Monoprice Monolith Liquid Platinum - By Alex Cavalli
Aug 31, 2020 at 6:49 PM Post #3,196 of 4,020

hemtmaker

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Big shout-out to Keith, aka ksorota for the parts and detailed advice on the cap mod. I managed to put everything together last night and it already sounded great without burn-in. I am rocking the Arya from a pulse infinity dac to the liquid platinum :)
701EDBDE-89D6-462E-96DA-0F3A2D83B0D4.jpeg
 
Sep 2, 2020 at 1:20 PM Post #3,202 of 4,020

ksorota

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Working on the write up, but I guess it’s time to show off the results of the latest mod!
Big shout out to @Guidostrunk for the cosmetic work... stealth black just looks perfect on this amp.

I have been low on time lately and have not been able to get photos organized quite yet but here is the summary of what has been done to the LP.

Bit of backstory...Sam and I have been working on modding the LP for a few months now with his original idea of upgrading the caps to Elna Silmic II's to see what kind of improvement it could bring. Many swaps later their remained the issue of a sub-par volume pot with low-mid level channel imbalance. Then the discussion turned to how to fix it.

Well, how hard could it be to swap out a volume pot, right?

Turns out that it is not terribly difficult to do so, but the pot we chose to use is the Alps RK27, sort of industry standard volume pot that is quite a bit larger than the stock knock off version.
pot_comparison.jpeg

Original thought was...maybe it could fit into the stock location, but after a few measurements it became clear that the Alps was too large, both in length and in height of the shaft. Turns out the Alps is wider than it is tall, and rotated 90 degrees, it fits perfectly between the stock pot location and the adjacent components to the left of it (such as in the picture above, but turned) So I went to work desoldering the OG pot and getting the board cleaned up for testing.

Couple issues to overcome:
  1. Determine the pin-map of the stock daughter board to the main circuit board, which of course was unique.
  2. Second test had me coming to terms with the fact that their really was not enough room in the case to apply my own daughter board at that I was going to have to just go direct from Alps to board.
  3. The new placement meant that the stock faceplate was going to have to have a new hole drilled.

The third problem was solved by @Guidostrunk . He filled in the original hole location and drilled and bored out the new one. He also went above and beyond with the finish paint work. Sanding the stock plate, painting, wet sanding, painting, clear coating...he did it all and it turned out fantastic and a great match for the original LP finish. Gone are all text and symbols, but I never needed those in the first place and prefer the murdered out look! The stock volume knob was usable with the new setup, but the larger one I ended up going with just felt a bit nicer. I like the larger diameter and knurled edge.

Knob

Number 1 and 2 were solved together and ended with me testing a number of difference resistance Alps pots to "try all possibilities" of attenuation. The stock pot is a 50K resistance pot. My finally settlement was for the same. I tried 10k and 100k. 10k sounded great with a little more low end, but also sound leakage at the lowest volume. The 100k also sounds great and provides a very smooth rotation to listening level, but ramps up quickly from 10-11, so back to the 50k which basically follows the stock pots profile and has me listening at 11 or so unless its late and quiet and then its much lower.

Here is one of the original test fits showing the tangle of cables and basically the proof of concept.
First_test_of_new_pot.jpeg
In this image I parted a Kimber PBJ cable for the wiring, but the gauge was way too big and became a problem removing the wires for further testing. I switched to some silver 24 gauge wire that was much easier to work with in the final iteration.

new_pot_with_old_face.jpeg
Here is the stock hole vs. the new hole and vol pot location. The Alps housing had to be glued to the board for a nice secure feel. Also realized at this point that the new hole had to be dished out like the stock location so that the threaded section would come through the front plate.

So how does it sound is the most obvious question. Good, very good is the answer. With the 10k pot, I never quite got to 0 volume, but it was very faint like whispers in your ear...but these whispers were very nicely balanced. The 100K pot allows to full 0 volume, but also retains a hint of channel imbalance at the whisper level. The 50K pot is just right! Tight volume matching, smooth attenuation and a really nice overall upgrade.

new LP.jpg

I hesitated to show this off since I currently I do not have a lot of bandwidth to offer this as an upgrade service like the cap upgrade (cap upgrade I can still do). But I have also alluded to this often and wanted to show that its possible, and does make an improvement. I also was directed that perhaps we could try and Alps RK09, compact volume pot, but I could not locate a 4-gang unit. I am sure they exist, but they might be special order parts from Alps.

