TubeScreamer+ Project - Part 3

CAPACITOR MOD

Before we get on to the mounting work, I thought I might follow up on one of the mods I referred to in the previous post. The folks at DIY Effects offered a suggestion of changing out one of the capacitors to provide additional low-end on the output signal. I liked the idea (and it's really a very simple mod), but I was concerned about losing the 'original' Tube Screamer sound. So as a compromise, I did both. By soldering the leads of both caps together, and connecting the other two leads to a switch, I could select between the original sound, and the extra low-end. Here's what that looks like (the switch is connected to the red, yellow, and black wires underneath the board).

After the photo was taken, I dropped a small amount of hot glue on the capacitor leads to provide a little stability, and to ensure they never touch.

PREPARING THE ENCLOSURE

I picked up this enclosure from Pedal Parts Plus. They have a good selection of enclosures (all cast aluminum), but more than that, they have made ordering the finish a breeze. You just add the case, and a paint charge to your shopping cart, then add a finish to the shopping cart. They have a few finish pricing models (based upon the complexity/cost of the finish), so you do have to make sure the finish charge you add to your cart is appropriate for the finish type that you add. I ordered this on a Sunday night. Monday morning I received an e-mail saying that the case shipped, and had a tracking number. It arrived on Friday.

Step 1 is to mark the holes. There's nothing too complicated here: just draw the lines, mark your holes, then, using a punch or nail, tap a dent in the center of each hole to keep your drill bit from 'walking' along the surface as you're starting to drill.

WARNINGS

A few items are worth mentioning at this stage. DIY provides a diagram of where the holes should go, including diameters. It's a 1-page PDF file. The first time I printed this out, the dimensions all lined up perfectly on the box. The second time I printed it (on a different printer), the output was slightly smaller than the enclosure surface. To be safe, use the measurements; don't rely on the size of the printed output as an accurate guide. Also when you look at the diagram, the top face appears as you would expect: the controls are at the top, and the foot switch is at the bottom. As you look at the front face, however, it is actually upside down, relative to how the pedal sits. It shows the in/out jacks at the top, when in fact, they should be at the bottom. There is even the word "TOP" printed on what should be the bottom, further inviting you to drill holes in the wrong place. Check, recheck, then check one more time.

Once the holes are marked, it's time to drill some guide holes. I like a 1/8" drill bit for this. It's large enough to force the step drill bit in the right direction, but small enough that if the bit shifts, you can recover with some manual effort. (The cases are cast aluminum, The nature of casting metals is that some areas will be more dense, and some less. As a result, even if you properly tap the holes as described above, the bit can still shift as you are drilling.)

After drilling guide holes, it's time for the actual holes. All of the hole diameters specified in the enclosure prep guide provided by DIY Effects matched up nicely with the sizes of the actual components, but you can't undrill a hole, so be sure to recheck the actual components before you start. If in doubt, since we're using a step drill bit, make the hole a little smaller, and have the components on hand to check the fit. To keep myself from drilling the holes too large, I placed a piece of tape above the final step. This gives a really good visual cue to help you know where to stop. One last tip: if you have access to a drill press, that makes life much easier. You can do it with a regular drill, but the press helps with straightness, and preventing some of the issues with the bit moving above.

Once your holes are drilled, you have a box ready for mounting the board and components. If you go with the DIY Effects plans, you'll notice some changes to the original layout. I added the second switch above the original for the capacitor mod, and I moved the hole for the power indicator LED up a little to give the second switch some extra room.

Mounting the components was pretty simple, though I've left out an important step. It's a good idea, before you get to this stage, to set the board up on a bench and test it out. There are a number of steps at which a mistake could happen:a cold solder joint, a drop of solder touching an unintended contact, a bad component, etc. Troubleshooting the pedal in the case is no fun, and with this design, getting the board in and out means soldering, and desoldering the 9v and ground wires to the power receptacle each time. As it happens, with this one, I discovered that the power receptacle has a short in it. So, my final assembly will have to wait until I get a replacement.

PART 1 ~ PART 2 ~ PART 3 ~ PART 4 ~ PART 5