T+A Elektroakustik R 2500 R CD-Receiver Measurements

Link: reviewed by Killain Jones on SoundStage! Hi-Fi on December 1, 2024

General Information

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

The T+A R 2500 R was conditioned for 1 hour at 1/8th full rated power (~17W 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 R 2500 R under test offered one set each of balanced (XLR) and single-ended (RCA) line-level analog inputs, one RCA moving-coil (MC) phono input (moving-magnet and no phono input is also available), one digital coaxial (RCA) input, two digital optical (TosLink) inputs, one USB digital input, one HDMI input, left/right pre-outs, two sets of speaker level outputs (A and B), and one headphone output over a balanced 4.4mm TRRS connector. A Bluetooth input is also offered.

For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (XLR) line-level, and phono (MC), as well as the headphone output. The balanced line-level input offers 6dB less gain than the unbalanced input, and about 10dB less distortion in the 3rd signal harmonic (see FFTs in this report).

Most measurements were made with a 2Vrms line-level analog input and 0dBFS digital 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 140W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum. The R 2500 R offers six digital filters for the digital inputs, labeled: long FIR, short FIR, Bezier/FIR, Bezier, NOS 1, NOS 2 . Unless otherwise noted, the long FIR filter was used.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the R 2500 R volume control is digitally controlled but operating in the analog domain. The R 2500 R overall volume range is from -51dB to +33.2dB (balanced line-level input, speaker output). It offers 1dB increments over 85 steps.

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 T+A  for the R 2500 R compared directly against our own. The published specifications are sourced from T+A’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 and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the R 2500 R was able to sustain 285W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (28.5W) for 5 seconds for 5 continuous minutes without triggering a fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top and sides of the R 2500 R were only slightly warm to the touch.

Our primary measurements revealed the following using the phono-level input, MC configuration (unless specified, assume a 1kHz 0.5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms input/output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

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

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the R 2500 R is essentially perfectly flat within the audioband (20Hz to 20kHz, 0/-0.1dB). The -3dB point is at roughly 100kHz, and 0dB at 5Hz. The R 2500 R appears to be DC-coupled. 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.

Frequency response (8-ohm loading, line-level analog input, bass and treble at min and max)

Above is a frequency-response (relative to 1kHz) plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +7/-5dB of gain/cut is available at 20Hz, and 20kHz.

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

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 R 2500 R does not invert polarity and yields only about -20 degrees of phase shift at 20kHz.

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

The chart above shows the frequency response (relative to 1kHz) for the MC phono input. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). We see a very flat response from 20Hz to 20kHz, within roughly +/-0.2dB of the RIAA target. Below 20Hz, there is a significant rise in the frequency response (+2dB at 10Hz).

Phase response (MC input)

Above is the phase response plot from 20Hz to 20kHz for the MC phono input, measured across the speaker outputs at 10W into 8 ohms. The R 2500 R phono input does not invert polarity. 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 of about -60 degrees at 200Hz and 5-6kHz.

Frequency response vs. input type (8-ohm loading, left channel only)

The chart above shows the R 2500 R’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency-response graph above (but limited to 80kHz). The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, the digital signals yielded a flat response down to 5Hz, same as the analog response. The -3dB points are: 21.1kHz for the 16/44.1 data, 45.8kHz for the 24/96, 73.2kHz for the 24/192 data, and 100kHz for the analog input. Also of note, the 16/44.1 data showed brickwall-type high-frequency filtering, while the 24/96, 24/192, and analog data did not.

Frequency response vs. filter type (16/44.1, left channel only)

The chart above shows the R 2500 R’s frequency response (relative to 1kHz) as a function of filter type measured across the speaker outputs at 10W into 8 ohms for a 16/44.1 digital input (left channel only). The blue plot is the default long FIR filter, the purple trace is the short FIR filter, the pink trace is Bezier/FIR, red is Bezier, orange NOS 1, and green NOS 2. We can see how the long FIR filter offers true brickwall filtering just past 20kHz (21kHz), while all the other filters yielded varying degrees of softer filtering between 10kHz and 20kHz. The Bezier/FIR filter yielded a +0.7dB boost centered around 12/13kHz. The -3dB points are: long FIR: 21.1kHz, short FIR: 19.3kHz, Bezier/FIR: 20.4kHz, Bezier: 17.6kHz (-0.5dB at 10kHz), NOS 1: 18.3kHz (-0.8dB at 10kHz), NOS 2: 19.0kHz (-0.8dB at 10kHz).

