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Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
indiana -
When posting scope shots, please provide the background information required to understand what's going on. On the latest shots, where are the scope probe tip and ground connected?
Since you are just getting familiarized with your new scope & this circuit, why not spend some time poking around in the circuit with your scope, looking at the electrical signals at each stage? First, take a quick look with the board not powered up at all, and make sure that you are not picking up noise from some other source. Then, starting at the DC power supply section, make sure that the DC is clean, and then work your way towards the GDTs.
Also, you mention that you are running the bridge at up to 400V. During this testing, how is the bridge "loaded"? Dummy resistive load? Actual Tesla coil primary, with no secondary present? Or primary and secondary both present?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
indiana wrote ...
Herr Zapp, thanks for the advice. I am going to go through the circuit and do just that.
For those tests up to 400V there was a dummy resistive load of a light bulb.
Things are looking good on the build. Still some work to do, but little by little it's getting there.
I have it set up driving a secondary coil now. There are no significant heat issues all the way up to 110V input from the variac.
I have not put a toroid on the top, as my hope was to get one concentrated spark which was audio modulated for an upcoming experiment.
I'm hoping to get one clean stable and powerful spark to ground with a clean audio signal.
My test breakout point is simply a piece of wire attached to the top of the secondary.
With this configuration, I get at 110V input about a 3/4 inch spark which fans out to about 1/2 inch width.
This is when tuned to its maximum.
When I play an audio signal through it I can just BARELY hear it. It's there, but so subtle.
I see in Dan's videos a much more intense spark output, and a much much higher sound volume.
Would that larger output be caused solely because of the toroid and breakout point configuration?
Or are there possibly other issues going on?
When I bring a ground wire close I get one controlled spark maxing out at about 1 1/4 inches.
Thanks again all,
Lucas
You should be using a toroid. This will help lower the fres of the system and keep losses to a minimum.
Regarding audio, your audio source is too low. You can adjust the bias / level of audio using the pots on the board per the instructions. Also, if you're not getting much arc, you're probably not in tune. Note, you need to retune every time you use your coil.
Registered Member #2009
Joined: Tue Mar 03 2009, 07:07PM
Location:
Posts: 43
Thanks for the reply Dr.
As for the fres of the system, i've tested the resonance by putting a signal through the coil and picking it up with my oscope.
I found the resonant frequency of the coil to be about 106khz. Do I win anything particularly by keeping my fres lower than that?
My goal is to get one streamer to ground, playing music.
I'm certain that it is as in tune as it can get too.
I start with the measured resonant frequency, apply voltage to get a spark going, and adjust moving past the point of peak resonance in both directions, then moving back to the center where the spark is maximized.
I changed to a 2Vpp cd player, adjusted the bias all the way up and all the way down.
In the center somewhere it seems to work best. Only there can I hear anything at all, and there is where I get the very faint weak sound I was talking about.
You can just barely tell there's music there, and you can't make out what music it is. Just barely a beat.
What could be happening here?
The coil's resonant frequency is lower than I expected it to be, but I tested all the way up through 1Mhz and only found resonance at 106K.
That said, could it have something to do with the number of turns on the primary?
Edit: There's approximately 1400 turns of 26AWG magnet wire on the secondary. 18.25" High, 3.25" Diameter
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
[quote] Thanks for the reply Dr.
As for the fres of the system, i've tested the resonance by putting a signal through the coil and picking it up with my oscope.
I found the resonant frequency of the coil to be about 106khz. Do I win anything particularly by keeping my fres lower than that? [/quote]
Thats pretty low. So thats perfectly okay. A small top load is good anyways to protect the secondary from inadvertent arcing.
wrote ...
My goal is to get one streamer to ground, playing music.
You don't want it to arc to ground. You want it to arc to air for best results. I found that arcing to a grounded terminal or stick simply adds a lot of distortion to the audio. You get less hiss than arcing to air, but the audio quality is greatly diminished. Also, note that if you pull an arc with an object you *are* detuning it, so you must retune if you set-up anything permanent as far as arcing to an object.
I'm certain that it is as in tune as it can get too.
wrote ...
