Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 15 April 2024

Link: reviewed by Killain Jones on SoundStage! Solo on April 15, 2024

General information

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

The Bryston BHA-1 was conditioned for 30 minutes at 2Vrms at the output into 300 ohms before any measurements were taken. All measurements were taken with both channels driven.

The BHA-1 offers one set of unbalanced (RCA) inputs, one set of balanced inputs (XLR), and one mini stereo input (1/8″ TRS), which can be selected with a front panel switch. Outputs include one unbalanced headphone output (1/4″ female TRS) and two balanced headphone outputs over left/right three-pin XLR and a single stereo four-pin XLR. In addition, there are line-level balanced outputs on the rear panel so that the BHA-1 can be used as a conventional analog preamp. The front panel is adorned with a power switch, a volume control, a gain switch (high or low), an input selector and a balance control. Unless otherwise stated, measurements were made with the balanced inputs and outputs (four-pin XLR), gain set to high, with a 2Vrms output into a 300-ohm load.

Volume-control accuracy (measured at XLR outputs): left-right channel tracking

Based on the accuracy of the left/right volume channel matching (see table below), the BHA-1 volume control is likely a potentiometer operating in the analog domain.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Bryston for the BHA-1 compared directly against our own. The published specifications are sourced from Bryston’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 set at its maximum (DC to 1MHz), assume, unless otherwise stated, a 1kHz sinewave, 2Vrms input and 2Vrms output into a 300-ohm load, 10Hz to 22.4kHz bandwidth, gain set to 0dB, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the balanced line-level inputs (unless otherwise specified, assume a 1kHz sinewave, 2Vrms input and 2Vrms output into a 300-ohm load, 10Hz to 22.4kHz bandwidth, gain set to high):

Frequency response

In our frequency response (relative to 1kHz) plots above, measured into a 300-ohm load, the BHA-1 is perfectly flat within the audioband (20Hz to 20kHz). At the extremes, the BHA-1 is less than -0.1dB at 5Hz (an indication that it is AC-coupled) and about -0.3dB at 80kHz. 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

Above is the phase response plot from 20Hz to 20kHz. The BHA-1 does not invert polarity, and it yielded a worst-case 5 degrees or so of phase shift at 20kHz.

Frequency response (600-, 300-, 32-ohm loads)

In the frequency-response (RMS level relative to 0dBrA or 2Vrms at 1kHz) plots above, the blue trace is into a 600-ohm load, purple into 300 ohms, and pink into 32 ohms. Between the 600-ohms and 32-ohm loads, we find about 0.5dB of variation, an indication that the BHA-1 has a low (but not exceptionally low) output impedance.

THD ratio (unweighted) vs. frequency vs. load

The plot above shows THD ratios at the output as a function of frequency (20Hz to 20kHz) for a sinewave input stimulus and 2Vrms at the output. The blue and red plots are for left and right channels into 600 ohms, purple/green (L/R) are into 300 ohms, and pink/orange (L/R) are into 32 ohms. THD values are very low and virtually identical into all three loads. At low frequencies, THD values were slightly higher (0.002% at 20Hz for the left channel), although this may be due to the analyzer’s confounding of signal harmonics with power-supply-related noise harmonics. The evidence for this is that the left channel yielded much higher noise at the power-supply second harmonic (120Hz) than the right channel, and it’s the left channel that yielded the higher low frequency THD in the plots above.  Above 100Hz, THD ratios are flat and consistent for both channels up to 20kHz, hovering at a very low 0.0005%.

THD ratio (unweighted) vs. output power vs. load (low gain)

The plots above show THD ratios measured at the output of the BHA-1 as a function of output power for a 1kHz input sinewave using the low gain setting. The blue and red plots are for left and right channels into 600 ohms, purple/green (L/R) are into 300 ohms, and pink/orange (L/R) are into 32 ohms. The 600-ohm data yielded THD ratios from about 0.005% at 1uW, down to as low as 0.00008% (left channel) at 10mW, then up to 0.0005/0.001% (left/right) at the “knee” at about 300mW, then up to the 1% THD mark at 580mW. The 300-ohm data yielded THD ratios from 0.007% at 1uW, down to as low as 0.0001% at 20mW (left channel), then up to 0.0005/0.001% (left/right) at the “knee” at about 700mW, then up to the 1% THD mark at 1.14W. The 32-ohm data yielded higher THD ratios from about 0.02% at 1uW, down to as low as 0.00005% (left channel) at 500mW, then up to 0.0005% at the “knee” at about 3W, then up to the 1% THD mark at 5.8W.

THD+N ratio (A-weighted) vs. output power vs. load (low gain)

The plots above show THD+N ratios (A-weighted) measured at the output of the BHA-1 as a function of output power for a 1kHz input sinewave with the low gain setting. The blue and red plots are for left and right channels into 600 ohms, purple/green (L/R) are into 300 ohms, and pink/orange (L/R) are into 32 ohms. The left channel consistently yielded higher THD+N ratios (by about 5dB) due to the increased noise (see FFTs below). The 600-ohm right channel data yielded THD+N ratios from 0.03% at 1uW, down to as low as 0.0003% at 20mW. The 300-ohm right channel data yielded THD+N ratios from 0.04% at 1uW, down to as low as 0.0004% at 200mW. The 32-ohm right channel data yielded higher THD+N ratios of about 0.1% at 1uW, down to as low as 0.0004% at 300mW.

THD ratio (unweighted) vs. output power (high gain into 32 ohms)

The plots above show THD ratios measured at the output of the BHA-1 as a function of output power for a 1kHz input sinewave into a 32-ohm load for the high gain setting. The right channel outperformed the left by about 5dB. THD ratios for the right channel range from 0.03% at 1uW, down to as low as 0.0001% at 200mW, then up to 0.0005% at the “knee” at about 3W, then up to the 1% THD mark at 6.8W.

THD+N ratio (A-weighted) vs. output power (high gain into 32 ohms)

The plots above show THD+N (A-weighted) ratios measured at the output of the BHA-1 as a function of output power for a 1kHz input sinewave into a 32-ohm load for the high gain setting. The right channel outperformed the left by about 10dB. THD+N ratios for the right channel range from 0.3% at 1uW, down to as low as 0.0004% at 1-2W, then up to 0.001% at the “knee” at about 3W.

FFT spectrum – 1kHz (balanced in, balanced out, high gain)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output into a 300-ohm load at 2Vrms (0dBrA), for the balanced-in/balanced-out/high-gain configuration (default for these measurements). We see that the signal’s second harmonic, at 2kHz, is at around -120/110dBrA (left/right), or 0.0001/0.0003%, while the third harmonic, at 3kHz, is higher at around -105dBrA, or 0.0006%. On the right side of the signal peak, the power-supply fundamental (60Hz) noise peak is seen at around -120dBrA, or 0.0001%, while the second harmonic (120Hz) dominates at -95/110dBrA (left/right), or 0.002/0.0003%.  Higher-order power-supply-related harmonics can also be seen throughout most of the spectrum at -120dBrA, or 0.001%, and below. There is also a broad unknown peak at 20kHz at -125dBrA, or 0.00006%.

FFT spectrum – 1kHz (balanced in, balanced out, low gain)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output into a 300-ohm load at 2Vrms (0dBrA) for the balanced-in/balanced-out/low-gain configuration. The volume-control position was maintained at the same level, with the input signal on the analyzer increased to compensate. The main differences compared to the default configuration FFT are predictably, slightly lower noise with the left channel 120Hz peak down to -100dBrA, or 0.001%, and higher signal harmonics, with the 3kHz peak dominating at -95dBrA, or 0.002%.

