Active humbucker DIY build kit guide

Your kit will include -

2x mini humbucker bobbin

2x mini humbucker blade

2x plastic spacer

1x bar magnet

1x partially populated PCB

2x mounting screws

2x mounting springs

1x headed output cable

To begin, the passive pickup must be made. Wind the two mini humbucker bobbins with wire, the winding area is quite narrow, high tension is likely to be necessary. Typical active pickups will be wound with approximately 5700 winds of 42 AWG wire on each bobbin. You can reduce the wind count for a lower output, brighter tone, or change wire gauges up to 43, or even 44, for a darker tone.

Once the coils are wound, insert the blades through the centre of the bobbins until they are flush with the top of the coils. Place the magnet at the base of the blades so that it can magnetise both of them simultaneously. You can connect fly leads onto the coil starts and ends (we suggest white denotes start, and black end, for clarity). If you are more advanced you can connect the wire directly onto the PCB pads.

Place the plastic spacers on the opposite side of the underside of the bobbins from the magnet to create a flat surface for the PCB to sit upon.

You should populate the PCB prior to connecting it with the passive pickup. The PCB is pre-populated with an output header, a diode, a filter capacitor, and an amplifying chip. These components are necessary and are not user adjustable. The other components of the circuit are to be determined by the user for the desired tone and response.

 

The pairs of pads are labelled with R for resistor, or C for capacitor. The component should be placed between the appropriate pads and each leg soldered to one of them. Details about the function of each component will be given below for your reference -

The IC is an inverting op amp. It takes the outputs of both coils, flips coil 2's phase, then combines them. It then amplifies the combination to be louder.

R1 is the series resistor for coil 1. This resistor will darken the tone of this individual coil. It works in conjunction with R5 to set the gain of the circuit (R5 divided by R1 is the gain factor). It also works in conjunction with R2 to determine the symmetry of the coils – a greater difference between the values of these resistors will result in a more scooped, clear tone, at the cost of hum reduction. Normal values for R1 are 10k-100k

R2 is the series resistor for coil 2. It functions as R1 does, but it has no influence on the gain of the circuit. Normal values for R2 are 10k-100k

R3 is a bias setting resistor. R3 should always be kept as an equal value to R4 to ensure that the bias point is at the middle range of the power rails so that the preamp does not internally clip. This loads the coil, lowering the peaks of the frequency. A higher value will produce a more natural, less compressed, and brighter tone. Normal values for R3 are 200k-1m

R4 is a bias setting resistor too. It additionally loads the coil in an identical way to R3. The overall loading of R3 and R4 combined on the coil should be half the resistance of either resistor when they are equal, because they are both in parallel with each other. Normal values for R4 are 200k-1m

R5 is the gain setting resistor. It works in conjunction with R1, as stated above, to set the gain of the preamp. It additionally loads coil 1 in addition to R7 (add the values together). This lowers the peaks of the frequency. A higher combined value will produce a more natural, less compressed, and brighter tone. Normal values for R5 are 100k-500k

R6 is the impedance setting resistor. The resistor is in series with the output of the preamp. A lower output impedance will reduce the effect of external resistances and capacitances have on the tone of the pickup. The inverse ratio of values of R6 to R7 will determine how much of the output will be rolled off (for example 10k to 100k will be an approximately 10% output loss). This should be around 2k-15k for normal pot taper with standard 25k active controls.

R7 is a loading resistor. This works in conjunction with R5 to load coil 1, and in conjunction with R6 as a volume roll off. Normal values for R7 are 30k-100k.

C1 is the series capacitor for coil 1. A lower value will trim off more bass from the tone of this coil, making the overall tone of the coil brighter. Trimming more bass and mids from the tone will additionally reduce the output. Normal values for C1 are 10nf-47nf

C2 is the series capacitor for coil 2. This works exactly as C1 does for coil 1. Normal values for C2 are 10nf-47nf

C3 is the series capacitor for the preamp output. This works exactly as the the two prior capacitors. Normal values for C3 are 47nf-100nf

As long as the recommended values for each component are followed, any circuit variation should be functional. If you are unfamiliar with circuit design, you are likely to have to swap values out until you reach your desired tone. You could fix your PCB to the back of your pickup with double sided tape until you are happy with the tone of your preamp design.

When the preamp population is finalised, you can solder on the coil starts and ends to the applicable pads labelled coil 1/2, start/finish. Each one can be fed through the back of the PCB via the corners, with the exception of coil 2 start, which is to be fed through the epoxy hole. Plug in your output cable and test the pickup output before epoxying the pickup (and being unable to repair!). If the output is as expected, you can mix your epoxy mixture and pour it down the hole and over the PCB to encase the pickup. Ensure that you do not excessively fill it, preventing the output cable from being installed properly. Leave the epoxy to cure for at least 24 hours before using the pickup.