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differential hybrid parafeed headphone amplifier

Construction - PCB part 5

The IEC inlet is actually shorter than the PT. However, after putting together a lot of these, Dsavitsk suggested the best method for installing the IEC inlet and the back plate. The best method requires you to go ahead and mount the IEC inlet to the backplate, first, then mount it to the PCB and solder the IEC pins in place. The reason this is done is because there a wide tolerance is needed with the back plate fit up with the case. The reason is with this sort of length of PCB and case (14"), the variances in tolerance - if you solder the IEC inlet to the PCB first - may very well result in your not being able to get the back plate flush with the back of the case.

So, mounting the IEC inlet to the back plate first - solves this problem. For somewhat similar reasons, the tolerance fit of the IEC inlet and the large rectangular opening is quite small. Your initial attempts to get the IEC inlet protrusion fit through the rectangular opening may fail. The tight fit is there for a purpose - safety first. I have seen a builder take serious unapproved shortcuts and simply press fit the IEC inlet to the back plate without any mounting hardware at all. DO NOT DO THIS - IT IS NOT SAFE. Instead, work carefully to press fit the IEC into the back plate opening. When you get all four corners through the opening, then use the mounting hardware to get the IEC inlet flush. Otherwise, you may bend the back plate. Usually, all it takes is a small file to round off the corners and the inlet will fit.

The recommended hardware is two sets of 4-40 x 3/8" socket head cap screws with washers on both sides, and lock washer plus nut on the inside. Obviously, if you are at all interested in looks, please use the black washers on the outside (supplied in the kit).

Here we have the back plate with the IEC inlet mounted in place. The arrows indicate where you should file if the fit is too difficult:

And a view from the inside:

As noted, the arrows indicate where the flat washer, lock washer, and nuts are to go. Please do not neglect this hardware and ensure that everything is flush, snug, and tight before proceeding further. This is where the mains voltage comes in and ensuring that this is assembled and installed properly is for your own safety.
When attaching the back plate assembly to the PCB, line up the IEC inlet pins with the pads on the PCB and line up the RCA jacks with the holes in the back plate. The RCA jacks have plastic circular bosses that protrude from the RCA jack assembly, ahead of the actual metal jacks themselves. The holes in the back plate are sized for these bosses, but you must make certain that they line up and that the bosses are poking through the holes. As it is, there is enough variance that the back plate will actually stick out a bit further from the PCB on the RCA jack side, but it's not enough to affect the final assembly from being flush.

Use the same hardware mounting that you used on the back plate, except black finish washers are not needed on the inside. The silver ones are fine. So, socket head cap screw with washer on top of the IEC mounting tab, then washer, lock washer, and nut on the bottom of the PCB. Do this in two places.

Mounting hardware on the other side in this view:

Once you do this and everything is bolted up tight, then and only then - solder the pins of the IEC inlet on the bottom of the PCB.

You might have noticed in the last couple of pics that I had already soldered the safety ground in place, but here's a look on the back side, along with the IEC inlet pins all soldered up nicely:

The arrows represent the IEC pins that need to be soldered.

Meanwhile, you can also see the safety ground. I like to use some extra length so that I can bend it easily. That makes it easier for me to line up the lug with the hole in the PCB and the mounting hole in the bottom of the case. If you figure out a better method, use it and then let me know about it. I also both crimp the lug and put some solder in there between the hookup wire end and the metal part of the lug.

In this view, you can see the safety ground, IEC pins, and most importantly - the back plate's position relative to the back edge of the PCB. As noted previously, you can see that the RCA jack side of the back plate sticks out a bit further than the other side. Make sure the RCA jack bosses are sticking through the back plate holes. Even so, there will be the difference in clearance shown here, even with the jacks as flush as you can make them. Not to worry, though, everything will fit up tight and flush with the case.

The PCB is now complete and ready for assembly into the case!


file last changed:Saturday, October 31, 2015 7:17:48 AM
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