FFT spectrum – 1kHz (balanced in, unbalanced out, high gain)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output into a 300-ohm load at 2Vrms (0dBrA) for the balanced-in/unbalanced-out/high-gain configuration. The volume-control position was maintained at the same level, with the input signal on the analyzer increased to compensate. The main differences compared to the default configuration FFT are lower noise with the right channel 120Hz peak down to -130dBrA, or 0.00003%, and higher signal harmonics, with the 3kHz peak dominating at -95dBrA, or 0.002%.

FFT spectrum – 1kHz (unbalanced in, unbalanced out, high gain)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output into a 300-ohm load at 2Vrms (0dBrA) for the unbalanced in/unbalanced out/high gain configuration. The volume control position was maintained at the same level, with the input signal on the analyzer increased to compensate. The main differences compared to the default configuration FFT are lower noise with the right channel 120Hz peak down to -125dBrA, or 0.00006%, and higher signal harmonics, with the 3kHz peak dominating at -90dBrA, or 0.003%, and the right channel 2kHz peak not far behind at -95dBrA, or 0.002%.

FFT spectrum – 1kHz (unbalanced in, balanced out, high gain)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output into a 300-ohm load at 2Vrms (0dBrA) for the unbalanced-in/balanced-out/high-gain configuration. The volume-control position was maintained at the same level, with the input signal on the analyzer increased to compensate. The main differences compared to the default configuration FFT are slightly higher signal harmonics, with the 3kHz peak dominating at -100dBrA, or 0.001%, and the 2kHz peak at -110/100dBrA, or 0.0003/0.001%.

FFT spectrum – 50Hz

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output into a 300-ohm load. 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 from the power supply’s second harmonic (120Hz) at -95/110dBrA (left/right), or 0.002/0.0003%.  The signal’s second harmonic (100Hz) is at -115dBrA, or 0.0002%, while the third harmonic (150Hz) is at -105dBrA, or 0.0006%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output into a 300-ohm load. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 2Vrms (0dBrA) at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is just above the noise floor for the left channel at -140dBrA, or 0.00001%, while the right channel is at -130dBrA, or 0.00003%. The second-order modulation products are buried amongst power-supply-related upper harmonics at the -120 to -140dBrA level, especially in the left channel. The third-order modulation products, at 17kHz and 20kHz, are at -115dBrA, or 0.0002%.

Intermodulation distortion FFT (APx 32 tone)

Shown above is the FFT of the output of the BHA-1 with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 2Vrms into 300 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier. In this case, most of the visible peaks in the spectrum are due to power-supply noise harmonics (60/120/180/240Hz, etc.). The grassy noise floor where the IMD products would lie are at -130dB, or 0.00003%, and below the reference level.

Square-wave response (10kHz)

Above is the 10kHz squarewave response at the output into 300 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the BHA-1’s slew-rate performance. Rather, it should be seen as a qualitative representation of its 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. The BHA-1’s reproduction of the 10kHz squarewave is very clean, with no ringing or overshoot in the corners.

Output impedance vs. frequency (unbalanced output, 20Hz to 20kHz)

The final chart above is the output impedance as a function of frequency. Both channels show a nearly constant and identical low output impedance across the audioband, between 2.22 and 2.15 ohms. The balanced outputs have the same output impedance as seen above but on each of the positive and negative portions, combining for a summed output impedance of 4.3.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 January 2023

Link: reviewed by James Hale on SoundStage! Xperience on January 1, 2023

General information

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

The Helm Audio DB12 AAAMP was conditioned for 30 minutes at 2Vrms at the output into 300 ohms before any measurements were taken. All measurements were taken with both channels driven.

The DB12 AAAMP offers one unbalanced input (1/8″ male TRS) and one unbalanced output (1/8″ female TRS). There is a volume control, but it does not control the amplifier gain or provide onboard attenuation; rather, it sends volume control signals to the source device (e.g., smartphone). There is also a Bass+ (Bass Boost) switch. Unless otherwise stated, measurements were made with the Bass+ switch disabled, the DB12 fully charged but unplugged from the USB charging port, with a 2Vrms output into a 300-ohm load.

One noteworthy attribute of the DB12 AAAMP is that if the unit is off (or the battery were to die), signals are passed through at unity gain.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Helm Audio for the DB12 AAAMP compared directly against our own. The published specifications are sourced from Helm Audio’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 1kHz sine wave, 0.5Vrms input, and 2Vrms output into a 300-ohm load, 10Hz to 90kHz bandwidth, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the balanced line-level inputs (unless otherwise specified, assume a 1kHz sine wave, 0.5Vrms input and 2Vrms output into a 300-ohm load, 10Hz to 90kHz bandwidth):

Frequency response

In our measured frequency-response plots above, the blue/red traces are with the Bass+ (Bass Boost) function disengaged, while the purple and green represent the responses with the bass-boost engaged. The DB12 is essentially perfectly flat within the audioband, into a 300-ohm load. Worst-case deviations are +/- 0.03dB. The DB12 also appears to be DC coupled, as it is ruler flat down to 5Hz. The DB12 also offers an extended bandwidth, only down about 0.4dB at 80kHz. With Bass Boost engaged, there’s a +5.5 to 6dB bump in the response between 5Hz and 100Hz. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue, purple or pink trace) is performing identically to the right channel (red, green or orange trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Frequency response vs. load

In the frequency-response plots above, the blue/red traces are into a 600-ohm load, purple/green into 300 ohms, and pink/orange into 32 ohms. The 600- and 300-ohm data are essentially identical, but into a 32-ohm load, there is a roll-off a high frequencies: -0.2dB at 20kHz, and nearly -2.5dB at 80kHz. This corroborates Helm Audio’s claim of +0.01/-0.2dB from 20Hz to 20kHz into 32 ohms.

Phase response

Above is the phase response plot from 20Hz to 20kHz. The DB12 AAAMP does not invert polarity, and yielded a worst-case 40 degrees or so of phase shift at 20kHz.

THD ratio (unweighted) vs. frequency vs. load

The plot above shows THD ratios at the output as a function of frequency (20Hz to 20kHz) for a sine-wave input stimulus and 2Vrms at the output. The blue and red plots are for left and right channels into 600 ohms, purple/green (L/R) are into 300 ohms, and pink/orange (L/R) are into 32 ohms. THD values are very low and almost identical into 600 and 300 ohm loads. These ranged from 0.0003% from 20Hz to 5kHz, them up to 0.0005% at 20kHz. The 32-ohm data yielded higher THD ratios, from 0.0004% from 20Hz to 200Hz, then a steady rise to 0.003% at 10kHz to 20kHz.

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

The plots above show THD ratios measured at the output of the DB12 as a function of output power for a 1kHz input sine wave. The blue and red plots are for left and right channels into 600 ohms, purple/green (L/R) are into 300 ohms, and pink/orange (L/R) are into 32 ohms. The 600-ohm data yielded THD ratios from 0.0002% at 0.2mW, down to as low as 0.0001% at 1 to 2mW, then up to 0.0005% at the “knee” at about 12mW, then up to the 1% THD mark at 13.6mW. The 300-ohm data yielded THD ratios from 0.0003% at 0.2mW, down to as low as 0.0001% at 2 to 3mW, then up to 0.0005% at the “knee” at about 22mW, then up to the 1% THD mark at 27mW. The 32-ohm data yielded higher and relatively flat THD ratios of about 0.001% from 0.2mW through to the “knee” at about 120mW, then up to the 1% THD mark at 164mW.

THD+N ratio (A-weighted) vs. output power vs. load

The plots above show THD+N ratios (A-weighted), measured at the output of the DB12 as a function of output power for a 1kHz input sine wave. The blue and red plots are for left and right channels into 600 ohms, purple/green (L/R) are into 300 ohms, and pink/orange (L/R) are into 32 ohms. The 600-ohm data yielded THD+N ratios from 0.001% at 0.2mW, down to as low as 0.0003% at 3 to 5mW, then up to 0.0005% at the “knee.” The 300-ohm data yielded THD+N ratios from 0.0015% at 0.2mW, down to as low as 0.0003% at 5 to 10mW, then up to 0.0005% at the “knee.” The 32-ohm data yielded higher THD+N ratios of about 0.005% at 0.2mW, down to as low as 0.001% from 10mW to the “knee.”

