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:

LPB-1 Schematic Diagram
LPB-1 Schematic

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

LPB1 Components
LPB1 – Components
TypeValueQtyLabelNotes
Breadboard1A breadboard
Resistors390 Ohm1R4
10K Ohm1R2
43K Ohm1R347K alternative
430K Ohm1R1470K alternative
Capacitors100 nF2C1, C2
Potentiometer100KA pot1RV1See notes below
Pin ordering matters
Transistor2N39041Q1NPN transistor.
See notes below
Connectors1/4″ Jack2J1, J2Mono.
But see notes below
Battery Snap9V Battery
snap on
1BT1
Battery9V Battery1
WiresTo connect various parts on the board
Material for breadboarding LPB-1

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.

Transistor 2N3904 Pinout
2N3904 Pinout

Connecting transistor might also be a bit confusing at times because transistors come in different packages and pinouts. Here is a pinout from transistor’s datasheet.

It is always a good idea to consult the parts datasheet if in any doubt.

Jacks

Here I’m using Switchcraft 12B (stereo) and 11 (mono) jacks. For this breadboarding exercise either is fine. Most pedals support both DC power and battery power, and use stereo jack to cleverly detect when guitar is plugged in and preserve battery, but that’s for another time.

Wiring up of the jacks depends on the ones you have. I used both stereo and mono jacks and here’s how to wire them up.

How to wire up jacks
LPB1 – Wiring up Jacks

As shown on the diagram, mono jack has Tip spring and Sleeve terminal (they are marked as T and S both on the breadboard diagram and on the schematic diagram). Stereo has Ring spring as well but that can be ignored for the time being (attach it to ground).

In the pictures above I soldered wires directly to some breadboard jumper wires, but you can use crocodile/alligator clips and just attach them one side to the terminals on the jacks/potentiometer, the other to a piece of solid core wire and plug it into the breadboard.

Potentiometer

How to wire up potentiometer
Wiring up a Potentiometer

To be honest, I always need to triple check how to wire-up a potentiometer. I check resistance with a multimeter just in case while I’m turning the shaft.

When we turn the shaft clockwise (CW) we want the effect to sound louder, if we go counter-clockwise (CCW) we want it less loud. Going CCW, resistance between pins 1 and 2 decreases, and resistance between pins 2 and 3 increases. Going CW, it is opposite, resistance between 1 and 2 increases and between 2 and 3 resistance decreases. Looking a the diagram within the picture: resistance between 1 and 3 is always the same, but depending on the position of the wiper (S), which we control by turning the shaft, resistance between pins 1 and 2 and between 2 and 3 changes.

Just keep in mind, it’s a breadboard, you can always rewire it quickly if it does not work as expected.

Step by Step

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

LPB-1 on a breadboard diagram
LPB-1 on a breadboard

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:

Trying out the breadboarded effect

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.

23 replies on “Let’s Build a Simple Pedal”

Hello, this is a really great tutorial and I followed it step by step, using the same components, boost pedal works, but I have one issue, I have some humming noise and when I turn boost up the humming gets louder, if I touch with my finger jack it dissapears. What may be the cause?

Hi Tadas, common source of noise when doing breadboarding is interference and poor grounding. This looks like grounding issue – ground is your reference for all the signals, so noisy ground gives you noisy output 🙂 When you touch the jack you improve it a bit. Keep in mind that when you screw the jacks onto a metal enclosure you’re doing something similar (this is oversimplification on my part, but it’ll do :)).
Btw, this is common issue with most if not all breadboards. Most of the time, when you put everything into a pedal, the noise goes away.

You might run into interferences as well, I had to switch off lights in my room for some videos because the wires on the breadboard were simply picking up whatever my “high-tech” light bulb was emitting. All those wires act as antennae so they pick up all sorts of noise.

Hi, I’m using a circuit very like yours except I’m using a c5k pot (reverse log) to ground from transistor. Currently, with pot turned fully anticlockwise my signal is boosted above unity volume. When turned clockwise the volume increases as required. Can you advise which resistor I should change to reduce the minimum volume (fully anticlockwise) please? I assume I want to reduce the bias voltage into transistor? Thanks

Hey John,
If I understand you correctly, you want to remove RV1 completely from the circuit (for volume control), and control gain of the circuit by replacing R4 with a C5K pot?

That’s a bit tricky. Roughly, at max resistance, your gain is 2 (or 6dB). The gain is very roughly R2/R4. You could change R2 to 5K, that’s the simplest. The issue with that is that your undistorted input level is just 100mV (and this is for minimum gain setting). This will cause distortion. If that’s what you want then, that’s fine 🙂

If not, then you need to increase R3 somewhat. If you use 470K for R1 and 100K for R3, this will increase voltage across R4 (and thus biasing current) and give you some extra headroom. This will maybe give you some extra 0.5V of headroom. You could increase R3 all the way to 470K, but maybe the sweet spot is around 220K. That might give you the most headroom.

