[TCML] Audio modulated coils: where to start?

[Curtis Cherry]

Hello everyone.  My name is Curtis Cherry

    Let me start out by saying that I have not ever actually built a tesla 
coil, but I have been researching them for over a year now.  I have 
concentrated on the SSTCs because I too intend to audio modulate some day. 
If fact my interest in tesla coils was spurred by the video of Steve Wards 
DRSSTC2 on you tube playing super mario brothers.

    As I said Ive never built a tesla coil but I will share the info I have 
learned.  Most of the info comes from Steve Wards site www.stevehv.4hv.org 
Just click on musical tesla coils.

    There are 2 basic forms of audio modulation.  Amplitude Modulation is 
the first type.  It works by changing the duty cycle of the output of a coil 
while it is oscillating at its resonant frequency.  This changes the amount 
of total power going into the coil.  Changing the amount of power going into 
the coil changes the volume of plasma being produced which in turn causes 
the air to contract and expand.  This creates pressure wave that we hear as 
sound.  This technique works the best with a CW(Carrier Wave) coil.  The 
amount of total power in CW mode is quite considerable and I am not sure if 
anyone makes silicon that handle the amount of power it would take to make 2 
foot sparks for any considerable amount of time.  This type of coil is 
capable of faithfully reproducing audio.

    The second method of audio modulation is PRF (Pulse Repetion Frequency). 
This coil fires "bursts" of plasma out at certain frequencies to create 
pressure waves.  This type of coil suits itself well to any pulsed type of 
tesla coil such as DRSSTCs.  This is the type of coil you want to build if 
you want big sparks due to the lower average power output, but the audio is 
quite a bit more harsh and doesnt lend itself to playing "complex" tones. 
Steves coil runs off of a microcontroller to create the pulses but it would 
work just about as good to use a "zero-crossing" circuit hooked to a 
keyboard or any other audio source.

    You can also get some good info from A guy names Dan McCauley (Sorry if 
I spelled it wrong).  His site is www.easternvoltageresearch.com He sells TC 
driver boards if you dont want to start from scratch.  He also sells audio 
interfaces that can work with any type if SSTC.  And boards for an audio 
modulated coil called the "plasmasonic".

    Please keep in contact with me throughout the process of planning and 
constructing your coil so that we can share ideas and information.  I have 
accumulated all the parts to build my coil and will start half-bridge 
construction soon.  Good Luck to all.