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

ElVendrick

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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:)

I can attest to that. My volume knob started scratching about 8 months in and it has gotten really annoying. I'll be taking the same course of action as you did.
I think overall it's a great device for the price, except for this one flaw.

Does anyone know a way to actively prevent the pot-issue from the start?
 
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Moderate Dionysianism

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Does anyone know a way to actively prevent the pot-issue from the start?

Not sure if it's fully preventable, as you're relying on a mechanical part here. From reading around, it has a lot to do with the quality of the pot itself. Note how the mfrs provide an 'operating life' spec for them. The Sanni is rated at 15,000 cycles, and interestingly, the same figure is given for the well-regarded ALPS RK27.

It surely doesn't tell the whole story, as the ALPS pot in my HUD-mx1 (I don't recall the precise model Audinst used) lasted almost a decade before becoming noisy, and the DAC was also used almost daily, transported etc. I cleaned it, used the DAC for a few months, then put it in storage for ~2 years. Plugged it again yesterday, and the pot is still dead silent.

I'd also suspect (more experienced members may correct me) that it has to do with the 'seal' quality of the case. E.g. my Topping NX4DSD has virtually no gaps, hence little risk of dust etc. getting inside. No issues with that pot in 4 years of use.


Ultimately, you can avoid this with a digital volume control, but personally I can't get used to the lower accuracy (going from 'too quiet' to 'to loud' in one step). One day, I'd like to try the TCA HPA-1, which measures great and uses top quality parts (there's a review here on ASR, pot reliability mentioned on page #2). It is 4.5x the price of the 887 though:)
 

ElVendrick

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Not sure if it's fully preventable, as you're relying on a mechanical part here. From reading around, it has a lot to do with the quality of the pot itself. Note how the mfrs provide an 'operating life' spec for them. The Sanni is rated at 15,000 cycles, and interestingly, the same figure is given for the well-regarded ALPS RK27.

It surely doesn't tell the whole story, as the ALPS pot in my HUD-mx1 (I don't recall the precise model Audinst used) lasted almost a decade before becoming noisy, and the DAC was also used almost daily, transported etc. I cleaned it, used the DAC for a few months, then put it in storage for ~2 years. Plugged it again yesterday, and the pot is still dead silent.

I'd also suspect (more experienced members may correct me) that it has to do with the 'seal' quality of the case. E.g. my Topping NX4DSD has virtually no gaps, hence little risk of dust etc. getting inside. No issues with that pot in 4 years of use.


Ultimately, you can avoid this with a digital volume control, but personally I can't get used to the lower accuracy (going from 'too quiet' to 'to loud' in one step). One day, I'd like to try the TCA HPA-1, which measures great and uses top quality parts (there's a review here on ASR, pot reliability mentioned on page #2). It is 4.5x the price of the 887 though:)

These are some interesting facts to know. The 'seal' quality - theory seams plausible to me as well. Would it not be possible to solve that with some kind of silicone spray/gel between the knob and the chassis?

The Monolith is my first dedicated amp, so I do not have any other referencepoints yet. I'd like to try the D90 or the Gustard H20, but those are quite expensive as well. I'll probably upgrade my DAC first (right now I'm running 3.5 from a docking station to rca-in on the amp :D)

The HPA-1 looks nice as well! Especially the decision to go nearly fully balanced (input and signal chain) but to terminate into se.
 

jackdanyal

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Just bought this amp brand new from monoprice.eu for 204 euros, delivered today. The SE output on max gain is weaker than the output of Liquid Spark on low gain, what is a quite interesting considering the original price of LS(130 euros) and original price of THX (407 euros). Decided to purchase an XLR balanced cable. Now I have 2 questions:
1. Who can describe me the gains on this amp? I mean the first one is low or normal? Like as 1 - Low, 2 - Normal, 3 - High, or 1 - Normal, etc.
2. If I will use dongle with balanced pentacon output, can I connect it to this amp through xlr inputs, as 4.4 -> 2 xlrs 3 pin?
 

sq225917

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Unlikely to be a sealing issue, it's the wiper and track degrading and cleaning it flushes the crud out, particles of wiper and track. It's hard to find good 10mm pots.