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outputs of the R 2500 R, where 0dBFS was set to yield 1Vrms. For this test, the digital input is swept with a dithered 1kHz input 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 data were essentially perfect as of -100dBFS down to 0dBFS. The 24/96 data were at +1dB at -120dBFS, while the 16/44.1 data were +4/+2dB at -120dBFS.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of the R 2500 R. The blue trace is for the long FIR filter, which yielded a typical symmetrical sinc function response. The purple trace is for the short FIR filter, which also yielded a symmetrical sinc function response but with less pre/post-ringing.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of R 2500 R. The pink trace is for the Bezier/FIR filter, which yielded an asymmetrical response with more post versus preringing. The red trace is for the Bezier filter, which yielded close to the same response as the short FIR filter.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of R 2500 R. The orange trace is for the NOS 1 filter, which yielded a typical symmetrical sinc function response, much like the long FIR filter.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of R 2500 R. The green trace is for the NOS 2 filter, which yielded a response with almost no pre/post-ringing, approximating that of a true non-oversampling DAC.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outputs of the R 2500 R where 0dBFS is set to 1Vrms. J-Test was developed by Julian Dunn on the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave 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 -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision to show how well the DAC rejects jitter.

Here we see a relatively strong J-Test result, with several peaks in the audioband but below the -130dBFS level. This is an indication that the R 2500 R DAC should have good jitter immunity.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outputs of the R 2500 R. The optical input yielded essentially the same result compared to the coaxial input.

J-Test (coaxial, 100ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the R 2500 R, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The result is identical to the result without the jitter injected. This is another indication of the R 2500 R DAC’s strong jitter immunity.

J-Test (optical, 100ns jitter)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the R 2500 R, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are essentially the same as with the coaxial input.

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

The chart above shows a fast Fourier transform (FFT) of the R 2500 R’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 using the long FIR filter. The steep roll-off around 20kHz in the white-noise spectrum shows that the long FIR filter is of the brickwall-type variety. There are no aliased image peaks within the audioband. The primary aliasing signal at 25kHz is suppressed at -90dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near or above the same level.

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 see that the deviations between no load and 4 ohms are very small at roughly 0.04dB. This is a very strong result and an indication of a very low output impedance, or very high damping factor. With a real speaker load, deviations measured lower at roughly 0.03dB.

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 near the rated output at 130W. The power was varied using the R 2500 R volume control. The 11W THD ratios were the lowest, ranging from 0.003% from 20Hz to 2kHz, then up to 0.02% at 20kHz. The 10W THD ratios were just slightly higher by a few dB. At 130W, THD ratios ranged from 0.005% at 20Hz to 1kHz, then up to 0.2% at 20kHz

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

The chart above shows THD ratios as a function of frequency plots for the MC phono input measured across an 8-ohm load at 10W. For this test, the input sweep is EQ’d with an inverted RIAA curve. The THD values for the MC configuration vary from around 0.05% (20Hz) down to 0.005% (80Hz to 3kHz), up to 0.02% at 20kHz.

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 R 2500 R 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). THD ratios into 8 ohms are roughly 5-8dB lower than the THD ratios into 4 ohms. THD data into 8 ohms range from 0.002% at 50mW, down to 0.004-0.005% in the 2 to 130W range. The “knee” into 8 ohms can be found just past 130W, while the 4-ohm knee can be seen around 230W. The 1% THD marks were hit at 152W and 278W into 8 and 4 ohms.

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 R 2500 R 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). THD+N ratios into 8 ohms are roughly 3-6dB lower than the THD+N ratios into 4 ohms. THD+N data into 8 ohms range from 0.02% at 50mW, down to 0.005% in the 2 to 130W range.

