Lyngdorf Audio TDAI-1120 Integrated Amplifier-DAC

Link: reviewed by Roger Kanno on SoundStage! Hi-Fi on August 15, 2021

General Information

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

The TDAI-1120 was conditioned for 1 hour at 1/8th full rated power (~6W 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 TDAI-1120 offers a multitude of inputs, both digital and analog (unbalanced), a set of configurable line-level analog outputs (fixed or variable, full-range or with crossover), and a pair of speaker-level outputs. For the purposes of these measurements, the following inputs were evaluated: digital coaxial (RCA) and optical (TosLink) S/PDIF, and the line-level and moving-magnet (MM) phono analog unbalanced (RCA) inputs. The TDAI-1120 is a sophisticated integrated amplifier capable of room correction (RoomPerfect) and bass management. As such, a factory reset was performed before measurements were performed, and particular attention was paid to ensure room correction was disengaged, and that both the line-level and speaker level outputs were set to full-range (i.e., no crossovers).

Based on the accuracy and repeatability at various volume levels of the left/right channel matching (see table below), the TDAI-1120 volume control is likely operating in the digital domain. Consequently, all analog signals are digitized at the TDAI-1120’s inputs so the unit may perform volume, bass management, and room correction.

All measurements, with the exception of signal-to-noise ratio (SNR), or otherwise stated, were made with the volume set to or near unity gain (0dB) on the volume control. SNR measurements were made with the volume control set to maximum. At the unity gain volume position, to achieve 10W into 8 ohms, 2Vrms was required at the line-level input and 11mVrms at the phono input. For the digital inputs, 0dBFS required the volume set to -8.5dB to achieve 10W into 8 ohms at the output.

Because the TDAI-1120 is a digital amplifier technology that exhibits considerable noise just above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

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 Lyngdorf Audio for the TDAI-1120 compared directly against our own. The published specifications are sourced from Lyngdorf’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 22.4kHz, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the line-level inputs (unless specified, assume a 1kHz sine wave, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the TDAI-1120 was able to sustain 130W into 4 ohms using an 80Hz tone for 500 ms, alternating with a signal at -10dB of the peak (13W) 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 of the TDAI-1120 was just slightly warm to the touch.

Our primary measurements revealed the following using the phono-level input (unless specified, assume a 1kHz sine wave, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

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

In our measured frequency-response plot above, the TDAI-1120 is nearly flat within the audioband (20Hz to 20kHz). At the audioband extremes the TDAI-1120 is -1.5dB down at 20Hz and +0.4dB at 20kHz. These data do not quite corroborate Lyngdorf’s claim of 20Hz to 20kHz (+/-0.5dB). The TDAI-1120 cannot be considered a high-bandwidth audio device as the -3dB point is just shy of 50kHz. In the chart above and most of the charts 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 vs. input type (8-ohm loading, left channel only)

The plot above shows the TDAI-1120’s frequency response as a function of input type. The green trace is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital signal from 5Hz to 22kHz, the purple trace is for a 24/96 dithered digital signal from 5Hz to 48kHz, and, finally, pink is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same across input types: -1.5dB at 20Hz. The behavior approaching 20kHz for all input types is also identical, in that there is a rise in level beginning around 5kHz. However, the 16/44.1 signal exhibits a sharp, brick-wall-type attenuation right around 20kHz. The 24/96 digital input also exhibits a sharp, brick-wall-type attenuation near the limit of its frequency range (48kHz), peaking around +2.2dB at around 40kHz. The 24/192 digital input frequency response is identical to the 24/96 plot, despite the extended theoretical range up to 96kHz.

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

The plot above shows frequency response for the phono input (MM), and shows the same maximum deviation of -1.5dB at 20Hz and +0.4dB at 20kHz as seen for the line-level analog input. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQd with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). In the flat portion of the curve, the worst-case RIAA and channel-to-channel deviations are from 5 to 6kHz, where the left channel is -0.1dB down and the right about -0.2dB down.

Phase response (MM input)

Above is the phase response plot from 20Hz to 20kHz for the phono input from 20Hz to 20kHz. 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 -400 degrees at 200-300Hz. This is an indication that the TDAI-1120 likely inverts polarity on the phono input. If we look at the phase response at 20Hz, the phase shift is 200 degrees. If we assume a polarity inversion (180 degrees), then there would only be 20 degrees of extra phase shift at 20Hz.