FFT spectrum – 1kHz

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output into a 300-ohm load at 2Vrms (0dBrA). We see that the signal’s second harmonic, at 2kHz, is at around -120dBrA, or 0.0001%, while the third harmonic, at 3 kHz, is higher at -110dBrA, or 0.0003%. Higher-order even harmonics (4/6/8/10kHz) can be seen below the -130dBrA, or 0.00003%, level. On the right side of the signal peak, only a very small peak at the power-supply fundamental (60Hz) can be seen at a vanishingly low -140dBrA, or 0.00001%.

FFT spectrum – 50Hz

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output into a 300-ohm load. 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 from the signal’s third harmonic (3kHz) at -110dBrA, or 0.0003%. The second signal harmonic (100Hz) is at -130dBrA, or 0.00003%. There are no visible power-supply-related noise peaks.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output into a 300-ohm load. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 2Vrms (0dBrA) at the output. We find that the second-order-modulation product (i.e., the difference signal of 1kHz) is at -125/-130dBrA (left/right), or 0.00006/0.00003%, while the third-order modulation products, at 17kHz and 20kHz, are just above -120dBrA, or 0.0001%.

Squarewave response (10kHz)

Above is the 10kHz squarewave response at the output into 300 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the DB12’s slew-rate performance. Rather, it should be seen as a qualitative representation of its relatively high bandwidth. An ideal squarewave 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 DB12’s reproduction of the 10kHz squarewave is clean, with only mild ringing in the corners.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 10 August 2022

Reviewed on: SoundStage! Solo, August 2022

I measured the KZ AZ09 using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator and an Audiomatica Clio 12 QC audio analyzer. This is not the kind of comprehensive measurements SoundStage! would normally do with audio electronics; it’s merely an attempt to gauge the basic operating parameters and performance limits of the device. All measurements involving earphones are “flat”; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the AZ09’s frequency response measured straight into the Clio 12 QC analyzer, with no load. The measurement level was at a “medium” level of 178mV (the drive level required to reach 1mW into a 32-ohm load). Bass rolloff is about -0.1dB at 10Hz; treble rolloff is about -0.3dB at 20Hz—pretty good for a $30 device, and not enough to cause noticeable colorations. There’s a roughly 0.02dB level mismatch between the left and right channels, which will not be audible. The glitches at 5 and 7kHz appeared consistently in both channels; I suspect they are Bluetooth artifacts. They are of too high a Q and too low in magnitude to be audible.

This chart shows how the AZ09 affected the response of the TinHiFi T3 Plus and CCA C10 earphones versus a cabled connection from those earphones to a Musical Fidelity V-CAN headphone amp. With both earphones, the AZ09 produced a tiny bit of extra bass compared with the wired connection: about +1dB at 10Hz for the T3 Pluses, and +1.5dB for the CCA C10s. There are also some tiny differences in the treble, but these are likely due to ordinary measurement-to-measurement variation.

This chart shows the total harmonic distortion plus noise (THD+N) of the AZ09 at gradually increasing output levels, measured into a 32-ohm load. (I would normally measure this into 250- and 600-ohm loads as well, but I have never encountered earphones with such high impedances so the measurement would be irrelevant.) As we see with almost all amplifiers, the signal-to-noise ratio falls as the output increases. Measured at 1kHz, the AZ09 reaches its minimum THD+N at its maximum output of 4.07mW, so at that frequency, it seems impossible to make the AZ09 clip. Wondering if the AZ09 could perform as well in the bass, I reduced the test frequency to 20Hz, and at that frequency, I was able to make the AZ09 clip—although THD+N rose only to 0.73% at the maximum 20Hz output of 4.175mW. That’s not an audible level of distortion at such a low frequency.

Note that the above chart also shows that the AZ09’s output peaks at about 4mW into 32 ohms. That’s not much, but with a typical set of earphones rated at 105dB sensitivity with a 1mW signal, that’ll get you up to 111dB SPL peaks, which is plenty, and enough to damage your hearing if you run the AZ09 at max volume for long periods of time.

Best-case latency I measured from the AZ09 was about 80ms, which is excellent for a true wireless product, although the latency sometimes jumped up into the 300ms area with some of the measurements I did; that’s more typical for a true wireless product. This is probably irrelevant, though, because latency only matters when you’re watching videos or playing games, and it seems unlikely this product would be used for those purposes.

Output impedance of the AZ09, measured at 1kHz, is 9.1 ohms—which is fairly low compared with other headphone/earphone amps, and probably not high enough to alter the frequency response of any earphones the AZ09 would be used with.

Bottom line: Obviously, the AZ09 has performance limitations compared with a conventional headphone amp or DAC-amp, but it seems well-designed overall, and is unlikely to present any audible problems.

. . . Brent Butterworth
brentb@soundstagenetwork.com

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 July 2022

Link: reviewed by James Hale on SoundStage! Xperience on July 1, 2022

General Information

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

The iFi Audio Go Bar was conditioned for 30 minutes at 0dBFS (2Vrms out) into 300 ohms before any measurements were taken.

The Go Bar allows for a USB input only. There are two headphone outputs: one unbalanced over 3.5mm TRS: and one balanced over 4.4mm TRRS.  Comparisons were made between unbalanced and balanced outputs for a 24/96 0dBFS input, in terms of noise, THD, and dynamic range. Other than the extra 6dB of gain and output voltage, the two outputs were virtually identical.

The Go Bar offers an in-ear-monitor (IEM) matching selector, which lowers output voltage for sensitive IEMs and increases the output impedance; this switch was left in the Off position for the measurements. There is also a Turbo Mode associated with the use of volume. Engaging Turbo Mode allows for the Go Bar full output-voltage potential. Turbo Mode was left engaged for the measurements. There are also four user selectable digital filters. All measurements below, unless otherwise stated, are for the balanced output, using the standard STD filter. The four filters are described as follows in the Go Bar manual:

• Bit-Perfect (BP): no digital filtering, no pre- or post-ringing
• Standard (STD): modest filtering, modest pre- and post-ringing
• Minimum Phase (MIN): slow roll-off, minimum pre- and post-ringing
• Giggs-Transient-Optimized (GTO): upsampled to 352kHz or 384kHz, minimum filtering, no pre-ringing, minimum post-ringing

Because the Go Bar exhibits considerable noise 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 FFT measurements. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

Based on the accuracy and repeatable results at various volume levels of the left/right channel matching (see table below), and the lack of analog inputs, the Go Bar volume control is likely applied in the digital domain. The volume control offers 53 steps in 2dB to 0.5dB increments.

