How To Build A JFET Transistor Buffer Pedal
Jack Orman, the godfather of DIY effects pedals really knows his stuff when it comes to buffers.
This JFET buffer is based on his designs and is simple enough for you to be up and running within an hour. As this buffer utilises a JFET, it produces a little less noise than a BJT alternative and has much higher input and output impedance possibilities.
If you’re after a buffer with lower input impedances, take a look at my DIY BJT transistor buffer pedal here.
This is a fairly easy build with only 8 components:
R1 – 10M Resistor
R2 – 2M2 Resistor
R3 – 2M2 Resistor
R4 – 10K Resistor
R5 – 100K Resistor
C1 – 100nF Film Capacitor
C2 – 1uF Electrolytic Capacitor
Q1 – J201, 2N5457 or MPF102 Transistor
2 ¼ Inch Mono Input Jacks
1590A Hammond Enclosure
There are a couple of different options when building this buffer. You can either build it using the kit/PCB from Musikding or you can build it using stripboard.
Here is a link to the kit from Musikding:
If you’re happy to source your own components and looking to save a bit of money, why not check out their standalone PCB:
The other option is to build it on stripboard and this is how I built my buffer using the below layout:
This is a little different to the version from the kit, but the principles are the same.
Before starting out with any build, I like to take all of the components necessary for a pedal and lay them out on a labelled sheet of paper. This will make it much easier to grab each piece as and when they’re needed. It will also let me see if there are any missing components before I start a build.
With everything laid out in front of you on your labelled sheet of paper, turn your soldering iron on to get it heated up to the necessary operating temperature. Whilst you’re waiting for this to heat up, grab a dry cloth or a tissue and wipe down the PCB/stripboard and the leads for all of your components to remove any oil or grease. Giving them a quick clean will help ensure you get as good a connection as possible when soldering your components into place.
With your freshly cleaned PCB or stripboard and your soldering iron up to the necessary temperature, it’s time to start building the circuit.
As always, we need to start out with the lowest profile components and in this instance, we’ll start with the resistors. With your needle nose pliers, bend the wires on your resistors to a 90-degree angle at the necessary length to fit in your spaces. Doing this upfront will not only save time, but it will also make your circuit much neater and easier to troubleshoot.
With all of the resistors in place, we can move onto the transistor socket. Whenever you’re working with transistors, I would strongly recommend that you make use of sockets to ensure that you never solder transistors directly onto your board. This will help you swap out transistors if you wanted to test the sound of different components.
Now that the transistor socket is in place, we can move onto the final onboard components, the capacitors. For this circuit, we have one film capacitor which can be soldered onto the board any way around. However, we also have one electrolytic capacitor which is a polarised component. Please take special care to ensure this is correctly orientated. The long leg of your capacitor, the anode, goes to the square pad of the PCB (if you’re using the Musikding PCB).
With all components in place, we can add the transistor to the socket (pay close attention to the pinout).
The circuit is now complete and ready to test.
Test The Buffer
Before adding this completed circuit into your pedal enclosure, I would highly recommend that you test it out to make sure that it actually works. This will make it much easier to reflow any dry solder joints or swap out any dead components if needed. Once this is in the enclosure, it will be a little more difficult to troubleshoot.
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 inside of the enclosure once we know everything works.
If our new JFET buffer works, we can move onto the next phase. However, if you spot any issues, why not work through my DIY guitar effects pedal troubleshooting guide.
Drill The Enclosure
As this is a standard buffer with no extra features, we only have three holes to drill. One for the input jack, one for the output jack and one for the power jack.
Below is a guide for how big each of these holes needs to be:
2 Input Jacks – 10mm
1 DC input Jack – 12mm
Now that we have tested our buffer to make sure it works and drilled the enclosure, we can start piecing everything together into a complete pedal.
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 connection wires between the input jacks, power jack and circuit. 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 a little more difficult.
This is a super simple pedal to create and whilst it may not be the most exciting item on your pedalboard, it can really improve your guitar tone.
If you’re new to building pedals and not comfortable working within the confined space of a 1590A enclosure, why not try the 1590B or 125B enclosure. This will give you a little more room to work with whilst you build up your confidence. You can always rehouse it at a later date if you want to save a bit of space.
If you have any questions about this build, please let me know.