After building that 4U Serge-format QFG for
Prunesquallor, I decided that I wanted one too! However, my modular is in 5U format, so... I redid the layouts for 5U. I'm going to make this into a little "build diary" a la
Rex Coil 7 (but not as elaborate) which will hopefully inspire some others to take up synth DIY, version Crazy-Person.
So, it all starts with the schematic. Here is the schematic as reconstructed from the Intellijel originals, which were virtually unreadable and indecipherable. I printed the original Eagle schematics as a PDF (where everything was just dumped willy-nilly onto the same page), cut out the various circuit bits and pieces and taped them to pieces of paper to indicate signal flow. I don't know about most people, but I can't really make sense of a schematic unless I can see the signal flow clearly, and when you are building something complicated, being able to understand the schematic is the first and most critical step. Of course, I designed 80% of this circuit myself, but it was almost 10 years ago and I had forgotten most of it. I had to re-educate myself about the Quadra, and this was how I did it.
(Note: this is just one of the four channels. There is actually about four times this much circuitry.)
Schematics.jpeg
The next step is panel layout. I draw my panels in Front Panel Designer. Because I build Panel PCBs, I tend to position all the panel components on a strict 0.1" grid (actually a 0.05" grid for the panel) to accommodate my Excel layout scheme. I quickly realized that this panel had to be 4U wide to accommodate all of the jacks required (22 altogether). That meant that the module was going to be 7" wide. Here is a picture of the freshly baked panel cooling on the oven rack -- it turned out perfectly -- I seem to have finally mastered the art of baked-on Lazertran:
11_Hot_Panel.jpeg
For the PCB layout, I started with the Circuit Board layout I did for the 4U build. However, since this module is an inch wider, I could make the PCBs an inch wider as well -- 6.9" wide instead of 5.9" wide. That extra inch allowed me to make all the inter-circuit connections on the Circuit Board. For the 4U build, many of the inter-circuit connections (connections from on discrete block of circuitry to another) had to be relegated to the Translator board, and this made laying out that board much harder and necessitated a bunch of flying wires. In this build, no flying wires were required and the Translator board was easy to lay out. Here are the layouts of the three PCBs:
Circuit Board:
5U Quadra Circuit Layout.png
Panel Board:
5U Quadra Panel Layout.png
Translator Board:
5U Quadra Translator Layout.png
You'll notice that the Panel Board has two large square holes -- this is to accommodate two jacks which are not at the bottom of the module (for the OR A+B and OR C+D outputs). I was worried about these, but they turned out to be very easy to make. I just drilled a few 1/8" holes along the edge of each hole, then snipped the pieces out with wire snippers, then filed the edges flat. It took about five minutes to do both holes.
Also, I'm very proud of the Translator Board layout. I color-coded the traces for the four different channels. To make layout easier and error-free, I created color-coded labels for each pin. Then all I had to do was to connect similarly labeled pins together. Here is the layout again with the labels superimposed (you'll notice that A and B and C and D go from right to left -- this is because the panel is on the other side of this board -- it is important to remember to flip the Panel Board layout horizontally to derive the arrangement of pins for the Translator board -- a lesson I learned the hard way with my Rubicon 2 build):
Translator Layout with Labels.png
Again, the role of the Translator Board is to connect all the pins on the back of the Circuit Board to all the sockets on the back of the Panel Board. This Translator Board also has to accommodate the Quadra Expander circuitry. My technique for laying out Translators is to run all the horizontal traces as actual traces and all the vertical traces as jumper wires. Hence, I start by having very long jumper wires running up and down. This allows me to draw horizontal traces freely without having to worry about crossing other traces. I just have to avoid running traces into the wrong pins. Once all of the connections are made, then I set about removing unnecessary jumper wire, making each jumper as short as possible and filling in the gaps with traces. Also, if a bunch of vertical jumpers are crossing just one or two traces, I'll break my rule and create horizontal jumpers. I think you'll agree that the result is quite elegant.
So, here are some pictures of the actual build. I haven't drilled the panel yet, and as of now only one of the four channels works, so tomorrow I'll drill the panel, mount the Panel PCB and wire up all the jacks, then do some troubleshooting.
First, the PCBs with the PnP-Blue transfer paper pressed on:
1_PnP_Blue.jpeg
Next, the plastic sheets are removed and the transfers are corrected with a felt-tip pin to fix any broken traces, and pads which are too close together or touching are scratched away with a sharp metal tool:
2_Corrected_Transfers.jpeg
Next, the boards are etched (you can see from all the felt-tip pen marks that the Panel Board transfer was a little rough, but the Circuit and Translator Board transfers were much smoother -- if transfers are too rough I typically just rub them off with acetone and start over, but this one was good enough to salvage with some felt-tip microsurgery):
3_Etched.jpeg
Then they are drilled and tinned:
4_Drilled.jpeg
... continued on another post...
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