I just posted this on the DX90 Bug Thread, http://www.head-fi.org/t/715434/ibasso-dx90-bug-thread-post-any-firmware-bugs-issues-here/375#post_11334544
Thought it worth putting in this thread also.
Quote:
I've found a mechanical defect in my DX90.
There is a golden pin soldered into the player's board. Its purpose is to ground the metal battery cover. There is a hole in the back panel for the pin to go through. But, the back panel has a conductive tape inside, for electrical contact between the battery holder and the battery cover. In my DX90, the tape prevented the pin to go through the hole.
I've cut the tape inside the hole, and now the pin goes outside, and a corresponding scratch appeared on the battery cover, which means, they have connected now. On the picture you can see both the pin and the scratch.
It also means, that, in the original assembly, the board experiences mechanical stress under the pin (and so does the back cover), which is not good for the long run.
If you don't see the pin like on the picture, I'd suggest you to cut the hole and allow the pin to go out.
Note: If you see the pin protruding through the hole, even covered by that conductive tape, you may leave it as it is! My problem was that the pin didn't come out, stressing the board and the back cover, with no a trace of the contact on the battery cover.
Note 2: Mine was manufactured in May, 2014. There is an information from a recent buyer that in the latest batch the pin has a spring inside, i.e. the problem seems was fixed later...
I bought my DX90 in early May, in H.K. The pin is covered by tape. After I cut the tape, and used a sharp pin to expose the golden pin, I see that it is spring loaded. i.e. I can push on it, and it will pop back out again. Thinking about this, I assume that iBasso engineers had a good reason to ground the back cover. I believe this is to create a Faraday cage/shield, to ground the EMI that is present in the player. I saw another reader's comment about the digital circuits in other players having metal shields covering them, but noting that this was not present in the DX90. This golden ground pin may be an essential part of the design, to absorb the EMI by sending it to ground. Without this, the EMI may bounce around, and build up, and have a major impact on the electronics.
Another finding is that there is a notch in the back cover, so that the edge of the cover will not catch on the pin, but the notch allows the cover to slide over the golden pin. There is another common defect here, that the back plate is anodized, so there can be no electrical connection between the pin and the back cover. This is a common failing in the manufacturing process, that this small detail is overlooked, making the grounding scheme ineffective. All that is needed is to tape the spot where the pin needs to make connection, before anodizing the metal. Then peel the tape off afterwards, to expose the bare metal.
I used a push pin to scrape the anodization off the area where the pin should ground the back cover, and this I believe is what the engineers meant to do, to ground the metal back cover plate, to reduce EMI.
I believe the above is essential to do, to implement the original engineering design.
I did the above, and also put new silicone earbuds on my IE800, to create a better seal. (Audio Technica ER-CKM55L works well, I find, for many earphones. For the IE800, they are fitted onto a IE800 small earbud shaft, with the original earbud removed.) I did this without thinking that there would be any changes in the SQ, from these very minor changes. Better bass extension with the better earbud seal, I expected.
What I experienced was a major SQ change. Bass extension that I had not heard before, with impact and speed, and "slam", and more micro details and textures, with major improvements in "stage". Repetetive bass lines which I had though boring, became mesmerizing. In short, a lot of music was more involving, and had that "toe tapping" urge.
The only reason I can think of for these major changes is that the proper grounding is "sinking" the EMI that was previously polluting the processing, and the overall SQ. Getting rid of it allowed the circuitry to work without handling the noise. Kind of like cleaning up the AC with a regenerator, or filtering out the noise. These kind of changes have a major impact on everything. Deeper background, micro details are not masked, more power available for the Bass, etc.
So, for such a minor, no cost change, which just needs a little work, I think this is a must do. If you get some or all of the improvements which I'm seeing, great. Even if you get much less, you will still be doing the right thing, to ground the back cover properly. And maybe you'll get some good SQ improvement.......Anyways, what do you have to lose? And I would be very curious to see if anybody else observes improvements.
