Welcome to Part 3 of the Mod.It.Yourself series where we have previously looked at the basics of Tools and Techniques in Part 1 and how to mod the Diode Clipping in a pedal in Part 2. Part 3: Switches will look at an important component in the pedal modder’s toolkit. Switches are mechanical devices that allow an instantaneous flip to either turn part of a circuit on or off (break the circuit), or introduce a new part to the circuit. The latter function is useful in doing reversible modifications, or mods that use the original stock component. This part of The M.I.Y series will explain a bit about common switches and some ideas on how to use them in your own pedal mods.

The two most common mechanical switches used in modifying pedals are the push button switch and toggle switch [above]. Both of these switches use common nomenclature for their components that must be understood before selecting them for your next project. Below is a look at some of the more common names of switches that are used for pedal mods and an explanation of their specs:

Each switch is named with respect to the functions of their contacts, i.e the part of the switch that is in contact with your wire, component, PCB etc. Also called a lug or pin. The two terms are poles (denoted by P) and throw (denoted by T). A pole is the number of switch contact sets of pins/lugs, and are labelled SP- for single pole, DP- double pole, 3P- for triple pole etc. The diagram [below left] shows the poles of a 4PDT switch.

Most switches used in pedals have three pins per pole. The center pin is common ie. is always connected to either outer pin of the three. Moving the toggle either up or down selects [above right] between these two connections or conducting positions. These positions are known as throws and are denoted -ST for single throw or -DT for double throw. A single throw switch only has two pins with the third pin shorting to ground, thus having only one position.

Common switches used in modifications are single pole double throw (SPDT) or double pole double throw toggle (DPDT) switches, and true bypass foot switches are known as triple pole double throw (3PDT). So using this knowledge of switches, here are a couple of mods you can try on your next pedal designs or mods.

KILL SWITCH

To get a stuttering effect made famous by guitarists Tom Morello and Buckethead in stompbox form, you can make use of a type of push button switch called a momentary switch. By using a push-to-make momentary or “normally open”, when pressing the switch you are breaking the circuit thus creating a staccato effect. To do this, all you need to do is cut the wire that goes from the output of the PCB to the bypass switch. Wire each of these two ends to a normally open SPST momentary switch and you have a momentary kill switch [diagram below]. The effect signal will stay on until you step on the switch, cutting all volume of your signal. By pressing at rhythmic intervals, you can create unique guitar rhythms heard in many RATM riffs. Momentary switches are great for these “stab” like effects and can be used for feedback loops, or wiring to a potentiometer in a delay pedal to get that spaceship, oscillation sound.

DIODE  CLIPPING SWITCH

As previously discussed in Part 2 of the M.I.Y series, we can mod a pedals’ clipping diodes to create a different tone of the distorted sound. We could use different diode material , symmetry, combinations etc to get our desired sound. But what if you liked two diode sounds and wanted to switch between them? Using an SPDT switch, you can do just that and is a common feature on many effects pedals.

The schematic [above left] shows the clipping diode structure of many distortion pedals – a hard clipping pair at the output of the IC. One end of the pair shunts to ground, while the other end is in the signal path. If this end on the signal path (A) is wired to the common pin of the SPDT switch, we can then switch between two differing pairs of diodes. Wire the end of two pairs to ground, and the other end to (B) and (C) of the switch and you can select between your favourite clipping tones [above center]. The symmetry of the clipping can be controlled using this switching layout as well – just use different symmetrical pairs for (B) and (C).

You can also use this principle to switch between two components of differing values ie. the output capacitor to provide more/less bass into the circuit. Remove the initial capacitor from the PCB where one pad will have one wire running to (A) and two wires from the other pad to one end of either capacitor you wish to switch between [above right].

Hopefully this info and diagrams will give you ideas on how to mod your next pedal, or to modify your next pedal build. Also, I would suggest getting a multimeter with a continuity test function. By putting either probe on any two connections, a beep or sound should be heard. This is very useful to test your new connections.

Happy modding,

C.

After reading Part 1 of the M.I.Y series: Tools and Techniques, you should have a good grasp of what is required to get into your pedal and start modding. But before we flick on the soldering iron, I thought I’d write a few points about the diode, the key component to Part 2 of the M.I.Y series: Diode Clipping.

A diode is an electronic component that allows electricity to flow in one direction, much like a valve does letting water go one way but not the other. Diodes can be seen in nearly all effect pedal schematics and are noted as this symbol (left). They are integral in creating that overdrive or distortion sounds in your favourite dirt pedals, and come in different packages, materials and sizes. Each diode has a positive side (anode) and negative side (cathode). This polarity is what resembles a valve, and dictates the flow of electricity.

But how does a diode contribute to that overdrive sound? If we look at an audio signal (represented as a sine wave) we can distort the signal by “clipping” the tops and bottoms of the wave. This clipping produces harmonics that we hear as overdrive.

Image source: www.geofex.com

If a signal is clipped evenly on both top and bottom of the wave, this is referred to as symmetrical clipping and is used in pedals such as the Ibanez Tubescreamer. If a signal is clipped more heavily at one peak than the other, this is called asymmetrical clipping as heard in the BOSS SD-1 Overdrive. The more heavily a peak is clipped, the more a sine wave moves closer to a square wave, and closer to distortion and fuzz.

