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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

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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

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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

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 20 July 2020

Reviewed on: SoundStage! Solo, July 2020

I measured the DB12 AAAMP using a Clio 10 FW audio analyzer. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality.

This chart shows the frequency response of the left and right channels at 1mW into a 32-ohm load, referenced to 1kHz. Channel matching is excellent, with the left just 0.012dB below the right at 1kHz. Response is dead flat down to 10Hz, -0.31dB at 20kHz, and -0.72dB at 40kHz.

Here you can see how the frequency response differs with 32-, 250- and 600-ohm loads, all referenced to 1mW at 1kHz. At 250 ohms, it’s still flat down to 10kHz, but the bandwidth is even better: -0.11dB at 20kHz, -0.28dB at 40kHz. At 600 ohms, the numbers are -0.09dB at 20kHz and -0.25dB at 40kHz.

This chart shows the effect of the Bass Boost mode, measured with a 32-ohm load. This mode raises the volume slightly, by +0.27dB at 1kHz. With the volume normalized at 1kHz, the boost is +3dB at 176Hz and +6dB at 87Hz. Note that this is a shelving-type control; the boost has a slight resonant peak centered at 87Hz, but it more or less levels off below that. It also has no effect at frequencies above 300Hz, so it shouldn’t produce the upper-bass muddiness that many bass-boost functions exhibit. It’s obvious that whoever designed the Bass Boost mode put some thought and knowledge into it.

This chart shows the output of the DB12 AAAMP vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads at 1kHz. Rated power (all with frequency unspecified) is 109mW into 16 ohms and 111mW into 32 ohms, both at 1% THD. My measurements at 1kHz showed output into 32 ohms at 166mW at 0.5% THD and 175mW at 1% THD. Into 250 ohms, the numbers were 31mW and 32mW, respectively. Into 600 ohms, the numbers were 13mW and 14mW.

Here you can see the harmonic distortion spectrum and noise floor of the DB12 AAAMP. I’m showing two measurements because the profile at moderate power levels (such as the 40mW level shown in green) is interesting -- the amp seems to show a fairly consistent level of even-order (2nd harmonic, 4th harmonic, etc.) harmonic distortion. This is something we typically see in single-ended tube amps, and one reason that’s commonly given as to why audiophiles like them. Because the distortion occurs in even-numbered octaves above the fundamental, at moderate levels it can be heard as increasing the depth and density of the sound, rather than as a harsh distortion. That said, the loudest harmonic (the 2nd) is at -83.8dB relative to the fundamental, so you’d never hear it, but it does show something interesting is going on inside this amp. At full clipping (190mW, red trace), the odd- and even-numbered harmonics balance out, which is a more typical result.

Output impedance is rated at 0.3 ohms, frequency unspecified. At 1kHz, I measured 0.4 ohms. Thus, the DB12 AAAMP’s output impedance will have no audible effect on the response of your headphones or earphones. This little amp measures extremely well overall, as good as or better than specified.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 July 2020

Reviewed on: SoundStage! Solo, July 2020

I measured the iFi Audio Hip-dac using Audiomatica Clio FW 10, QuantAsylum QA401, and Neutrik ML-1 audio analyzers, and TrueRTA spectrum analyzer software. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality.

In addition to Diego Estan’s SoundStage! Solo review, I’ll state that I have been using the Hip-dac for a few months and have found that it sounds very good and can deliver excellent sound quality with all my headphones (including the very-low-sensitivity HiFiMan HE6se open-back headphones, which, with most music recordings, it can drive to a moderately loud level at full volume). The only problem I had with it is that the USB connection with the supplied cable was sometimes intermittent with my Lenovo laptop, a problem I attribute to the cable.

This chart shows the frequency response in the left and right channels at a 96kHz sampling rate into 32 ohms from the unbalanced output. Response is 0.0dB at 20Hz, -0.05dB at 20kHz, and -0.24dB at 40kHz, all referenced to 0dB at 1kHz. From the balanced output (not shown), the results were -0.26dB at 20Hz, -0.13dB at 20kHz, and -0.37dB at 40kHz. Channel level was about 0.2dB lower in the right channel. Output into 250- and 600-ohm loads was practically identical. Pretty good all-around -- this DAC-amp is not going to change the tonal balance of your headphones.

This chart shows the function of the xBass button. The bass boost starts to happen below 300Hz or so, rising to 4.5dB at 100Hz and 11dB at 20Hz.