Volume-control accuracy (measured at headphone output): left-right channel tracking

Published specifications vs. our primary measurements

The table below summarizes the measurements published by iFi Audio for the Go Bar compared directly against our own. The published specifications are sourced from iFi’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 set at its maximum (DC to 1MHz), assume, unless otherwise stated, the coaxial digital input (1kHz sine wave sampled at 96kHz at 0dBFS/2Vrms out), the balanced line-level output into 300 ohms, using a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

* into 300 ohms, THD for the left channel was the same as the right, at 0.0026%

Our primary measurements revealed the following using the coaxial input and the balanced output (unless specified, assume a 1kHz sine wave sampled at 96kHz at 0dBFS/2Vrms out, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

Frequency response (16/44.1, 24/96, 24/192)

The plot above shows the Go Bar frequency response as a function of sample rate. The blue/red traces are for a 44.1kHz sampled dithered digital input signal from 5Hz to 22kHz, the purple/green traces are for a 96kHz sampled dithered digital input signal from 5Hz to 48kHz, and, finally, orange/pink represents 192kHz sampled data from 5Hz to 96kHz. The behavior at low frequencies is the same for the digital input—perfectly flat down to 5Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering sharp filtering around 22k, 48k, and 96kHz (half the respective sample rate). The -3dB point for each sample rate is roughly 21.1, 45.9 and 89.7kHz, respectively. This corroborates iFi’s claim of a frequency response of 20Hz-45kHz (-3dB). It is also obvious from the plots above that all three responses offer “brick-wall”-type behavior. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue, purple or orange trace) is performing identically to the right channel (red, green or pink trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Frequency response (96kHz, xBase on/off)

The plot above shows the Go Bar frequency response with and without xBass engaged, for 96kHz dithered sampled data. The blue/red without xBass and the purple/green traces are with xBass engaged. We can see that xBass applies about 8dB of boost at 20Hz, and is flat by about 300Hz.

Frequency response (44.1kHz, all four filters)

The plots above show frequency-response for 44.1kHz sampled input data for filters 1 through 4 into a 300 ohm-load for the left channel only. The Standard (STD) filter is in red, Giggs-Transient-Optimized (GTO) in purple, Bit-Perfect (BP) in green, and Minimum Phase (MIN) in pink. The graph is zoomed in from 1kHz to 22kHz, to highlight the various responses of the filters around the “knee” of the response. At 20kHz, the STD filter is at +0.1dB, the GTO filter is at -0.3dB, the BP filter is at -3dB, and the MIN filter is at 0dB. The STD and MIN filters have nearly identical frequency response behaviors.

Note: the filter characteristics are described under General Information section above. Our measured frequency responses generally match the descriptions provided by iFi Audio.

Digital linearity (96kHz)

The graph above shows the results of a linearity test for 96kHz sampled input data. 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 is a straight flat line at 0dB (i.e., the amplitude of the digital input perfectly matches the amplitude of the measured analog output). The data is perfectly linear down to -100dBFS and only -1dB or better at -120dBFS.

Impulse response (44.1kHz, STD and BP filters)

The graph above shows the impulse responses for the first two filter types (STD and BP), for 44.1kHz sampled dithered data, using the Audio Precision’s Transfer Function/Impulse Response function. STD is in blue and BP in pink.

Note: the filter characteristics are described under General Information above. Our measured impulses responses generally match the descriptions provided by iFi Audio.

Impulse response (44.1kHz, GTO and MIN filters)

The graph above shows the impulse responses for the two other two filter types (GTO and MIN), for 44.1kHz sampled dithered data, using the Audio Precision’s Transfer Function/Impulse Response function. GTO is in purple and MIN in green.

Note: the filter characteristics are described under General information above. Our measured impulses responses generally match the descriptions provided by iFi Audio.

J-Test

The plot above shows the results of the J-Test test for the USB input measured at the balanced line level output of the Go Bar. 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 (the main peak). 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 -144dBrA (fundamental at 250Hz) down to -170dBrA for the odd harmonics.  The test file can also be used in conjunction with artificially injected sine-wave jitter by the Audio Precision, to also show how well the DAC rejects jitter.

The FFT shows some of the alternating 500Hz peaks in the audio band but at low levels—below -130dBrA. This is an indication that the Go Bar should not be sensitive to jitter.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (STD filter)

The plot above shows a fast Fourier transform (FFT) of the Go Bar balanced output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sine wave at -1dBFS sampled at 44.1kHz (purple/green), using the STD filter. The sharp rolloff above 20kHz in the white-noise spectrum shows the implementation of the brick-wall-type reconstruction filter. There are two imaged aliasing artifacts in the audio band above the -135dBrA noise floor, at around 6kHz (-110dBrA) and 13kHz (-115dBrA). The primary aliasing signal at 25kHz is at -115dBrA, with subsequent harmonics of the 25kHz peak near -80 and -70dBrA.

Note: the filter characteristics are described under General information above. Our measured FFTs generally match the descriptions provided by iFi Audio.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (BP filter)

The plot above shows a fast Fourier transform (FFT) of the Go Bar balanced output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sine wave at -1dBFS sampled at 44.1kHz (purple/green), using the BP filter. As advertised, the BP filter uses no filter at all, which is evident in the very slow rolloff in the noise spectrum. As a consequence, there are obvious imaged aliasing artifacts in the audio band above the -135dBrA noise floor, as high as -90dBrA at 6kHz and 13kHz. The primary aliasing signal at 25kHz is hardly suppressed at all, as is expected, and sits at -5dBrA.  

Note: the filter characteristics are described under General information above. Our measured FFTs generally match the descriptions provided by iFi Audio.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (GTO filter)

The plot above shows a fast Fourier transform (FFT) of the Go Bar balanced output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sine wave at -1dBFS sampled at 44.1kHz (purple/green), using the GTO filter. The GTO filter offers a softer rolloff above 20kHz in the white-noise spectrum compared to the STD and MIN filters. There are two imaged aliasing artifacts in the audio band above the -135dBrA noise floor at around 6kHz (-100dBrA) and 13kHz (-100dBrA). The primary aliasing signal at 25kHz is only mildly suppressed at -20dBrA, with subsequent harmonics of the 25kHz peak below this level.

Note: the filter characteristics are described under General information above. Our measured FFTs generally match the descriptions provided by iFi Audio.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (MIN filter)

The plot above shows a fast Fourier transform (FFT) of the Go Bar balanced output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sine wave at -1dBFS sampled at 44.1kHz (purple/green), using the MIN filter. The sharp rolloff above 20kHz in the white-noise spectrum shows the implementation of the brick-wall-type reconstruction filter. There are two imaged aliasing artifacts in the audio band above the -135dBrA noise floor, at around 6kHz (-110dBrA) and 13kHz (-115dBrA). The primary aliasing signal at 25kHz is at -65dBrA, with subsequent harmonics of the 25kHz peak near -80 and -70dBrA. The behavior of the MIN filter is similar to that of the STD filter.

Note: the filter characteristics are described under General information above. Our measured FFTs generally match the descriptions provided by iFi Audio.

THD ratio (unweighted) vs. frequency vs. load (24/96)

The chart above shows THD ratios at the balanced output into 600 ohms (blue/red), 300 ohms (purple/green) and 32 ohms (pink/orange) for a constant 2Vrms output as a function of frequency, for 96kHz sampled dithered input data. Into 600 ohms, the right channel clearly outperforms the left by almost 10dB. Into 300 ohms, THD ratios are between 0.002 and 0.003%, the same as the right channel into 600 ohms. At 6kHz, THD ratios into 300 ohms are nearing 0.005%. Into 32 ohms, THD ratios are a bit higher, between slightly above, and below 0.005%.

THD ratio (unweighted) vs. output (600, 300, and 32 ohms) at 1kHz

The chart above shows THD ratios at the balanced output into 600 ohms (blue/red), 300 ohms (purple/green), and 32 ohms (pink/orange) at 1kHz as a function of output voltage, for 96kHz sampled dithered input data. Up to about 50mVrms, all three data sets track, with a THD ratio of about 0.005%. From 50mVrms to about 2Vrms (125mW), the 32-ohm data is fairly flat between 0.005% and 0.01%. At 200mVrms, the 600 and 300-ohm data still track closely, at just above 0.001%. From 200mVrms to about 2Vrms (13mW), the 300-ohm data is fairly flat between 0.001% and 0.002%. The 600-ohm data reaches a THD low of about 0.0006% at 400mVrms, then up to 0.002% at 2Vrms (6.7mW). The 1% THD mark is close to the same into 600 ohms (95mW) and 300 ohms (177mW), just over 7Vrms. Into 32 ohms, the 1% THD mark is just over 5.5Vrms, at 1W.

