 0.06dB.

**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 left and right at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 66W. The power was varied using the volume control. The 10W data outperformed the 1W data by 3-4dB from 20Hz to 1kHz, hovering between 0.001% and 0.0006%. From 2kHz to 20kHz, both the 1W and 10W data performed similarly, with THD ratios ranging from 0.0008% up to 0.005%. The 66W THD values were higher, starting at 0.002% at 20Hz, and then rising steadily past 1kHz up to 0.03% 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 phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from around 0.005% (20Hz) down to 0.0006% (1kHz), then up to 0.004% (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 40n 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). The right channel into 4 ohms exhibited much higher THD ratios than the left. The test was repeated to rule out any anomalies, and the results were repeatable. While the left channel ranged from 0.005% (50mW) down to 0.001% (2W to 50W), the right channel ranged from 0.005% up to 0.02% between 2W and 50W. The 8-ohm data showed THD ratios from 0.002% (50mW) down to 0.0005% (5W to 20W). The “knees” were observed just past 60W for the 8-ohm data, and just past 100W for the 4-ohm data. The 1% THD marks were hit at 78W (8 ohms) and 127W (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 output of the 40n 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). Aside from the right channel into 4 ohms (described above), overall, THD+N values for both loads were similar up to 50W. The 8-ohm data ranged from 0.02% down to just below 0.002%. The 8-ohm data outperformed the 4-ohm data by 3-4dB.

**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 40n as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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. The 8-ohm and 4-ohm track closely from 20Hz to 500Hz, between 0.001% and 0.0006%. Above 1kHz, the 4-ohm data yielded about 5dB more distortion, and measuring 0.005% at 20kHz. The 2-ohm data yielded much higher distortion, hovering between 0.02% and 0.03% from 20Hz to 20kHz.

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

The chart above shows THD ratios measured at the output of the 40n 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). Between 500Hz and 20kHz, all three data sets have similar THD ratios, between 0.001% and 0.005%. Below 500Hz, there are signficant differences between the dummy load and the real speakers. While the dummy load yiedled the same constant 0.001% down to 20Hz, the three-way Paradigm was at 0.005%, and the two-way Focal at 0.05%.

**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 40n 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 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). All three data sets track fairly closely, with both speaker data yielding slightly lower IMD ratios than the dummy load. The 8-ohm dummy load yielded a fairly constant 0.002%, while the three-way Paradigm yideld the lowest IMD ratios—as low as 0.0007%.

**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 40n 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 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 data sets are close enough to be judged as identical, hovering around the 0.005% mark.

**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 -105dBrA, or 0.0006%, while all subsequent harmonics are below -110dBrA, or 0.0003%. Power-supply-related noise peaks are evident, but at a very low -120dBrA, or 0.0001%, level and below.

**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 and power-supply-related noise peaks are very similar in level to the analog input FFT above, though between 40 and 50kHz, we can see the IMD products of the sample rate (44.1kHz) and the main signal at 43.1kHz and 45.1kHz.

**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 and power-supply-related noise peaks are very similar in level to the analog input FFT above, although without the 44.1kHz sample rate IMD products.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 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 very low-level power-supply related peaks at -120dBrA, or 0.0001%, and below.

**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 very low-level power-supply related peaks at -120dBrA, or 0.0001%, and below.

**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 MM phono input. We see the second (2kHz), third (3kHz), and fifth (5kHz) signal harmonics at very low levels: -110 and -120dBrA, respectively, or 0.0003%, and 0.0001%. The most significant power-supply-related noise peaks can be seen at 60Hz at -90dBrA, or 0.003%. Higher-order power-supply related peaks can also be seen at lower amplitudes. This is a very clean MM phono FFT for an integrated amplifier.

**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. The most dominant (non-signal) peak is the second signal harmonic (100Hz) at -105dBrA, or 0.0006%. Power-supply-related peaks are at -120dBrA, or 0.0001%, and below.

**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 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) peak is from the 60Hz power-supply fundamental at -90dBrA, or 0.003%. Signal-related harmonics are all but non-existent 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 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 -120dBRa, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are just below -110dBrA, or 0.0003%. This is a very clean IMD result.

**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 -120dBRa, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are just below -110dBrA, or 0.0003%.

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

Shown above is an FFT of the intermodulation (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 -120/-115dBRa (left/right), or 0.0001/0.0002%, while the third-order modulation products, at 17kHz and 20kHz, are just above -110dBrA, or 0.0003%.

**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 MM phono input. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is just above the noise floor for the left channel only at -115dBRa, or 0.0002%, while the third-order modulation products, at 17kHz and 20kHz, are around -105dBrA, or 0.0006%.

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

Above is the 10kHz square-wave 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 40n’s slew-rate performance. Rather, it should be seen as a qualitative representation of the 40n’s 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 40n’s square-wave response is superb, showing no visible over/undershoot, or ringing near the corners.

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

The final graph above is the damping factor as a function of frequency. We see a relatively constant, and high damping factor, and both channels tracking closely, around 230 from 20Hz to 20kHz.

*Diego Estan*

Electronics Measurement Specialist