#498 Tesla Coil Plasma Speaker Kit

Playing with a Tesla coil circuit that also acts as an audio speaker with pulsing LED effects.

Build

Here’s a quick demo, spinning a little Baby Diner:

Notes

The “Mini Music Tesla Coil Plasma Speaker” is a pretty popular kit, widely available on ebay or for example here on aliexpress. I was encouraged to pop one in my cart (USD6.29 at the time) after seeing the build video by NFM:

Kit and Parts

The kit may or not come with a schematic (mine didn’t), but it is not needed for construction - only understanding!

Most sellers specify

voltage: 15-24V DC
current: 2A

Part list:

Ref	Item	Qty
C1	10µF 50V electrolytic capacitor	1
C2	1µF 105J 100V polyester capacitor	1
D1	LED red	1
D2	LED blue	1
R3,5	2kΩ resistor	2
D1,4	10kΩ resistor	3
Q1	BD243C High Power NPN 100V	1
Q2	80NF70 N-channel 68V Power MOSFET	1
	pre-wound coil	1
	stereo audio socket	1
	power jack	1
	heatsink	2
	3.5mm stereo audio cable	1
	wire	15cm
	strip double-sided tape	5cm
	screws	8 (only 6 required)
	brass standoffs	4
	PCB	1

kit_parts

kit_pcb

Circuit Design

The circuit is based on what is commonly known as a “slayer exciter” version of a Tesla transformer. The slayer exciter circuit uses feedback from the secondary coil to produce a self-governing oscillation.

This version of the circuit makes some clever additions:

audio input modulates the current to the coil via the 80NF70 NFET (Q2)
one LED is modulated by the audio input (D2)
one LED is modulated by the coild oscillations input (D1)
the audio-modulated coil (amazingly) vibrates and the plastic tube that is the core of the coil resonantes for this to act as a speaker!

Schematic

The essence of the circuit is the “slayer exciter” self-governing oscillation:

Initially Q1 on, current flow builds in promarimy winding
magnatic field induces currentin the secondary winding
secondary sees a very small air-ground capacitor at one end, so initially cannot conduct but starts to pull Q1 base negative
until Q1 base current throttled enough to turn off
magnetic field collapses, and flyback voltage discharges into the air (generating a plasma!)

The scope trace below shows these the operation with VCC=14V and no audio input, with channels connected to J1, J2, J3 (see schematic).

CH1 (Yellow): J3
CH2 (Blue): J1
CH3 (Red): J2

MusicalKit_scope

Note the frequency: 3.9 MHz, just a bit above the 80m amateur radio band. This is a few components away from being a morse/CW transmitter;-)

My testing showed:

at takes about 14V to start arcing
increased up to 20V but after about 16V it doesn’t have an appreciable affect on the arc or sound volume

Some measurements of actual power consumption at different voltages:

Voltage	Current	Power
14V	0.5A	7W
18V	0.7A	13W

Testing the Completed Kit

All finished:

MusicalKit_build_complete

Here’s a quick demo, spinning a little Baby Diner:

It can even be used as a basic nixie tube tester!

testing_nixies

Credits and References