Let’s Build a Simple Pedal

Getting into DIY guitar pedals world is super exciting. There is no greater satisfaction than making something with your two own hands. More so if at the end of the process you get something that helps you make a delightful sound coming out of your amp.

What does it take to build a pedal? I had no idea when I was starting with all of this, but along the way I picked up a couple of things and came up with my own way of doing it. It turns out there’s quite a bit more to it than I initially thought.

I like to learn about how things work and why along the way, so some of the steps are not strictly necessary. Maybe getting a kit would be an easier way to go. With a kit you get everything needed and you just have to assemble it yourself, but my motivation is also to design some pedals on my own so I’ll do it more roundabout way.

The first step is to make something real simple that will work and can be built quickly. I’ll rush through this real quick so there’s something tangible at the end of this article, and later on I’ll be going through the steps in more detail.

What are we building?

We’ll be building Electro Harmonix LPB-1 clone. LPB stands for Linear Power Booster, and originally appeared back in the late ’60s. This is a very simple circuit and it’s great to get us into DIY pedal building. It is a booster, essentially amplifying the guitar signal and making it louder. This is useful to boost your solos, push your amp into overdrive more easily, make up for signal loss, etc.

Schematic Diagram

First we need schematic for it:

The above diagram shows that only a handful of components are needed: 4 resistors (R1-4), 2 capacitors (C1, C2), one potentiometer (RV1), two 1/4″ Jacks (IN and OUT), a battery (BT1) and the only active component here is Q1 – transistor. Sparkfun has a good article on how to read schematic.

Now, very quickly, what is that above all about in as few words as possible.

• Mechanical components are input, output and battery – input is where you plug in your guitar, output is where you plugin cable to the amplifier, and the effect is powered by a 9V battery – in this case it will be battery connector rather than actual battery.
• Passive Components
  • Resistors – they are setting up working conditions for the transistor
  • Capacitors – they are DC blocking capacitors. They block any DC current coming in or going out in order to pass through only the audio signal
  • Potentiometer is there to control output volume
• Active component
  • Transistor is the actual amplifying device (with the resistors it actually forms the amplifier)

I’ll get into detailed analysis of the circuit at some other time. Let’s get into building this circuit.

Breadbording the Effect

It would be of little use to solder everything up and only then figure out the thing does not work. Schematic could have errors, we could misread it etc. So it is always a good idea to do something less permanent first in order to check it out and experiment with it.

A breadboard is a construction base for prototyping of electronics.

Because the solderless breadboard does not require soldering, it is reusable. This makes it easy to use for creating temporary prototypes and experimenting with circuit design.

Wikipedia

Let’s breadboard it then.

Material needed

Type	Value	Qty	Label	Notes
Breadboard		1		A breadboard
Resistors	390 Ohm	1	R4
	10K Ohm	1	R2
	43K Ohm	1	R3	47K alternative
	430K Ohm	1	R1	470K alternative
Capacitors	100 nF	2	C1, C2
Potentiometer	100KA pot	1	RV1	See notes below Pin ordering matters
Transistor	2N3904	1	Q1	NPN transistor. See notes below
Connectors	1/4″ Jack	2	J1, J2	Mono. But see notes below
Battery Snap	9V Battery snap on	1	BT1
Battery	9V Battery	1
Wires				To connect various parts on the board

Component Notes

Some notes first. In the table, I specified values 43K and 430K for resistors R3 and R1 respectively, but what actually matters is ratio between them. R1 should be 10 times higher value than R1, hence alternative values of 47K and 470K. The alternative values are slightly more common. The other resistor values do matter and they affect gain.

Transistor

Also, in the list I have 2N3904 transistor. It’s commonly available part, I didn’t have 2N5088. 2N3904 is not great for audio but will do for now, and I’ll be experimenting with different transistors later. Btw, 2N5088 can be sourced from Mouser, I thought it was obsolete, thanks for the commenters pointing out.

This is a common theme, design of all of the old pedals depended much upon availability and cost of the components at the time. Even 2N5088 transistor isn’t the original part.

Step by Step

With all that, here is how the board should look like in the end:

So let’s do it step by step – in pictures:

The above should look straight forward enough all the way until getting the input and output jacks wired up and the potentiometer when things get a bit entangled. If in doubt go back to the Component Notes and hopefully the notes will clear it up.

Trying out the Effect

How does it sound? It should sound pretty much the same as your guitar just louder. Time to give it a go:

Final Notes

There it is, a simple guitar effect, not yet a pedal but still, something that works and is loud (Loud is good, no?). The next steps are to refine this design slightly, experiment with different parts and then when happy with it, make it permanent.

Few more notes:

There’s a great and detailed article on Sparkfun on how to use breadboard. In context of building a pedal – a quick guide can be found on Small Bear site. A way more detailed article (and a more complex circuit) can be found on DIYStompboxes.

For schematic I used KiCad, it’s a free and Open Source EDA (Electronic Design Automation Suite). It very powerful but quite complex. For breadboard schema I used DIY Layout Creator, also Open Source and free tool.

Edited on 3rd Feb ’23: Added note that 2N5088 is not obsolete.