SPL Performer m1000 Mono Amplifiers

Link: reviewed by Aron Garrecht on SoundStage! Ultra on July 15, 2021

General information

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

The SPL Performer m1000 was conditioned for 1 hour at 1/8th power (52W, 8 ohms) before any measurements were taken. Unless otherwise stated, the m1000 was connected to a dedicated 120V/20A circuit.

The m1000 offers a balanced (XLR) input connector, as well as a trim pot to attenuate the input signal between 0 and -5.5dB in 0.5dB increments. This knob was left at the 0dB position for all measurements.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by SPL for the m1000 compared directly against our own. The published specifications are sourced from SPL’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 is set at its maximum (DC to 1MHz), assume, unless otherwise stated, a measurement input bandwidth of 10Hz to 90kHz.

Our primary measurements revealed the following using the balanced line-level inputs (unless specified, assume a 1kHz sinewave, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

For the continuous dynamic power test, the m1000 was able to sustain 464W (0.43dB over rated output and roughly 1% THD) into 8 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (46W) 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 and sides of the m1000 were slightly warm to the touch.

Frequency response (8-ohm loading)

In our measured frequency response plot above, the m1000 is essentially flat within the audioband (20Hz to 20kHz), and only -0.4dB down at 20kHz. SPL’s claim of 10Hz-80kHz -3dB is only half corroborated, as we found the amplifier -3dB point at 60kHz (SPL claims 80kHz). The m1000 should not be considered a high-bandwidth audio device.

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, swept from 5Hz to 100kHz. The blue plot is into an 8 ohms load, the purple is into a 4 ohms load, the pink is an actual speaker (Focal Chora 806, measurements can found here), and the cyan is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we find that there’s a total deviation of less than 0.2dB in the flat portion of the curve, which is an indication of a relatively high damping factor, or low output impedance. At 20kHz, the spread is larger, at just over 0.3dB. The maximum variation in RMS level when a real speaker was used as a load is very small, deviating by about 0.1dB within the flat portion of the curve (20Hz to 10kHz), with the lowest RMS level, which would correspond to the lowest impedance point for the load, exhibited around 200Hz, and the highest RMS level, which would correspond to the highest impedance point for the load, at around 3-5kHz.

Phase response

Above is the phase response plot for the m1000 from 20Hz to 20kHz. The SPL does not invert polarity, and there is virtually no phase shift throughout the audioband, with a worst case of just under +20 degrees at 20kHz.

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

The chart above shows THD ratios at the m1000’s output into 8 ohms as a function of frequency (20Hz to 20kHz) for a sine wave stimulus at the balanced line-level input. The blue plot is at 1W output into 8 ohms, purple at 10W, and pink at the rated 420W. Between 20Hz and 5kHz, the lowest THD ratios were achieved at 420W, and the highest THD values at 1W, with a near 10dB difference. The 10W data lies in the middle. Like most amplifiers, THD ratios rose as a function of frequency above 2kHz or so. At 420W, THD values ranged from 0.02% from 20Hz to 1kHz, then up to 6% at 20kHz. At 10W, THD values ranged from 0.04% to 0.4%, and at 1W, from 0.05% to 0.9%.

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

The chart above shows THD ratios measured at the output of the m1000 as a function of output power for the balanced line-level input, for an 8-ohm load (blue) and a 4-ohm load (purple). As is typical, the 8-ohm data yielded slightly lower THD values (about 5dB). At 50mW, THD values are around 0.15/0.2% (8/4 ohms), and at 200W, around 0.02/0.04% (8/4 ohms). The “knee” occurs in the 8-ohm data around 400W, hitting the 1%THD mark at 495W. Into 4-ohms, the “knee” occurs around 800W, hitting the 1% THD mark at 850W.

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

The plot above shows THD+N ratios measured at the output of the m1000 as a function of output power for the balanced line-level input, for an 8-ohm load (blue) and a 4-ohm load (purple). Once again, the 8-ohm data outperformed the 4-ohm data by about 5dB. At 50mW, THD+N values are just above (4-ohm) and below (8-ohm) 0.2%, dipping down to around 0.02% (8-ohm) and 0.04% (4-ohm) at 200W.

THD ratio (unweighted) vs. frequency at 8/4/2 ohms (left channel only)

The chart above shows THD ratios measured at the output of the m1000 as a function of load (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 balanced 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 small 2-3dB degradation in THD performance from 8 to 4 ohms and then from 4 to 2 ohms across most of the audioband, where values ranged from 0.03 to 0.04 to 0.05%. At 20kHz, all three data sets show THD near 0.3%. This graphs shows that the m1000 is stable and a solid performer when presented with a 2-ohm load.

FFT spectrum – 1kHz

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. We see that the second harmonic, at 2kHz, is at -70dBrA, or 0.03%, while the third and fourth harmonics, at 3kHz and 4kHz, are at -80 dBrA, or 0.01%. Higher-order signal harmonics are also visible but at lower amplitudes. Below 1kHz, we see noise artifacts, with the worst-case peak at 120Hz (second harmonic of the 60Hz fundamental) at -100dBrA, or 0.001%. Other multiples of the fundamental noise harmonic (e.g., 60Hz, 180Hz, 240Hz, etc), as well as IMD products, are visible below -100dBrA.

FFT spectrum – 50Hz

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W. 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 harmonic (150Hz) of the 50Hz signal are at -70dBrA and -80dBrA respectively, or 0.03% and 0.01%. The peaks from noise harmonics are between -130dBrA and -100dBrA, or 0.00003% and 0.001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)

Shown above is the FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the balanced 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 -75dBrA, or 0.02%, while the third-order modulation products, at 17kHz and 20kHz, are near -85dBrA, or 0.006%.

Square-wave response (10kHz)

Above is the 10kHz square-wave response of the m1000 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 m1000’s slew-rate performance. Rather, it should be seen as a qualitative representation of the m1000’s somewhat limited 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 and corners. The m1000’s reproduction of the square wave is clean, but with some softening of the edges and corners.

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

The final plot above is the damping factor (8 ohms) of the m2000 as a function of frequency. Between 20Hz and 2kHz, the damping factor is fairly constant at near 140. Above 2kHz, the damping factor dips down to just below 60 at 20kHz.

Diego Estan
Electronics Measurement Specialist