ARC Plasma Speaker Assembly Instructions


The Plasma Speaker is a dangerous device. When operating it, ALWAYS keep the following precautions in mind:

  • NEVER under any circumstances should you touch the arc or the electrodes with fingers or metal or combustible objects while the speaker is on.
  • Don't touch it. Seriously. It's really freaking hot and you will regret it.
  • When you turn off the device, always use an insulated metal tool such as a pair of pliers to bridge the electrodes. You should usually hear a small pop or zap. This discharges the capacitors in the transformer's internal voltage multiplier, which will give a painful zap even when the device has been powered off for a while.
  • When adjusting the electrodes, ALWAYS turn the device off first and ALWAYS use an insulated pair of pliers or other metal tool. Also keep in mind that after turning the speaker off, the electrode screws retain a high temperature for a fair bit of time.
  • Do not use the speaker for sessions longer than 30 minutes, over usage may result in damage to the speaker.
  • Do not leave the speaker on with no active audio input, this may result in permanent damage to the D1 diode and the speaker. Always turn off the speaker when it's inactive.


List of components

This is a full itemization of what you should get in the box.

If you know what you're doing, you can skip to step 3.

Otherwise, read on to step 1.

Either way, you will probably need to refer back to this list a couple times.

Electrical components
Name Value Description/markings
R1 10Ω Brown-Black-Black-Gold-Brown
R2 6KΩ Blue-Black-Yellow-Brown-Brown
R3 12KΩ Brown-Red-Black-Red-Brown
R4 150Ω Brown-Green-Black-Black-Brown
R5 100Ω Brown-Black-Black-Black-Brown
R6 200Ω 10W White rectangular resistor
C1 470μF 25V Smaller Black Capacitor
C2 10μF "106 K2C"
C3 0.047μF "473K"
C4 0.1μF "104Z"
C5 1nF "102"
C6 220μF 250V Large Brown Capacitor
D1 Diode "6A6"
U1 LM386N Audio Amplifier
U2 SE555P Oscillator
Q1 STP120NF10 Power MOSFET
Q2 BS170
VR1 5KΩ Blue potentiometer
J1 N/A Audio jack
Electromechanical and other hardware
Quantity Name Description
8 Enclosure screw Phillips head machine screws
8 Enclosure nut
2 Electrode screw Stainless sheet metal screws
1 MOSFET screw, washer, and nut Small, short screw
2 IC socket
1 Power switch
1 Power jack

Enclosure parts

  • Control panel
  • Vented short side panel
  • Vented long side panel
  • Blank long side panel
  • Vented bottom panel
  • Etched face plate
  • Electrode mounts (2x)
  • Cover flaps (2x)
  • Circuit board brace

Loose parts

  • 12V 5A power supply with cable in box
  • Flyback transformer
  • 8" of triple-insulated black wire
  • 6" of thin blue wire
  • Male-male audio cable
  • Extra brown wire


Gather materials

  • You will need the following tools:
    • a soldering iron and solder,
    • a pair of needle-nose pliers,
    • a phillips head screwdriver,
    • a pair of wire strippers,
    • and a pair of nice pointy wire cutters.
  • Optionally, it would be nice to have:
    • a solder sucker for mistakes,
    • some tape to hold components on the board while soldering,
    • and a ruler.
  • Make sure you have all the materials you need. The box should contain:
    • a bag containing MDF and/or acrylic enclosure pieces (eleven in total) and the PCB,
    • a smaller bag containing an anti-static bag full of electronic components and screws,
    • a flyback transformer,
    • a 12V 5A power supply with cord,
    • an audio cable, and
    • an extra brown wire. You will probably not need this, but it has been provided for your convenience.
  • Make sure you have all the other components and hardware.
  • Make sure you have all the enclosure pieces.