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 R 2500 R 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 pink trace the 2-ohm load. We find a roughly 5dB increase in THD from 8 to 4 to 2 ohms across the sweep. The 8-ohm data ranged from 0.004% from 20Hz to 2kHz, then up to 0.02% at 20kHz. Even into 2 ohms, the R 2500 R yielded reasonably low THD ratios from 0.02% to 0.05%.

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 R 2500 R 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 more variable versus frequency than those measured across the resistive dummy load, hovering both above and below the resistive dummy load data. The differences ranged from 0.03% at 20Hz down to 0.0004% at 1.5kHz for the 2-way speaker versus a steady 0.003% for the resistive load (up to 2kHz). The three-way speaker ranged from a low of 0.0015% at 3kHz and a high of 0.02% at 20kHz. This is a relatively strong result.

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 R 2500 R 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 generally, the IMD data into real speakers were lower (0.001 to 0.003%) than the steady 0.004% into the resistive load. The three-way speaker IMD data did reach 0.007% from 10kHz to 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 R 2500 R 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 1kHz 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, 0.01% from 40Hz to almost 500Hz, then down to 0.001% from 500Hz to 1kHz.

FFT spectrum – 1kHz (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 balanced analog line-level input. We see that the signal’s even-order harmonics (2/4/6/8/10kHz) dominate, with ratios at -90/-100/-110/-115/-120dBrA. This corresponds to a range between 0.003 and 0.0001%. The odd-order harmonics (3/5/7kHz) are lower, with ratios at -115/-120/-130dBrA. This corresponds to a range between 0.0002 and 0.00003%. On the right side of the signal peak, we find only two small power-supply-related noise peaks (left channel only) at -125dBrA (180Hz) and -130dBrA (300Hz).

FFT spectrum – 1kHz (line-level input, unbalanced)

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 analog line-level input. The result is very similar to the FFT above for the balanced input except for a 10dB higher 3kHz signal harmonic.

FFT spectrum – 1kHz (MC phono 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 phono (MC) analog line-level input. We see that the dominant signal harmonics are at 2kHz, with a level of -85dBrA, or 0.006%, and 4kHz, with a level of -100dBrA, or 0.001%. Power-supply related noise peaks can be seen at 60/180/300Hz, at -70 to -85dBrA, or 0.03% to 0.006%.

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

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 coaxial digital input, sampled at 16/44.1. Here the 2/3/4kHz signal harmonic peaks dominate at -90/-95/-105dBrA. This corresponds to a range between 0.003 and 0.0006%. There are no noise peaks visible above the -130dBrA noise floor.

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

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 coaxial digital input, sampled at 24/96. We see essentially the same result as with the 16/44.1 FFT above, but with a lower noise floor due to the increased bid depth.

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 sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, with no signal harmonics above the -135dBrA noise floor.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and signal harmonic peaks at a very low -130dBrA, or 0.00003%, and below level.

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. The most predominant (non-signal) peak is the second (100Hz) signal harmonic at -90dBrA, or 0.003%. Subsequent signal harmonics can be seen at and below the -100dBrA, or 0.001%, level.

FFT spectrum – 50Hz (MC phono 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 MC phono 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. The most predominant (non-signal) peaks are the 60Hz fundamental power-supply noise peak and its third (180Hz) harmonic at -70dBrA, or 0.03%, and -80dBrA, or 0.01%. The signal harmonic peaks (e.g., 100/200Hz) are difficult to discern and very low, at below the -100dBrA, or 0.001%, level.

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 -90dBRa, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz are around the -110dBrA, or 0.0003%, level.

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

Shown above is the FFT of the speaker-level output of the A25 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 very low -115dBrA, or 0.0002%, level.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)

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 digital coaxial input at 16/44.1 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -95dBrA, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)

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 digital coaxial input at 24/96 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -95dBrA, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MC phono 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 MC phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -55dBrA, or 0.2%, while the third-order modulation products, at 17kHz and 20kHz, are much lower at -110dBrA, or 0.0003%.

Squarewave 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 R 2500 R’s slew-rate performance. Rather, it should be seen as a qualitative representation of the R 2500 R’s high 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 relatively clean corners, with only mild softening and no overshoot.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor around 450 and above through most of the audioband. This is a very strong result for a medium-powered solid-state integrated amplifier.

Diego Estan
Electronics Measurement Specialist