NAD C 3050 LE Integrated Amplifier-DAC Measurements

Link: reviewed by Dennis Burger on SoundStage! Access on March 1, 2023

General Information

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

Note: The latest firmware (released February 25, 2023) was applied to the C 3050 LE by NAD because an issue was discovered with the original firmware. The C 3050 LE preamp section is intended to provide a maximum of 12dB of gain; however, with the original firmware, a maximum of 0dB of gain (unity gain) was measured. Dennis Burger’s review sample would have had this issue, and explains his experience of having to turn the volume up higher than normal.

The C 3050 LE was conditioned for 1 hour at 1/8th full rated power (~12W 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 C 3050 LE offers one unbalanced line-level analog input (RCA), one unbalanced moving-magnet (MM) phono input (RCA), one coaxial (RCA) and one optical (TosLink) S/PDIF digital input, Bluetooth connectivity, HDMI and Ethernet connections for streaming (using the included MDC BluOS module), one line-level subwoofer output (RCA), one set of line-level pre-out and main-in (both RCA) inputs and outputs, and two pairs of speaker-level outputs. On the front of the unit is a 1/4″ TRS headphone output. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, and the analog line-level and MM unbalanced inputs.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, and 0dBFS digital input. The C 3050 LE digitizes all incoming analog signals (line-level and phono) using a 48kHz sample rate. 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 100W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, but with a lower input voltage to achieve the same 100W output.

Based on the accuracy and reasonably repeatable results at various volume levels of the left/right channel matching (see table below), the C 3050 LE volume control is likely operating fully in the digital domain. The volume control offers a total range from -51dB to + 41dB between the line-level analog input and the speaker outputs, in 0.5dB increments.

The analyzer’s input bandwidth filter was set to 10Hz–22.4kHz for all measurements, except for frequency response and FFTs. Because the C 3050 LE is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), the 22.4kHz bandwidth setting was maintained for THD versus frequency sweeps as well. For these sweeps, the highest frequency was 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 NAD for the C 3050 LE compared directly against our own. The published specifications are sourced from NAD’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 from DC to 250kHz, assume, unless otherwise stated, 10W into 8ohms 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 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the C 3050 LE was able to sustain 171W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (17.1W) 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 C 3050 LE 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 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 output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

*THD into 32 ohm load = 0.004%

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

In our measured frequency response chart above, the C 3050 LE is essentially flat within the audioband (20Hz to 20kHz), corroborating NAD’s claim of ±0.3dB. At the extremes the C 3050 LE is about 0.1dB down at 20Hz, and 0.15dB down at 20kHz. It is clear that the C 3050 LE digitizes the incoming analog signals because of the brickwall-type behavior just past 22kHz. The FFTs below also show that analog signals are sampled at 48kHz. 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), 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 are frequency response plots 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 +/-6dB and +/-5.5dB, respectively, of gain/cut are available at 20Hz and 20kHz.

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

The chart above shows the C 3050 LE’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 digital 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 brick-wall-type filtering, with a -3dB at 21.0kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 46.1kHz and 71.8kHz, respectively. The analog input data yields a -3dB point at 22.9kHz, in line with a 48kHz sample rate.

Frequency response with subwoofer-crossover engaged (120Hz, 8-ohm loading)

Above are two frequency-response plots for the analog input, measured at 10W (8 ohms) at the speaker outputs, and at the line-level subwoofer output, with the crossover set at 120Hz and the subwoofer option enabled in the BluOS app. The C 3050 LE DSP crossover uses a slope of 18dB/octave.

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

The chart above shows the frequency response for the MM 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). Here again we find sharp attenuating just past 22kHz, meaning the phono input is also digitized with a 48kHz sample rate.  The very strict adherence to the RIAA curve likely means that EQ is applied in the digital domain.

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 C 3050 LE 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 -40 degrees at 3kHz, and +40 degrees at 20Hz.

