Preamp.

Since I had finished my first board a couple weeks ago, this is still pretty much all summary, although hopefully I'll be done after this. At least this enables me to skip over the rather painful details of the whole process, since I was still learning a lot at the same time.

So the physical board itself looks a bit like this:


It is, in fact, a rather simple and tame board, in retrospect. Notice the large gaping hole in the center on the bottom, along with the seven other, much smaller holes. They are just board cutouts, for placement with other boards after it was completed. The light green, the main stuff of the board, is copper, the conducting material on which charge can flow freely; the dark green is insulating material. Finally, the silvery stuff would be solder, where the copper was eroded away.

Notice the many little squares on the board? Those are pads, the parts on which the actual components would stand. Each pair would hold either a capacitor or resistor, depending on how I assigned it, and there were also transistor triplets lurking here and there. The shields around each of the 12 sections are rather unusual, however, as they are not often found on boards.

The theory behind this board is rather simple: Signals come in through the four center holes from the bottom, snake their way through the (essentially) identical circuits, each having three parts, and come out on the other end. In other words:


I really don't know what the circuits do to the input signals (although "preamp" most likely has something to do with it); I just know this is how it works. You may also be wondering how on earth do the electrons travel in such precise paths? Well, if you can make it out, there are routes within each of the shielded sections that guide them through. As for crossing each section and out into the output holes, the traces actually go a layer deeper.


This is how the board's second layer looks like. In fact, there are no fewer than four layers to the board, with every layer but the third classified as a ground layer (the third is the power layer). If you remember from physics, ground allows for the dissipation of an electric signal, whereas power would do the opposite. Hence, for this particular board, the darker green insulating material was key to producing the circuit tracing on the top: It surrounds the lighter green copper, forcing the electrons to travel along a particular path rather than dissipating through the rest of the board.

The key element allowing for the interaction among the layers is the through hole, or via. If you look carefully, you can make out (and certainly in the above CAM file) small holes scattered everywhere. They are friendly to the excited electrons, and allow them to progress from the top layer to another. Where they are supposed to flow, conducting material is soldered around the via; otherwise, they are blocked by the dark green material. A closer inspection of the back will show what I mean.


Some of the vias are surrounded fully by the insulation, others only partially. And still others have the full silvery material around them for full conduction. And finally, one of the circuits is shown below in schematic form (the other three are nearly identical), if you should want an idea of how the input signal gets to the output. Notice the many grounds throughout the circuit, as well as the one power source at the top. Some of the vias allows for a physical connection to the power layer; others link the grounded pads outside the shields for dissipation. Since layers 1, 2, and 4 are all ground layers, it doesn't make a difference where they are linked to.

Anyway, that's enough talking about how the first board works. Details of how I accomplished my goal of reproducing it in PADS will accompany those of the board I am working on now--since it is the same process, there is no point in explaining it more than once. All together, it took over a month (although that was mostly due to the learning process and my own laziness, more on that later). But it is more or less finished by now, a proud product of a month's hard work.


It is, I must admit, quite beautiful, and as close to the original as I could make it. As for the changes, they were just additions here or deletions there, but they did not impact the board very much. The one thing that did change significantly were the input and output connections at the center and bottom sides. They are no longer one huge hole (or pin, in technical terms), but five, with the major connection in the center. That was a source of constant agony for me, and they have to do with the other two boards that this particular one is connected to. But they are done with and finalized, and they will (hopefully) torture me no more.