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[owner's thread] Monoprice Monolith THX AAA 887 headphone amp

RickSanchez

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Creating this thread to have all the owners and members have a place to discuss the Monoprice THX 887 amp without creating extra posts in the official review thread. Feel free to post any questions and concerns that you may have regarding this amp in this thread.

1dbbb839-c4a0-48e5-bc10-624b3bab220c.__CR0,52,1852,573_PT0_SX970_V1___.jpg
 
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RickSanchez

RickSanchez

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Reference Info
Amir's measurements/review: https://www.audiosciencereview.com/...thx-887-balance-headphone-amp-new-champ.8942/
Product Page: https://www.monoprice.com/product?p_id=39359
Product Page (EU): https://www.monoprice.eu/products/m...lifier-featuring-thx-aaa-887-technology-eu-uk
User Manual: (I could not locate a downloadable PDF user manual)

Specs (per Monoprice)
  • Analog Inputs:
    • 1x Gold plated stereo 3‑pin XLR
    • 1x Gold plated stereo RCA
  • Outputs:
    • 1x Gold plated 1/4" (6.35mm) TRS,
    • 1x Gold plated 3.5mm TRS,
    • 1x Gold plated 4‑pin balanced XLR,
    • 1x Gold plater stereo RCA pass‑through
  • Frequency Responses:
    • Balanced: 20Hz ~ 20kHz +0.01dB/‑0.03dB
    • Single‑Ended: 10Hz ~ 50kHz +0.05dB/‑0.15dB
  • Input Impedance: 50 kilohms
  • Chassis Material: High grade CNC‑milled aluminum with black anodized finish
  • Input Power: 24 VDC
  • AC Adapter Input Power: 100 ~ 240 VAC, 50/60 Hz
  • Dimensions: 8.7" x 7.8" x 2.0" (221 x 198 x 51 mm)
  • Output Impedance:
    • Balanced: <0.1 Ω (Amir measured ~0.4 Ω)
    • Single-Ended: <0.05 Ω
 
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brokemember

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I have this amp paired with a SMSL SU 9 dac. I want to connect active computer speakers for those rare occasions. Would it be better do use the RCA outputs on the DAC or to use passthrough on the amp?

Also, has anyone had any success in locating a manual for the amp. Don't think I have ever run into a product where the manual was so hard to find online.

Thanks
 
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RickSanchez

RickSanchez

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For your speaker connections:
  1. Where are you currently controlling the volume, the SU-9 or the Monoprice THX 887?
  2. Is the output in the SU-9 selectable? I don't believe the output on the 887 is. Which means the signal is always being output to both the headphone out and the RCA outs.
I haven't been able to locate a manual for the THX 887. In looking at the Monoprice product page -- specifically looking at the Questions & Answers section -- the same question was asked and no one mentioned being able to find a manual. On this post from @T.J. Turner he also mentions there is no manual, either printed or downloadable.

Maybe @MonolithGuy can confirm about the user manual?
 

brokemember

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No manual. It's so straightforward I didn't think it needed one.
Was trying to figure out what "Timed off" and "bypass" were referring to... I'm guessing it has to do with auto-shutoff...would be nice to now what the time limit on that is... plus always just liked reading manuals.
 

brokemember

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For your speaker connections:
  1. Where are you currently controlling the volume, the SU-9 or the Monoprice THX 887?
  2. Is the output in the SU-9 selectable? I don't believe the output on the 887 is. Which means the signal is always being output to both the headphone out and the RCA outs.
I haven't been able to locate a manual for the THX 887. In looking at the Monoprice product page -- specifically looking at the Questions & Answers section -- the same question was asked and no one mentioned being able to find a manual. On this post from @T.J. Turner he also mentions there is no manual, either printed or downloadable.

Maybe @MonolithGuy can confirm about the user manual?

1) In the current setup I'm controlling the volume thorough the THX 887
2) No the outputs are not selectable as far as I can tell. I figured I would simply have the volume on the active speakers turned off whenever I didn't want to use the speakers. And when I wanted to use them and not the headphones I would simply turn the volume off on the amp. With passthrough it wouldn't affect the volume of the speakers.

That's the plan so far. Currently trying to find RCA cables in my pile of forgotten cables!
 

brokemember

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No manual. It's so straightforward I didn't think it needed one.
What exactly are the Pass RCA ports for? If you read my post right above, you will see that it is not doing anything.


Maybe I'm not understanding how the PASS is supposed to be used.

Could you expand on it a bit.
 

Moderate Dionysianism

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What exactly are the Pass RCA ports for? If you read my post right above, you will see that it is not doing anything.


Maybe I'm not understanding how the PASS is supposed to be used.

Could you expand on it a bit.

The passthrough is exactly what it claims to be - the analog signal from the RCA inputs bypasses the THX amplification stage and the volume control. See some info from the Q&A section on the product page linked by @RickSanchez :

1646907458656.png


1646907373718.png



So this leaves very little flexibility for your desired use case as you have no selectable output on the SU-9 and no volume control for the passthrough on the Monolith.

