Atoll Electronique IN200 Signature Integrated Amplifier Measurements

Link: reviewed by Dan Kong on SoundStage! Hi-Fi on June 1, 2022

General Information

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

The Atoll Electronique IN200 Signature integrated amplifier was conditioned for 1 hour at 1/8th full rated power (~15W 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 IN200 Signature offers five unbalanced (RCA) line-level analog inputs, four unbalanced (RCA) line-level analog outputs (Tape Out, By-pass and two pre-outs), and one pair of speaker-level outputs. On the front of the unit is a 1/4″ TRS headphone output.

Most measurements were made with a standard 2Vrms line-level analog input. The signal-to-noise ratio (SNR) measurements were made with the same input signal values, but with the volume set to achieve 1% THD at the output (8 ohms). For comparison, an SNR measurement was also made with the volume at maximum, where only 0.42Vrms was required to achieve 104W into 8ohms.

Based on the accurate and non-repeatable results at various volume levels of the left/right channel matching (see table below), the IN200 Signature volume control is likely digitally controlled but still operating in the analog domain. The volume control offers a total range of 0 to 80 on the display, which measured from -38dB (position 1) to +37dB between the line-level analog input and the speaker outputs, in increments of 2dB from positions 1 through 15, 1dB from 16 to 47, and 0.5dB from 48 to 80.

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 Atoll for the IN200 Signature compared directly against our own. The published specifications are sourced from Atoll’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 500kHz, assume, unless otherwise stated, 10W into 8ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channel.

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 90kHz bandwidth):

For the continuous dynamic power test, the IN200 Signature was able to sustain 178W into 4 ohms (~4% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (17.8W) for 5 seconds, for 5 minutes without inducing any protection or shut down circuits. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the IN200 was quite warm to the touch.

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):

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

In our measured frequency-response chart above, the IN200 Signature is nearly flat within the audio band (20Hz to 20kHz). At the extremes the IN200 is at 0dB at 20Hz, and -0.4/0.3dB (left/right) at 20kHz. Atoll claims a frequency response of 5Hz to 100kHz, however, they do not specify deviations relative to 1kHz. At these extremes, the IN200 measured -0.1dB and -12/-11dB (left/right channels). 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, line-level input)

Above are the left- and right-channel phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The IN200 Signature does not invert polarity and exhibits, at worst, about 30 degrees (at 20Hz) of phase shift within the audio band.

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 audio band of about 0.15dB from 4 ohms to no load, which is an indication of a mid-level damping factor, or average output impedance. The maximum variation in RMS level when a real speaker was used is less, deviating by about 0.13dB within the flat portion of the curve (20Hz to 5kHz). Note that the dip in RMS level at higher frequencies is a result of the frequency response of the IN200 signature, and not a damping factor issue, as all four plots show the same dip, at roughly the same rate.

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 the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 95W. The power was varied using the volume control. The IN200 yields consistently high THD ratios across a wide range of power output levels. Above about 500Hz, THD is roughly the same at all power levels, ranging from about 0.2% up to 3-5%. Below 500Hz, the 1W data shows the lowest THD values, at 0.05% at 20Hz. The 10W data is just above at about 0.7% at 20Hz, while the 95W data is at 0.2% (30Hz).

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 IN200 Signature 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 8-ohm THD ratios ranged from about 0.5% at 50mW down to about 0.2-0.3% from 30W to the “knee,” which is at roughly 80W. The 4-ohm data yielded THD ratios roughly 5dB higher, except for the right channel below 1W, which tracked the 8-ohm data very closely. The “knee” in the 4-ohm data occurs around 120W. The 1% THD values are reached at about 105W (8-ohm) and 170W (4-ohm). These measurements do not corroborate Atoll’s specified power ratings for the IN200 Signature of 120W and 200W into 8/4 ohms. It is possible that the European version, which would use 220VAC mains, does achieve this power rating. Note: our mains supply is a dedicated 120VAC/20A circuit, and it never dipped below 123VAC during these measurements.

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 IN200 Signature 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). Since the IN200 produces high levels of THD, these dominate when measuring THD+N; therefore, the THD+N plots look very similar to the THD versus output power plots above.

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 IN200 Signature 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. We find increasing THD values from 8 to 4 to 2 ohms; however, the differences are fairly small (2-3dB). Into 2 ohms, THD ratios range from 0.1% at 40Hz, up to almost 5% at 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 IN200 Signature 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). All three plots track relatively closely, ranging from 0.05% at low freqeuncies, up to 5% at 20kHz.

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 IN200 Signature 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 3-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three plots are similar. Just like the measured THD ratios, IMD ratios are high, ranging from about 0.3% up to almost 5% 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 IN200 Signature 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). The 8-ohm dummy load and 2-way speaker tracked almost perfectly, with a constant 0.2% IMD. The three-way speaker yielded IMD results about 10dB higher, hovering around 1%.

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. The signal harmonics are evident and very high in amplitude.  The odd harmonics (3/5/7/9kHz, etc.) are higher than the even harmonics (2/4/6/8kHz, etc.) at -60dBrA and below, or 0.1%, compared to the even harmonics at -75dBrA and below, or 0.02%. The exception is the second harmonic (2kHz) at just below -60dBrA. On the left side of the main signal peak, we find noise peaks at the fundamental (60Hz) and all subsequent harmonics at -90dBrA, or 0.003%, and below. At the second harmonic (120Hz) noise peak and above, the left channel yielded higher peaks than the right, by roughly 10dB.

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 second harmonic (100Hz) dominates at -60dBrA, or 0.1%, while even and odd signal and power-supply noise-related harmonics at lower levels (-90dBrA or 0.003% and below), as well as their resultant IMD products, can be seen throughout.

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 -70dBrA (left/right), or 0.03%. The third-order modulation products, at 17kHz and 20kHz, are quite high at around -50dBrA, or 0.3%.

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 IN200’s slew-rate performance. Rather, it should be seen as a qualitative representation of the IN200’s mid-level 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, as well as softening of the edges. Here we can see an average looking square-wave reproduction, with softened corners but little to no ringing.

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 500Hz, right around 116. Above 500Hz, the right channel outperforms the left, with a damping factor as high as 130 at 15kHz, compared to the left channel’s 92 at 20kHz.

Diego Estan
Electronics Measurement Specialist