A.M SSTC / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

A.M SSTC

1 2 next

Move Thread

LAN_403

f0rd

Fri Jan 04 2008, 06:24AM

Registered Member #1209 Joined: Fri Jan 04 2008, 06:07AM
Location: England
Posts: 2

Afternoon, right first things first, I am not a coiler, nor am I an electrician.

But I am doing a project at present on plasma speakers and high quality audio reproduction, I have already covered the early for runners such as the Ionophone, Plasmatronics et al.

And this has led me onto Audio-Modulated Tesla Coils, I have been doing some research so far onto modulating the SSTC, thatâ€™s how I found this forum from stevehvâ€™s blog.

So far I have got â€˜Amplitude Modulationâ€™ and â€˜Pulse Repetition Frequency Modulationâ€™, of course did the went to wikipedia to see what other forms of analog modulation there is.

Essentially what I am asking, what other methods of audio modulating an SSTC have been implemented that you, or can be used, advantages/disadvantages?

Any information or point in the right direction would be grateful.

Thanks

Dalus

Fri Jan 04 2008, 11:05AM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

I'm currently trying to get a drsstc working with FM modulation. It's basically a class-D amplifier. The feedback signal goes trough an integrator to get the triangle reference waveform. This wave gets FM modulated by using a high speed comparator. This FM modualted signal is fed to the gate drive circuit which drive a halfbridge.

HV Enthusiast

Fri Jan 04 2008, 11:20AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Well, the most popular methods are AM modulation and PWM (pulse width) modulation with PWM modulation being the most common and efficient.

AM modulation is actually the best, especially if done on the high side (modulating the power supply) as it will provide the best sound quality. But PWM modulation (i.e. modulating the gate) is best due to ease and high efficiency, albeit at a degrade in audio quality.

Dalus wrote ...

I'm currently trying to get a drsstc working with FM modulation. It's basically a class-D amplifier. The feedback signal goes trough an integrator to get the triangle reference waveform. This wave gets FM modulated by using a high speed comparator. This FM modualted signal is fed to the gate drive circuit which drive a halfbridge.

Not sure how FM modulation would work as you would effectively be detuning the coil during operation. However, it sounds from what you are describing is not FM modulation, but just PWM modulation.

Dalus

Fri Jan 04 2008, 03:32PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

PWM modulation causes fm modulation

'This is also an FM, or frequency-modulated system -- the varying pulse-width translates into a varying frequency. And it is the core principle of most Class-D switching power amplifiers. The analog input is converted into a variable pulse-width stream used to turn-on the output switching transistors. The analog output voltage is simply the average of the on-times of the positive and negative outputs. Pretty amazing stuff from a simple comparator with a triangle waveform reference.'

I found it in an article at

HV Enthusiast

Fri Jan 04 2008, 05:50PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Dalus wrote ...

PWM modulation causes fm modulation

'This is also an FM, or frequency-modulated system -- the varying pulse-width translates into a varying frequency. And it is the core principle of most Class-D switching power amplifiers. The analog input is converted into a variable pulse-width stream used to turn-on the output switching transistors. The analog output voltage is simply the average of the on-times of the positive and negative outputs. Pretty amazing stuff from a simple comparator with a triangle waveform reference.'

I found it in an article at

Uh, no. PWM does not frequency modulate the signal. PWM merely varies the pulsewidth of the carrier signal. Input an analog single into the comparator and compare with a sawtooth, and you'll get out a varying pulsewidth signal (of the SAME frequency) vs. the amplitude of the original sampled analog signal.

FM modulation is completely different. Its basically where you are modulating the carrier frequency.

See article below:

http://en.wikipedia.org/wiki/Frequency_modulation

Marko

Fri Jan 04 2008, 08:10PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Steve used FM modulation on PLL:

FM modulation of input causes AM modulation of coil output.

CT2

Fri Jan 04 2008, 08:59PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

I used Steves PLL for an audio modulated coil. It works pretty good, although I haven't tried any other types so I don't have much to compare too. I have a video of it on youtube;

. It is fairly clear (a little distortion, depends how high you have the volume cranked on the input signal, an ipod) and it is very loud considering how small the coil is, I can hear it on the top level of my house and the coil is in the basement (3 levels).

teravolt

Sat Jan 05 2008, 04:12AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

that paper is interesting and I atempted to repair one of those 2000w power audio bass amps. The method they use is to combine PWM with the audio input to charge a set of caps baisicly. the problem is that the load is fixed and not dynamic like a DRSSTC. If a DRSSTC load is used it mite take some clever electronics to enshure the cap voltage tracks with a audio input

Dalus

Sat Jan 05 2008, 12:20PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

teravolt wrote ...

that paper is interesting and I atempted to repair one of those 2000w power audio bass amps. The method they use is to combine PWM with the audio input to charge a set of caps baisicly. the problem is that the load is fixed and not dynamic like a DRSSTC. If a DRSSTC load is used it mite take some clever electronics to enshure the cap voltage tracks with a audio input

Could you post the circuit diagram of that amplifier, I would like to try as many methods of audio modulation. I'm still in the breadboarding phase so it will be fairly easy to swap things around. And hear what it sounds like.

f0rd

Sat Jan 05 2008, 03:23PM

Registered Member #1209 Joined: Fri Jan 04 2008, 06:07AM
Location: England
Posts: 2

Thanks for the help so far guys, another question MOSFETs vs Spark Gaps, I take it MOSFETs are preferred due to spark gaps creating quite a bit RFI and are noisy?

And from what I am reading, am I correct in stating SSTC don't need a large transformer? Well large as in 15 kV.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob