Review and Measurements of Monoprice Portable Amp and DAC with THX

[amirm]

Was going to run a test and by chance I had Dirac Sensaround on and noticed a phase shift. Playing with it, I noticed it was frequency dependent. So decided to run a sweep on it:

What surprised me was the fact that one channel is completely pass through (blue). The other channel goes through frequency dependent phase shift. This explains why I only heard the effect of some sound moving in one channel and not the other.

Running the same test but looking at amplitude alone we get this:

We see the selective frequency dependent transformation better here.

There is 1+ dB of amplification would give a bonus positive impression regardless of what it is doing. Or perhaps it is a compensation for negative swings where the transform is occurring.

Anyway, we are not going to figure out what it is doing this easily but thought I share the measurements anyway.

 

[Jorj]

These tests do seem to bear out my impression that the lower frequencies are cut dramatically when Sensaround is enabled. I'm sure some other computations are going on but the frequency response is being altered in a way that makes it hard to believe this was the intended result.

I have no idea what to think about the phase shifting in one channel and nothing in the other. Is it broken, or did they design it this way?

 

[AndrewMason]

Hi Jorj. I'll head over to your thread.

 

[amirm]

Hi @amirm

Thank you for the review.

I think the "spurious noise" you've flagged in the 1kHz and 12kHz plots is a non-issue common to all DACs and if so, unfair to point out. It appears to be 16-bit quantization noise as result of not enabling dither on the AP when using 16-bit source

Hi Andrew. Thanks for commenting.

The test used for jitter is 24-bit j-test. It is not generated by APx555. For best resolution this test should be run undithered or you destroy the 250 Hz square wave that is embedded in the low order bit.

Still, I ran it dithered and the results are roughly the same (noise floor raises naturally of course):

So dither is not a contributing factor.

We can troubleshoot this by changing the input to Toslink and testing with and without USB power:

The blue graph is with the unit running on battery power and Toslink input. Response is very clean with none of the noise I showed in my measurement.

As soon as we plug in the USB cable, we get the graph in red showing the noise that existed when I performed my review using USB input.

So the source of the noise is USB, not instrumentation/dither or no dither.

On the topic of CD and dither, the DAC is capable of playing 24-bit data so we don't set a limit of 16 bit CD playback for its performance.

I want to emphasize that at -120 dB, the USB performance is not at all an audible concern. It is just something we like to see as clean as possible.

 

[amirm]

I have no idea what to think about the phase shifting in one channel and nothing in the other. Is it broken, or did they design it this way?

The fact that level is transformed in both channels, I can't figure out why the phase difference only exists in one channel. It would take specific intent to make that happen so I don't think is a bug.

 

[Veri]

So basically it's noise from the USB. Great that you isolated it @amirm , for the desktop monoprice unit I'll just avoid using USB then which is no problem really I'm thinking the Sensaround from DIRAC is not going to be a game changer either but whatever really. Stellar dac and amp performance is the most important thing.

 

[amirm]

Desktop one doesn't have a battery so it may be better in this regard to the extent some of this noise is due to charging circuit. We will have to test it to be sure.

 

[AndrewMason]

Hi @amirm . Thanks for clarifying. Massdrop engineering is working on replicating this. Could you share the J-Test file you use so they can continue debug? And is there possibility that your USB 5V power source is introducing this noise into the measurement? Thanks!

 

[AndrewMason]

@amirm We're having trouble replicating the spurious USB noise. Did you use the charger supplied with the product? Or a different (perhape noisy) one. Thanks.

 

[amirm]

@amirm We're having trouble replicating the spurious USB noise. Did you use the charger supplied with the product? Or a different (perhape noisy) one. Thanks.

Hi Andrew. Great to see you/monoprice investigating. For the last set of tests, I ran on batteries so no charger. Mere connection of USB cable to the computer induces that noise.

And sure, it will be system dependent since USB characteristics vary from port to port.

On J-test, Audio Precision has a custom utility that includes it. Alternatively, I can send you one in dropbox.

 

[AndrewMason]

Hi Andrew. Great to see you/monoprice investigating. For the last set of tests, I ran on batteries so no charger. Mere connection of USB cable to the computer induces that noise.

And sure, it will be system dependent since USB characteristics vary from port to port.

On J-test, Audio Precision has a custom utility that includes it. Alternatively, I can send you one in dropbox.

Thanks Amir. Sounds like we need to investigate when connected to various PCs.

It might be a common mode artifact disturbing the DAC or the AP analyzer since there become multiple dirty ground loops (monitor, PC, perpherals, etc etc) once the PC and AP are connected to the DUT.

Did you use unbal or bal AP probe, and was AP analyzer ground connected to the 3.5mm sleeve or just floating? This will help us narrow down the permutations to investigate. We appreciate your helpfulness here!

 

[Deleted member 3718]

For those interested the desktop version is finally up for sale:

https://www.monoprice.com/product?p_id=24459

 

[xineis]

For those interested the desktop version is finally up for sale:

https://www.monoprice.com/product?p_id=24459

I was just going to post this. The wait is over, the game is on!

 

[wadec22]

For those interested the desktop version is finally up for sale:

https://www.monoprice.com/product?p_id=24459

I ordered one to check it out

 

[garbulky]

Ohhhh now that looks quite nice

 

[Roen]

The topping NX4 DSD is a portable unit. So is Chord Mojo.

The Topping DX3 Pro is also portable but not battery operated. That one is in my new measurements template to provide a reference point of performance. To the extent something doesn't outperform that combo of DAC+amp, it is not groundbreaking. And such is the story with the Monoprice.

How is the DX3 Pro portable? Can you use it without an AC source present?

 

[Veri]

How is the DX3 Pro portable? Can you use it without an AC source present?

Nope.

 

[Roen]

Nope.

Ah, so the implication must be size portability rather than usage. Thanks.

 

[amirm]

This unit is available for sale by the way. Just make me an offer....

 

[AresHarvest]

I wish I had seen your comment earlier, Amir. I bought this direct from Monoprice last week, when they were doing a 20% off thing.

Honestly I really like it. I bought an active optical splitter for $20, using it to feed the optical output of my TV to both my receiver and the DAC/amp. When I need/want to use headphones, I just turn off the receiver and turn on the portable.

It was pricey, I'll admit, and I really dislike that it uses USB micro instead of USB-C... But all things considered I'm very happy with it. I don't use the built-in compressor or EQ or DIRAC, but it functions well enough without the bells and whistles enabled. Has enough juice for all of my headphones, with the edge case being my Fostex T50RPmk3 and Hifiman HE560, which require the gain to be nearly or fully maxed out with quieter source material. But that's okay, because my usual choice for movies and such is either the HE400i, HD650, or the M1060C, which don't require nearly as much gain.