These are all very rough calculations. I did them on the fly without testing any of this. If you have this breadboarded already, I’d go with:
#1 Replace R2 with 5K resistor (5.1K or slightly bigger should work, 4.7K will work just thereabouts) and try that, see how you like it
#2 Next replace R3 with 100K, see how you like it
#3 Replace R3 with 220K (or whatever you have around that value, 2x100K will work too etc.) see how you like it
#4 replace R3 with 470K … give it a try

None of that may work 😀 so do breadboard this before bringing out the soldering iron. Let me know how it went 🙂

Sorry for the late reply (I only saw this today) – if you breadboard it as above, there’s no bypass, so if the battery is disconnected you won’t have any output.
See:
https://barbarach.com/articles/building-a-simple-pedal/finalizing-the-pedal-design/

Somewhere towards the end of the article (Final Schematics heading), there’s how to wire up stomp switch so it has true bypass. If true bypass is used, the signal will pass through unaffected.

Note that pedals that don’t have true bypass, like Tube Screamer for example or lots of Boss pedals, if you don’t have power supply or battery in, there won’t be any signal going through even when bypassed (well, you can’t bypass them if there’s no power).

Hey Eduardo, you can’t really add LED properly on a breadboard. You would need a 3PDT switch that you can use on a breadboard, which is rather rare. I use DPDT switch when I’m testing and for that I don’t need an LED.
Having said that, I think what you’re looking for is:
https://barbarach.com/articles/building-a-simple-pedal/finalizing-the-pedal-design/
I go through the list of things you need to do to complete the pedal. Among other things – there’s how to wire-up your stomp switch and how to add LED to the finished pedal. Have a look and see if that makes sense.

I couldn`t fit everything into enclosement 😀 maybe I`ll come back to this project later, maybe I`ll make or order a new enclosement.

Hey guys! I’m crazy new at this. I’m just trying to wrap my head around it. The R3 resistor seems to run from the power rail to the negative leg of the transistor, C1 capasitor, and R1 resistor. Why is that?

That R3 goes from ground. That’s the green wire from battery negative pole, it goes to power rail but on the blue line side. R1 goes from positive battery pole (red line side of the power rail). So we have +9V -> R1 -> R3 -> GND. R1 and R3 thus form a voltage divider and bias our transistor. I hope I didn’t confuse you even more 🙂

Hey guys! I have a question if I can word it right. So, I used capasitors way to small and it lowered the volume. I then took out the capasitors and hooked the battery straight to the transistor and got no sound passing through. I’m wondering what the capasitors do in the circuit? I know they store engergy and release it. Sorry for my ignorance here.

Apologies for not replying earlier, looks like I’m not getting notified when a new comment is added, I need to figure this out.

Regarding capacitors, in this circuit in particular, they are coupling capacitors. What this means is they are coupling two circuits together and only allowing AC signal to pass through. By doing this, they prevent any DC component interfering with our biasing.

See: https://en.wikipedia.org/wiki/Capacitive_coupling#Use_in_analog_circuits

There are other uses, they can be used as decoupling/bypassing capacitors, could be used in filters. In this circuit they are intended to be used just as coupling capacitors. Since there are resistors in the circuit as well, some high pass filters are formed. So if you use capacitors that are too small they would cause lower gain at lower frequencies.

I’m not sure what you mean by connecting battery directly to the transistor – if you did not use either of R1 or R2, that would’ve disturbed biasing of the transistor and it would not work correctly. All resistors there are used for getting transistor to work properly as an amplifier. While there is some leeway to the values of the components, you can’t make big relative changes between them without disturbing the biasing too much. The circuit above is a “common emitter amplifier” and that’s just typical configuration.
There are other configurations, like “common collector amplifier” where some leads of the transistor may be connected directly to the battery, but those are used for different application (like buffers).

Hi – this is excellent, thanks for taking the time to share the schematic, and the demo too. My entire rig is now DIY built, and I’m so proud of it – a little noisy cricket amp, a bazz fuss pedal and a tremolo pedal that is currently on the breadboard but sounding great. I’ve been desperate for a bit of a volume boost, and just stumbled across this… I also happen to have all of the components from my other builds so I’m properly chuffed!

I’m off to have a browse through your other articles 🙂

Hey, thank you for this excellent tutorial. I wasn’t able to resist building one for myself.
Also added some artistic design to the PCB – the lines form a rocket on mine 🙂 You can have a look on my newly created blog: https://rocketsciencepedals.blogspot.com

I surely will come back to your site for further project – next things I would like to build are a fuzz face and a BOSS OD-1 quad amp clone.

Hey Kristian,
That PCB looks great 🙂 Impressively you etched it yourself! Last time I tried that years and years ago it was way less impressive and barely working :D:D:D:D
I’m looking forward to seeing your next project.

I’m clearly missing something. I’ve built this 4 times trying to get it to work. My circuit looks exactly like your photo. I even rebuilt it to match while troubleshooting. My resistor values are off by a little and my capacitors are for 50v but I get zero signal. Where would you start with trouble shooting?

Hey CosmaNot, let’s see … capacitors 50V should be OK. What are the values of the resistors that you’re using? Are you using 2n3904 transistor or some other? If you’re using a different transistor it could be the pinout.

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