Digital linearity (16/44.1 and 24/96 data)

The chart above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level output of the TDAI-1120. The digital input is swept with a dithered 1kHz signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both digital input types performed similarly, approaching the ideal 0dB relative level from 0dBFS to -90dBFS. At -110dBFS, both channels at 16/44.1 overshot the ideal output signal amplitude by about 1dB, while the left/right channels at 24/96 undershot by 1dB.

Impulse response (16/44.1 and 24/96 data)

The graph above shows the impulse responses for a -20dBFS 16/44.1 dithered input stimulus (red), and 24/96 dithered input stimulus (green), measured at the line-level output of the TDAI-1120. The shape is similar to that of a typical sinc function filter, although with less pre- and post-ringing for the 24/96 input data.

J-Test (coaxial and optical inputs)

The plot above shows the results of the J-Test test for the optical digital input (the coaxial input performed identically) measured at the line-level output of the TDAI-1120. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically a -3dBFS undithered 12kHz square wave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz square wave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sine wave. In addition, an undithered 250Hz square wave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBFS and below.  The test file can also be used in conjunction with artificially injected sine-wave jitter by the Audio Precision, to show how well the DAC rejects jitter.

As mentioned, both the coaxial and optical S/PDIF TDAI-1120 inputs performed identically, showing only spurious peaks in the audioband at -125dBFS and below. When sine-wave jitter was injected at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection, absolutely no peaks were observed above the noise floor with both inputs on the TDAI-1120, even at the maximum jitter level available of 1592ns, indicating excellent jitter immunity.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)

The plot above shows a fast Fourier transform (FFT) of the TDAI-1120’s line-level output with white noise at -4 dBFS (blue/red), and a 19.1 kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. The aliased image at 25kHz is extremely low at -125dB, and any resultant intermodulated signals (between either the alias or signal harmonics) within the audioband are all very low, below -120dBrA, or 0.0001%. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are much higher in amplitude, lying between -80 and -95dBrA, or 0.01% and 0.002%.

RMS level vs. frequency vs. load impedance (1W, left channel only)

The plots above show 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 is an actual speaker (Focal Chora 806, measurements can found here), and the cyan is no load connected. We find a maximum deviation within the audioband of about 3dB (at 20kHz), which is an indication of a low damping factor, or high output impedance. The maximum variation in RMS level when a real speaker was used as a load is smaller, deviating by a little less than 0.5dB within the flat portion of the curve (30Hz to 20kHz), 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 5kHz.

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

The plot above shows THD ratios at the output into 8 ohms as a function of frequency (20Hz to 6kHz) for a sine-wave stimulus at the 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 full rated power of 60W. The power was varied using the volume control. All three THD plots are relatively flat. The 10W data exhibited the lowest THD values, between 0.006% and 0.015%, although there is an almost 5dB difference between channels in favor of the right channel. The 1W data show THD values between 0.01 and 0.02%. At the full rated power of 60W, THD values ranged from 0.01 to 0.03%.

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

Next is a THD ratio as a function of frequency plot for the phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from about 0.006% to just above 0.01%, but are fairly flat from 20Hz to 6kHz. Again, the right channel outperformed the left by as mush as 5dB.

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

The plot above shows THD ratios measured at the output of the TDAI-1120 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). Although there are fluctuations before the “knee,” both the 4-ohm and 8-ohm data are roughly the same, ranging from 0.005% to 0.02%. The “knee” in the 8-ohm data occurs just past 50W, hitting the 1% THD mark between 60 and 70W. For the 4-ohm data, the “knee” occurs around 100W, hitting the 1% THD around 130W.

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 TDAI-1120 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). There’s a distinct 5dB jump in THD+N (also visible in the THD plot above, but to a lesser degree) when the output voltage is around 1.5-1.6Vrms (i.e., 0.3W into 8 ohms, 0.7W into 4 ohms), and then a sharp 10dB decrease in THD+N at around 4-5Vrms at the output (i.e., 2/5W into 4/8 ohms). This behavior was repeatable over multiple measurement trials. Overall, THD+N values before the “knee” ranged from around 0.01% (3 to 10W) to 0.2% (50mW).

