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Review and Measurements of LH Labs Go2Pro DAC and Headphone Amp

amirm

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#1
This is a "naked" review and measurements of the LH Labs Go2Pro DAC and headphone amplifier. I say naked because in in the interest of time, I am posting its results by itself. I am hoping by now you all are familiar with the norms in my measurements and can see its fidelity. Actually there is one measurement that includes a comparison.

I can't find its retail price but it is on sale now with 20% off at $480 on LH Labs website. So quite pricey. The unit is on kind loan from a member.

Anyway, this is a self-powered device (although I tested it while connected via USB) and includes a 3,200 mah battery. That combined with a metal enclosure makes for one hefty device.

LH Labs Go2 Pro DAC Headphone Amplifier.jpg


I find the user interface maddening. There is a simple on/off switch but then the "up" volume control is overloaded as meaning both extra gain, and filter??? I confess I could not figure it out. :) Pushing the up volume to max did light up one of the many colored LEDs which I assumed meant high-gain. The lights are surface mount LEDs and as tiny as they can get. Seemingly they are wasted for DSD rates??? I told you that I found the interface maddening. :) Someone with more patience than me may be able to figure it out.

Fortunately the device is UAC 2 compliant so worked plug-and-play with Roon/Windows WASAPI interface for bit-exact transmission.

BTW, one thing about the name: they seem to sometimes put a space after "GO2" and sometimes not. I followed their lead by mixing the two ways of writing it just the same. :)

Here are the formats it advertises as supporting to Roon:

upload_2018-3-29_15-14-59.png


So pretty extensive.

Size-wise the unit is almost as wide as my Samsung S8+ but much less tall. So you could rubber band it to the back of it.

I am sure you are anxious to see the measurements so let's get into that. If you are not familiar with my measurements, I suggest reading my tutorial on audio measurements here: https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/

Measurements
Let's start with simple frequency response:

GO2Pro DAC Frequency Response Measurement.png


So we are down 1/4 of a dB at 20 kHz at 48 kHz sampling. I assume this is with the default filtering. I did not try to change it per my introduction.

Next let's look at jitter:

GO2 Pro DAC jitter Measurement.png


Noise floor is very good and low. We see a number of little spikes but they are all at -130 dB down so not an audible concern.

Let's look at distortion products:

GO2 Pro DAC THD vs level Measurement.png


For reference here, I have included the "speaka" USB thumb DAC. See review here: https://www.audiosciencereview.com/...-speaka-usb-dac-and-headphone-amplifier.2423/. That is a nice bargain of a DAC at around $30. Alas it doesn't do as well as the Go2 Pro.

The above measurement is in maximum gain mode. We see a knee of rising distortion which we can decipher much more easily in the spectrum of distortion:

GO2 Pro DACresidual harmonic distortion Measurement.png


Wow. Look at the high amount of harmonic distortion in red when we are in high-gain/max volume mode. Just dropping the volume one notch/disabling high-gain mode results in far better performance.

Let's look at linearity now:

GO2Pro DAC Linearity Measurement.png


Performance here is pretty good. My arbitrary 0.1 dB of deviation occurs at -110 dB and 18 bits of resolution. Response past that up to -120 dB is still very good.

Likewise our -90 dB sine wave looks pretty reasonable:

GO2Pro DAC -90 db Measurement.png


Switching from DAC testing to headphone testing, I measured the output impedance a very low 0.5 ohm.

GO2 Pro DAC Output Impedance Measurement.png


This means that it should have no effect on the frequency response of the headphone even if that latter is pretty low.

Now let's look at power versus distortion. This is all in high-gain mode with a 400 Hz tone, both channels driven:

GO2 Pro DAC power Measurement.png


I must say, these are lower than I expected. Max power is naturally at 33 ohm load with onset of clipping at 40 milliwatt. I tried to find specs for power but could not find any. If anyone knows them, I appreciate seeing what they state.

So enough with measurements, let's see how it sounds.

Listening Test
This being a naked review, I didn't know what to test it against. So I just picked my laptop (HP z series), thinking it is a decent representation of a portable player, cell phone, etc.

Usually I expect outboard amplifiers to clean the clocks of my laptop with respect to power but such was not the case. Using both Sennheiser HD-650 and Hifiman HE400i, I could roughly get the same volume out of my laptop as I could with the Go2 Pro. Yes, in high-gain mode the Go2 Pro was somewhat louder but I did not like that mode. Dropping down one notch would give me decent volume but with no headroom.

Subjectively, in AB testing, the LH Go2 Pro had a bit more detail and resolution as compared to my laptop. So it does something good. I just wished it had more power.

Switching to Grado SR60e provided more power and on pop and rock, it was plenty loud. But once again, on audiophile recordings that avoid the peaks, the volume was just enough.

Conclusions
The LH Labs GO2 Pro DAC and headphone amplifier seems solidly built, both in performance and heft of the unit. Standard DAC measurements don't indicate any faults in low-gain mode. High-gain mode though is a distortion factory and one that I would not use. The user interface is also confusing to impatient people like me. Fidelity is good but in my opinion, the output power is insufficient for any power hungry headphones.

The biggest issue in my opinion is the high cost at over $500 retail. For that, I would really want my headphones to flap in the air with power. :D

I will be testing the iFi self-powered DAC that I have in the future. Will be interesting to see how well it does in the same tests.


