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|20th July 2017, 09:13 PM||#161|
Metal nose 35RAPC4BHN2 3.5mm jack works IF panel modification
Summary of this O2 modification: The Switchcraft 35RAPC4BHN2 metal-nose 3.5mm jack will work in the O2 headphone amp, but requires major modifications to the front panel, a modification to the jack, and some care when soldering.
I wish NwAvGuy had used this Switchcraft 35RAPC4BHN2 in his O2 headphone amp PC board layout! I personally think the metal nose looks a lot more "pro", plus Switchcraft is likely to have higher quality contacts than Kycon/CUI. I can only speculate why he went with the Kycon. He put absolute lowest cost as his #1 priority with the O2, to the designs' detriment sometimes I think. The Kycon is 40 cents less than the Switchcraft. The Kycon nose being 4mm taller also does put the jack hole more in line with the push button switches and volume contro from a "looks" standpoint, so maybe that was a factor.
A couple of months ago someone was insisting to me via email that a Switchcraft metal-nose 35RAPC4BHN2 3.5mm jack would work in the O2. I had looked at jacks for the O2 pretty extensively over the years and the original plastic-nose Kycon and copycat CUI were the only ones that had ever come up as workable jacks. From the mechanical drawing it looked close, but had some small but potentially significant differences. One of those things where it was necessary just to get one and try it. The Switchcraft jack has been sitting here ever since. I finally got some time today to open up an O2 headamp, extract an existing jack with the solder sucker, and try it.
Well... the good news is the 5 leads fit in the O2 holes just fine and electrically the contacts inside are correct. The jack will work electrically. The Switchcraft jack also fits in the white switch outline area on the O2 PC board just fine too, doesn't extend back or to the side any farther to bump into anything.
But one problem comes with the height. The Switchcraft jack is 4 mm lower (closer to the PC board) than the Kycon or CUI (exact copy) specfied in the O2 BOM. The Kycon/CUI jack has a plastic rail on the bottom which raises the jack nose 6.5 mm above the PC board. The Switchcrafft nose center-line is just 2.5 mm from the PC board. This means the the hole in the O2 front panel won't match up anymore. You would have to make a new front panel with the 3.5mm jack hole 4 mm lower (in both positions, if you use the Switchcraft jacks for input and output).
In addition there are two plastic alignment studs that have to be clipped off the bottom of the Switchcraft jack, photo below. The jack has 4, clip the two closest to the front of the Switchcraft jack. The Kycon/CUI jack only has the back two. If these are not clipped the rear two go into the O2 PC board alignment holes just fine, but the front two don't result in the jack sitting at an angle.
Then a more serious mechanical issue, shown in the photo below. The Switchcraft jack has a rectangular plastic nosepiece sticking out about 1.0 mm that the Kycon/CUI jack does not have. It will interfere with the front panel sitting flush on the front of the O2 case unless a matching rectangular cutout is milled into the backside of the panel. The Box Enclosures panel is 2mm thick, so that milling will go about 1/2 of the way through the panel. FPE would be able to do it. If NwAvGuy had used the Switchcraft in the O2 this issue would have been easily solved by moving the 3.5mm jack PC board holes back 1 mm on the O2 PC board. Plenty of room to do that behind the output jack, although the input jack would need all the resistors and caps behind it moved down that far.
In addition there is a "shoulder" plastic area in back of the jack's plastic nosepiece. There is some play front-to-back with the Switchcraft jack in the O2 PC holes. It is important to make sure the jack is pushed back in the holes (away from the PC board edge) when soldering to make sure that shoulder area is flush with the front of the PC board. Otherwise it will stick out about 0.2 mm and interfere with the backside of the panel.
Another soldering-related issue is a tiny via hole in the front part of the O2 PC board under the output jack. The via doesn't matter with the original Kycon/CUI jack since they are all plastic underneath. But the Switchcraft unfortunately has a metal plate under the front part that would short against the via hole. The solution is to put a thick piece of paper, or 3 or 4 pieces of paper stacked, under the front part of the Switchcraft when soldering to use as a spacer. This insures the jack won't short again that via.
And finally the jack noses are slightly different diameters. The Switchcraft is 6.0 mm in diameter, while the Kycon is 6.8 mm. This one would have been OK on the original panel, since the Switchcraft is smaller, but the Switchcraft panel hole needs to be 4mm lower.
* 5228 shows the Switchcraft inserted in the O2 input jack PC board holes (with the front two plastic alignment pins on the jack cut off, below), with the BOM-specified Kycon jack (blue) next to it for size comparision. The Kycon sits higher off the PC board due to that plastic ridge under it. You can also see the rectangular plastic nosepiece that sticks out of the Switchcraft jack, something that isn't on the Kycon (completely flat jack face). The larger diameter of the Kycon nose shows up here too.
* 5226 shows the Switchcraft jack on the O2 PC board. The front two black plastic alignment pins have been clipped (below).
* 5225 shows the front two black plastic alignment pins clipped, where the tweezers are pointing.
* 5230 shows the problematic via under the output jack, and the metal plate under the jack it would short too, unless a few sheets of paper are placed under as a spacer while soldering.
* 5223 shows the rectangular part on the face of the Switchcraft jack sticking about half way into the 2mm thick front panel. This section would have to be milled out on the rear of the panel.
* 5221, 5220 and 5219, the black Switchcraft vs. the blue Kycon/CUI.
Clicking the arrows in the lower left corner will make the photo bigger, hovering the mouse shows the photo number.
Last edited by agdr; 20th July 2017 at 09:43 PM.
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