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 TDAI-1120 as a function of load (8/4/2 ohms) for a constant input voltage that yielded 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W 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 increasing levels of THD from 8 to 4 to 2 ohms, with about a 5dB increase with each halving of the load. Overall, even with a 2-ohm load at roughly 20W, THD values ranged from 0.015% at around 1kHz to just below 0.04% at 6kHz.

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. We see that the signal’s second harmonic, at 2kHz, is at -80dBrA (left), or 0.01%, and -95dBrA (right), or 0.002%. The third harmonic is at -85dBrA, or 0.006%; the remaining signal harmonics range from -90dBrA to -120dBrA, or 0.003 and 0.0001%. Just above 20kHz, we see a steep rise in the noise floor, up to -70dBrA, or 0.03%. Below 1kHz, we see no power-supply noise artifacts.

FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)

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 coaxial digital input, sampled at 16/44.1. We see essentially the same signal harmonic profile as with the analog input. The noise floor, however, is reduced here below 100Hz by about 15dB compared to the analog input.

FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)

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 coaxial digital input, sampled at 24/96. We see essentially the same signal harmonic profile as with the analog input and the digital coaxial input with a 16/44.1 signal. The noise floor, however, is reduced here above 5kHz by about 5dB compared to the 16/44.1 sampled FFT above.

FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We only see the 1kHz primary signal peak, at the correct amplitude, with a slightly raised noise floor at low frequencies with respect to the 0dBFS FFT above.

FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We only see the 1kHz primary signal peak, at the correct amplitude, with a slightly raised noise floor at low frequencies with respect to the 0dBFS FFT above.

FFT spectrum – 1kHz (MM phono input)

Shown above is the FFT for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input. We see essentially the same signal harmonic profile as with the analog line-level and digital inputs. The highest peak from power-supply noise is at the fundamental (60Hz), reaching about -85dBrA, or 0.006%, and the third noise harmonic (180Hz) is just below -90dBrA, or 0.003%.

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 line-level input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. Once again, here there are no noise signals to speak of. Instead, the most predominant peaks are that of the signal’s second (100Hz) harmonic at -80/-95dBrA (left/right), or 0.01/0.002%, and third harmonic (150Hz) at about -85dBrA, or 0.006%.

FFT spectrum – 50Hz (MM phono 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 phono input. The most predominant peaks are that of the signal’s second (100Hz) harmonic at -80/-95dBrA (left/right), or 0.01/0.002%, and third harmonic (150Hz) at about -85dBrA, or 0.006%. Peaks due to power supply noise are visible at 60Hz (-85dBrA or 0.006%) and 180Hz (-90dBrA or 0.003%). 

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

Shown above is an FFT of the intermodulation disortion (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 -85/-95dBRA (left/right channels), or 0.006/0.002%, while the third-order modulation products, at 17kHz and 20kHz are higher, at around -80dBrA, or 0.01%.

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 sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input. Here we find essentially the same result as with the line-level analog input, with the exception of the expected elevated noise floor at low frequencies due to the RIAA equalization, and the absence of a 2kHz peak at -110dBrA, or 0.0003%, for the left channel that was visible in the line-level IMD FFT.

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 TDAI-1120’s slew-rate performance; rather, it should be seen as a qualitative representation of its 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. The TDAI-1120’s reproduction of the 10kHz square wave is poor, with noticeable overshoot and undershoot, due to its limited bandwidth, and the 400kHz switching-oscillator frequency used in the digital amplifier section clearly visible modulating the waveform.

FFT spectrum of 400kHz switching frequency relative to a 1kHz tone

The TDA-1120’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width modulated (PWM) square-wave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The TDAI-1120 oscillator switches at a rate of about 400kHz. This chart plots an FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sine wave. We can see that the 400kHz peak is quite evident, at -25dBrA below the main signal level. There is also a peak at 800kHz and 1200kHz (the second and third harmonics of the 400kHz peak at -50 and -65dBrA). Those three peaks—the fundamental and its second and third harmonics—are direct results of the switching oscillators in the TDAI-1120 amp left- and right-channel modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and is therefore inaudible—as well as so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final chart above is the damping factor as a function of frequency. Both channels show a general trend of a higher damping factor at lower frequencies, and lower damping factor at higher frequencies. The right channel outperformed the left with a peak value around 80 from 20Hz to 1kHz, while the left channel achieved a damping factor of around 40 within the same frequency range. Both channels’ damping factors are down to around 10 at 20kHz.

Diego Estan
Electronics Measurement Specialist