Assemble circuit board

  • Start soldering the components into the circuit board. Match up the part numbers with the markings on the board silkscreen. Make very certain that the components are soldered in the right direction:
    • The orientation of the C1/C6 capacitors is as follows: the side with the white stripe on the side is the negative.
    • The stripe on the diode matches up to the stripe on the silkscreen.
    • The shape of the transistor Q2 matches with the outline on the board.
    • Resistors don't care about direction.
    • The knob on VR1 should be facing outwards.
    • Match the notch on the U1/U2 sockets to the notch outline on the PCB. After soldering the socket onto the board, insert the U1/U2 chips into the socket. The short-side of the U1/U2 chips with a notch and/or small circle should be placed so that it is aligned with the notch on the socket/circuit board. Orientation is crucial!
  • It's a good idea to start with the shorter components like small resistors and capacitors, and work your way up to the taller ones.
  • To make your life easier, tape the components down before you flip the board over so they don't move around.
  • Make sure you push the component leads all the way through the holes before soldering. This prevents extra wire sticking out from causing trouble later.
  • If you've never soldered before, it would be a good idea to watch this video on how to solder properly. A proper soldering job will eliminate a whole class of bugs.
  • Leave the washer and nut off of the potentiometer for now.
  • Ignore J1 for now.
  • Make sure you trim the leads fairly close to the board after soldering. Not too high, not too low.
  • When you put the MOSFET in, bend the leads 90° towards the back as shown, so that the tab sits flat on the back.
  • Screw the tab into the board with the included MOSFET screw, washer, and nut before soldering it in so it doesn't fall out.


Control panel

  • Peel the protective stickers off of the enclosure pieces. On MDF, the side with burn marks (without the sticker) will face inwards. For the clear kits, the acrylic panels come with protective stickers on both sides
  • Push the power switch into the rectangular hole in the control panel enclosure piece, with the O facing the round power jack hole.
  • Attach the power jack with the included washer and screw as shown. Make sure that the solder lugs are in the same orientation as you see here.
  • Take one of the clipped diode leads (because they're nice and thick) or strip a section of a discarded transformer wire and solder it across as shown. Clip any hanging ends.
3.3 3.2
  • Cut two segments about 3" each from the included black wire and strip the ends as shown, with one side of one extra long.
  • Solder the wires as shown, with the long stripped segment going through the bottom and left loops of the power jack.
  • Similarly, cut two segments about 2" each from the included blue wire and strip the ends as shown. Make sure you get the long stripped side as close to 9/16" as possible. This will make the next step easier.
  • Solder the wires into the audio jack as shown.
  • Solder the other ends into the circuit board at J1. The wire attached to only one solder ring should be in the hole farthest from the J1 label.
  • This step will require a bit of tricky maneuvering. Assemble the control panel and the circuit board by first fixing the potentiometer through its hole with the washer and nut. Don't tighten it too much yet. The solder terminals on the switch and power should face inwards.
  • Fix the audio jack through its hole with the included nut. Angle it about as shown.
  • Put the black wires through the holes on the bottom left of the board. The one coming out of the switch should go through the hole with the square pad. The wire connected to the switch is positive and the wire connected to two pins on the power input is negative. Make sure the board makes a flat 90° angle with the control panel, and tighten the potentiometer nut to hold it in place.
  • Solder the power wires and trim the excess. Maneuver the black wires away from the large white resistor, which will heat up a lot during operation.
3.3 3.3
  • Take this time to push an enclosure nut into each of the slots in the control panel, one on each corner. Do the same with the opposite panel, the other one with ExcelPhysics etched on it.
  • Opposite flats of the nut should sit flush with the edges of the notch.


Flyback transformer

  • Snip the grey, white, and thinner red wires (which should all be bundled up) from the flyback transformer. Keep the white one and discard the rest. Strip about an inch from either side of the white wire.
  • Snip the cable tie on the brown wire and wiggle it out from around the ferrite core. Cut it in half and strip the cut ends.
  • Cut the suction cup from the end of the thick red wire and strip about an inch off the end. You can probably get away with cutting an inch or two of the wire off.
  • Snip pins from the bottom of the transformer as close to the base as you can get them, leaving only the shown pins (clockwise: #2, #3, and #7). This is where a pointy pair of wire cutters will help a lot.
  • Using needle nose pliers, bend a loop in one end of the white wire. It doesn't have to be perfect, just enough to mimic a solder terminal like on the power switch.
  • Solder the brown and white wires to the remaining pins on the bottom of the transformer as shown, with the red tube side on the first pin, and white wire on the last.
  • Solder the brown wires to the circuit board above the MOSFET, with the red tubed wire in the hole with the square pad.
  • Make sure the insulation on the wires is as close to the flyback pin or pad as possible; you don't want any extra wire hanging around that could touch each other or other pins.