My bpbp has a bourns pot in it, 7 years young, used every day, left on 24-7, no noise.

PTD902-2015F-A103
 

arrow0309

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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.
Also interested mate, I have an E50 and this Monolith 887 both incoming in a week or less, also customade TRS to XLR balanced cables. So without any se connection you get no audio on the quarter inch out?
I thought (understood) this amp didn't use a real balanced circuit.
And having to connect both the balanced cables for the Sundaras (got no SE headphones 3.5mm cable) and the rca for the other headphones would be a little pain in the arse.
I'd also want to pass the audio to the active speakers and (maybe) control the volume with the preamp of the E50. Hmmmm, anyone doing similar stuff?
 

Jimbob54

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So without any se connection you get no audio on the quarter inch out?
Poster forgot to enable the input switch. Get Se out and XLR out with either an XLR or RCA input if you toggle right input
Also interested mate, I have an E50 and this Monolith 887 both incoming in a week or less, also customade TRS to XLR balanced cables. So without any se connection you get no audio on the quarter inch out?
I thought (understood) this amp didn't use a real balanced circuit.
And having to connect both the balanced cables for the Sundaras (got no SE headphones 3.5mm cable) and the rca for the other headphones would be a little pain in the arse.
I'd also want to pass the audio to the active speakers and (maybe) control the volume with the preamp of the E50. Hmmmm, anyone doing similar stuff?
The RCA out is pass thru but assuming you mean RCA from E50 then it will pass it back out at whatever level its coming in from the E50. Cant pass thru the XLR input.
 

arrow0309

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Poster forgot to enable the input switch. Get Se out and XLR out with either an XLR or RCA input if you toggle right input
The RCA out is pass thru but assuming you mean RCA from E50 then it will pass it back out at whatever level its coming in from the E50. Cant pass thru the XLR input.
Perfect.
For the pass thru then I suppose I'll have to connect them speakers to the E50 directly and use it in Preamp mode (at least when I'm using them rarely).
 

arrow0309

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Lol, I'm happy with mine so far however I didn't see (or hear) much improvement over the A50S I previously had. And a little bit I suppose is coming from the new dac E50 (had the E30 II).
Anyway I think I'll enjoy this new setup and make it last :cool:
 

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cosmom3

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what DAC is everyone using for their 887?

Also - is it worth using the balanced inputs on the 887 from my SMSL D-6?
 
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cosmom3

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Update: the 887 sounds perfectly fine via balanced TRS output from the SMSL D-6 DAC.
 

rozel

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Hi all - my journey using a DAC has been an ongoing one and is constantly evolving. Currently I'm feeding a Gustard X-16 DAC with Audio via a Zidoo 1000 Pro media player. From the Dac I feed a Yamaha A1070 receiver and from there to a pair of Audio-Technica ATH-M50X Headphones. Quality is very good for me. But I've always wanted to try a decent Headphone amp so have ordered a slightly used Monoprice Monolith THX 887. Not sure what difference in sound quality I will experience but I will connect the Monolith to the DAC with a balanced pair of XLR cables. As I have bought most if not all my equipment following reading the excellent forums on here, I would welcome anyone's thoughts and/or recommendations. Thanks
 
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cosmom3

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Not sure what difference in sound quality I will experience but I will connect the Monolith to the DAC with a balanced pair of XLR cables. As I have bought most if not all my equipment following reading the excellent forums on here, I would welcome anyone's thoughts and/or recommendations. Thanks
Someone here can correct me if I'm wrong, but I believe going balanced with both the DAC and the AMP will increase the Amp output, particularly the balanced headphone output of the THX 887?
 
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