[parabellum777]

Thank you so much for your answer.

UM3x is 7-8 year old model, it's amazing if you have been using it for that long and it's still working great! Btw, I love PICO, reviewed it on HF; too bad it doesn't get as much attention, plus Lotoo killed fw development so no English updates I assume you got UM3x RC with a removable cable, right?

Yes, they have removable cable.

With UMPro30, early batches had issues, as it was noted before. That's probably what you have. With right side not working, did you try to spin/turn the mmcx connector, to make sure it's not loosing the contact? How about switching Left/Right sides of the cable, does the problem stays with a right side or follows the cable? If it's a cable, that's an easy replacement fix. Also, be careful with BA iems, dropping them can damage the driver.

I tried different cables, but I was not able to make it work. Maybe the problem is caused by the MMCX connector part which is in the earphone side, but I don´t know how to check it. I opened it to try to find a disconected cable, but it seems that everything is ok.

Regarding the sound, typically BA drivers don't go through burn in, but the crossover component could. I have noticed sound changes even with multi-BA iems after the burn in, so give it a few days of play time Another thing, when you are comparing, are you using exactly the same eartips? Eartips can have a noticeable effect on the sound. The seal controls the low end impact and the top end sparkle. If you use silicone vs foam eartips, or smaller vs bigger size tips, they can affect low end.

I wish the distortion stops after some time of use, but I´m skeptical. It starts at normal volume and it is very noticeable when the volume is increased.
On the other hand, I only use Comply Foam tips.

 

[twister6]

...
I tried different cables, but I was not able to make it work. Maybe the problem is caused by the MMCX connector part which is in the earphone side, but I don´t know how to check it. I opened it to try to find a disconected cable, but it seems that everything is ok.

I assume you are outside of 2 year warranty period? Otherwise, Westone should replace it under warranty. If you looked inside and didn't find a broken cable (connecting to mmcx socket or between the crossover and drivers), maybe the issue with a driver. Still, kind of strange. You bought it long time ago, never used it until now, and 2 weeks after the use one driver goes dead. Damn!

I wish the distortion stops after some time of use, but I´m skeptical. It starts at normal volume and it is very noticeable when the volume is increased.
On the other hand, I only use Comply Foam tips.

And you are hearing the distortion with all of your DAP sources? Even when switching gain setting? And with silicone tips? For example, 380+AMP or LPG could be pushing it harder. Another thing, you can't discount that UM3x unit you received is not damaged, I'm sure it has been used for years. Also, maybe try to clean the nozzle with that pocker/brush tool. If there is some dirt or accumulated wax, it could affect the sound.

 

[parabellum777]

I don't have the invoice of any of my Westone IEMs, so they are all out of warranty coverage.
I don't really know the reason why the left side of my UMPRO30 stopped working, but I can assure you that I take care of all my audio gear, and they were almost unused when it happened.

The new UM3X I have just bought were used just a couple of hours by the previous owner, so there are no dirt problems. They are like new.

The distorsion can be heard with any of my DAPs. With my old UM3X there is no distorsion, so the source is not responsible for this problem. And what's more interesting is that the IEMs are perfectly balanced, so the distorsion happens on both sides simultaneously.