Build Guide

PCB

The EAGLE files for the PCB are included on the GitHub page. These files include the schematic, the board layout, the gerber files, and a library of components.

The original PCBs were manufactured by JLCPCB with the default settings.

If you need to re-design the PCB, here are some points to keep in mind:

• A library of components is included with the PCB files.
• The dimensions of the board should be 3x3 inches (to match the heatsink that it will be mounted on).
• The mounting holes have a diameter of 0.125 inches. They are inset from the corners of the PCB by 0.2 inches (edge of board to center of hole). If you are using new heatsinks as well, then you can change these specs. If this is the case, you will need to drill and tap mounting holes in the new heatsinks.
• Make a hole in the PCB around the power MOSFET (Q2) screw hole. The MOSFET will be soldered in so that is underneath the PCB and in contact with the heatsink. After the PCB is mounted, you will need to screw the MOSFET to the heatsink. You will want a hole in the PCB so you can do that. (Note: it may actually be easier to mount the MOSFET before mounting the PCB. Once both are screwed down, you can solder the MOSFET leads to the PCB.)
• The primary coil of the flyback transformer will, in short bursts, sink a ton of current. This will be sourced from the 24V supply and the capacitor bank (C9-14) and will also pass through the power MOSFET (Q2) and high-voltage capacitors (C15-17). The traces between these components (as well as the ground plane) need to be short and very thick (I recommend doing pours instead of actual traces).
• For the rest of the PCB design, you can do whatever you like. The world is your oyster.

Flyback Transformer

The flyback transformer is a complicated beast. This is because you must wind your own primary coil, and since the secondary coil has internal diodes, you must wind the primary coil in the right direction and connect it to the driver with the correct polarity.

What you will need:

• A flyback transformer.
• Four feet of stranded 14 AWG wire.

The flyback transformer has an exposed ferrite core. You will wind the wire around this core. With the transformer pins facing down and the exposed core facing you, wind the wire from top to bottom in the clockwise direction. You should make 9 turns of wire. The wire coming off of the top of the coil will connect to the positive output terminal on the PCB, and the wire coming off of the bottom will connect to the negative terminal.

Note: Typical 14 AWG wire is stiff and difficult to bend. If you use wire with a high strand count and silicone insulation, it will be a lot more flexible and easier to wind around the transformer core.

Note: The flyback transformer has a fixed number of turns on the secondary coil. If you wind more turns on the primary coil, the turns ratio will be lower and you will get a lower voltage on the secondary coil. This translates to smaller arcs. Likewise, if you wind fewer turns on the primary coil, the turns ratio will be higher and you will get bigger arcs. However, there is a limit. If you use fewer turns, the primary coil will draw more current. This could potentially damage the power supply, the PCB, or even the wire that makes up the primary coil. (At one time we were using a thinner wire for the primary coil. We reduced the number of turns until the insulation melted off the wire.)

Now you need to find the cathode of the flyback transformer. It is one of the pins on the base. With the base of the transformer facing upward, and the ferrite core facing you, it will be the [PIN]. This is where you will connect the cathode wire. The anode wire is the thick red wire coming out of the top of the transformer. When in operation, the arcs will form between the anode and cathode.

The remaining pins will need to be cut off and and the stubs coated in paraffin wax. This is done to prevent arcing between them. Arcs between the pins can cause damage to the transformer.

Arc Gap

The arc gap is fairly simple, but there are some things you must do to make it successful:

• The specific materials you use for the arc gap are not important (I mean, they obviously need to be conductive). However, we found that the material making up the cathode side of the arc gap will get very hot. For this reason we used a heatsink.
• Keep the anode and cathode wires away from each other. We will be running the flyback transformer at well over its rated voltage, and the insulation on the wires may not be enough to prevent arcing between them.
• Do not connect either the anode or the cathode of the arc gap circuit to ground! You want this circuit to be isolated from everything else. Connecting this circuit to ground would allow a path for current to flow if someone were to touch it, and you don't want that.
• Make the gap length 1.5 inches. If you make the gap too big, it will be difficult to get it to arc. If you make it too small, you will blow the power MOSFET.

Note: The larger the arc gap, the higher the voltage you will get. However, if you make it too big, then it will be difficult to get an arc. This will degrade the quality of the sound. Also, if the voltage gets too high, arcs can occur between windings of the secondary coil, which will delaminate the wire and ruin the transformer. On the other hand, the smaller the arc gap, the more current will flow. If you pull too much current, you will blow the power MOSFET on the driver circuit. This will appear as a short on the power supply, and the power supply will shut down.

Enclosure