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Review and Measurements of Gustard H20 Headphone Amp

amirm

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#1
This is a review and detailed measurements of Gustard H20 balanced input and output headphone amplifier. It is on kind loan from a member. The H20 costs USD $930 but I see it on sale from shenzhenaudio for USD $840. I think it was also sold on Massdrop for $800. Either way you look at it, it is not cheap.

The H20 comes in black and silver. The unit I have for testing is the silver:

Gustard H20 Balanced Headphone Amplifier Audio Review.jpg

The H20 is quite heavy and large. Controls feel good although I am not a fan of relay controlled volume. There is a racket that is sharp pitched as you adjust the volume.

The two 1/4 inch jacks are not the same. The first one has a resistor inline (see measurements). The second is straight through.

On balanced XLR output, you have a choice of stereo 4-pin or dual three pin. I tested with the former.

The back panel sports a good set of connectors:

Gustard H20 Balanced Headphone Amplifier Audio Review Back Panel.jpg

There are a set of RCA inputs to the left and two sets of XLR. There is one set of pass through XLR outputs.

Gustard has no website I can find so don't know if the unit has passed regulatory certifications or not.

Headphone Audio Measurements
I run my dashboard test using 1/4 inch output and results there were quite disappointing:
Gustard H20 Balanced Headphone Amplifier Audio Measurements.png


I am using XLR inputs yet we still have lots of mains noise. That aside, the dominant problem is the very high second harmonic at 2 kHz. SINAD of 90 dB is quite poor even for a cheap headphone amplifier let alone a high-end one.

The other odd thing is the gain. As you see, with maximum volume and gain switch set to highest we only have a 2 dB gain? Why so low? This is bound to cause issues for music that is recorded at low levels.

Power output using 300 ohm 1/4 inch jack is also disappointing for a unit in this class:
Gustard H20 Balanced Headphone Amplifier Power at 300 Ohm.png


We don't even crack 100 milliwatts?

Notice that setting the gain to low makes no difference at all other than slightly less max power. One usually expects a lower noise floor in low gain. And bigger difference in max power.

Same situation persists with 33 ohm and 1/4 output:

Gustard H20 Balanced Headphone Amplifier Power at 33 Ohm.png


Output impedance was 51 ohm out of the first 1/4 inch port, and 1.1 ohm on the second:
Headphone Output Impedance Measurements and Review.png


Balanced Output Performance
Switching to balanced output substantially improves performance. Here is the power versus THD+N for example at 50 ohm:
Gustard H20 Balanced Headphone Amplifier Power at 50 Ohm.png


The H20 actually slightly beats the Massdrop THX AAA 789 in noise department. It is a negligible difference but good to see it. Power though is still less than THX amp. The specs for H20 are well above this, going up to nearly 6 watts for 64 ohm. That must be for one channel driven and even there, it is still too high relative to what I am seeing.

Measuring signal to noise ratio shows the very low noise level at max volume:
Gustard H20 Balanced Headphone Amplifier Signal to Noise Ratio Audio Measurements.png


It was hard to figure out how to get the 50 millivolt results. I adjusted the volume until it got close and then dialed down the input to 2.5 volt. Results were very good but not class leading:
Headphone Amplifier 50 mvolt SNR Review.png


Frequency response was dead-flat:
Gustard H20 Balanced Headphone Amplifier Frequency Response Audio Measurements.png


Listening Tests
I am still not setup for balanced headphone listening. You all don't give me a minute to go and build my cable and I am too cheap to buy one off-the-shelf. :)

So I did my testing with 1/4 jack. Here, with Sennheiser HD-650 the experience was excellent with lots of bass and good power. I could turn it up to max and still tolerate it -- something I prefer not to be able to do. But good enough.

The situation with the Hifiman HE-400i was not the same. Somehow distortion would set it close to max and there simply was not enough gain there for some of my test tracks even in high gain.

Conclusions
It is clear Gustard has aimed high to build a top-end headphone amplifier. But there are some serious misses. One is the low max gain and gain settings that are so close to each other as to not be useful. Unbalanced/1/4 inch output is an afterthought with performance that is quite subpar subjectively. Objectively it was good with Sennheiser HD-650 but not with my low impedance Hifiman HE-400i. Overall, I would not buy this unit for unbalanced headphone listening.

Even with balanced output, I am struggling to find a reason to buy the H20. The massdrop THX AAA 789 has proper gain settings, and far better unbalanced output. Yes, availability is an issue with massdrop THX so another excellent option is the JDS Labs Atom. It sounds so good and has so much power that you don't need to mess with balanced cables and such. And it only costs USD $99.

Really, the JDS Labs Atom and Massdrop THX AAA 789 have changed the landscape so much that products like Gustard H20 don't stand a chance anymore. Yes, it is a heavier box than both of those combined but I can't see a reason to spend so much more money and get less. So sadly I can't recommend the H20.

------------
As always, questions, comments, recommendations, etc. are welcome.

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#3
If only you could actually purchase a THX.... Every time it drops, it's in limited quantity and unless you're on the website when it happens, it's sold out before you get the email notification.
 
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#5
Probably because people think they need all the power, even though most headphones aren't going to need more than the atom will provide. My HE-560 are the only HP I own that might need more. Clearly JDS has a more scalable manufacturing capability.

I think at this point, I'll stick with what I have (dx7s, magni3, jotunheim), since they all sound good to me with various headphones and music, and I can scarcely tell the difference from one to the other even though their measurements would indicate large differences.
 

JJB70

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#7
Headphone amplifiers are one of those products where you really don't have to spend much at all to reach SOTA. The O2 demonstrated that good design and implementation did not need to cost much and although I will admit that I would like a nicer case in performance terms I really can't see any point going beyond the JDS Atom.
 
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#8
Amir, since Atom and 789 get all the comparisons, can you please update 50mv SNR chart with those? I understand that back-testing everything for that chart is not possible, but if you have those 2 - it would help on that chart.
 

amirm

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#11
Amir, since Atom and 789 get all the comparisons, can you please update 50mv SNR chart with those? I understand that back-testing everything for that chart is not possible, but if you have those 2 - it would help on that chart.
I measured the THX amp this way. Look for it in a review tomorrow. :)
 
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#13
I'm the one who loaned this Amp, and am so appreciative of this review Amir!
I'll give some of my own thoughts: I really love this Amp but it's definitely not without its flaws. I use the balanced connection only and it sounds excellent. Fully balanced use was always my end goal. I'm glad that the balanced portion measures well.

It's too bad that the unbalanced connections appear to be implemented in such a disappointing way. If not done right they shouldn't have bothered at all. Maybe we could have had a balanced-only version with a smaller form factor and less expensive by a few hundred dollars. The gain switches are also odd how close they are together, they are almost like a tone control as the changes are so minor. In the H20 PDF manual, it lists the lowest gain as normal gain; vs middle gain, then high gain.

Personally I prefer the stepped attenuator for it's volume matched stereo at low volumes. 64 steps is great as it offers more variability so that one step up or down is not too drastic. I'd love a 124 step version and I actually think the internal clicks sound cool.

What sucks is that this Amp is not the best value for the money in a technical sense.
I'm loving my THX AAA 789, but prefer my H20 to it though not by much. This review only only just reminds me what a fantastic value the THX is. The downside of the THX is that since it is a normal potentiometer there is that stereo volume mismatch at low levels.
 
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