This chart shows the unbalanced output of the Hip-dac vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads at 1kHz. (Note that I produced this chart on the QA401, but the results below come from direct measurements from the Clio 10 FW; as the QA401 is new, I’m still learning to use it and thus trust the Clio numbers, but the chart does show the shape of the THD vs. power curves accurately.) Rated power from the balanced output is 280mW into 32 ohms and 3.2V (17mW) into 600 ohms, both at 1% THD (frequency unspecified). Into 32 ohms, I measured output of 267mW at 1% THD and 252mW at 0.5%. Into 250 ohms, at maximum volume with a 0dBFS sine wave, output is 38.5mW at 0.008 THD, and into 600 ohms under the same conditions, the numbers are 16.1mW at 0.007% THD. So my results are at most 0.39dB lower than iFi’s.

This chart shows the balanced output of the Hip-dac vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads at 1kHz. Rated power from the balanced output is 400mW into 32 ohms and 6.3V (66mW) into 600 ohms, both at 1% THD (frequency unspecified). Into 32 ohms, I measured output of 420mW at 1% THD and 340mW at 0.5%. Into 250 ohms, output is 109mW at 1% THD and 107mW at 0.5%, and into 600 ohms the numbers are 50.5mW and 47.7mW, respectively.

Here you can see the harmonic distortion spectrum and noise floor of the Hip-dac. I’m showing two versions because the profile changes as the amp goes into clipping. The first is referenced to 163mW, the second to 259mW, both into a 32-ohm load. At high levels just below clipping, third-order harmonics are stronger than the second-order harmonics, but at full clip they’re more or less balanced. Remember, though, that it’s unlikely you’ll even push this amp into distortion; even at full-crank with the HiFiMan HE6se’s (the least-sensitive headphones I have), the Hip-dac did not produce audible distortion.

Output impedance is not rated. At 1kHz, I measured 0.2 ohm from the unbalanced output, which won’t contribute significantly to total impedance and will thus have no audible effect on the response of your headphones.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 June 2020

Reviewed on: SoundStage! Solo, June 2020

I measured the Focal Arche using a Clio 10 FW audio analyzer and a Neutrik Minilyzer ML1. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality. Except as noted, I used the analog input and the unbalanced output.

This chart shows the frequency response in the left channel at 1mW unbalanced output into 32-, 250- and 600-ohm loads in Voltage mode, and into 32 ohms in Hybrid mode. If there’s any response variation among the different loads and modes, it’s not visible on this chart. Response is -0.02dB, -0.32dB at 20kHz, and -1.86dB at 50kHz, all referenced to 0dB at 1kHz. The response at 20kHz is a little more rolled-off than I expected, but that’s a difference that would be just barely audible to people who can hear to 20kHz -- which isn’t many of us.

This chart shows the unbalanced output of the Arche vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads at 1kHz. Rated power is 1W at 1kHz into 32 ohms; the distortion level, the amplifier mode and whether the spec is at the balanced or unbalanced output, are all unspecified. Let’s start with Voltage mode. Into 32 ohms, output is 1.64W at 0.5% THD and 1.70W at 1%. Into 250 ohms, the output is 0.25W at 0.5% and 1% THD, and into 600 ohms, the numbers are 0.10W and 0.11W, respectively. They’re a little lower in Hybrid mode: at 0.5% THD, output is 1.11W into 32 ohms, 0.23W into 250 ohms, and 0.10W into 600 ohms.

Here you can see the harmonic distortion spectrum and noise floor of the Arche. I’m showing two versions because the profile changes as the amp goes into clipping. The first is referenced to 1.3W, the second to 1.65W, both into a 32-ohm load. At high levels, second-order harmonic distortion predominates; the second harmonic is an octave above the original tone and generally doesn’t sound objectionable. When the amp is pushed into clipping, higher-order harmonics predominate.

Here’s the difference between using the Focal Utopia headphones with the amp in the default Voltage mode and in the Utopia EQ mode. You can see that while there’s a difference, it’s subtle -- a bass boost of less than 1dB.

Here’s the difference between using the Focal Stellia headphones with the amp in the default Voltage mode and in the Stellia EQ mode. Again, it’s a subtle difference: a bass boost of less than 1dB, and a cut of less than 1dB stretching from about 1kHz all the way to the top of the audioband.

Output impedance is not rated. At 1kHz, I measured 2.4 ohms in Voltage mode and 9.9 ohms in Hybrid mode. In Voltage mode, the output impedance shouldn’t have an audible effect on the response of the headphones. In Hybrid mode, there might be a slight effect, depending on the headphones you use.