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-outs of the C 3050 LE for a 1Vrms (at 0dBFS) output signal. 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. In these tests, both data were essentially perfect as of -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were about +1.5/1dB (left/right) above reference, while the 24/96 data were within +1dB above reference. This is a good linearity test result.

Impulse response (24/44.1 data)

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 C 3050 LE. We can see that the C 3050 LE utilizes 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 pre-outs of the C 3050 LE. J-Test was developed by Julian Dunn in 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 sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks in the audioband, around 6kHz and 18kHz on either side of the primary signal peak, at -125dBrA. This is a reasonably good J-Test result, indicating that the C 3050 LE 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 pre-outs of the C 3050 LE. The optical input exhibits low-level peaks in the audioband, around 6kHz and 18kHz on either side of the primary signal peak, at -125dBrA. This is a reasonably good J-Test result, indicating that the C 3050 LE DAC should yield good jitter immunity.

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

Both the coaxial and optical inputs were also tested for jitter immunity by injecting 500ns of artificial sinewave 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 relatively high 500ns jitter level. The C 3050 LE DAC did lose sync with the signal when jitter was increased beyond 500ns. The optical input jitter result was very similar to the coaxial input result shown above.

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

The plot above shows a fast Fourier transform (FFT) of the C 3050 LE’s line-level pre-outs with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. There are low-level aliased image peaks in the audioband at the -115dBrA  and below level. The main 25kHz alias peak is near -60dBrA. The second, third and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are between -70dBrA and -90dBrA.

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 can see a maximum deviation within the audioband of a little more than 0.1dB from 4 ohms to no load, which is an indication of a mid-level damping factor, or mid to low output impedance. The maximum variation in RMS level when a real speaker was used is even less, deviating by just under 0.08dB.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange near the rated 100W (about 95W). The power was varied using the volume control. At 1W and 10W, THD ratios were relatively flat and low at around 0.005%. The 95W THD values are higher and constant, just below 0.04%. These data did not quite corroborate NAD’s claim of 100W at 0.03% THD. We found that the 0.03% THD threshold was crossed at 92W.

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

The chart above shows THD ratios as a function of frequency plots for the MM phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.02% (20Hz) down to 0.003% at 6kHz.

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 C 3050 LE 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 fairly closely up to 20W or so, ranging from 0.002% to 0.005%. With an 8-ohm load, the “knee” occurs at about 100W, while the 4-ohm “knee” occurs at around 160W. The 1% THD values are reached at 111W (8 ohms) and 167W (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 C 3050 LE 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, ranging from 0.01% down to 0.005%, with the 8-ohm data outperforming the 4-ohm data by about 2-5dB.

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 C 3050 LE 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 THD values of 0.02% to 0.01% for the 4- and 2-ohm data. This is a strong result and shows the C 3050 LE is stable into 2- ohms loads. For the 8-ohm data, THD ratios are lower, and also fairly constant at around 0.01-0.005%.

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 C 3050 LE 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). From 400Hz to 6kHz, all three loads yield identical 0.005% THD ratios. At lower frequencies, the two-way speaker yielded the highest THD ratios, as high as 0.07% at 20Hz, but as low as 0.002% at 50Hz. The three-way speaker ranged from a high of 0.01% at 30Hz, down to 0.002% at 40Hz.

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 C 3050 LE 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 results are similar, with IMD ratios from as low as 0.005% up to 0.04% at 20kHz.

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 C 3050 LE 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 two-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are nearly identical, with flat IMD results just over 0.01%.

FFT spectrum – 1kHz (line-level input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second and third harmonics, at 2 and 3kHz, are around -90dBrA, or 0.003%. The subsequent signal harmonics are around or below -110dBrA, or 0.0003%. There are low-level power supply related noise peaks (60Hz, 180Hz, 300Hz) on the left side of the main 1kHz peak, at -120dBrA, or 0.0001%. There is also a rise in the noise above 20kHz, characteristic of digital amplifiers. Also visible are the IMD products between the 48kHz sample rate used to digitize the analog signal and the 1kHz signal, at 47kHz and 49kHz.