THD+N ratio (unweighted) vs. output (96kHz for 600, 300, and 32 ohms) at 1kHz

The chart above shows THD+N ratios at the balanced output into 600 ohms (blue/red), 300 ohms (purple/green), and 32 ohms (pink/orange) at 1kHz as a function of output voltage, for 96kHz sampled dithered input data. All data sets track closely up to about 200mVrms, where THD+N ratios measure 0.015%. Beyond 200mVrms, the 32-ohm data reaches a low of 0.005% at 2Vrms, while the 300 and 600-ohm data track almost perfectly, and reach a THD+N low of just over 0.002% at 2Vrms.

Intermodulation distortion vs generator level (SMPTE, 60Hz:4kHz, 4:1 for 600, 300, and 32 ohms)

The chart above shows intermodulation distortion (IMD) ratios measured at the balanced output into 600 ohms (blue/red), 300 ohms (purple/green), and 32 ohms (pink/orange) from -60dBFS to 0dBFS, for 96kHz sampled dithered input data. Here, the SMPTE IMD method was used, where the primary frequency (F1 = 60Hz) and the secondary frequency (F2 = 7kHz) are mixed at a ratio of 4:1. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 600-ohm data yielded the highest IMD ratios, from 2% down to 0.06% at -30dBFS, then up to 0.3% (left) at -18dBFS, then back down to roughly 0.02% at 0dBFS. The 300- and 32-ohm data track perfectly down to -30dBFS, where IMD ratios measured 0.02%. Beyond this threshold, the 32-ohm data flattens out and reaches 0.01% at 0dBFS. The 300-ohm data reaches an IMD low of nearly 0.002% just shy of 0dBFS.

FFT spectrum – 1kHz (44.1kHz data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 300 ohms sampled at 44.1kHz. We see the third signal harmonic (3kHz) dominating at -95dBrA, or 0.002%, while the second harmonic (2kHz) is between -100 and -110dBrA (left/right), or 0.001 and 0.0003%. Subsequent odd harmonics (3, 5, 7, 9kHz) can be seen at and below -110dBrA, or 0.0003%. There are no power-supply noise peaks to speak of to the left of the main signal peak.

FFT spectrum – 1kHz (96kHz data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 300 ohm sampled at 96kHz. Within the audio band, we see essentially the same FFT as with the 44.1kHz sampled data above.

FFT spectrum – 1kHz (44.1kHz data at -90dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 300 ohms, sampled at 44.1kHz at -90dBFS. We see the main peak at the correct amplitude, surround by an elevated noise floor at around -100dBrA.

FFT spectrum – 1kHz (96kHz data at -90dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 300 ohm, sampled at 44.1kHz at -90dBFS. We see the main peak at the correct amplitude, surround by an elevated noise floor at around -100dBrA. The noise floor is identical to the 44.1kHz FFT above because as a USB DAC, bit depth could not be altered and is held at 32 bits for all sample rates. 

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 44.1kHz)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the balanced output into 300 ohms sampled at 44.1kHz. The input dBFS values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 2Vrms (0dBrA) at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -95/100dBRa (left/right), or 0.002/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are also at -95dBrA.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 96kHz)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the balanced output into 300 ohms sampled at 44.1kHz. The input dBFS values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 2Vrms (0dBrA) at the output. Within the audioband, we see essentially the same IMD FFT as with the 44.1kHz sampled data above.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 April 2021

Link: reviewed by Mark Phillips on SoundStage! Solo on April 1, 2021

General information

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

The Kinki Studio Vision THR-1 was conditioned for 1 hour with 2Vrms at the output (into 300 ohms) before any measurements were taken.

The THR-1 offers one set each of balanced (XLR, Ch2) and unbalanced (RCA, Ch1) inputs, one set of variable line-level balanced (XLR) outputs, one 4-pin XLR headphone output (Phone1), and two ¼″ TRS headphone outputs (Phone2 and Phone3). There is a button on the front panel to select between Ch1 (RCA) and Ch2 (XLR) inputs, as well as a switch to select between the headphone outputs (Phone, all three always active when selected), or the preamp outputs (Output).

There were a couple peculiarities with the THR-1 that merit pointing out. The balanced inputs and outputs are not actually balanced; they are single-ended connections with balanced XLR connectors. For the XLR input, pin 1 is connected to ground, pin 2 is connected to the input, and pin 3 is connected to a 50k ohm resistor then ground. For the XLR line-level output, pin 1 is connected to ground, pin 2 to the output, and pin 3 to ground through a 100-ohm resistor. For the XLR headphone output, pins 1 and 3 are connected to the output, while pins 2 and 4 are grounded. There are no differences between Phone1 (XLR) and Phone2 (¼″ TRS, also labelled High) outputs other than the physical connectors. Pins 1/3 (L/R) from Phone1 are electrically connected to the tip/ring (L/R) of Phone2. The only difference between Phone3 (also labeled Low) and outputs Phone1 and Phone2 is that 1 and 2 have a 50-ohm output impedance, while Phone3 has a 100-ohm output impedance.

The next peculiarity is that the THR-1 inputs and line level outputs are not buffered and are directly connected to the 10k ohms potentiometer used as the volume control. This means that the input and output impedances of the THR-1 are variable. When used as a preamplifier, the variability of the input impedance will depend on the input impedance of the amplifier following it; the higher the amplifier input impedance, the closer the input impedance of the THR-1 will appear as a constant 10k ohms. The line-level output impedance will vary depending on the volume position. When set near minimum, it’s 110 ohms, at 2 o’clock 2.6k ohms, and at maximum, 564 ohms. When used as a headphone amplifier, the input impedance varies between 10k ohms (volume minimum) to 775 ohms (volume maximum). The effect this will have on overall system performance will depend on the source’s (connected to the THR-1) output impedance and ability to drive loads below 1k ohms (if the volume pot is used near its maximum setting). If the source’s output impedance is high (e.g., 1k ohm), raising the volume (i.e., reducing the input impedance) in the THR-1 will have two opposing effects: raising the gain inside the THR-1, as well as lowering the signal output level out of the source component.

Unless otherwise specified, the balanced input connection was used for all measurements. Most measurements were done with the volume set to unity gain (about 2 o’clock), with the exception of the signal-to-noise ratio (SNR), where volume was set to maximum. Outputs 1 and 3 (Phone1 and Phone3) were used as outputs in the tables below, while Output 1 (Phone1) was used for the charts below. When used as a preamplifier (which is actually passive and just a 10k ohm potentiometer), gain (volume maximum) was measured at -0.5dB (-6.5dB for the balanced input) into the Audio Precision’s 200k ohm input load. Decreasing the input impedance of the next device in the audio chain will decrease the gain, which is the nature of a passive preamp.

Volume-control accuracy (measured at XLR outputs): left-right channel tracking

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Kinki Studio for the Vision THR-1 compared directly against our own. The published specifications are sourced from Kinki Studio’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 90kHz, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the balanced line-level inputs (unless specified, assume a 1kHz sine wave, 2Vrms output, 300-ohm loading, 10Hz to 90kHz bandwidth):

Frequency response

In our measured frequency response plot above, the THR-1 is essentially flat within the audioband (20Hz to 20kHz). Kinki’s claim of ±dB from 20Hz to 300kHz is not corroborated by our measurement, as the THR-1 is at +1dB at 140kHz. However, this is of zero audible consequence. The THR-1 can be considered a high-bandwidth audio device because of its high-frequency extension past 100kHz. 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.

Phase response

Above is the phase response plot for the THR-1 from 20Hz to 20kHz. The THR-1 does not invert polarity, and there is virtually no phase shift throughout the audioband.