I start with the measured resonant frequency, apply voltage to get a spark going, and adjust moving past the point of peak resonance in both directions, then moving back to the center where the spark is maximized.
This should work fine. Note you can also tune at lower power using a flourescent bulb.
wrote ...
I changed to a 2Vpp cd player, adjusted the bias all the way up and all the way down.
In the center somewhere it seems to work best. Only there can I hear anything at all, and there is where I get the very faint weak sound I was talking about.
Sounds like the audio source isn't strong enough or the gain not set high enough. Also, your bias needs to be set correctly as well. It should be set so the duty cycle is 25% with no audio ,and then 50% during full modulation.
wrote ...
That said, could it have something to do with the number of turns on the primary?
Yes, you can play with both number of turns and coupling. Coupling can be varied by lowering and raising the primary with respect to the secondary.
Registered Member #2009
Joined: Tue Mar 03 2009, 07:07PM
Location:
Posts: 43
Okay.
I've been playing around with it some more, changing the coupling, etc. I've managed to get a bit more spark from it. And, with a little more fiddling I think I can make it do even better.
As far as the signal not being strong enough, what are you using to send signal to your board, Dr.?
Would it be appropriate to feed the output from a cd player or computer sound card into a microphone preamp, and then into the plasmasonic board from there?
That would also give me a decent eq adjustment.
EDIT: I've done some research on preamps, and the ouput gain is a voltage control. you can vary the voltage from about 0 to 28V pp on most models. Since the CD player is already a 2V pp source, how can I get more gain?
When I turn the gain clockwise, the signal falls off to almost nothing. When I turn it all the way counter clockwise I get the results I've mentioned in my last couple posts.
And, let me make sure I'm setting the duty cycle properly. When you say 25% duty cycle, I would measure off TP22, and set the pulses for 25% on time, 75% off with no signal input.
Is this correct?
And, when I have my scope attached to TP22 and am sending a modulating signal through, should I notice a difference in the waveforms at that test point?
I presume so, but it doesn't appear to be making much difference at present.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I use the RCA output (just one channel) of a CD player. And i don't believe there is much difference between most CD players as i've used quite a number of them never making adjustments between them.
I don't think there is any need to use a pre-amp - a CD player has more than enough drive. It sounds like you just have a biasing / tuning issue with your coil. Check your pots. Pots are notorious for failing.
Try another CD player or DVD player. Also, you are following the notes on the schematic as far as the input filter goes right?
Registered Member #2009
Joined: Tue Mar 03 2009, 07:07PM
Location:
Posts: 43
looking around for a different cd player now. Pretty sure I'm following the input filter instructions correctly...
There's an inconsistency in the notes versus the schematic...
On the notes it says to use a 0 ohm jumper for R21 and R23. However, on the schematic, it's R22 and R23 which say "see note 1" and there's a 10k resistor for R21.
I have it set up as per the schematic.
I've checked the pots, and they seem to be fine. It's a bit of a mystery at present.
Registered Member #2009
Joined: Tue Mar 03 2009, 07:07PM
Location:
Posts: 43
Hi again all,
After having a job to do I'm back on the mission of the Plasmasonic.
Today, new weirdness from the front lines.
It hasn't been moved since I last was working on it. Now, however, I turn it on (just the low voltage side) and the IC's are heating up like crazy. Fast.
I'm afraid to even test it, as they just get HOT! I've checked all of the connections, taken the power off the board and checked the voltage on the transformer leads, I get 13.2V + off both leads.
Thing is, it's connected the same way it always was, and this is the first time there've been issues.
???
The waveforms look different too. They're ramping up and down, and the weird ringing seems to have gone? I have no idea what could have brought about the change. It's just been sitting there! WTF?
Any ideas? I was all excited after coupling the coil more closely. Was hoping to fire it up and have it just WORK.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Do you have a fan on the gate drivers? As the coil is operating at 100% duty (vs. low duty in DRSSTCs), and the gate drivers are driving (4) big MOSFETs, they will get hot. If you don't cool them, they could overheat and be damaged. I suspect you may have blown one up and thats why its heating excessively now.
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Plasmasonic II build
