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Monoprice Monolith THX AAA Portable DAC Amp

Jorj

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https://www.monoprice.com/product?p_id=24460

Monolith by Monoprice Portable Headphone Amplifier and DAC with THX AAA Technology
24460_01.jpg



The Monolith™ THX® Portable Headphone Amplifier and DAC features cutting edge technology to bring out the best in your headphones, playback device, and music library. Featuring a THX AAA™ 788 amplifier module for superior amplification and extended battery life, an AKM® 4493 DAC for an exceptionally musical experience, and Dirac Sensaround® II decoding for an out-of-your-head, larger than life soundstage, the Monolith portable amplifier is engineered for the finest in music reproduction from your phone or other portable playback device.
 
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Jorj

Jorj

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I thought it made sense to start a thread for this unit, rather than cluttering up the other threads.

Lots of interesting stuff here:
  • What is AAA 788? We know the 789 implementations we've seen have been excellent.
  • 3.5mm Line In and Optical in the same plug? That is a new one for me. I thought the Mojo Coax plug was interesting...
  • Have we seen Dirac Sensaround II used anywhere else? Was there a Sensaround I? How was it, if so?
  • The non-Dirac DSP, EQ & filters and compensation look interesting. I'm sure most will not be used, but this is a feature set you just don't see often on portable units.
  • They stuck with Micro USB instead of USB C, sadly. This means you'll need an OTG cable for Android devices.
  • It may not be compatible with Apple products.
I know Amir has one ordered, as do I. Looking forward to seeing how it measures!
 
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badboygolf16v

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I had a 3.5mm line/TOSLINK combo on my portable minidisc player. That's going back some! :)

My MacBook Pro 2015 has one too.
 

RedCometZero

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I thought it made sense to start a thread for this unit, rather than cluttering up the other threads.

Lots of interesting stuff here:
  • What is AAA 788? We know the 789 implementations we've seen have been excellent.
  • 3.5mm Line In and Optical in the same plug? That is a new one for me. I thought the Mojo Coax plug was interesting...
I know Amir has one ordered, as do I. Looking forward to seeing how it measures!
789 is the name THX gave to represent the balanced architecture they did for Massdrop using a pair of 788 circuits. The Massdrop x THX 789 uses two 788 circuits, but it's not a distinct circuit in and of itself in the way that the 888 is.

3.5mm form factor optical is pretty common. I think the most common use of it has been optical out from laptops. Macbooks used to support it until the re-design that replaced all ports with USB C ports. Here is an example of an adapter.
 
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Jorj

Jorj

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Mine arrived, and I have put a few hours into listening. What follows are my impressions and opinions, and as an objectivist, we both know exactly what those are worth.

Using the Cayin N3 as source, I listened to my repertoire of reference tracks, doing a lot of back and forth between the Cayin's own output, the Chord Mojo and the Monolith THX portable. All listening for this round was done using my Noble K10 CIEMs, mainly because they are awesome, and because the level of isolation they give help me focus on the music. I'll do another run with the HD6xx later on.

Knowing what I do about sight bias and the inaudibility of the minor differences in specs, I'm not going to ramble on about subjective impressions of the sound much. I'll do a little, but if that is what you like reading, you'll want to find something else to occupy a few minutes. I will, however, tell you about what I CAN hear, and what I think of the user interface.

First, and right away, it is clear that the Monolith is not a quiet device. Turning it on reveals a definite hiss, I'd say 15-20dB. This quickly spills over into the music, pushing the noise floor up in quiet spaces in recordings. The Mojo and Cayin do not do this. Otherwise, I'd say it sounds just fine. Not great, but fine. I understand that there is a brain-burn-in effect, and maybe since I listen to the Mojo often, I prefer it and the dead silence it provides when no sounds are required, but in changing back and forth, I found I also preferred the Cayin. I even tried the old trick of turning up the Monolith a bit, and still found it not quite as pleasing as the other two. This is not to say the Monolith sounds bad, it does not. It sounds fine. It's better than my Note 8 by a country mile.

Moving on to the user interface. Well, I think Amir found the same thing....it's fiddly, and if you're not fast enough, the menu closes and you have to start over. Fortunately, there are not a ton of settings to mess with. Once you get the auto input turned on, you can leave them alone for the most part. There are three presets for parametric EQ and high\low shelf EQ settings. DRC (dynamic range compression), yuck, I may play with it someday, but why? Ah, there it is!! The reason I was still excited about this unit, now that we know the measurements are good, but not up to the standards of the Massdrop box using a pair of the 788 chips. Dirac Sensaround II!