Frequency response (600-, 300-, 32-ohm loads)

The chart above shows RMS level (relative to 0dBrA, which here is 2Vrms at the balanced output into 300 ohms) as a function of frequency for the left channel only. The blue plot is into a 600-ohm load, the purple is into a 300-ohm load, and the orange is into a 32-ohm load. Here we find a deviation of about 7.5dB between 600 ohms and 32-ohms, which is a reflection of the relatively high output impedance of 51 ohms.

THD ratio (unweighted) vs. frequency (600-, 300-, 32-ohm loads)

The chart above shows THD ratios at the THR-1’s Phone1 output as a function of frequency (20Hz to 20kHz) for a sine-wave stimulus at the balanced line-level input for a 2Vrms output. The blue and red plots are for left and right channels into 300 ohms, purple/green into a 32-ohm load. THD into a 600-ohm load was also measured but yielded effectively identical results compared to the 300-ohm data, so those results were omitted for simplicity and clarity in the the chart. There is up to a 15dB improvement in THD ratios into 600 and 300 ohms versus 32 ohms. Into 600 and 300 ohms, the THD values are low from 20Hz to 2kHz, between 0.002% and 0.0005%. At 20kHz, THD ratios reach 0.1%. Into a 32-ohm load, THD values start at 0.005% at 20Hz, down to 0.001% at 200Hz, then steadily increase up to just over 0.1% at 20kHz.

THD ratio (unweighted) vs. output power at 1kHz (300- and 600-ohm loads)

The chart above shows THD ratios at the THR-1’s Phone1 output as a function of output power for the balanced line-level input for an 600-ohm load (blue/red for left/right) and a 300-ohm load (purple/green for left/right). At 1mW, THD values are just below 0.001% for both 600- and 300-ohm data. Above 20mW, the 300-ohm THD values are slightly lower than the 600-ohm values by 2-5dB. At the “knees,” the 600-ohm THD value is at around 0.04%, nearing 2W, while the 300-ohm THD value is at around 0.03% at about 3W. The 1% THD value for the 600-ohm data is at 2.2W, while the 300-ohm data is at 3.5W.

THD+N ratio (unweighted) vs. output power at 1kHz (300- and 600-ohm loads)

The chart above shows THD+N ratios at the THR-1’s Phone1 output as a function of output power for the balanced line-level input, for an 600-ohm load (blue/red for left/right) and a 300-ohm load (purple/green for left/right). At 1mW, THD+N values are between 0.01% and 0.02% for both 600- and 300-ohm data, then dipping down to as low as 0.003% at 50mW.

FFT spectrum – 1kHz

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across a 300-ohm load at 2Vrms. We see that the second harmonic, at 2kHz, is just below -100dBrA, or 0.001% (relative to the reference 0dB signal), while the third harmonic, at 3kHz, is at -110dBrA, or 0.0003%. The fourth and fifth harmonics are even lower, and are difficult to distinguish amongst the power-supply-noise harmonic peaks. Below 1kHz, we see noise artifacts, from the 60Hz fundamental at -105dBrA and the second harmonic at 120Hz at -100dBrA (left) and -105dBrA (right), as well as a long series of visible higher harmonics between -105 and -120dBrA.

FFT spectrum – 50Hz

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across a 300-ohm load at 2Vrms. 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 of the 50Hz signal (100Hz) is at -125dBrA, or about 0.0006%, while the third harmonic at 150Hz is even lower at -135 dBrA, or 0.00002%, for both channels. Here again, the noise artifacts due to power-supply noise dominate, between -100dBrA and -120dBrA, which are respectively 0.001% and 0.0001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)

Shown above is the FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone at the balanced input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 2Vrms (0dBrA) into 300 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at about -110dBrA, or 0.0003%, for the right channel; -125dBrA, or 0.00006%, for the left channel; while the third-order modulation products, at 17kHz and 20kHz, are at and just above -80dBrA, or 0.01%.

Square-wave response (10kHz)

Above is the 10kHz square-wave response of the THR-1 into 300 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the THR-1’s slew-rate performance. Rather, it should be seen as a qualitative representation of the THR-1’s extended 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. In the case of the THR-1, the square wave is reproduced cleanly, with mild overshoot and undershoot, which can be seen by the triangular-shaped spikes in the corners of the transitions.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 February 2021

Links: reviewed by Mark Phillips on SoundStage! Solo on February 1, 2021

General information

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

The Coda was conditioned for 30 minutes at 2Vrms at the output before any measurements were taken.

The Coda offers a USB Type A input and a 3.5mm TRS headphone output. The Coda also offers three digital filters: minimum phase, linear phase, and hybrid. Unless otherwise stated, the minimum-phase filter was used for our primary measurements and graphs. The Coda and the Audio Precision analyzer were connected to the same Microsoft Surface Pro 6 laptop via USB Type-A connection. The Coda also offers a volume control; however, volume changes are not performed by the Coda internally, but rather by the computer and its operating system in response to commands sent by the Coda. Volume was maintained at maximum for all measurements.

Published specifications vs. our primary measurements

The table below summarizes our primary measurements performed on the Coda. Here we can compare directly against Clarus’s own published specifications for the Coda, which are stated as follows:

• Maximum output voltage: 2.0Vrms
• Output impedance: <1 ohm
• Input impedance: MM/MC HIGH: 47k ohms, MC LOW: 1k ohms, MC VERY LOW: 110 ohms
• SNR: 120dB
• THD+N: -112dB (~0.0003%)

Our primary measurements revealed the following using the USB input (unless specified, assume a 0dBFS 1kHz sinewave input, 2Vrms output, 300-ohm loading, 10Hz to 90kHz bandwidth, minimum-phase filter):

The Clarus Coda’s maximum output voltage of 2.0Vrms was corroborated, where we measured 2.05Vrms for a 0dBFS input signal into a 300-ohm load.

Clarus’s claim of a 1-ohm output impedance was not quite corroborated by our measured 1.56-ohm output impedance, however, this is still very low and desirable for a headphone amplifier.

The signal-to-noise ratio (SNR) claim of 120dB (we are assuming A-weighted) was not corroborated by our dynamic range measurements of 105dB (A-weighted, 96kHz sample rate). For a DAC, dynamic range is a more appropriate measurement than SNR, because in some DACs, the output of the device is switched off when there is no signal. The Audio Precision uses the AES17 method for dynamic-range measurements, whereby a 0dBFS 1kHz sine wave input signal is applied, and the noise measurement is performed using a -60 dBFS stimulus, which is then notched out. That said, when we measured SNR (A-weighted) with the Coda, we measured slightly worse (lower) values compared to our dynamic-range measurements, though the values were still commendably high.

The THD+N claims from Clarus were not corroborated into a 300-ohm load at 0dBFS for a 1kHz input signal, where we measured (A-weighted, 96kHz sample rate) at worst 0.0015% (-98dB, shown in table above) and at best 0.0008% (-102dB, from our swept THD versus frequency graph shown below) compared to Clarus’s claim of 0.00025% (-112dB). However, as can also be seen in the THD versus frequency graph below, between 300 and 500Hz, into a 32-ohm load at -6dBFS, the Clarus did achieve 0.0003% (-110dB) THD, which is very low and extremely close to the specified value by Clarus.

Frequency response (44.1, 96, and 192kHz sample rates)

In our measured frequency-response plots above for a 0dBFS input signal sampled at 44.1kHz (blue/red = left/right channels), 96kHz (purple/green), and 192kHz (orange/pink) into a 300-ohm load, the Coda deviates less than +/-0.1dB from flat from 5Hz to 20kHz (with the exception of the 44.1kHz data). The -3dB points are at 17kHz (44.1kHz sample rate), 38kHz (96kHz), and 72kHz (192kHz). In the graph above and some of the graphs below, there may be two visible traces representing the left channel (blue, purple, or orange traces) and the right channel (red, green, or pink traces). On other graphs, only one trace may be visible. When there is only one trace visible, it is because the left and right channels are tracking extremely closely, so as not to show a difference with the chosen axis scales. When channels are not matched as well, two traces become visible.