Image source: www.diystompboxes.com

The location of clipping diodes has an effect on the sound as well. Soft clipping involves having two diodes connected on the feedback-path of an opamp or a transistor (Tubescreamer). Hard clipping is when two diodes shunt to ground, creating distortion as in the ProCo RAT. The material of the diode also affects the clipping. Silicon diodes have been described as being “sharper” and “tighter” whereas germanium diodes are described as being more”compressed” or “spongey”. You can also use LEDs (light emitting diodes), Zeners, Schottkys, MOSFETs etc… the experimental possibilities are endless.

So with all of that in mind, let’s crack open a pedal. We will need [1]:

• A pedal (I will be using a BOSS SD-1),
• A selection of diodes,
• Single in-line break away sockets (purchased from any electronics store),
• The schematic of the pedal (that can be found at the resources listed in Part 1 of the series).

Firstly, unscrew the back so we can get to the PCB. You should be able to see a trace side, full of tracks and solder joins [2]. Carefully lift up the PCB so we can see the component side, and look for a set of diodes [3]. The markings (e.g D3, D4, D5) should correspond to your schematic. Desolder these diodes, marking down their original orientation, and clear the holes. Solder in a socket for each hole from where the diode was removed [4] and place the PCB back into the pedal. We can now experiment with different diodes, and combinations of diodes, and immediately hear the difference between them.

Place the diodes (using the same polarity as you marked down earlier) back into the sockets, power up the pedal, plug in and play. No need to close the pedal back up, it will just be a bit noisier. Now remove the power, remove the diodes and try another combination. Power, plug and play – hear the difference. Now try a symmetrical configuration, then asymmetrical.

In the place of one diode, try a MOSFET like an MPF102 (note in [1] how I bent only the ground pin to remove). Or you could try germanium and silicon diode in series, a silicon and LED, two silicons in series, two germaniums in series etc. To solder diodes in series, ensure that the cathode is soldered to the anode [5]. Using diodes in series increases headroom and volume but sacrifices a bit of gain. Use MOSFETs for “tube-like response” and LEDs (reds are great) for crunch and higher gain. When you find a combination you prefer, desolder the sockets and solder in your killer selection. Close the pedal back up and you now have a diode clipping modded pedal. Common mods include placing different diode combinations on switches, or a symmetrical/asymmetrical diode switch. But we may leave that till next time…

Happy modding.

C.

DIY electronics for guitar effect pedals has become increasingly popular of late. Guitarists and musicians worldwide are downing instruments and picking up tools to build and modify their own pedals, searching for that unique tone. There are sites like Build Your Own Clone, General Guitar Gadgets and Tonepad that sell printed circuit boards (PCBs) and kits to create your own version of popular effect pedal designs. There are also websites like DIYstompboxes, Ampage, GEOFEX and AMZFX that provide a wealth of knowledge from a committed online community. However, all of this information is useless if you do not have the basic tools and techniques to enter the DIY realm. The Mod.It.Yourself (M.I.Y) blog series aims to give you those skills (plus a handful of ideas) so you too can begin deconstructing electronics to create your own personalised sound.

Part 1 of the M.I.Y series is starting from the beginning – Tools and Techniques. Without these fundamentals, you will no doubt be left with damaged parts, boards and burnt finger tips. So safety first! Be sure to work in a well-ventilated, well lit work area with a clear work space to avoid burning anything as a soldering iron can reach 900 degrees (480°C). Soldering produces fumes so ventilation is a must and safety glasses/goggles are also recommended as stray metal is known to fly around an electronics work space.

To build/modify any electronics you will need to have tools for soldering. Soldering is the melting of metal to join two components to form a conductive connection (solder joint), so you will need solder and a soldering iron to create this connection. Soldering irons come in many forms but a 40W iron is best to provide adequate heat transfer and solder flow. Solder comes in different compositions, with different types of metal. There are other tools required for building/modifying guitar pedals; long-nose pliers, side cutters (or snips), multimeter and wire strippers (as pictured). These tools will help in populating boards, cutting away component legs, checking proper connections and stripping insulated wire.

Now that we have the tools, let’s get to soldering technique.

To form a solder joint, place the component through the PCB hole and follow these four easy steps to ensure a solid joint is made:
(1) It is important to place the iron where the component passes through the board. Heat this spot for a second.
(2) Apply the solder to this spot.  Keep applying solder until a dome forms up the component leg (two seconds).
(3) Remove strand of solder while maintaining iron on spot. This allows the solder to flow through the PCB hole (one second).
(4) Finally, remove iron from spot. Cut off the remaining component leg and you should now have a shiny, solid solder joint.

But mistakes do happen, and a technique as important as soldering is desoldering, the process of removing solder from a joint. This skill is a must in electronics for removing components from a board, correcting a bad (or cold) solder joint etc. A desoldering pump and desoldering wick or braid (as pictured) are just as valuable as a soldering iron and are must haves in your toolbox. This video from Make Magazine runs through a few desoldering methods, as well as a brief soldering demonstration and is well worth watching.

So go off to your local electronics store, pick up these tools and an electronics kit and practice your soldering/desoldering technique. In Part 2 of the M.I.Y series, we will look at common modifications to overdrive/distortion pedals and how to hot-rod that old pedal on your shelf into a mean gain machine. Until then…

C.