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. The second (2kHz) signal harmonic is at -105dBrA, or 0.0006%, while the third (3kHz) signal harmonic is at -85dBrA, or 0.006%. Noise-related peaks are the same as the analog FFT above.

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. Within the audioband, the FFT is essentially identical as the 16/44.1 FFT above, except for a slightly lower noise floor due to higher 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, and a signal harmonic at 6kHz. The noise floor on the right channel is much higher, at -130dBrA, than the left channel, at just above -160dBrA.

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, and a signal harmonic at 6kHz. As with the chart above, the noise floor on the right channel is much higher, at -130dBrA, than the left channel, at -160dBrA.

FFT spectrum – 1kHz (MM phono input)

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input. The second (2kHz) signal harmonic is at -100dBrA, or 0.001%, while the third (3kHz) signal harmonic is at -90dBrA, or 0.003%. We see the primary (60Hz) power-supply related peak at -80dBrA, or 0.01%, and subsequent odd-order power-supply related peaks (180, 300, 420Hz, etc.) extending beyond the 1kHz signal peak, at -80 down to -120dBrA, or 0.01 down to 0.0001%.

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 second (100Hz) and third (150Hz) signal harmonics are at -90dBrA, or 0.003%. We also see odd harmonics of the 60Hz power-supply-related peak (180Hz, 300Hz, 420Hz) at -115dBrA, or 0.0002%, 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 from the 60Hz power-supply fundamental and its third harmonic at -80dBrA, or 0.01%. The signal’s second harmonic (100Hz) is at -100/-95dBrA (left/right), or 0.001/0.002%.

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 -100/-110dBrA (left/right channels), or 0.001/0.0003%. The third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. There are also a multitude of peaks throughout the FFT, at -100dBrA and below. This could certainly not be described as a clean IMD FFT. We also see the main aliased peaks at 29kHz and 30kHz around -70dBrA due to the 48kHz sample rate (48kHz-19kHz = 29kHz).

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. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100/-110dBrA (left/right channels), or 0.001/0.0003%. The third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -70dBrA due to the 44.1kHz sample rate (44.1kHz-19kHz = 25.1kHz).

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100/-110dBrA (left/right channels), or 0.001/0.0003%. The third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. There are also many peaks throughout the FFT, at -100dBrA and below. This could certainly not be described as a clean IMD FFT.

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 -105dBRa, or 0.0006%, while the third-order modulation products, at 17kHz and 20kHz, are around -90dBrA, or 0.003%.

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 C 3050 LE’s slew-rate performance. Rather, it should be seen as a qualitative representation of the C 3050 LE’s very restricted 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. Here we can see only the 10kHz fundamental (due to the digitization of the incoming signal with a 48kHz sample rate resulting in a 22kHz bandwidth), plus the 400kHz switching oscillator frequency used in the digital amplifier section, which is visibly modulating the waveform.

Square-wave response (1kHz, restricted 250kHz bandwidth)

Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz input bandwidth on the analyzer to filter out the 400kHz switching frequency. We see more evidence here, in the over/undershoot and soft corners of the squarewave, of the C 3050 LE’s low bandwidth with an analog input.

FFT spectrum (1MHz bandwidth)

The C 3050 LE’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width modulated (PWM) squarewave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The C 3050 LE oscillator switches at a rate of about 400kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sinewave. We can see that the 400kHz peak is quite evident, and at -35dBrA. There are also two peaks at 800kHz and 1.2MHz (the second and third harmonic of the 400kHz peak), at -60 and -90dBrA. Those peaks—the fundamental and its harmonics—are direct results of the switching oscillators in the C 3050 LE amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audio band—and 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. Both channels show a relatively constant damping factor from 20Hz to 20kHz, ranging from 200/244 (left/right channels) up to 213/266 (left/right channels) at 20kHz. This is a mid-tier-level damping-factor result.

Diego Estan
Electronics Measurement Specialist