Frequency response (600-, 300-, 32-ohm loads, 96kHz sample rate)

The chart above shows RMS level (relative to 0dBrA, which here is 1Vrms or -6dBFS at the input) as a function of frequency for the left channel only. The blue plot is into a 600-ohm load, the purple is into a 300-ohm load, and the orange is into a 32-ohm load. Here we find that all plots are very closely grouped together (within about 0.3dB), which is an indication of a very low output impedance.

Frequency response (linear-phase, minimum-phase, hybrid filters with 96kHz sample rate)

The plots above show frequency-response for a 0dBFS input signal sampled at 96kHz for the minimum phase filter (blue), the linear phase filter (purple), and the hybrid filter (orange) into a 300-ohm load for the left channel only. We can see that the hybrid filter provides the most “brick-wall” type response (i.e., a very steep rolloff), and the linear phase filter shows the earliest attenuation, visible above 10kHz. The -3dB points are at 39kHz (minimum phase), 36kHz (linear phase), and 40kHz (hybrid).

Frequency response (linear-phase, minimum-phase, hybrid filters with 44.1kHz sample rate)

The chart above shows the frequency-responses for a 0dBFS input signal sampled at 44.1kHz for the minimum-phase (blue line), the linear-phase (purple), and hybrid (orange) filters into a 300-ohm load for the left channel only. The graph is zoomed in from 1kHz to 22kHz, and extra sampling points were introduced around the corner frequency (the “knee”) to highlight the various responses of the three filters. As with the 96kHz chart above, we can see again that the hybrid filter provides the most “brick-wall”-type response, and the linear phase filter shows the earliest attenuation, visible above 7kHz. The -3dB points are at 19.2kHz (minimum phase), 19kHz (linear phase), and 21kHz (hybrid).

THD ratio (unweighted) vs. frequency (600-, 300-, 32-ohm loads)

The chart above shows THD ratio as a function of frequency into 600-ohm (blue/red), 300-ohm (purple/green), and 32-ohm (orange/pink) loads for a -6dBFS input signal (1Vrms output). THD values at 20Hz are just below 0.001% for all three loads. The 600- and 300-ohm THD data match very closely, where it’s mostly constant up to 3kHz, then there is a rise to 0.004% at 20kHz for the 600-ohm load, and 0.005% for the 300-ohm load. Between 50Hz and 1kHz, the 32-ohm load THD values are demonstrably lower (by almost 10dB between 300-500Hz) than the 600- and 300-ohm data. However, past 2kHz, the 32-ohm load THD data rises up past 0.01% between 10kHz and 20kHz. Interestingly, there’s a rise in THD at 200Hz and 2kHz for all data sets. This phenomenon was repeatable across several measurements over several days.

THD ratio (unweighted) vs. output power at 1kHz (600-, 300-, 32-ohm loads)

Above we can see a plot of THD ratios as a function of output power into 600-ohm (blue/red), 300-ohm (purple/green), and 32-ohm (orange/pink) loads for a 1kHz signal sampled at 96kHz swept from -60dBFS to 0dBFS. The 600- and 300-ohm plots are very similar (600-ohm performed 2-4dB better), showing THD ratios from about 0.5% at 20nW, down to near 0.001% at 5-10mW (0dBFS). The 32-ohm plot is near 1% just above 100nW, then dips down to near 0.001% at 50mW (about -4dBFS input signal), then a sharp rise in THD as the Coda’s output is no longer able to sustain the required current. The 1% THD value is reached just past 70mW.

THD+N ratio (unweighted) vs. output power at 1kHz (600-, 300-, 32-ohm loads)

Above is a chart of THD+N ratios as a function of output power into 600-ohm (blue/red), 300-ohm (purple/green), and 32-ohm (orange/pink) loads for a 1kHz signal sampled at 96kHz swept from -60dBFS to 0dBFS. The 600 and 300-load plots are very similar (600-ohm performed 2-3dB better), showing THD+N ratios from about 1.5% at 20nW, down to 0.002% at 5-10mW (0dBFS). The 32-ohm plot is near 1% just above 100nW, then dips down to near 0.002% at 50mW (about -4dBFS input signal), then a sharp rise in THD as the Coda’s output is no longer able to sustain the required current. The 1% THD+N value is reached just past 70mW. The Coda is a low-noise device, and because of this the THD+N and THD (above) charts are similar (i.e., THD ratios dominate above the noise).

Digital linearity (44.1kHz and 96kHz sample rates)

The plot above shows the results of a linearity test. For this test, the digital input to the Coda 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 down to the lowest possible level (-120dBFS). The results were identical for both 44.1kHz and 96kHz sample rates. The Coda approaches the ideal 0dB relative level just below -90dBFS, then yielding perfect results from -85dBFS to 0dBFS. At -120dBFS, both channels overshot the ideal output signal amplitude by about 25dB.

FFT spectrum – 1kHz (0dBFS, 44.1kHz sample rate)

Shown above is a fast Fourier Transform (FFT) of a 1kHz input sinewave stimulus at 0dBFS sampled at 44.1kHz, which results in the reference output voltage of 2Vrms into a 300-ohm load. Here we see the worst-case signal harmonic (2kHz) at -100dBrA. The third-order harmonic (3kHz) is at about -115dBRa. The other peaks (hovering just below -120dBrA) seen to the left and to the right of the primary 1kHz signal peak are likely digital-filter aliasing artifacts.

FFT spectrum – 1kHz (0dBFS, 96kHz sample rate)

Shown above is an FFT of a 1kHz input sinewave stimulus at 0dBFS sampled at 96kHz, which results in the reference output voltage of 2Vrms into a 300-ohm load. Here we see the worst-case signal harmonic (2kHz) at -100dBrA. The third- and fifth-order harmonics (3 and 5kHz) are at about -115dBRa. Beyond the second signal harmonic, the odd order harmonics (3, 5, 7kHz, etc.) are above -120dBrA and dominate the even-order harmonics (4, 6, 8kHz, etc.), which are below -120dBrA.

FFT spectrum – 1kHz (-90dBFS, 44.1kHz sample rate)

Shown above is an FFT of a 1kHz input sinewave stimulus at -90dBFS sampled at 44.1kHz, into a 300-ohm load. Here we see the worst-case signal harmonic (5kHz) at -100dBrA, with the 3kHz harmonic at -110dBrA. Most of the remaining peaks are likely digital-filter aliasing artifacts, ranging in level from -110dBrA to below -130dBrA.