Enabling this feature filled me with excitement, and you can imagine my dismay when I discovered that it kind of sounds like I stuffed a little bit of cotton in my ears before wedging the customs home. As Amir noted, it's a subtle effect, but noticeable. Rapidly popping the effect on and off, I found that it does add a sense of distance from the music, but it's weird, and a bit hard to explain. In one of my favorite tracks, Norah Jones is very close to the mic, and I like that. With the Dirac Sensaround enabled, she does not sound as close, and a bit muffled. Disabling it sounds preferable. Now, I'm not saying it's all bad. There are a few tracks, like Punch Brothers - Moonshiner, where three instruments are playing together and the Dirac effect seems to help....maybe....but once the tune gets busy, that effect is overcome by the muffled sound of distance that is just not realistic. It just seems to eat up some dynamics. The closest I've come to liking the effect is with a single vocalist recorded at a distance from the mic. I've not given up, there may be some music that this works really well with, but I've not found it yet. It really did damage to all the classical tracks I tried it with, muddying up the sound and just making it kind of unpleasant.

In summary, with very sensitive IEMs, this is not the HTRF-in-a-box you're looking for. It sounds acceptable, if you don't mind the hiss (which may not be a factor with the HD6xx), and it is definitely more capable than the shoddy afterthought DAC-stage in most smartphones. There will be more impressions as I try it with different gear and music styles, and I hope any others that lay hands on it can chime in with their thoughts as well. At this point I'd say it's an average effort at best. More to come....

Quick footnote: I jumped over to some of my more bass-heavy classical, and found that the Dirac effect simply decimates the lower registers. The booming reverberation of the big pipe in Felix Hell's recordings is just....gone. This is not at all what I'd hoped for.
 
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maverickronin

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In summary, with very sensitive IEMs, this is not the HTRF-in-a-box you're looking for

Too bad. It looked promising.

I guess my Leckerton UHA-4 isn't going anywhere.
 

AndrewMason

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Hi Jorj. Do you experience the same hiss with both 16-bit and 24-bit files?
 
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Jorj

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Hi Jorj. Do you experience the same hiss with both 16-bit and 24-bit files?

Yes, Andrew, the hiss is there from the instant the relay kicks the amp section in, both with 16/44 and 24/96 files.

Also, in the interest of fairness and science, I switched to my Oppo PM-3 closed planars, which are quite sensitive, but not IEM sensitive. The low-level hiss is not apparent during turn-on (my ears are not that good), BUT, it definitely adds that same 15-20dB of hiss to the noise floor in quiet sections of recorded music, and this is noticeable and distracting. Direct comparison with both my Chord Mojo, Topping D10, Topping DX7s, Cayin N3 and even my Samsung Note 8 with the same track, the noise floor is low-but-present, but with the Monolith, it is substantially higher. (test track: Punch Brothers - All Ashore - 01 - All Ashore.flac (24bit\96kHz)
 
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Jorj

Jorj

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Perhaps unsurprisingly, with less sensitive headphones that require higher volume levels, the added hiss is VERY noticeable and just plain un-enjoyable. I have to turn the volume down quite low in order for the hiss to vanish into the ambient, and that is no fun. It's much worse than my JDS Element, which I've always thought has some hiss (from rf sources), and worse (from memory) than the Audio-gd NFB28 I sold.

Now that I'm focused on it, I can clearly hear the hiss either partially or fully obscuring many of those fun little quiet musical details that your average listener never hears anyway. Not good. I begin to suspect that this unit may be defective. This is not the audiophile performance I would have expected.
 

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Now that I'm focused on it, I can clearly hear the hiss either partially or fully obscuring many of those fun little quiet musical details that your average listener never hears anyway. Not good. I begin to suspect that this unit may be defective. This is not the audiophile performance I would have expected.
Do you have a way to drive the unit using toslink instead of USB?
 
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Jorj

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Do you have a way to drive the unit using toslink instead of USB?

Unfortunately not. I actually don't think it would help, because the hiss is present even with no source connected. As soon as the relay clicks, hiss.
 

amirm

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Unfortunately not. I actually don't think it would help, because the hiss is present even with no source connected. As soon as the relay clicks, hiss.
Oh, I don't have that experience on mine or measurements would be much worse. I will test with my IEMs and see if I can hear something there.

For now, start a process with monoprice to get it replaced. It is super important to know if what you are hearing is normal for the unit.

Confirming, you hear the hiss with no cables (i.e. working on battery) connected to it. Correct?
 
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Jorj

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Confirming, you hear the hiss with no cables (i.e. working on battery) connected to it. Correct?

That is correct. With my K10's, the hiss is always there. With less sensitive headphones, I cannot hear it with no source connected, but it shows up as elevated noise floor in quiet recordings.

--edit--

I've started the RMA process with Monoprice for an exchange. There is no question that this device is either broken or badly designed. @amirm has not experienced the hiss issue, but given his propensity to SPL test gear with his own ears, we may have to look to another reviewer for confirmation. Just kidding, this is bad enough that it would show up instantly when connected to a spectrum analyzer. I wish I had a way to capture an image of it.

On another subject, I found that the USB jacks are slightly misaligned with the aluminum case edges, making it a real pain to get the USB cables inserted. Lots of wiggling and cursing.
 
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Jorj

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Despite believing that I've got a busted version, I did spend some time with it pushing electrons to my HD-6xx, as promised.

