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[moved] Audio Modulation Circuit Problem (was "What am I doing wrong here?")

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Ken M.

Mon Apr 09 2007, 05:21PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Well after getting my SSTC to run I decided I would try to switch some parts to allow more versatility and so I could try some ideas namely Interuptors and most of all Audio modulation. Right no it works using Steve Wards Micro SSTC driver with a 4429 instead of a 4420, removed 1 resistor and subbed another resistor for a 12turn trim pot. I decided I would try to use an interupt to see how it would effect me coil...well after setting the 555 to Fres of the coil I swapped out the 4429 for UCC37322, and tied the enable pin high so it would act like 4429. However the coil doesn't resonate anymore, Anyone have any idea why it doesn't work?

Edit: Changed all the DRSSTC to just SSTC upon correction of TC description.

Steve Ward

Tue Apr 10 2007, 01:26AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

The 4429 is an inverting driver and is generally NOT a good idea for the micro *SSTC* (youve been calling it a DRSSTC, and its technically not). If things fail to oscillate, it will just hold the MOSFET ON, and short out the power supply. The 37322 is a NON-inverting driver. So to make it work with the new non-inverting driver, then you need to swap your primary connections.

Ken M.

Tue Apr 10 2007, 07:30AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Well I was successfully able to exchange some parts and turn in into kind of a Class E, yet again simmilar to Steves. Now an odd situation has arisen, It will only resonate if my had in between the antenna and the coil, where as the old system let me just start it up and it would resonate, any ideas on how to get it to esonate at all times while power is applied, without my hands being near the antenna?

Brett Miller

Tue Apr 10 2007, 03:35PM

Registered Member #593 Joined: Tue Mar 20 2007, 12:32AM
Location:
Posts: 50

WhiteArc,

I built that project as my introduction to solid state tesla coiling as well (now I am working on designing my 3rd SSTC -- possibly a dual resonant)...it sounds like placing your hand near the antenna is causing your body to become an extention of your antenna and enabling it to more easily "see" the e-field of your MicroSSTC. You may want to try going with a longer antenna. Some like 12" or so.

-Brett

Ken M.

Wed Apr 11 2007, 02:44AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Thanks for the suggestion Brett, I tried it and it didn't work

so I went back to the same antenna I was using Heres the wayI have it set up with a 555 timer and it works just needs fine tuning from time to time.

But heres what I'm trying to do

And I have the unmodulated output to almost exactly the same as the out put waveform to waveform with the 55t imer circuit still using the 4429, and it doesn't even come close to resonating.

I was even thinking of combining the outputs at the input of the 4429 but he waveform gets all shaky. I'm unable to figure out why it won't work.

Ken M.

Sun Apr 15 2007, 03:48AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Ok got my coil aduio modulated thanks to Mike for linking his set up to modulate the signal, Brett for suggesting a longer antenna, all the test equipment i had connect (O-scope and Amp meter) where causing some resonate issues, and Steve for the primary swap suggestion and correcting me about the DRSSTC thing.

Heres the ultra simple schematic. (Hope noone minds me photoshopping the images together

)

Experimentonomen

Mon Aug 06 2007, 09:28AM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

Wouldent it be better to PWM the enable pin, rather than sending analog signals to it ?

Dalus

Mon Aug 06 2007, 10:25AM

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

That's asking for the hard way, surely it would be better to pwm the enable pin and it would sound better, but this will work good enough for most people.

Steve Conner

Mon Aug 06 2007, 01:20PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The transistor amplifier there is configured for such high gain that it will be more or less a zero-crossing detector. So I doubt the enable pin will be getting too much of an "analog" signal.

It also won't be too thermally stable. Bet you have to keep tweaking that 50K pot?

Marko

Mon Aug 06 2007, 01:31PM

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

Even if it did get analog signal I don't see what good would it do. It would still behave as a schmitt trigger of sorts.

If you want audio modulation, best options for now seem to be PLL or SG3525, a half or full bridge with some *really* good free wheeling diodes and relatively low operating frequency, <200kHz.

Single transistor circuit like this is rather a poor solution. Transistor will see very high voltage while it is off, burn lots of energy in avalanching and die after a while if it's not cooled well
enough.

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