  • Sanity check.
4.2 4.2 4.2 4.2
  • Begin to assemble the enclosure pieces to the control panel-circuit combo.
  • For the easiest time, do it in the order shown. The enclosure will try its hardest to fall apart, but you must not let it have its way.
4.2 4.2
  • When you get to the back panel, make sure the white wire from the flyback is sticking through the corner of the faceplate. When the panel is on, screw it on. Don't over-tighten the screws to avoid cracking the MDF.
  • Using the point of a screw or something else sharp, dig a notch in the side of the hole in an electrode holder piece. This will make room for the wire and prevent the screw threads from breaking it.
  • Stick the free end of the white wire through the notch and screw in an electrode screw about 2/3 of the way, keeping the wire in place.
  • Wrap the dangling end of the white wire around the screw threads.
4.2 4.2 4.2
  • Continue to assemble the electrode flap portion.
  • Pull out enough white wire so that the transformer sits inside the enclosure without bending the white wire inside too much.
  • Place the electrode holder with the screw facing towards the middle into its slot on the faceplate.
  • Continue with the flap in the order shown. Be careful not to snap the MDF. It will be a little difficult to wriggle it into place.
  • Repeat with the other side and the thick red wire.
  • Try to keep as little of the red wire inside the enclosure as possible. It will make putting the last piece on more difficult.
  • The exposed edge of the ferrite core on the transformer should be facing downwards.
  • The tab sticking off from the base of the protrusion where the white wire used to be should fit next to the large brown capacitor, with said protrusion on top.
  • The side of the transformer should be flush with the open edge of the enclosure.
  • Screw in the last piece of the enclosure.
  • The speaker is now assembled! But wait, you're not done, yet.



  • Screw the screws together until there is about 14" to 13" of a gap between them. This will be tweaked later, so don't worry too much about it.
  • Plug it in and test it.
  • Turn the volume almost all the way down to start out before turning it on for the first time.
  • The volume on your audio source (if you are using a phone, iPod, laptop, etc.) should most likely be all the way up.
  • Try using a cheap audio source first so that you don't accidentally damage something expensive.
  • The arc should look something like this.
  • If it doesn't, go on to the next step. Otherwise, you're done.
  • For extra credit, take the last enclosure piece off and use a few big globs of hot glue on the places where the transformer touches the case before putting it back in. This will ensure it doesn't fly around too much when handling the speaker.



Hopefully it should not come to this, but if your speaker does not work properly, there are a few things you can try. You can also post your build on our subreddit at and get some help/feedback from the community!

No response

If you turn it on and nothing happens at all, the best thing to do is to double-check that every component is connected properly and in the right direction. Check for cold solder joints.

If you have checked three or four times and are sure everything is in the right place, you may have a damaged part somewhere. Contact us and we'll work something out.

Nonexistant or weak arc

If the arc is thin and fizzling around noisily, or if you see no arc but some fizzling from the transformer, there could be a few things wrong.

Most likely, the arc gap is simply too wide. Turn the device off, and using a pair of insulated pliers, turn the screws so they are closer together. Then, try turning it on again.

It's also possible that the flyback transformer is damaged or faulty. Again, if you think this is the case, contact us about it.

Quiet audio

If the speaker produces very quiet audio, even when the volume on your playback device and the speaker are turned all the way up, there are a couple of possibilities.

Check for solder bridges on both sides of the board, especially between the two pins of the audio input J1.

Your audio amplifier U1 could be faulty. If that's the case, we can mail you a new one, or you can probably pick one up from Radio Shack, Fry's, or similar.

Copyright ©2014 ExcelPhysics, LLC

Last updated 2014-09-02