One way it could work for you would be:

Headphones: SU-9 BAL out → [XLR] → Monolith BAL in → headphone / volume controlled by the 887
Active speakers: SU-9 SE out → [RCA] → Monolith SE in → Monolith PASS out → Speaker RCA in / volume controlled in software or in the SU9 (will impact the headphone path too) or at the speaker if possible/desired.


Both paths will be active at all times, so you'll need to remember to turn the digital volume down when switching to speakers.

I guess it's clear now why so many on ASR are skeptical about the SINAD race and would prefer DACs with better feature set instead;)
 

brokemember

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The passthrough is exactly what it claims to be - the analog signal from the RCA inputs bypasses the THX amplification stage and the volume control. See some info from the Q&A section on the product page linked by @RickSanchez :



Headphones: SU-9 BAL out → [XLR] → Monolith BAL in → headphone / volume controlled by the 887
Active speakers: SU-9 SE out → [RCA] → Monolith SE in → Monolith PASS out → Speaker RCA in / volume controlled in software or in the SU9 (will impact the headphone path too) or at the speaker if possible/desired.


Both paths will be active at all times, so you'll need to remember to turn the digital volume down when switching to speakers.

I guess it's clear now why so many on ASR are skeptical about the SINAD race and would prefer DACs with better feature set instead;)


So this exactly what I did:
SU-9 SE out → [XLR] → Monolith XLR in → Monolith PASS out → Speaker RCA in / volume controlled in software or in the SU9 (will impact the headphone path too) or at the speaker if possible/desired.

However no sound would come of the Active speakers.

Next I did this:
SU-9 SE out → [XLR] → Monolith XLR in → SU-9 RCA out → Speaker RCA

In this case I am able to achieve my desired goals.

What is confusing me is why Option 1 didn't work.

Would the input going into the amp HAVE to be RCA for the passthrough to work. And if XLR is used for input to the monolith amp then the passthrough becomes disabled.


I just noticed that you already addressed this in your comment.

Is this a common feature in amps, (in general) that passthrough only works then using RCA inputs.
And XLR inputs are cutoff from passing any signal?
 
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Moderate Dionysianism

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Is this a common feature in amps, (in general) that passthrough only works then using RCA inputs.
And XLR inputs are cutoff from passing any signal?
I don't know whether this is common. My understanding is that the single-ended path has a signal splitter and they didn't implement another one for the balanced circuit to keep the cost low. The 887 is my first standalone HP amp (it replaced a HUD-MX1 DAC/amp combo) and personally I have no need for a pass/pre feature. More experienced members may be able to give a better answer.


There certainly are options out there. The JDS Atom works as a preamp (adjustable volume at the RCA output, no balanced circuit), but you can't 'uncouple' the volume control, so you need to unplug the headphone when switching to speakers.

Then there's the Topping A90 with selectable inputs and outputs and adjustable volume. See point #2 below:

1646936071496.png


That's a full-fledged HP amp+preamp for you, but at ~2x the price of the 887. I believe Gustard has a product with similar functionality, not sure about SMSL.

Then you may get an integrated amp where the headphone amplifier is often a discrete board, and you have full flexibility for the speakers. Of course it's also another topic money-wise, and maybe an overkill for active speakers.
 

Moderate Dionysianism

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The volume pot is certainly not the most reliable part of this amp:) The Monolith is my 'daily driver' at the work desk, getting ~6-7 hours of use every day. The noise (the usual 'crackling' and static, when turning past the 9 o'clock position) appeared after <6 months. I was disappointed tbh, as my good old HUD-MX2 had lasted several years before the pot needed cleaning. The unit was within the warranty period and had the 'no user serviceable parts inside' sticker, so I returned it and got another one. The 2nd unit lasted about 5 months too:(

I believe it's wasteful to keep shipping gadgets back and forth across Europe, so this time I opened the case and cleaned the pot.


Opening the case
Fairly easy:) Everything can be unscrewed with a star-shaped bit. The size marking in my set is 'T10':
1657391826355.png
1657391863189.png


First, remove all the screws from the back panel (don't miss the one between the RCAs) and the one at the bottom of the case.

Remove the back panel and gently push the gold-colored 'rods' running from the front to the back along the sides (see the attached overall shot of the board). The board will slide out towards the front, together with the front plate and the rods. All the knobs and switches stay in place.


Cleaning the pot
The pot itself is a 'Sanni RV91':
1657393206342.png


As usual, a plastic brush with some isopropyl, and then a special vol pot spray. Unfortunately, unlike with the Audinst, I couldn't remove the knob. I suspect it might be glued onto the shaft, didn't want to force it. I was afraid that the whole operation was pointless as I didn't see any opening in the pot case. Sprayed it gently nonetheless, aiming at the gap you see in the lower left corner of the pot case in the pic above, and 'exercised' the pot, by slowly turning it back and forth a good dozen times.