FFT spectrum – 1kHz (-90dBFS, 96kHz sample rate)

Shown above is an FFT of a 1kHz input sinewave stimulus at -90dBFS sampled at 96kHz, into a 300-ohm load. The worst-case signal harmonic (5kHz) is at -100dBrA, with the 3kHz harmonic at -110dBrA. Like the 0dBFS FFT, the odd-order signal harmonics dominate over the even order harmonics, which are below -130dBrA. The majority of the remaining peaks are likely digital-filter aliasing artifacts, which range in level from -110dBrA to below -130dBrA.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 0dBFS, 44.1kHz sample rate)

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output into a 300-ohm load, sampled at 44.1kHz. The input values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would result in a 0dBFS signal, or 2Vrms (0dBrA), at the output. We found that the second-order modulation product (i.e., the difference signal of 1kHz) is at -105dBrA, while the third-order modulation products, at 17kHz and 20kHz, are at -115dBrA.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 0dBFS, 96kHz sample rate)

Above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output into a 300-ohm load, sampled at 96kHz. The input values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would result in a 0dBFS signal, or 2Vrms (0dBrA), at the output. The second-order modulation product (i.e., the difference signal of 1kHz) is just below -100dBrA, while the third-order modulation products, at 17kHz and 20kHz, are at -115dBrA. The other peaks at 2, 3, 4, 5kHz, etc. are likely signal harmonics of the second-order 1kHz modulation product.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (44.1kHz sample rate)

The chart above shows an FFT of the Clarus’s output with white noise at -4dBFS (blue/red) and a 19.1kHz sinewave signal at 0dBFS (purple/green), sampled at 44.1kHz. The roll-off above 20kHz in the white-noise spectrum shows the implementation of the reconstruction filter. The significant peak at 25kHz (-35dBrA) is an aliased image due to the digital-filter implementation (as with all charts above unless noted, this was with the minimum-phase filter). The second-, third-, and fourth-order signal distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are much lower in amplitude, at around -95dBrA. Several other lower-level aliasing artifact peaks can also be seen at around -130dBrA. With the filter set to linear phase as well as hybrid (both not shown), the slope in the roll-off at around 20kHz in the noise spectrum was sharper (reflecting what the frequency response with the three filter settings sampled at 44.1kHz graph shown above demonstrates) and the main aliasing peak at 25kHz was lower in amplitude, at -90dBrA.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 20 December 2020

Reviewed on: SoundStage! Solo, December 2020

I measured the Topping A50s headphone amplifier using a Clio 10 FW audio analyzer. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality, and that reveal potentially audible problems in an amplifier.

Here you can see the frequency response of the A50s with 32-, 250- and 600-ohm loads, all referenced to 1mW at 1kHz. If memory serves, this is the flattest and most extended response I have measured from a headphone amp. Referenced to 0dB at 1kHz, it’s down 0.019dB at 10Hz, and dips down by 0.0845dB at 60kHz. Channel matching is essentially perfect, and there’s no significant variation as the load changes; any differences would be within the range of accuracy of my test gear. To the best of my memory, this is the first time I haven’t seen any variation in response with load impedance in a headphone amp.

This chart shows the balanced output of the A50s vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads at 1kHz. Normally we see a “hockey stick”-shaped trace, with an abrupt rise on the right side of the graph as the amp goes into clipping. But as I noted in the review, the A50s either shuts itself off before producing any significant distortion, or doesn’t have enough gain to produce distortion. Rated power (all with frequency unspecified) is 3500mW into 32 ohms and 760mW into 300 ohms, both at <1% THD. My measurements at 1kHz showed max output into 32 ohms at 2608mW at 0.0014% THD. Into 250 ohms, I measured 332mW at 0.0011% THD, and into 600 ohms, I got 139mW at 0.0013% THD. (Note that the Clio analyzer’s maximum output is 15Vrms, much higher than most DACs put out.) That little spike into 32 ohms at about 110mW does not appear to be a measurement anomaly—it appeared consistently in repeated measurements—but the THD rises only to 0.022%, so it’s of no concern.

This chart shows the unbalanced output of the A50s vs THD into 32-, 250- and 600-ohm loads at 1kHz. Here we see the same unusual lack of a clipping “knee” seen in the balanced measurement. Rated power (all with frequency unspecified) is 1400mW into 32 ohms and 192mW into 300 ohms, both at <1% THD. My measurements at 1kHz showed max output into 32 ohms at 624mW at 0.0016% THD. Into 250 ohms, I measured 83mW at 0.0009% THD, and into 600 ohms, I got 35mW at 0.0009% THD.

Here you can see the harmonic distortion spectrum and noise floor of the A50s, with a 1kHz tone at 2.04W into a 32-ohm load. Because the amp’s design prevents it from operating with significant amounts of distortion (or as I speculate it might be more accurate to say, shuts it down before the output devices get too hot), I wasn’t able to get it to produce significant amounts of distortion harmonics for long enough to grab a measurement. The upshot is, if you’re hearing distortion when using this amp, it’s coming from the headphones or the source device, not the amp.

Output impedance is rated at 0.2 ohms balanced, 0.1 ohms unbalanced, frequency unspecified. At 1kHz, I measured 0.13 ohms from the balanced output, and 0.19 ohms from the unbalanced output. Thus, the A50s’s output impedance will have no audible effect on the response of your headphones or earphones.

Bottom line: The A50s has truly outstanding frequency-response measurements, suggesting that some very talented engineers worked very hard on this amp. While its maximum output is apparently limited by design, and did not, in my tests, reach its rated power, the A50s does produce ample power for all but the most extreme listening situations, and the design of the amp prevents audible distortion.

. . . Brent Butterworth
brentb@soundstagenetwork.com

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 20 September 2020

Reviewed on: SoundStage! Solo, September 2020

I measured the Magnius using a Clio 10 FW audio analyzer. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality. All measurements were made at the high gain setting.

This chart shows the frequency response of the left and right channels at 1mW, unbalanced output into a 32-ohm load, referenced to 1kHz. In the right channel, it’s excellent: -0.003dB at 10Hz, -0.021dB at 20kHz, and -0.079dB at 50kHz. The left channel is even better: -0.0005dB at 50kHz. Channel matching is excellent, with the left just 0.008dB above the right at 1kHz. The result was similar for the balanced output: right channel -0.004dB at 10Hz, -0.023dB at 20kHz, and -0.106dB at 50kHz, with the left channel -0.118dB at 50kHz.

Here you can see how the frequency response from the unbalanced output differs with 32-, 250- and 600-ohm loads, all referenced to 1mW at 1kHz, right channel. The differences between the three loads were insignificant; this was also the case with the balanced output.

This chart shows the unbalanced output of the Magnius vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads at 1kHz, driven through the XLR inputs. Rated power (all with 1% THD, frequency unspecified) is 2W into 32 ohms, 300mW into 300 ohms, and 150mw into 600 ohms. My measurements at 1kHz showed output into 32 ohms at 1.84W at 0.5% THD and 1.93W at 1% THD. Into 250 ohms, the numbers were 278mW and 285mW, respectively. Into 600 ohms, the numbers were 117mW and 121mW.

From the RCA input, I wasn’t able to get such high numbers, as the amp wouldn’t go into clipping even when driven with the Clio’s maximum 3Vrms unbalanced output. The maximum unbalanced output from the RCA input was 1.33W into 32 ohms, 170mW into 250 ohms, and 71mW into 600 ohms, all well below 0.01% THD.

This chart shows the balanced output of the Magnius vs. total harmonic distortion (THD) into 32-, 250-, and 600-ohm loads at 1kHz, driven through the XLR inputs. Rated power (all with 1% THD, frequency unspecified) is 5W into 32 ohms, 1W into 300 ohms, and 500mW into 600 ohms. My measurements at 1kHz showed output into 32 ohms at 4.68W at 0.5% THD and 4.82W at 1% THD. Into 250 ohms, the numbers were 1.12W and 1.15W, respectively. Into 600 ohms, the numbers were 470mW and 480mW.

Here you can see the harmonic distortion spectrum and noise floor of the Magnius at 2.3W into 32 ohms, unbalanced. This is a typical result from a solid-state headphone amp. It’s primarily odd-order distortion, which is more sonically objectionable, but I had to push the amp 0.3W past its rated power to get it to distort to this degree, and it’s highly unlikely you’ll ever need to play it this loud, or that you’ll use a source device with a high-enough output voltage to push this amp into this much distortion.

Output impedance is rated at 0.1 ohms, frequency unspecified. At 1kHz, I measured 0.16 ohms from the unbalanced output, 0.11 ohms for the balanced output. Thus, the Magnius will have no audible effect on the frequency response of your headphones or earphones.

. . . Brent Butterworth
brentb@soundstagenetwork.com