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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Mates wrote ...
Ahoj Honzo, I'm not very experienced in the GDT design but I always had troubles to drive GDT in such low frequencies. Do you have proper ferrite material for such a low freq? Did you check your wave forms behind the GDT, ideally using two channels osciloscope? I think that using a GDT in audio modulated plasma devices is in general big source of distortion in case you use PWM. Can't you try driving it without GDT? I mean what about to try extra power source (e.g. 12V battery works great as a testing approach) and optically coupled transistor (optoÄlen) for one of the gates? For such a low freq. this could be very nice solution. You don’t need to change so much in your driver and at least you will see if the GDT is involved in the distortion. Just an idea...
Cheers and don't forget to send us some pictures/video of the setup!
Cau Matesi, the GDT is not a problem, it is tested down to 15kHz. Yes it is the right material, high-permeability ferrite. This is not the source of distortion, as the distortion varies depending on transformer used. I'm afraid some resonances of the secondary winding distort the sound a bit, thouth a perfect driver should output clean audio no matter of transformer used.
Tobias: I use copper screws. There is little hiss with no audio, but this is perfectly OK for me as the audio ultimately overpowers it :)
Here is a vid of the prototype, the camera records audio only to 5khz and the microphone adds distortion, but it§s the best recording I can make now :) (hopefully my bandwidth doesnt get used up if it does, try again the next day... and no comments about the mess )
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think I have solved the distortion problem - I found that during the time the primary is left floating, it oscillates with its own capacitance and creates a lot of ringing. So I put a series RC damping network on the primary, which wastes a lot of heat, but gets rid of the distortion. Maybe the dissipation can be lowered, I have yet to experiment with that,, but the main thing is that the distortion is gone.
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Singing arc/plasma speaker weird problems
if it does, try again the next day... and no comments about the mess 
)