How To Build A BJT Transistor Buffer Pedal
If you’re looking to build a buffer for your pedalboard, look no further than a circuit created by the legendary Pete Cornish himself.
The BJT transistor buffer circuit created by Pete Cornish in the late ’70s has been used by some of the greatest artists of all time. For example, Pink Floyd, Queen, Jimmy Page & Dire Straits to name just a few.
This guitar buffer works by feeding your signal into a fixed high impedance load. This is more or less identical to the input of a guitar amplifier. The signal is then distributed to your effects pedals and guitar amplifier by low impedance buffered feeds.
BJT buffers will generally have a lower output impedance than a JFET alternative but also a lower input impedance. If you would prefer your buffer to have a higher input impedance, check out my DIY JFET buffer pedal guide here.
This is a fairly easy build with only 17 components:
R1 – 100R Resistor
R2 – 10M Resistor
R3 – 1K Resistor
R4 – 120K Resistor
R5 – 120K Resistor
R6 – 200K Resistor
R7 – 7K5 Resistor
R8 – 20K Resistor
R9 – 150R Resistor
R10 – 50K Resistor
C1 – 100uF Electrolytic Capacitor
C2 – 100nF Film Capacitor
C3 – 1nF Film Capacitor
C4 – 4uF7 Electrolytic Capacitor
C5 – 22uF Electrolytic Capacitor
D1 – 1N4001 Diode
Q1 – BC549 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 FuzzDog or you can build it using stripboard.
Here is a link to the kit from FuzzDog:
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:
When starting out with any pedal build, I always like to lay out all of my components 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.
Now that you have everything laid out in front of you, it’s time to turn on your soldering iron and get it heated up to the correct temperature. Whilst you’re waiting for this to warm up, grab a cloth or a tissue and wipe down the PCB/stripboard and the leads for all of your components. Giving them a quick clean will help ensure you get as good a connection as possible when adding your components.
Once your board has been wiped down and all of your components have been laid out, your soldering iron should be at the correct temperature and we can make a start.
As always, I like to start with resistors. With your needlenose pliers, take each resistor and bend the leads 90 degrees a few millimetres away from each end of the actual resistor. Not only will this make your builds neater, but it makes it a little easier to get everything in place.
With all of the resistors in place, let’s move onto the diode. Ideally, we should take care of the lowest profile components first and then work up to the electrolytic capacitors which will most likely be the tallest components. As diodes are polarised, you need to take extra special care with the orientation of them on your board. The stripped end of the diode is the cathode (negative) and will connect to the square pad of your PCB (if you’re using the FuzzDog board).
With the diode in place, we can move onto the socket for the transistor. As transistors are so sensitive to the heat we can use sockets to help keep them safe. An additional benefit of using sockets for these components is that we can hot-swap transistors to see which work the best for your circuit.
Next, we can move onto the film capacitors as these are the next largest components. With these in place, we can move on to the electrolytic capacitors. Just like the diodes, these are polarised components that must be oriented correctly in order for this circuit to work correctly. The long leg of your capacitor, the anode, goes to the square pad of the PCB (if you’re using the FuzzDog board).
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 circuit into your enclosure, it makes sense to 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.
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 the 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 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 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 project to create and whilst it may not be the most exciting pedal 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. These will give you a little more room to work with whilst you build up your confidence.
If you have any questions about this build, please let me know.
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