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Registered Member #4350
Joined: Wed Jan 18 2012, 03:44AM
Location: South Carolina
Posts: 3
Hello all, I'm starting my first build, I'm planning on using the really simple schematic from here. My ultimate goal is to be able to modulate it and play music. I've found a decent amount of info on amplitude modulation, but I read about frequency modulation and I'm wondering if it's as simple as it sounds in my head.
I have a very basic knowledge of power electronics so please bear with me. The IRFP460 is the device driving the coil at whatever frequency it's happy correct? Could we not just attach the gate to an isolated controller and pulse it at the frequency of the sound we wanted to hear(this is what I gather from here)? Is it really that simple or am I completely missing some huge aspect of it?
Registered Member #4118
Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140
For audio TC modulation, you use AM not FM. Yes, the IRFP460 is the mosfet driving the coil. You can't just pulse the gate-- that would short out the power supply through the primary and probably blow up your mosfet. You have to send it pulsed rf. I don't know much about it, so look up interrupters.
Registered Member #4350
Joined: Wed Jan 18 2012, 03:44AM
Location: South Carolina
Posts: 3
"There are many ways of modulating a SSTC (solid state tesla coil), the 2 most popular being AM (amplitude modulation) and what i will call "PRF Modulation". PRF stands for pulse repitition frequency"..."Normally, a tesla coil might produce sparks at exactly 120 times per second, or in the case of a SSTC, you can choose this frequency to be just about whatever you desire. So, why not make the coil play a low C at 130.8hz? Or, why not allow it to play the entire scale? The idea is simple really, fire off sparks at a rate equal to the frequency of the musical note you want to play." --Quotes from
You can play music in more than one way. If I disconnect the feedback winding from the MOSFET gate, and use a completely separate circuit to pulse it, how would that short the primary winding? Note I am using this diagram
Registered Member #4118
Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140
When you turn on the mosfet, the power goes through the 100uH inductor, the primary, the mosfet, and back to ground. If you keep it on for the duration of a cycle of audio, the current spike will be huge because audio is such low frequency compared to what SSTCs run at. You have to send it RF when the audio signal is above a certain level, like this Do you want to play actual music or just midi notes?
Registered Member #4350
Joined: Wed Jan 18 2012, 03:44AM
Location: South Carolina
Posts: 3
Ah, so audio is just at too low of a frequency to prevent burning of the MOSFET. I was hoping to eventually play actual music. I've been doing some more digging. To my understanding, with VTTC setups, they tune the coil to such a high frequency that the human ear can't hear it, and then you can clearly hear the audio without the hissing of the coil, then use AM.
I will do some more reading and hopefully find more answers. Thanks.
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Audio Modulating SSTC question
