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Plasma Speaker - help

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yoni

Wed May 26 2010, 02:13PM

Registered Member #2366 Joined: Tue Sept 15 2009, 10:35AM
Location:
Posts: 14

hello guys.
i am working over a month on bulding a plasma speaker using a 555 timer to create a pwm modulation.
i will add my scheme so you guys can understand more what i did.
i have some questions:
first i heard the some guys can drive the flayback with 20 khz and more.. is that the sampeling rate? if i sample high i cant hear a thing i think this is because we can hear untill 20khz(in my case 15.. u think i am going too much to clubs haha ;) ) so how can people drive in such high freq and hear somthing?
second the arc is veryyyyyyyyyy veryyyyyyyyyy small..
if i just drive it with a clean 12 ptp rect signal it is much more high but still small.
thank you all!

Yoni Danzig
]plasma_speaker.pdf[/file]

Renesis

Wed May 26 2010, 02:50PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Some ssts's are even driven beyond the MHz mark, and it is true that when unmodulated they are as silent as a winter night. But by varying the power output, and thus the heat of the arc, at an audible frequecy, say 2kHz, one can make the 1MHz coil play a 2kHz note.

PWM or Pulse Width Modulation is a simpler form of modulation which recreates the same effect. By varying the amount of time the arc is on vs the time it is off (its duty cycle) at high frequencies, one can alter the coils average output and approximately reproduce any waveform.

yoni

Wed May 26 2010, 03:29PM

Registered Member #2366 Joined: Tue Sept 15 2009, 10:35AM
Location:
Posts: 14

thank you.. so if i understand the duty cycle is what affactiong on the hearing freq.
if so, what will give a high freq output signal? a low duty cycle or a high duty cycle?
i think it's more logic that a high dc(most of the time "on" - more anargy).. but if i remember well (i tryed that on the lab) a low dc caused a a higher freq. mayb it is because a low dc is more "alternating" then a high dc => this changing input current creates a changing magnetic field =>more transformer EMF ( d Î¦B / d t). am i right?
btw did you see my circuit? mayb you can help me with my second question (vert short arc) thank you.

Renesis

Wed May 26 2010, 05:39PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

yoni wrote ...

thank you.. so if i understand the duty cycle is what affactiong on the hearing freq.
if so, what will give a high freq output signal? a low duty cycle or a high duty cycle?
i think it's more logic that a high dc(most of the time "on" - more anargy).. but if i remember well (i tryed that on the lab) a low dc caused a a higher freq. mayb it is because a low dc is more "alternating" then a high dc => this changing input current creates a changing magnetic field =>more transformer EMF ( d Î¦B / d t). am i right?
btw did you see my circuit? mayb you can help me with my second question (vert short arc) thank you.

You are slightly misunderstanding. In a musical amplifier a high dutycycle will mean a high voltage level output, and a low dutycycle will mean a low voltage level output. An analog audio signal consists of voltage waves, and so to reproduce this by PWM the duty cycle must be constantly altered, even if you are playing a pure, constant note.

See how the green PWM signal alters duty cycle to mimic the red sinusoidal wave? When the red signal peaks the duty cycle is almost 100%, and at the bottom it is almost 0%.

Im sorry i cant help you with your other question, but i bet there are others here who can.

Some brainfood:

Sulaiman

Wed May 26 2010, 06:53PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

oops! second time I've misunderstood a post and deleted mine...
hope it's not an early 'senior moment' ..sorry

yoni

Wed May 26 2010, 07:54PM

Registered Member #2366 Joined: Tue Sept 15 2009, 10:35AM
Location:
Posts: 14

Thank you Renesis. :) things are much more clear now.
still i need help with my circuit.
hope someone will help me :)

GhostNull

Thu May 27 2010, 11:12AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

as the wise Mads Barnkob said:

Mads Barnkob wrote ...

Please do yourself a favor and read the forum rules before posting again, do your own research, experiment and ask questions that show insight, this will get you far :)

It is against the forum rules [

] to ask for specific schematics, search google for "audio modulated flyback" or "singing arc" etc and you will find alot of schematics.

look through previous posts, there is lots of plasma speaker schematics and discussion on the topic. I'm not sure you understand the principles of plasma speakers. I suggest you do some of your own reascearch into the topic and comeback and tell us what you have learnt.
Here are some pointers to get you started:

hope this helps

Ghost

Thu Jun 10 2010, 01:18PM

Registered Member #2911 Joined: Thu Jun 10 2010, 12:12PM
Location:
Posts: 2

I allso recently made me a Plasma speaker. Every thing worked fine but I had 1 problem. My mosfet keep on heating up.

My plasma worked good, but sometimes it had a very high pitch. Sometimes so high, that it hurt my ears.

Well the speaker itself didnt worked so good. There did came sound out of it, but the sound wern't very clear and u can only heard it if you were like 10 cm from the plasma. I have 2 difrent flybacks i tried and both of them failed.

I added my 2 circuits. The first circuit I founded on some or other. The second circuit is a modified curcuit that I modified to prevent the mosfet of heating up so much.

Ghost

Thu Jun 10 2010, 01:22PM

Registered Member #2911 Joined: Thu Jun 10 2010, 12:12PM
Location:
Posts: 2

Sorry. I don't know why the circuirs didnt show at the post before. Here are the circuits.

1276176086 2911 FT89849 Audiomodulatedflyback555irfp250

1276176086 2911 FT89849 Audiomodulatedflyback555irfp2502

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