Give me a few months to finish my home move and get school squared away and I will be able to some upgrades for folks at a slow pace. The upgrade involves the removal and replacement of the volume pot, but also some fairly heavy cosmetic work to finish off the product.

I am glad I took this on, and really love the new feel of the volume pot and the new improved sound.

If anyone is inclined to take this one, I can provide answers to any questions you would have, just let me know!
 
Sep 2, 2020 at 1:39 PM Post #3,203 of 4,020

ruinedx

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I'm all for a better volume pot and would gladly pay for this upgrade but I don't think the channel imbalance is an issue anymore on currently shipping units. People with this issue should be able to return under warranty and get a replacement. The range is still small but the channels are balanced in the 2 units I've tried of newer batch.
 
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Sep 2, 2020 at 2:37 PM Post #3,204 of 4,020

Gene4797

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Hi guys, I just bought on eBay ,2x TESLA E88CC (6922) Matched pair GOLD plated-pin! NOS! 1969y , what you think is it will be good match, if not what you can to advise ? Thank you
 
Sep 2, 2020 at 3:16 PM Post #3,205 of 4,020

ksorota

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I'm all for a better volume pot and would gladly pay for this upgrade but I don't think the channel imbalance is an issue anymore on currently shipping units. People with this issue should be able to return under warranty and get a replacement. The range is still small but the channels are balanced in the 2 units I've tried of newer batch.
You bring up the obvious and fair point. What was the point?

In this case the goal was to start working on the gain issue and see if we could attenuate the signal moreso than stock. I tried some other tricks that should have worked, but not going to get into that. It is something that can be done for relatively cheap if your willing to do it, and may help some of those who own the LP past warranty (is that possible at this point) and want to play around with making it a more competent amp.

Is this an upgrade/sidegrade/alt-grade? yes.

Would it really truly be worth it, probably not, but in the end...it was fun to do! I wondered if it could be done and I fulfilled my own curiosity and am very happy with the results. I am trying to get away from just buying different iterations of headphones and luckily playing with circuits is relatively easy...and its something fun to do while also focusing on the audio hobby.
 
Sep 2, 2020 at 5:11 PM Post #3,206 of 4,020

ruinedx

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You bring up the obvious and fair point. What was the point?

You stated "there remained the issue of a sub-par volume pot with low-mid level channel imbalance" and I was simply noting for people who might be new to the thread that newer revisions appear to have resolved this issue.
 
Sep 2, 2020 at 6:08 PM Post #3,208 of 4,020

Curtisvill

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You stated "there remained the issue of a sub-par volume pot with low-mid level channel imbalance" and I was simply noting for people who might be new to the thread that newer revisions appear to have resolved this issue.

I have one of the newer units and channel imbalance is not an issue for me. It is good to know that there is a fix for the earlier units.
 
Sep 2, 2020 at 6:45 PM Post #3,209 of 4,020

sennfan83261

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There's other factors besides balance issues. That alone is why I'll be getting mine done. Alps is known for quality. Cheap pots also create noise and distortion.
Yeah, cheap pots that are used in the CTH and the 789 definitely lead to "scratchy pot" syndrome, the CTH reaching that ignominious finish line far sooner than the 789. With the Alps pots, don't they get scratchy eventually? Obviously not as fast as the cheap pots used by Drop and Monoprice. With so many knock-off Alps blue velvet pots sold these days (often fraudulently passed off as genuine), can anyone be really sure that the one they purchased is the real mccoy?

If the pot replacement reduces/eliminates channel imbalance issues, makes tracking more linear, and last longer without developing scratchy pot ear-rape, then I'd consider that as a win in my books.
 
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Sep 2, 2020 at 6:48 PM Post #3,210 of 4,020

ruinedx

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Yeah, cheap pots that are used in the CTH and the 789 that eventually lead to a "scratchy pot" syndrome.
Fyi this can often be fixed by adding a drop of caig deoxit to the pot.

Worth noting these units have 5yr warranty so all this stuff (imbalance, scratchy pot, etc) should be covered by warranty in that time period for free.

Of course if you want to upgrade the pot for other reasons besides repair that's another story.
 
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