Chord Electronics Ultima Integrated Amplifier Measurements

Link: reviewed by George de Sa on SoundStage! Hi-Fi on July 15, 2024

General information

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

The Chord Electronics Ultima integrated amplifier was conditioned for one 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 Ultima offers four line-level analog inputs (three unbalanced over RCA, one balanced over XLR), one balanced (XLR) line-level set of pre-outs, and a pair of speaker level outputs. For the purposes of these measurements, the following input was evaluated: analog (XLR) line level.

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 rated output power of 125W (8 ohms). For comparison, SNR measurements were also made with the volume at maximum. There was no significant difference in terms of THD and noise between the RCA and XLR inputs (FFTs are provided as a point of comparison in this report), though there is an extra 6dB gain while using the unbalanced inputs.

Based on the inaccuracy and non-repeatability of the left/right volume channel matching (see table below), the Ultima volume control is a potentiometer operating in the analog domain. The Ultima overall volume range is from -56.5dB to +30.6dB (XLR line-level input, speaker output). One curiosity with this integrated amplifier is that the balance control does not have a center detent. The balance control was used to balance both channels with the volume control at the center position before the volume table was measured.

The analyzer’s input bandwidth filter was set to 10Hz to 22.4kHz for all measurements, except for frequency response and FFTs. Because the Ultima uses a digital switch-mode power supply that exhibits 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.

One final important note is that because of the unique output stage of the Ultima Integrated, which seems to dynamically adjust to the load it is driving, we could not attrain a reliable damping factory measurement. In fact, using our traditional means we derived a negative damping factor, which is impossible, but is likely because of the way the output stage behaves. As a result, no damping factor chart, which we usually provide, is shown.

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 Chord for the Ultima compared directly against our own. The published specifications are sourced from Chord’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 Ultima was able to sustain 265W into 4 ohms (~3.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (26.5W) 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 top of the Ultima was quite warm to the touch.

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 Ultima is near flat within the audioband (20Hz to 20kHz): 0dB at 20Hz and -2.5dB at 20kHz. At the extremes, the Ultima measured -0.2dB at 5Hz and -3dB at 65kHz. This does not corroborate Chord’s claim of 10Hz to 200kHz, ±3dB. 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 Ultima does not invert polarity and yields little phase shift, with less than +5 degrees at 20Hz (the Ultima is not DC coupled) and roughly -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 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 not only minuscule at less than 0.005dB, but also that the 4-ohm response is higher in amplitude than the 8-ohm data, which would imply a negative output impedance. This is, of course, impossible, but implies some sort of on-the-fly gain adjustments in the Ultima as the load is changed. It also made our typical damping factor measurements impossible to perform. In any event, with a real speaker load, deviations measured just below the 0.01dB level, which is an extraordinary result.

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 at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 125W. The power was varied using the Ultima volume control. Generally, THD ratios are on the high side for a solid state amplifier. The left channel outperformed the right channel by as much as 10dB at lower frequencies. THD ratios, at all power levels, ranged from 0.003%/0.02% at 20Hz, up to 0.03%/0.07% at 6kHz.

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 Ultima 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 data outperformed the 4-ohm data by roughly 7-8dB. The 8-ohm THD ratios were steady at roughly 0.02/0.03% from 50mW to the “knee” at roughly 130W. The 4-ohm THD ratios were steady at roughly 0.04/0.05% from 50mW to the “knee” at roughly 200W. The 1% THD marks were hit at 140W and 257W.

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 Ultima 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).  The 8-ohm data outperformed the 4-ohm data by roughly 5dB. The 8-ohm THD+N ratios ranged from 0.2% at 50mW down to 0.03% at 50-130W. The 4-ohm THD+N ratios ranged from 0.4% at 50mW down to 0.05% at 20-200W.

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 Ultima 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 a roughly 5dB increase in THD every time the load is halved. Into 2 ohms, THD ratios ranged from 0.006% at 20Hz, up to 0.2% at 6kHz.

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 Ultima 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 very similar to the resistive dummy load, although still high for a modern solid-state amplifier. These ranged from 0.006% at 20Hz up to 0.1% at 5kHz. Of note is that the Ultima maintained low THD at 20-30Hz into the two-way speaker, which often yields much higher THD ratios when used with a typical class-AB integrated amp.

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 Ultima 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 3-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads up to 7kHz, between 0.007 and 0.02%. Above 7kHz, the three-way speaker yielded the highest IMD results, 0.09% at 20kHz, compared to 0.02/0.03% for the two-way speaker and resistive load.

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 Ultima 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 three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, steady at a high 0.1% from 40Hz to 500Hz, then down to 0.05% to 1kHz.

FFT spectrum – 1kHz (line-level XLR 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/fourth (3/4kHz) harmonics dominate at a fairly high -80dBrA, or 0.01%, and -85dBrA, or 0.006%, while subsequent signal harmonics range from -90dBrA, or 0.003%, down to -110dBrA, or 0.0003%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak at a relatively high -90dBrA, or 0.003%, and its harmonics (120, 180, 240, 300Hz, etc.) at the -100dBrA level, or 0.001%, down to -110dBrA, or 0.0003%. The base noise floor, at -130dBrA to -120dBrA, is also relatively high for a solid-state amplifier.

FFT spectrum – 1kHz (line-level RCA 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 unbalanced (RCA) analog line-level input. We see essentially the same FFT as with the balanced input 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 balanced 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), third (150Hz), and fifth (250Hz) signal harmonics and the primary noise peak at 60Hz. These are all at the -80dBrA (right channel), or 0.01%, to -90dBrA, or 0.003%, level. We can also see that the THD ratios for the left channel on the third (150Hz) and fifth (250Hz) signal harmonics are 20dB lower than the right channel.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input, two-channel mode)

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 -85dBRa, or 0.006%, while the third-order modulation products, at 17kHz and 20kHz, are at -75dBrA, or 0.02%. This is a weak IMD result for a modern solid state amplifier.

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

Shown above is the FFT of the speaker-level output of the Ultima 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 -100dBrA, or 0.001%, level. The low energy peaks that rise near and above -90dBrA are due to power-supply 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 Ultima’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Ultima’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, due to the Ultima’s use of a digital-type switch mode power-supply, we see an oscillator frequency riding on top of the 10kHz waveform.

Square-wave response (10kHz)—250kHz bandwidth

Above is the 10kHz 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 switching frequency. We see evidence here, in the soft corners of the squarewave, of the Ultima’s mid-tier bandwidth.

FFT spectrum of 500kHz switching frequency relative to a 1kHz tone

The Ultima’s use of a digital swith-mode power supply that yields a rising noise floor above 2kHz, as well as several peaks, as high as -35dBrA, beyond the audioband. Those peaks are direct results of the switching oscillators in the Ultima. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

Diego Estan
Electronics Measurement Specialist