Stereo Audio Modulator for my SSTC's

This is my new battery powered audio modulator (interrupter). It has 2 channels (L&R) for 2 Teslacoils. It is about half the size of my previous version and uses 3 AAA batteries.

The old version needed a external positive and negative power supply and had only 1 channel. It also had to be configured manually. This new version is completely plug and play, the only tweaking you need to do is the input audio level (volume) of your audio source. Here you can see the completed design and a picture to compare it with the old one.

What this device basically does is compare the audio signal with a reference voltage (8mV). It turns the teslacoil on if the signal is higher than the reference and off when it gets lower. This effectively ruins the sound and provides a very crude (but effective) way of modulation. Only the lowest notes in a signal will display correctly. I made the design on a PCB to shield all the traces and to make it fit in a standard Hammond enclosure. It should be able to run about 70Hrs on one set of batteries (I'm not sure if I ever have to replace them). You can download the construction files (schematics, cam, bom etc.).

It has an input band pass filter wich only passes all frequencies from 20Hz to 20Khz, which automatically limits the duty cycle to 50%. It has only 1 drawback, I intended to use it with standard RCA (like the old one), but it needs a little higher amplitude to work correctly. So I just hooked it up to the headphone output of my PC speakers. This works fine. A standard mp3 player probably won’t do though...

The output is short circuit protected (the series resistor for the optocoupler is placed on the board instead of inside the teslacoil) you can also hook it up to a headphone or small speaker to check the functionality.

Here are some pictures of the inside:

And here is a short movie demonstrating the modulator on my V2.0 AMSSTC with my favorite song of Duke Nukem:

I was actually just playing a modified MIDI file on my laptop, I removed all the chimes and drums to make the sound more clear.

One more thing I found out while running 2 Teslacoils at the same time is that the feedback of each coil disrupts the other. This unfortunately destroyed my V3.0 (because it has a lower resonance frequency than the 2.0). Next time I will put them further apart. This is why I shot this video with V2.0. My next teslacoil (V4.0) will be digitally controlled, so it won't have this problem.

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