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Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
Dr Gigavolt wrote:
1. Your ground plane really isn't doing anything or acting as a ground plane. What a ground plane should do is to ensure return currents from signals on the top layer travel directly underneath the currents on the top plane (extremely small loop area and inductance). However, your ground plane is broken up with big islands, etc... So any return current on the bottom plane will be forced to travel in large loops around those traces, etc... Move the traces up to the top layer.
I'm working on improving that now. TwoSpoons did mention that before and I already start working to get a real one. Will post soon a update on that.
2. Also, if you are resonanting at 120kHz, you are NOT going to get crystal clear sound no matter what you do. You are still going to get harmonics in the arc down into the audio range at that frequency and get a "hiss" sound. It has been proven that you need to be switching at 3MHz+ to get truly clean sound.
Sad to know that. I read about crystal clear sound on Richards (timetec) youtube page.. I'm so interested to get a better design because I got complete silence on the arc without the opamp on the circuit!! With a one inch arc...
3. Finally, the DC power that is feeding your switching circuit is UTMOST CRITICAL to be as clean as possible with no ripple whatsoever. Either have a regulated DC supply with a bandwidth much greater than 20kHz, or provide enough capactiance so that ripple / droop is minimum, otherwise you are going to "hear" it in the arc.
So... based on my response to "2." I already have that! Only when I plug in the opamp I get a hiss...
If you want crystal clear sound, scrap this design and build a class-e 4MHz+ coil.
I built one recently and its fabulous. It switches at 4MHz, and the DC supply is regulated as well so the DC feeding the class-e is pristine.
I'll read about it for sure! And try to make one... I just want to finish this work before trying a complete different design. Ill try to get the best results I can. Thats my first HV work so I want to have something as close as possible to a 'final product design'.
Just for background.. I am a Mechanics Engineer, I teach mechanics on a technical school that has electronics courses as well. And I'm liking to play with electronics =P
If anyone here need some help with mechanical design, parts, CAD or whatever just ask.. And thanks for the help you already gave me so far!!
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
Here it is! What I did:
- Got the components closer, trying to keep my traces as short as possible - Tied together the ground of the HV side components and made a track of that up to the ground input pin. - Made the space between the HV and the low voltage side wider. - Got my ground plane that's not a ground plane closer to the tracks, filing some giant holes I had before. - Created a ground plane on the top layer (double sided board will be, no tracks on it)
But I have a important question now: I was reading about ground planes and found that the better points to make the connection with the other side of the board are closer to the components that are critical.
So I made my ground plane only on top of my low voltage side and made all the GND pins of those components a 'connection point' to the upper plane by soldering the pins on both sides. Did I get it right?
My work so far:
And with the top plane disabled to better understand of the tracks side:
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Ground planes are tricky things to get right. It's extremely difficult to put forward a set of rules that anyone can follow to acheive a good result, as there are just so many ways to get it wrong. But the simplest ones, in some order of importance are:
If you want a ground plane, make sure it's a plane. It is OK to have holes in it, it's not OK to have slots, it's not OK to let several holes merge together to form something like a slot.
Copper fills, if they don't result in a plane as defined above, are generally to be avoided. You'll end up with something complicated that needs lots of checking. Even if you have a ground on one side, don't random fill the other. It can lull you into a false sense of security, and doesn't really help. It can even create problems if you have an inadvertant long dangling track terminating in a decoupling cap resonating at a frequency the board uses.
If you can't get a good plane then it's far better to track individual returns. Doing individual tracks makes you think about where the current is flowing, and where it should be flowing. It's harder work up front, but you'll have done the work to understand the circuit anyway by the time the board is debugged.
A "Manhattan" layout can work extremely well, for ground, as well as power; that's EW on the top of the board and NS on the bottom, nailed together at every interection to form a grid. Note that this does not need a double sided board, as the top can be wires. It's a good way of getting good performance out of single-sided stripboard (veroboard).
Even if you have got a plane, or a fine Manhattan grid, it is not zero impedance. If an interferring current returns across a distance, it will generate a small voltage. If you have sensitive amplifier inputs straddling that distance, then they will pick up the interference. Keep such loops that you don't want coupled small and far apart.
Knowing how to connect the ground of one system to the ground of another is the next hurdle. If you think differential signals, instead of signal+ground, that may help with the mind set.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
tobias wrote ...
Here it is! What I did:
- Got the components closer, trying to keep my traces as short as possible - Tied together the ground of the HV side components and made a track of that up to the ground input pin. - Made the space between the HV and the low voltage side wider. - Got my ground plane that's not a ground plane closer to the tracks, filing some giant holes I had before. - Created a ground plane on the top layer (double sided board will be, no tracks on it)
But I have a important question now: I was reading about ground planes and found that the better points to make the connection with the other side of the board are closer to the components that are critical.
So I made my ground plane only on top of my low voltage side and made all the GND pins of those components a 'connection point' to the upper plane by soldering the pins on both sides. Did I get it right?
My work so far:
And with the top plane disabled to better understand of the tracks side:
On the outputside (right), just be sure to have your RTN traces UNDERNEATH the top layer traces. You want to avoid "loops" as much as possible as they are inductive and are proportional to the loop area made by the traces. For example, if you have a single trace going on top to a switch, then the return current trace for that switch should be directly underneath.
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
After a long time I'm back having time to do my stuff. So after designing this thing a few months ago I've built and test it last week and I want to post here my results, togheter with thanks to anyone that helped me.
The arc is completly silent with no audio input, no hiss no nothing. And the volume is pretty decent. I'm using ~62 kHz so the audio quality is not 'crystal clear', but it's impressive for sure. This is my fourth attempt to build a plasma speaker and I'm finally happy with it.
I've made a small video with my compact camera showing it: I hope you enjoy it =)
Registered Member #2385
Joined: Thu Sept 24 2009, 01:26AM
Location: Waxhaw, North Carolina (Or Charlotte near UNCC)
Posts: 26
I've heard that sharpie markers are a cheap alternative for drawing circuits on both sides of a copper clad, you just have to be really good at using a sharpie :P - the industrial ones are some what chemical resistant so you can use it to protect certain areas during etching. Something to look into. (probably not the best quality however!)
Registered Member #2385
Joined: Thu Sept 24 2009, 01:26AM
Location: Waxhaw, North Carolina (Or Charlotte near UNCC)
Posts: 26
what do you think tobias, I have to fit it within a 3x5 area (inches) Im using only DIP parts as well so I don't know is I should continue the ground plain because im afraid that some parts will accidentally ground themselves.
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
GhostlyFigures
I have to start saying that I'm not expert on this subject.
My first plasma speaker worked pretty well and the PCB I did following timetecs work (search that on youtube). But with no sound in, a hiss could be heard.. so I decided to get this noise out and the project got complicated.
As I learnd, If you don't create a good ground plane, you don't need to do it at all. So you can either simplify your design getting out the top plane, or you can go complicated and do a 'real ground plane'. The choice depends on your aims for the project.
As Steve Maurer told me, "A double-sided board layout would permit reduction of your loops that may pick up fields from your HV section. Keep your loop areas small and you will reduce some of your noise. If you need to stay with a single-sided board, then I would still try to keep your traces as short as possible and keep your loop areas small."
Reading the entire topic you will find all the good information that I used to create my PCB layout.
If you did not tried a plasma speaker design yet here it is good information: the ground plane and other complicated modifications that I did made the plasma veeery silent. But playing music the quality of the sound, even without noise, does not improves to much.
I made a entire page at about my project if you want to go the easy way! Best regards
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PCB design - Noise on Flyback driver
