DIY Lovepedal JTM Pedal Build

One Knob Guitar Pedal

The Lovepedal JTM pedal is a single knob drive that will help you capture the tones of a vintage 1960s Marshall JTM 45 amp, also known as the Bluesbreaker (Not to be confused with the Marshall Bluesbreaker pedal).

You can really take this pedal from an awesome clean, slightly oversaturated boost to a classic crunchy Marshall tone.

Overview

Build Difficulty – 1/5

Build Time – 1 – 1.5 hours

Pedal Style – Overdrive

Total Cost – ~£30

Parts List

This is a fairly easy build with only 13 components for the PCB:

Components

R1 – 1M Resistor
R2 – 2M2 Resistor
R3 – 3K3 Resistor
R4 – 330 Resistor
R5 – 3K3 Resistor

C1 – 47nF Box Capacitor
C2 – 100nF Box Capacitor
C3 – 47uF Electrolytic Capacitor
C4 – 47uF Electrolytic Capacitor

Q1 – 2n5089 Transistor

D1 – BAT46 Diode
D2 – BAT46 Diode

Bias – 5KB (Linear) Potentiometer

Hardware

2 ¼ Inch Mono Input Jacks
DC Input
5mm LED
LED Bezel
3PDT Footswitch
3PDT Footswitch Daughterboard (Optional)
1590B Hammond Enclosure

Preparation

When starting out with any pedal build, I like to get all of my components out and lay them on a labelled sheet of paper. This not only helps me pick up each component as and when it’s needed but also highlights any missing components before you start.

If you don’t want to make your own, you can download and print off this checklist. Download here.

Now that you have everything laid out in front of you, it’s time to turn on your soldering iron and get it up to temperature. Whilst you’re waiting for this to heat up, grab a cloth or a tissue and wipe down the PCB and the connectors for all of your components. Giving them a quick clean will help ensure all of your connections are good.

Build

With your soldering iron at the correct temperature, components laid out in front of you and cleaned, we can make a start.

I always like to start with the resistors and get all of these in place first. Take your time and add them to the PCB, one at a time. Add one resistor, solder it into place, trim off the excess wire and check your joints. If everything looks good, we can move onto the next resistor. If you spot any gaps in the connection, just add a little more solder to ensure a solid joint.

Once all of the resistors are in place, we can move onto the capacitors.

This build only requires four capacitors. Two box film capacitors and two electrolytic capacitors. Both of the box film capacitors go onto the same side of the board as your resistors whilst the two electrolytic capacitors go on the other side of the board. The box film capacitors can go into the circuit any way round, however, take note of the necessary orientation for the electrolytic capacitors. If you get these the wrong way round you can really mess up your circuit and maybe even fry some components.

Next, let’s move onto the clipping diodes. These can go onto the same side of the board as the resistors but just like the electrolytic capacitors these are polarised and must be put in in the correct orientation. Match up the stripes on the diodes to the lines on the PCB. This is a hard-clipping circuit so the pedal has a fair amount of gain on tap. Be careful when soldering diodes as they are quite sensitive to heat and holding your soldering iron onto them could fry them.

The next piece to add is the transistor. While not in the official build documentation, I’d strongly recommend using a three-prong transistor socket. This will allow you to switch out transistors much easier and will ensure you don’t apply too much heat to the transistor and burn it out. If you’re using the correct transistor from the build materials list, you can simply match up the shape of the transistor to the shape on the PCB.

The final component to add to the PCB is the 5K bias potentiometer. You can add this directly to the PCB or connect it using wires but I’d recommend going straight into the board as it will make things much neater.

With all of these components in place, your PCB is fully populated and ready to test.

Test Circuit

Before adding your circuit into your enclosure, it makes sense to test out your circuit to see if it actually works. This will make it much easier to add more solder or swap out any dead parts if needed.

Wire this circuit up directly to the input jacks and a DC input jack. The wiring here doesn’t need to be neat as we’ll be redoing all of this in the enclosure once we know it all works.

If you’re building lots of pedals, you may wish to build a test rig with crocodile clips to help speed this process up for future builds.

You may notice a bit of interference with the sound at this stage but that is to be expected. Once everything is in the metal enclosure, the circuit will be shielded from this noise

If you notice any other strange issues, check out my troubleshooting guide here.

Once you’re happy that the pedal works and sounds like it should, we can prepare the enclosure.

Drill Enclosure

As previously mentioned, this pedal only requires one knob so we don’t need to drill too many holes.

Below is a guide for how big each of these holes needs to be:

1 Potentiometer – 8mm
1 LED Bezel – 8mm
2 Input Jacks – 10mm
1 DC input Jack – 12mm
1 3PDT Footswitch – 12mm

You can find my drilling guide for this pedal here:

1 Knob 1590B Drill Template

Final Assembly

Now that we have tested our circuit to make sure it works and drilled the enclosure, we can start piecing everything together.

I’d suggest installing all of the hardware first and tightening all of the nuts to ensure there’s no unnecessary movement.

With all of the hardware in place, you can start adding all of the wires between the footswitch, input jacks, power jack and LED. As everything is now in the correct place, you should be able to cable manage your pedal much more efficiently. You want everything to look as neat as possible as unnecessarily long connection wires may create interference and will make any future troubleshooting more difficult.

Test Pedal

With everything fully wired up, it’s time to add it to your pedalboard and plug it in! You should notice that any interference you found during the testing phase has been rectified, but if any new noises appear, you can narrow it down to a hardware connection issue.

Finishing Thoughts

This is a very simple build and the pedal sounds awesome!

My only thoughts on it are that the bias knob doesn’t really make a huge difference to the sound until you’re up to 7 or 8.

There is a little bit of noise when you turn the knob as the transistor rebiases but this is to be expected.

If you have a little more experience with pedal builds, you could quite easily fit this in a 1590A enclosure and save some space on your board but on the whole, I think this pedal sounds really great and is a good addition to anyone’s board.

If you have any questions on this build, please let me know.

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Hi, I'm Pete!

I have been a guitar and effects pedal enthusiast since 2005 and electronics tinkerer since 2017.

I’m here to help you begin your journey with building DIY guitar effects pedals. Get in touch with me if you have any questions.

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