Re-assembly:
Just as easy as dismantling the unit:) At first I slid the board in from the wrong end:facepalm: (quite hard to be sure with both panels removed). When inserted correctly, the hole at the bottom of the case will align with the slot near the center of the board, so don't start screwing the back panel on until you put the bottom screw in:)


Result:
Well, I wasn't getting my hopes up as the knob wouldn't come off, but I'm delighted to report that after an hour of testing, the noise is gone:D Let's see how long it's going to last this time.


Bonus:
If you made it all the way to the end of this post, I've got a bonus question for you;) Does it make sense to procure a better pot (an Alps for example) and have it installed in the 887? There is a good audio repair shop in my town, so I started thinking about such option. Basic cleaning is about all I'm qualified to do with electronics, so please advise if replacing the Sanni pot with something better is feasible and reasonable. I'm saving up for a TCA HPA-1, but I'd still like to squeeze some carefree years out of the 887:)
 

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Chester

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The volume pot is certainly not the most reliable part of this amp:) The Monolith is my 'daily driver' at the work desk, getting ~6-7 hours of use every day. The noise (the usual 'crackling' and static, when turning past the 9 o'clock position) appeared after <6 months. I was disappointed tbh, as my good old HUD-MX2 had lasted several years before the pot needed cleaning. The unit was within the warranty period and had the 'no user serviceable parts inside' sticker, so I returned it and got another one. The 2nd unit lasted about 5 months too:(

I believe it's wasteful to keep shipping gadgets back and forth across Europe, so this time I opened the case and cleaned the pot.


Opening the case
Fairly easy:) Everything can be unscrewed with a star-shaped bit. The size marking in my set is 'T10':
View attachment 217383View attachment 217384

First, remove all the screws from the back panel (don't miss the one between the RCAs) and the one at the bottom of the case.

Remove the back panel and gently push the gold-colored 'rods' running from the front to the back along the sides (see the attached overall shot of the board). The board will slide out towards the front, together with the front plate and the rods. All the knobs and switches stay in place.


Cleaning the pot
The pot itself is a 'Sanni RV91':
View attachment 217394

As usual, a plastic brush with some isopropyl, and then a special vol pot spray. Unfortunately, unlike with the Audinst, I couldn't remove the knob. I suspect it might be glued onto the shaft, didn't want to force it. I was afraid that the whole operation was pointless as I didn't see any opening in the pot case. Sprayed it gently nonetheless, aiming at the gap you see in the lower left corner of the pot case in the pic above, and 'exercised' the pot, by slowly turning it back and forth a good dozen times.


Re-assembly:
Just as easy as dismantling the unit:) At first I slid the board in from the wrong end:facepalm: (quite hard to be sure with both panels removed). When inserted correctly, the hole at the bottom of the case will align with the slot near the center of the board, so don't start screwing the back panel on until you put the bottom screw in:)


Result:
Well, I wasn't getting my hopes up as the knob wouldn't come off, but I'm delighted to report that after an hour of testing, the noise is gone:D Let's see how long it's going to last this time.


Bonus:
If you made it all the way to the end of this post, I've got a bonus question for you;) Does it make sense to procure a better pot (an Alps for example) and have it installed in the 887? There is a good audio repair shop in my town, so I started thinking about such option. Basic cleaning is about all I'm qualified to do with electronics, so please advise if replacing the Sanni pot with something better is feasible and reasonable. I'm saving up for a TCA HPA-1, but I'd still like to squeeze some carefree years out of the 887:)
Great post, recently acquired one of these out of interest and was wondering the same.
 

cosmox

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My unit has different sound on high gain when i plug heaphones to 6.3mm jack and when using 3,5 mm jack. The volume is the same but there is a difference in sound scene and instruments positioning for sure - 6,3m plays wider, i'd say too wide even. I wonder if there is something faulty or it should be that way. It's seems weird to me. Did you notice such thing in your units too?
 

sjeesjie

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I just noticed now that the analogue passthrough is classified as an input on the back of this device. That’s a little flaw if you ask me.
 

ampguy

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No balanced passthrough doesn't work for me, otherwise, I would give it a try.
 

Jds81

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Edit: unless you want to read a brain fart, ignore me. There's an input switch. I blame my crowded desk.
Having a little issue, not sure what to try.
I have the 887 and SMSL DO100. Both arrived this week. Used existing RCA interconnects, and was working fine. Got balanced cables from Amazon today, and get no throughput. My headphones are connected to the 1/4" jack.
I do not see any way to change the output on the DAC, seems like everything should be hot. I have no other balanced equipment to check.
SE is fine for now, but specifically got these to run balanced interconnects.
Might be a DAC issue, but thought I'd ask here to see if anyone has any tips.
 
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ampguy

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How do you like the 887, any distortion w highest gain setting and balanced in?
 
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