Guitar Pedal - Selectable Diode Tube Screamer

Built after the original Tube Screamer 808.

The Ibanez Tube Screamer is one of the most popular overdrive pedals ever made. Especially popular with blues players, it boosts mids to mimic the sound of a vintage tube amp. Likewise, due to its popularity, it is very commonly modded.

By changing the diodes at certain points in the circuit, you can greatly change the sound of the overdrive. Adding diodes can create a more tube-like asymmetric sound. Similarly, bypassing a capacitor can add more bass response and give additional boost. There is a wealth of modifications and explanations of the circuitry online (http://www.electrosmash.com/tube-screamer-analysis), as well as thorough detail of these mods (http://www.generalguitargadgets.com/pdf/ggg_its8_mods.pdf), so I won't cover that here.

Typically, these mods work by replacing diodes in the circuit with various makes and models to create different sounds. This pedal combines the most common modifications to be able to change on the fly without ever having to open up the enclosure.

We will use rotary switches to select between a bank of different diodes to change the clipping stage as well as having switches to turn on/off other mods.

The circuit was designed in Cadsoft Eagle (http://www.cadsoftusa.com/) to create PCBs of the circuit. The ".sch" file contains the schematic and the ".brd" contains the board layout.

The attached images show the parts list and order form, respectively, for the retailers I used.

You may need to find alternatives for some of these parts, but follow the item list and double check against the schematic.

Now comes the fun part. Sorting the parts and soldering is left as an exercise to the reader.

If you choose to get a professionally created PCB, this will be a little easier as everything is labeled. Otherwise, follow the schematic carefully and take your time.

To make all the parts to fit properly inside the 125B enclosure, I recommend creating each part in Sketchup http://www.sketchup.com/. When everything aligned the way you want, print out a 1-to-1 view of each side and drill the holes from the template.

If you don't use sketchup, be careful to take measurements and ensure that your parts will all fit, with enough room to wire, and mark out all drill holes prior to drilling.

Wiring is fairly straightforward but very tedious. Try to make the wires as short as possible (there's a lot to fit in this small enclosure) and wire up each component to it's appropriate jumper according to the schematic.

Plug it in before installing the back panel of the assembly and check that everything works right. Check first that the light turns on after pressing the footswitch. Due to the number of components and tight fit of the enclosure, be especially careful of shorting something. If the light doesn't turn on, unplug it and inspect the circuit.

Test playing through it and if everything works right, screw the back panel on and rock on.