. . . Brent Butterworth
brentb@soundstagenetwork.com

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 10 March 2020

Reviewed on: SoundStage! Solo, March 2020

I measured the IL-DSP using a Clio 10 FW audio analyzer, a Neutrik NL-1 Minilyzer, and TrueRTA software with an M-Audio MobilePre USB interface. Because my Clio 10 FW analyzer isn’t compatible with USB-only devices, I could only run very basic measurements; I had to plot most of them by hand, or use noise signals with a spectrum analyzer. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality.

This chart shows the matching of the IL-DSP channels at 1mW into a 32-ohm load at a 44.1kHz sampling rate. This measurement does show some roll-off before it hits 20kHz, but when I tried the same measurement using white noise and a spectrum analyzer, I didn’t see this roll-off. Mainly what to take away from this is that that response is basically flat and the channels are well-matched; the left channel is -0.048dB below the right channel at 1kHz, an inaudible difference.

This chart shows the output of the IL-DSP vs. total harmonic distortion (THD) into 32- and 250-ohm loads at 1kHz. Rated power is 30mW into 32 ohms at 0.0007% THD. Output into 32 ohms is 37mW at 0.5% THD and 39mW at 1% THD. Output into 250 ohms is 4.7mW at 0.5% THD and 5.1mW at 1% THD. That means that with something like the Sennheiser HD 600 headphones (rated 300 ohms, 97dB sensitivity), you’ll get about 103dB max usable volume, which is not enough for full dynamics.

Output impedance at 1kHz is rated at 1.08 ohms (according to the support community forum on miniDSP’s website); I measured 0.31 ohm. Either way, the amp’s output impedance will not interact significantly with the reactance of headphones or earphones, and thus won’t alter their frequency response -- although of course the reason you would buy this product is to change the headphones’ frequency response.

. . . Brent Butterworth
brentb@soundstagenetwork.com

Details

Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 November 2019

Reviewed on: SoundStage! Solo, November 2019

I measured the RH-5 using a Clio 10 FW audio analyzer and a Neutrik NL-1 Minilyzer. Note that my focus with these tests is on measurements that confirm these devices’ basic functionality. Except as noted, I used the unbalanced output.

This chart shows the frequency response in the left and right channels at 1mW into a 32-ohm load. Channel tracking is good, with the right channel 0.015dB louder at 1kHz, and 0.095dB less roll-off in the right channel at 20kHz. Response measures -1.0dB at 20Hz, -0.53dB at 20kHz, and -5.66dB at 75kHz. This shows the unbalanced output; the balanced output was essentially the same except for -1.91dB additional roll-off at 10Hz. This measurement was taken with gain set to 3. At gain 2, output is reduced by 4.34dB at 1kHz. Gain 1 reduces the output by an additional 3.78dB.

This chart compares the Rogue’s frequency response with 1mW unbalanced output into 32-, 250-, and 600-ohm loads. Into 250 ohms, the numbers are -0.04dB, -0.45dB, and -4.85dB, respectively. Into 600 ohms, the numbers are -0.02dB, -0.45dB, and -4.78dB, respectively. The bass roll-off into 32 ohms, and the treble roll-off into all loads, isn’t impressive -- tubes at work here! -- but in both cases it’s modest enough that you’d be unlikely to notice it.

This chart shows the unbalanced output of the Rogue vs. total harmonic distortion (THD) into 32-, 250-, and 600-ohm loads at 1kHz. Rated power is 3.5W into 32 ohms; the distortion level, the frequency, and whether the spec is at the balanced or unbalanced output are all unspecified. Into 32 ohms, output is 1.9W at 0.5% THD and 2.0W at 1%; while this may (or may not) fall short of the spec, it’s certainly plenty enough power to drive any headphones to very high volume. Into 250 ohms, the output is 0.37W at 0.5% THD and 0.39W at 1%. Into 600 ohms, the numbers are 0.16W and 0.17W, respectively. Solid performance here.

Here you can see the harmonic distortion spectrum and noise floor of the Rogue, referenced to 5.66Vrms (1W) output at 600Hz into 32 ohms. This shows what I’d expect from a hybrid amp. The sonically benign (because it’s exactly one octave above the fundamental tone) second-order harmonic is stronger than we’d probably see with an all-transistor amp, but it’s not as dominant as we’d probably see in an all-tube amp.

Output impedance is rated at less than 0.1 ohm at 1kHz; I measured 0.07 ohm. This means that the output impedance of the amp will not significantly interact with the reactance of the headphones, so you’ll get consistent response no matter what type of drivers your headphones use.

. . . Brent Butterworth
brentb@soundstagenetwork.com