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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.
 
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