As always, questions, comments, corrections, jokes, etc. are all welcome!
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#2
For reference here, I have included the "speaka" USB thumb DAC.
Speaking of the Speaka, do you have an ETA for the review of the 'XtremPro Portable USB DAC Headphone Amplifier'?
Performance here is pretty good. My arbitrary 0.1 dB of deviation occurs at -110 dB and 18 bits of resolution.
In your 'Understanding Audio Measurements' post, you claim that 20 bits are required for audible transparency. Now your maximum deviation threshold appears to be arbitrary. Can you clarify this a little? The whole linearity measurement seems a little sketchy to me.
So I just picked my laptop (HP z series), thinking it is a decent representation of a portable player, cell phone, etc. Subjectively, in AB testing, the LH Go2 Pro had a bit more detail and resolution as compared to my laptop.
Would it be possible for you to measure your laptop?
 
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amirm

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#3
Speaking of the Speaka, do you have an ETA for the review of the 'XtremPro Portable USB DAC Headphone Amplifier'?
I don't know that I will get to it anytime soon. But I am 100% confident they are clones of each other based on the two tests I ran.
 

amirm

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#4
In your 'Understanding Audio Measurements' post, you claim that 20 bits are required for audible transparency. Now your maximum deviation threshold appears to be arbitrary. Can you clarify this a little? The whole linearity measurement seems a little sketchy to me.
Well, ideally we would have zero deviation at 20 bits. Instrumentation limitation stops me from going for such a metric as my analyzer also has some noise at -120 dB (20 bits). So I picked 0.1 dB as the threshold to allow for some variations in both the device and measurement system.
 

amirm

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#9
I would expect balanced to be used for maximum output power - it gives a better-looking number, after all :D

Did you test the GO2Pro in low or high gain mode for these measurements? The numbers would just about add up if it was in low gain, I believe.
 
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#11
Well, ideally we would have zero deviation at 20 bits. Instrumentation limitation stops me from going for such a metric as my analyzer also has some noise at -120 dB (20 bits). So I picked 0.1 dB as the threshold to allow for some variations in both the device and measurement system.
What you're saying about the 0.1 dB limit does make sense to me, but I still don't understand where the 20 bits figure is coming from. How do you know anything less than 20 bits might not be audibly transparent?
I have actually. See https://www.audiosciencereview.com/...of-shozy-alien-digital-audio-player-dap.2058/. I also have measurements of my Samsung S8+ phone there.
I see nothing in these measurements which suggests that your laptop should sound any different from the LH Labs Go2Pro when listening with HE-400i. You're probably too old (no offense) to be affected by the high-frequency roll-off of the Go2Pro and the high output impedance of the laptop doesn't affect planars.
 

amirm

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#12
What you're saying about the 0.1 dB limit does make sense to me, but I still don't understand where the 20 bits figure is coming from. How do you know anything less than 20 bits might not be audibly transparent?
Ah, please see this article: https://audiosciencereview.com/forum/index.php?threads/dynamic-range-how-quiet-is-quiet.14/

In a nutshell, we can compute the the threshold of hearing as far as noise level. Then compare that to the loudest real-life music presentations. That gives us a range that goes a bit beyond 120 dB which translates to 20 bits. You can also arrive it from the point of view of the dynamic range of the ear.
 

Timbo2

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#13
Wow. Look at the high amount of harmonic distortion in red when we are in high-gain/max volume mode. Just dropping the volume one notch/disabling high-gain mode results in far better performance.
This seems to be a problem with more than a few DACs.

So a hypothetical questions for everyone, as a rule of thumb if you were using an DAC that hasn't been measured by anyone would it be better automatically drop the volume level a notch or two and live with the tradeoff of the possible "lossy" way the DAC is reducing the volume?
 
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#14
Ah, please see this article: https://audiosciencereview.com/forum/index.php?threads/dynamic-range-how-quiet-is-quiet.14/

In a nutshell, we can compute the the threshold of hearing as far as noise level. Then compare that to the loudest real-life music presentations. That gives us a range that goes a bit beyond 120 dB which translates to 20 bits. You can also arrive it from the point of view of the dynamic range of the ear.
I read the article, and as you said, it boils down to the fact that 20 bits are needed for the desired 120 dB of dynamic range.
Another article, that frequently gets mentioned in 16-bit vs 24-bit debates, is this one: https://xiph.org/~xiphmont/demo/neil-young.html
It argues that "the effective dynamic range of 16 bit audio reaches 120dB in practice", which means 16 bits would be enough for transparency.
 

amirm

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#15
It argues that "the effective dynamic range of 16 bit audio reaches 120dB in practice", which means 16 bits would be enough for transparency.
That only happens using a technique called noise-shaping. Problem with that is that you are the mercy of whoever masters the content from 24 bits to 16 bits to use it. So it doesn't happen "in practice." No one knows what percentage of distributed music uses noise shaping.

Even if noise shaping is used, you need to have higher sampling rate than 44.1. Because if you don't, too much ultrasonic content may be jammed in there causing some problem with some equipment.

Net, net, the idea of a 20 bit channel is that it provides unconditional transparency, for all content and all people. Anything else, has "ifs" in it.
 

amirm

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#17
What music? There is no way to determine bit depth of music without statistical modeling.

And no, the analysis is not done with tones. It is performed using analysis of real recording venus, measuring their noise level relative to hearing threshold, and maximum dynamic range of unamplified music presentation.
 

amirm

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#19
This has a balanced output?
Yes, it has a separate 3.5 mm output jack. I am told by the owner that its balanced output is quite a bit louder, remedying the issue I had with it. I am going to build a fixture to test balanced headphone output for future reviews.
 
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#20
I have the lauded Geek Out V2+ from LH Labs and I must say subjectively it's pretty stellar both balanced and Single Ended. @amirm give this new model a listen with the balanced output. It should be a bit better, but honestly if this newer model doesn't live up to it's price I wouldn't be surprised. Either way thanks for the post!
 
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