As with the PM-3, the post-turn-on hiss is not audible. After going through my test tracks, I'm comfortable saying that 99% of users would not have noticed the elevated noise-floor in this pairing. Cranking up the volume to overcome the infiltrating ambient room noise hides the hiss almost completely, and tracks with a nice low noise-floor don't make the added noise obtrusive in the way it is with good isolation and high sensitivity. Further, while I was able to hear the hiss quite often with the PM-3, it takes real effort to find it with the Sennheisers.

Beyond that, gobs of power push the HD-6xx with ease, and I did find myself enjoying the Monolith. Back and forth with the Chord Mojo, and while I don't guarantee it, I do think I could A\B between it and the Mojo, and do find the Mojo preferable. The music just seemed a little more 'alive', and I wonder if that is due to having some of the DR masked by the noise of the Monolith. It could all be in my head. Suffice it to say that with an inefficient open-back design headphone, you won't notice if your Monolith is noisy or not, and it sounds very nice.

Let's see if the replacement version is better behaved. If we can get rid of that extra noise, I think the Monolith should compete with the Mojo, sound-wise, for a good deal less money ($279 vs$532).
 
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This is part II of my review of this device. I RMA'd the first one due to completely unacceptable levels of hiss, poor USB plug fit and a swelled case. This replacement did not have the issues with USB plug openings and the case-back was nice and flat. Hopeful!

After letting the unit come up to room temp, I turned it on to see where the battery level was. Nearly full, like the first one. Since the mini USB cord was handy, plugged it in to top up while I dug out a few different sets of IEMs. I noticed that it dropped down to two bars of battery and then the flashing\increasing indicator for charging. Odd, but OK, moving on. When I got back to my desk a few minutes later, it had stopped blinking and showed full. Still odd.

First with my customs, which are extremely sensitive. No audio source, just the CIEMs plugged in and turning the unit on. Hiss. Not nearly as much as the first one, maybe 10dB on the right and 5-7dB on the left. Better! I can deal with that for now, but still not satisfied given how quiet the Cayin and Mojo pair are. On to music, sourced from the Cayin N3 via USB. Nothing. Grr. Oh, yes, into settings for the Input Auto select.

Once the music starts, the hiss is harder to hear, but I'm getting a noticeable channel imbalance. Just for fun, I decide to enable Sensaround II. Yuck. This does not sound like the first unit. It has a weird sibilant effect with cymbals and seems to...drift. Off it goes.

I know it's not fair to judge this unit by my Noble K10's only, so I grabbed some TFZ Exclusive 5's, a bit less sensitive. Source removed, power on, I can still hear the hiss clearly, and the imbalance, right side is louder. Odd the display is wavering between MUTE and -61dB. I've never seen it show -61dB before, it has only gone to -60. Oh, well. I go to check Settings, and the buttons are acting odd. Jumping around between options is laggy and even more difficult as a result. IT training to the rescue, restart the unit. This time it goes to MUTE and stays. Plug in source, fire up a song. Nothing, as expected. Turn the knob the tiniest little bit, and it goes to -61dB, and for a moment no sound, then BAM! Deafening. I rip the IEMs out of my ears instantly, but my heart is racing and I'm PISSED. If I had been using the K10, I'd have been deaf. Those are hard to get out in a panic and I would have taken a few seconds to think of some other response, like turn the unit off or yank the USB. Oddly, I have not been able to get it to show -61dB again.

Needless to say, this one is going back, and I'll not trust my ears to Monoprice audio gear again. There were a number of other eccentricities with this unit as compared to the first one that I'm not bothering to write up, as it is not worth my time. I'm still smouldering over the ear-blasting for no reason, which did not just break the camel's back, but smashed the camel flat. I try hard to protect my hearing, and thinking about the damage that blast did is infuriating.

This unit is not ready for prime-time. Eardrum punishment, channel imbalance easily audible, non-zero level of hiss and a super-flaky user interface. Count me out, it is going back to Monoprice. Not recommended.
 

amirm

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I too noticed the odd charging behavior. I left it plugged in and it kept saying it was charging.

The volume control logic is for sure faulty as I reported in my review. It is as if the person has never implemented such thing. There seems to be no formal testing of these products.

I think monoprice should never jump ahead of the queue and try to be pioneer with new technologies. Their strength is to sell commodity products. They should stick to that.
 
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Jorj

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Just to close this out, I got my refund from Monoprice, and I'm glad to say good riddance to the THX portable. It was sadly unable to unseat the Chord Mojo.

I do wish we'd had someone from Dirac show up and lend a bit of insight about the implementation, but given how poor it sounded to my ears, and how strangely it tested, my guess is they gave it up for a bad job or have no marketing team getting search\hit metrics from Adwords.

The quest for portable + canned HRTF simulation via DSP continues.
 

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Does anyone have any imagery of the internals of this device?

Somewhat unrelated question: Can other amp designs implement feed-forward into designs to improve their output? I wouldn't think that something like that could really be patented. I'm thinking that an amp that is already nearly as quiet as THX AAA could implement feed-forward, and see improvements. Something based on say, an OPA1622 from TI, or a product like the Atom from JDS.
 
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