: Hey Bert,
: My goal is to have a SSTC to act as a plasma speaker. Based on your reply
: and additional research into the flyback design, I found that it will give
: me a better audio sample and the design is somewhat easier than the
: air-core transformer design but I feel as though I am cheating myself and
: I am not getting the full Tesla Coil design experience. I am in the
: process of switching my design to using an air-core transformer using a
: sphere top load. What supply voltage do I need in order to operate the
: coil? I have seen many sites that use a 12Vdc supply to power their SSTCs
: while others use high voltage transformers (NST in particular). I am
: looking to produce sparks of 30cm and I feel that using a 12Vdc supply
: will not give me enough power to achieve this.
Most solid state coils operate from relatively low DC supply voltages - from tens to to hundreds of volts. A few special systems use costly high voltage power transistors (such as Greg Leyh's new solid state coils). These may operate with DC supply voltages as high as 1-3 kV.
All Tesla Coils using NST's either use spark gap switching or a newer solid state "equivalent" using a stack of Sidac IGBT Spark Gap (SISG) solid state switching modules. (Look up SISG in the Pupman archives at www.pupman.com for more information). NST-powered coils are not easily modulated for audio.
Tesla Coil spark length is a function of design/construction efficiency and input power. A well-designed Tesla Coil can easily deliver at least 30 cm (~12" sparks with an input power of 90 watts. The input power could be supplied by a 12V power supply capable of supplying 7.5A, or a 90 volt supply delivering 1A... either will work as long as the SSTC circuit is designed to work at the desired voltage.
If your focus is to make a coil that you can use to drive a relatively high fidelity plasma "speaker", and if you don't have much prior electronics design experience, you may want to check out the Plasmasonic Tesla Coils and kits from Dan McCauley at Eastern Voltage Research. The best audio fidelity tends to occur with coils operating at high frequency (1 MHz+) and short output sparks (actually more like an almost silent flame-like corona) that's only 1/2" - 2" long. This severely limits low frequency performance. Systems that generate longer sparks often use DRSSTC's or higher power SSTC's. While you can get much louder sound from these larger systems, they tend to have poorer audio fidelity due to spark-generated artifacts (hissing, crackling). Also, audio modulated DRSSTC's are limited to hundreds of Hz to a few kHz by the nature of their operation.
For some ideas for both types of systems, see Dan's site: