This is a very simple and cheap circuit to produce an audio modulated plasma arc or singing arc.
A power mosfet IRF740 transistor is turned on and off by a square wave generated around a NE555 timer. This transistor induce a high voltage in the output coil of thge High Voltage Transformer - HV XFMR (See Fig1)
NE555 timer running frequency is set, given by R1, P1 and C1. In this case, P1 is set at 1.6 Kohm in order to have a frequency of about 32 KHz (HV XFMR resonance frequency). Power supply is +12 VDC / 3 Amp max.
Audio input is coupled to pin #5 of NE555 timer via a C2, a 470nF/25v electrolytic capacitor. This input modulates the running frequency of the 555 timer with the the audio volume intensity.
The HV XFMR is a hand wound transformer with independant primary and secondary coils. A TV flyback may be used instead. Just wind 10 to 20 turns around the core to construct the primary coil ( see HVFB Generator. ).
Circuit schematic is given below:
Some images of the circuit and HV XFMR
A video with the circuit and actually plasma arc at here You Tube video.