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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

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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

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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

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 10 October 2019

Reviewed on: SoundStage! Solo, October 2019

I measured the Lehmannaudio Linear USB II 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. I used the analog inputs; unfortunately, I’m currently unable to interface Clio’s coax digital output to USB-only DACs.

This chart shows the Linear USB II’s frequency response with 1mW output into a 32-ohm load in the left and right channels. Channel matching is excellent, with the right channel measuring just 0.01dB lower in level than the left, and the two having neatly overlapping curves out to 40kHz.

Here you can see how the Linear USB II’s frequency response differs into 32-, 250-, and 600-ohm loads. Into 32 ohms, the response measures -0.01dB at 20Hz, -0.14dB at 20kHz, and -1.18dB at 75kHz. Into 250 ohms, the numbers are -0.02dB, -0.11dB, and -1.15dB, respectively. Into 600 ohms, the numbers are -0.02dB, -0.11dB, and -1.16dB, respectively. From a frequency-response standpoint, the Linear USB II’s response can be described as load-invariant, meaning the amp’s tonal balance won’t change depending on the headphones you use.

This chart shows the output of the Linear USB II vs. total harmonic distortion (THD) into 32-, 250-, and 600-ohm loads with a 1kHz signal. Rated power is 400mW into a 60-ohm load and 200mW into 300 ohms, both at unspecified distortion at an unspecified frequency. Into 32 ohms, the power/distortion curve looks peculiar because it rises rather quickly to a plateau of typically 1.6% THD, and doesn’t hit its “clipping knee” until 1.35W at 2.1% THD. It hits 0.5% THD at 127mW, and 1% THD at 176mW. This is the only deviation I found from excellent measured performance. With higher-impedance loads, the Linear USB II performs more as I’d expect. Into 250 ohms, output at 0.5% THD is 327mW, and output at 1% THD is 347mW. Into 600 ohms, output at 0.5% THD is 141mW, and it’s 149mW at 1% THD.

Here you can see the harmonic distortion spectrum and noise floor of the Linear USB II, referenced to 2.59Vrms (210mW) output at 600Hz into 32 ohms. This is pretty typical of a conventional solid-state amp, with much stronger odd-order (3rd, 5th, 7th, and so on) harmonics than even-order (2nd, 4th, 6th, etc.) harmonics. Odd-order harmonics are more objectionable because they occur at non-harmonic intervals to the fundamental tone, but this measurement was done at a far higher level than you’d encounter in normal listening.

Output impedance at 1kHz measures 5.6 ohms, close to the rated 5 ohms. This relatively low output impedance ensures that the amp’s output impedance will have very little interaction with the reactance of the headphones or earphones, so the headphones or earphones will deliver the frequency response they were designed for (assuming they were designed using an amp with low output impedance).

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 20 September 2019

Reviewed on: SoundStage! Solo, September 2019

I measured the Nickel 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.

This chart shows the Nickel’s frequency response with 1mW output into 32-, 250- and 600-ohm loads. Into 32 ohms, the response measures -0.51dB at 20Hz, -0.26dB at 20kHz, and -2.80dB at 75kHz. Into 250 ohms, the numbers are -0.48dB, -0.22dB, and -2.49dB, respectively. Into 600 ohms, the numbers are -0.47dB, -0.21dB, and -2.50dB, respectively. For a tiny, portable amp like this one, these are respectable numbers.

This chart shows the matching of the Nickel’s channels at 1mW into a 32-ohm load. The right channel is 0.069dB lower in level at 1kHz than the left channel, a negligible difference, and the shapes of the response curves match precisely within the audioband.

This chart shows the output of the Nickel vs. total harmonic distortion (THD) into 32-, 250-, and 600-ohm loads at 1kHz. Rated power is 250mW into 32 ohms, THD and frequency unspecified. Output into 32 ohms is 150mW at 0.5% THD and 156mW at 1% THD; the highest output I was able to measure is 203mW at 10% THD. Output into 250 ohms is 32mW at 0.5% THD and 34mW at 1% THD. Output into 600 ohms is 14mW at 0.5% THD and 15mW at 1% THD.

Here you can see the harmonic distortion spectrum and noise floor of the Nickel, referenced to 174mW output at 600Hz into 32 ohms. The distortion is predominantly odd-order (3rd, 5th, 7th harmonics, etc.), although I had to push the amp a little past its limits to even see any even-order (2nd, 4th, 6th, etc.) harmonics.

I measured no-load gain at 5.4dB, a little lower than the rated 6.5dB. Output impedance at 1kHz measures 0.78 ohm. This means the amp’s output impedance will not interact significantly with the reactance of headphones or earphones, and thus won’t alter their frequency response.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 01 August 2019

Reviewed on: SoundStage! Solo, June 2019

I measured the Euterpe 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. I used the analog inputs; unfortunately, I’m currently unable to interface Clio’s coax digital output to USB-only DACs.

This chart shows the Euterpe’s frequency response with 1mW output into 32-, 250- and 600-ohm loads. The impedance switch on the amp was set to L for the 32-ohm load, and H for the 250- and 600-ohm loads. Into 32 ohms, response measures -8.24dB at 20Hz, -1.9dB at 20kHz, and -20.76dB at 75kHz. Into 250 ohms, the numbers are -7.74dB, -0.67dB, and -14.25dB, respectively. Into 600 ohms, the numbers are -9.91dB, -0.027dB, and -11.01dB, respectively. As you can see, the response curve basically shifts higher in frequency into higher-impedance loads, but in any case, this is an extreme amount of bass roll-off, and a substantial amount of treble roll-off.

