Marantz Model 50 Integrated Amplifier Measurements

Link: reviewed by Dennis Burger on SoundStage! Access on May 1, 2024

General Information

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

The Marantz Model 50 was conditioned for one 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 Model 50 offers four line-level analog inputs (RCA), one moving-magnet (MM) phono input (RCA), a sub output and left/right variable and fixed pre-outs plus a power amp input (all RCA), two pairs (A and B) of speaker-level outputs, and one headphone output over 1/4" TRS connector. For the purposes of these measurements, the following inputs were evaluated: analog line-level and phono.

Most measurements were made with a 2Vrms line-level analog input and a 5mVrms phono input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 70W (8 ohms). For comparison, SNR measurements were also made with the volume at maximum.

Based on the variability and non-repeatability of the left/right volume channel matching (see table below), the Model 50 volume control is digitally controlled operating in the analog domain. The Model 50 overall volume range is from -57.6dB to +41.8dB (line-level input, speaker output). It offers 0.5dB increments throughout the volume range.

Our typical input bandwidth filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs. frequency sweeps, where a bandwidth of 10Hz –90kHz was used. Frequency response measurements utilized a DC to 1MHz 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 Marantz for the Model 50 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 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 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Model 50 was able to sustain 145W into 4 ohms (~3.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (14.5W) for 5 secondss, for 233 seconds of the 500-second test before inducing the fault-protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the Model 50 was warm to the touch.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz sinewave at 5mVrms, 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-ohm 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 Model 50 is essentially perfectly flat within the audioband (20Hz to 20kHz). At the extremes, the Model 50 is -0.1dB at 5Hz and -0.2dB at 100kHz. The Model 50 can be considered a high-bandwidth audio device. 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 (relative to 1kHz) 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 +/-11dB of gain/cut is available at 20Hz, and roughly +/-10dB of gain/cut at 20kHz.

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 Model 50 yields very little phase shift (as expected given the extended frequency response), with less than +5 degrees at 20Hz (the Model 50 is not DC coupled) and less than -5 degrees at 20kHz.

Frequency response (line-level pre and sub outputs)

Above is a frequency response plot measured at the line-level outputs into 8 ohms, where the left/right pre-outs are in purple/green and the sub-out is in blue.  The pre-outs show an extended frequency response, -0.1dB at 5Hz and -0.5dB at 70kHz. The sub-out is low-pass filtered with a -3dB point at around 150Hz.

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

The chart above shows the frequency response (relative to 1 kHz) for the phono input (MM configuration) and shows very small maximum deviations of about +0.25/-0.1dB (100-200Hz/20kHz) from 20Hz to 20kHz. What is shown in this chart 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 phono input, measured across the speakers outputs at 10W into 8 ohms. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and -90 degrees at 20kHz.

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 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 around 0.15dB. This is a reasonably strong result for an integrated class-AB amp, and an indication of a low output impedance, or high damping factor. With a real speaker load, deviations measured just below the 0.07dB level—well below the threshold of audibility.

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 left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 70W. The power was varied using the Model 50 volume control. Between 20Hz and 2kHz, all THD ratios are fairly constant and similar, between 0.004 and 0.006%. Between 2kHz and 20kHz, THD ratios were higher at higher power levels, but not by a significant margin. At 20kHz, we measured around 0.01% at 1W and 10W, and 0.03% at 70W.

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

The graph above shows THD ratio as a function of frequency plot for the phono input measured across an 8-ohm load at 10W. The input sweep was EQ’d with an inverted RIAA curve. The THD values vary from 0.01% (20Hz) down to between 0.001 and 0.002% from 200Hz to 3kHz, then up to 0.006% 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 Model 50 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). THD ratios were essentially identical into 8 and 4 ohms up to the 8-ohm “knee” at roughly 70W (the 4-ohm “knee” is at roughly 100W). These ranged from 0.003% at 50mW, down to 0.001% at 1 to 3W, then up to 0.005% at the “knees.” The 1% THD values were hit at 83W and 132W into 8 and 4 ohms, respectively.

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 Model 50 as a function of output power for the 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 closely, but the 4-ohm data yielded a couple dB more noise than the 8-ohm data. THD+N ratios into 8 ohms ranged from 0.02% at 50mW, down to 0.002% at 10W, then up to just below 0.005% at the 8-ohm “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 Model 50 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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 essentially identical THD ratios (0.005%) into all three loads up to about 1kHz. From 3kHz to 20kHz, there is a roughly 5dB increase in THD between the 2-ohm load and the 8/4-ohm loads. At 20kHz, we measured 0.015% into 8/4 ohms, and 0.025% into 2 ohms. This is a strong result, and shows that the Model 50 is stable into 2 ohms.

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 Model 50 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 similar to the resistive dummy load, with the expection of the two-way speaker at 20 to 30Hz. THD ratios hovered between 0.007 and 0.01% from 40Hz to 20kHz for all three loads. At 20Hz, the THD ratio was 0.07% into the two-way speaker. This is a relatively strong result, and shows that the Model 50 will yield consistently low THD results into real-world speaker loads.

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 Model 50 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). We find essentially identical IMD ratios into all three loads, at a relatively flat and constant 0.005%.

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 Model 50 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 thee-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical IMD ratios into all three loads, at a relatively flat 0.02% from 40Hz to 500Hz, then down to 0.0015% from 500Hz to 1kHz.

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 (2kHz) and third (3kHz) harmonics dominate at -85dBrA, or 0.006%, and -105dBrA, or 0.0006%, while subsequent signal harmonics are below -110dBrA, or 0.0003%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak and its harmonics (120, 180, 240, 300Hz, etc.) at and below the very low -120dBrA, or 0.0001%, level.

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 phono input, configured for MM. We see the second (2kHz) signal harmonic dominate at -95dBrA, or 0.002%, while subsequent signal harmonics are below the -110dBrA, or 0.0003%, level. The noise related peaks are at and below the -85dBrA, or 0.006%, level.

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) peaks are the second (100Hz) and third (150Hz) signal harmonics at a -90dBrA, or 0.003%, and -105dBrA, or 0.0006%. Noise related peaks can be seen below the -110dBRa, or 0.0003%, level.

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 phono input configured for MM. The most predominant (non-signal) peaks are that of the power-supply fundamental (60Hz) and third (180Hz) harmonics at -90dBrA, or 0.003%, and -85dBrA, or 0.006%. The signal’s second (100Hz) harmonic is at the -95dBrA, or 0.002%, level.

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 were 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 -95dBRa, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz are at -100dBrA, or 0.001%.

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

Shown above is the FFT of the speaker-level output of the Model 50 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 -120dBrA, or 0.0001%, level.

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 phono input configured for MM. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBRa, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are at the same level.

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 Model 50’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Model 50’s extremely 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, due to the Model 50’s very extended bandwidth, we see a near-perfect squarewave, with sharp corners and no ringing.

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 right around 200, from 20Hz to roughly 20kHz. This is a relatively strong damping factor result for an affordable class AB integrated amp.

Diego Estan
Electronics Measurement Specialist