Engström Arne Integrated Amplifier

Link: reviewed by Jason Thorpe on SoundStage! Ultra on June 1, 2026

General information

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

The Engström Arne was conditioned for 1 hour at 1/8th full rated power (~3W 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 Arne offers four line-level analog inputs (two XLR, two RCA).  For the purposes of these measurements, the following input was evaluated: balanced analog (XLR) line-level. There were no appreciable differences in terms of THD, noise, and gain between the unbalanced and balanced analog inputs (FFTs provided in this report for comparison).

Most measurements were made with a 2Vrms line-level analog input. 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 30W into 8 ohms. For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the Arne volume control is a stepped attenuator operating in the analog domain. The Arne overall volume range is from -59dB to +22dB (balanced line-level input, speaker output).

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 Engström for the Arne compared directly against our own. The published specifications are sourced from Engström’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 (unless specified, assume a 1kHz sinewave at 2Vrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Arne was able to sustain 40W into 4 ohms (~4% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (4W) 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 Arne was very hot.

Frequency response (8-ohm loading)

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the Arne is at about -1dB at 20Hz and -0.5dB at 20kHz. The -3dB points are at 10Hz and 60kHz. The roughly +/-0.5dB “glitch” at about 4.5kHz is real, and was repeatable in bench mode by manually tuning the input frequency. 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.

Phase response (8-ohm loading)

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 Arne yielded just over +20 degrees of phase shift at 20Hz, and about -30 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 8ohms 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 see that the deviations between no load and 4 ohms are significant at over 3.5dB. This is a very poor result and an indication of a high output impedance, or low damping factor, typical of tube amplifiers with zero negative feedback. With a real speaker load, deviations were smaller, but still in the audible range at roughly 2.5dB.

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 29W (just below the rated output of 30W). The power was varied using the Arne’s volume control. The 1W and 10W data are relatively close together, between 0.02% and 0.5%. At 29W, THD ratios were around 3-4% across the sweep.

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 Arne 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). Due to THD differences between channels (the left channel yielded up to 10dB less THD), the 8-ohm and 4-ohm data are not distinctly different when glancing at the graph. For the left channel, the 8-ohm data ranged from 0.01-0.02% from 50mW to 3W, then up to the 1% THD mark at 23W. For the 4-ohm load (left channel), THD ratios ranged from 0.01% at 50mW to 100mW, then a steady increase to the 1% THD mark at 25/27W (let/right).

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 Arne 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). Due to THD differences between channels (the left channel yielded up to 10dB less THD), the 8-ohm and 4-ohm data are not distinctly different when glancing at the graph. Since THD ratios are high for this amplifier, the THD+N plots are very close to the THD plots in the previous graph. The main differences are at low power where THD ratios are lower and noise may dominate. At 50mW, THD+N is around 0.05-0.1% for all four traces.

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 Arne as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 5W at the output into 8 ohms (and roughly 7W into 4 ohms, and 8W into 2 ohms) for the analog line-level input (note: the output impedance of the Arne is high at 2 ohms). The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. There is roughly a 15-20dB increase in THD every time the load is halved between 100Hz and 2kHz. Into 8 ohms, THD ratios ranged from 0.4% at 20Hz, down to 0.03% at 1kHz, then up to 0.4% at 20kHz. Into 4 ohms, THD ratios ranged from 0.2-0.3% from 20Hz to 4kHz, then up to 0.6% at 20kHz. Into 2 ohms, THD ratios were fairly constant at 1-1.5%.

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 Arne 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 close to those measured across the resistive dummy load, with the exception of the two-way speaker below 40Hz (3% THD at 20Hz). Otherwise, THD ratios ranged from 0.01% to 0.3%.

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 Arne 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 that all three IMD traces are close to one another, ranging from 0.03% to 0.2%.

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 Arne 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 2-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a 3-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads; 0.1% up to 500Hz, then down to 0.02% up to 1kHz.

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 balanced input. We see significant signal harmonic peaks, ranging from the highest at 2kHz (-50dBrA, or 0.3%, left channel) down to the -120dBrA, or 0.0001%, level in the 20kHz to 30kHz range. On the right side of the signal peak, we find significant power-supply-related noise peaks up to the limits of the FFT (90kHz), up to -80dBrA, or 0.01%. This is a very poor FFT result, but not a suprising result for a tube amplifier with zero negative feedback.

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 unbalanced input. We see effectively the same result as with the balanced input FFT above.

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. Signal harmonics are reaching near -50dBrA, or 0.3% (left channel), and power-supply-related noise peaks are reaching -80dBrA, or 0.01%.

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 -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are at roughly the -70dBrA, or 0.03%, level.

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

Shown above is the FFT of the speaker-level output of the Arne 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  -80dBrA, or 0.01%, level. The other larger peaks are from power-supply-related noise.

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 Arne’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Arne’s mid-tier 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 soft corners without any ringing or over/undershoot.

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

The final graph above shows damping factor as a function of frequency. Both channels track very closely, with the damping factor remaining fairly constant at roughly 4 across the audioband. This is a very poor result, as is typical of tube amplifiers with zero negative feedback, and the low damping factor means the amplifier could interact significantly with a loudspeaker’s impedance curve, potentially causing audible variations in the speaker’s performance.

Diego Estan
Electronics Measurement Specialist