I don’t normally include this chart because in most headphone amps, the channels are so closely matched that the difference isn’t worth noting. This difference here is, though. The right channel (measured into 32 ohms) is 0.36dB higher in level at 1kHz than the left channel is. Although it’s hard to see without normalizing the two curves at a certain frequency, you can see that the right channel’s frequency response is basically shifted to higher frequencies.

This is another chart I don’t usually show, but I thought it important to show the effects that the Euterpe’s high output impedance will have on the sounds of a couple of different headphones, so I compared the frequency response of two headphones driven by the Euterpe and by the Musical Fidelity V-CAN (output impedance 5 ohms). The lower traces show the response with the Audeze LCD-Xes, a planar-magnetic headphone that has a largely resistive impedance that makes it relatively insensitive to headphone amp output impedance. Still, the Euterpe’s output impedance (with the impedance switch set to L) is enough to reduce the LCD-Xes’ bass by 2.35dB at 50Hz. With the Beyerdynamic Amiron Homes, a dynamic-driver design, the effect is more pronounced -- the Euterpe reduces the Amiron Homes’ bass by 2.73dB at 50Hz, and also tilts the treble up by about 0.84dB. Bottom line: This amp is not neutral, and it will change the sound of your headphones relative to what you’d hear with most other headphone amps, especially ones with a low output impedance.

This chart shows the output of the Euterpe vs. total harmonic distortion (THD) into 32-, 250- and 600-ohm loads. Rated power is 0.9W, into an unspecified load at unspecified distortion at an unspecified frequency. Into 32 ohms, the lowest distortion I measured, at 0.01W, is 0.5%; the amp breaks my 1% THD max at 0.038W, and at the rated 0.9W max output, THD is 5.49%. Into 250 ohms, THD at 0.01W was 0.52%; output at 1% THD is 0.035W, and THD at the rated 0.9W is 5.89%. Surprisingly, the performance at 600 ohms easily bests the performance into lower-impedance loads -- output at 0.5% THD is 0.042W, and it’s 0.165W at 1% THD. At the rated 0.9W, THD measures 2.43%.

Here you can see the harmonic distortion spectrum and noise floor of the Euterpe, referenced to 3.1Vrms (0.3W) output at 600Hz into 32 ohms. This is a classic profile of the distortion of a single-ended tube amp, with the second-order distortion predominant. Because second-order harmonic distortion adds a harmonic precisely one octave above the fundamental, it’s less sonically offensive than third- or fifth-order harmonic distortion.

Output impedance at 1kHz measures 51 ohms with the impedance switch set to L, and 350 ohms with the switch set to H. This is extremely high output impedance relative to what I’m used to measuring; with any headphones that exhibit a significant impedance swing (such as earphones with balanced-armature drivers, and large over-ear headphones with dynamic drivers), the amp’s output impedance will interact with the reactance of the headphones or earphones to change the frequency response.

This is an amp with audible frequency response errors and high distortion. There are some audio writers who consider these idiosyncrasies a badge of honor, but I’m not one of them.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Amplifier Measurements

Created: 20 April 2019

Reviewed on: SoundStage! Solo, April 2019

I measured the Liquid Platinum 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. Because I didn’t have the necessary four-pin XLR adapter that would allow me to measure the balanced output, the measurements below are all with the amp in single-ended mode (using the 1/4” TRS headphone output). I have the parts on order to build the adapter and hope to add those results later. Meanwhile, I was able to measure the frequency response of the HiFiMan HE6se headphones from the balanced and unbalanced outputs, and the results were identical.

This chart shows the Liquid Platinum’s frequency response with 1mW output into 32-, 250-, and 600-ohm loads. Into 32 ohms, the response measures -0.014dB at 20Hz, -0.041dB at 20kHz, and -0.276dB at 75kHz. Into 250 ohms, the numbers are -0.015dB, -0.031dB, and -0.307dB, respectively. Into 600 ohms, the numbers are -0.015dB, -0.027dB, and -0.232dB, respectively. These are very good results.

This chart shows the single-ended output of the Liquid Platinum vs. total harmonic distortion (THD) into 32-, 250-, and 600-ohm loads. Note that Monoprice’s power ratings are specified at 33, 56, 150, and 300 ohms, so my measurements are not directly comparable, but Monoprice’s specs seem well in line with my results. Output into 32 ohms is 1.71W at 0.5% THD and 1.85W at 1% THD. (Monoprice’s most comparable rating is 1.78W into 33 ohms, THD unspecified.) Output into 250 ohms is 275mW at 0.5% THD and 289mW at 1% THD. (Monoprice’s most comparable rating is 230mW into 300 ohms, THD unspecified.) Output into 600 ohms is 117mW at 0.5% THD and 122mW at 1% THD.

Here you can see the harmonic distortion spectrum and noise floor of the Liquid Platinum, referenced to 1.5Vrms (1W) output at 600Hz into 32 ohms. Distortion is low, and no particular distortion harmonic dominates the spectrum; the first several harmonics are down in the -72dBFS range (plus or minus a couple of dB) relative to the level of the fundamental tone. (For reference, -70dBFS equates to 0.03% harmonic distortion.) We can see some 60-cycle AC hum and its harmonics, typically in the range of -70dBFS. The noise floor of the amp at this level is down around -92dBFS, which is pretty good for a device with tubes in the signal chain.

I measured output impedance of the 1/4” headphone jack at under 0.3 ohm at 1kHz, which is about as low as I can measure with my voltage divider; Monoprice rates it at 0.07 ohm. Either way, it’s easily low enough that the output impedance won’t react significantly with the reactance of the headphones, and thus won’t change their frequency response.

. . . Brent Butterworth
brentb@soundstagenetwork.com