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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Herr Zapp wrote ...
Austin -
For all those who have been following your tribulations with this coil, what did you do that finally got it running? Found a wrong component value, a soldering defect, or something else? In your previous update on coil performance (Sunday, May 11) you mentioned that you still were not getting any output from U4. Suddenly on July 9th the coil is working.
What changed?
Regards, Herr Zapp
The problem was that the 5V Voltage Reference IC was installed backwards. Thus, the volume envelope control circuit was not working.
Also, the random outputs you are getting could be due to noise from our audio source. If your audio source isn't "clean", which I know my computer output sources are not (static, etc...), any noise present could indeed trigger the coil.
You could try changing the hysteresis resistor across the comparator (U3) from 1Meg to 100K and see if that helps at all.
You can confirm this by scoping the output of the xenosonic (without coil connected), but connected to your audio source (no music playing) and see if you get extraneous pulses.
Registered Member #1524
Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38
I think I mayhave my 5v ref. ic installed backwards too, I was getting about 2.45vdc at the center leg but when I changed it around I got 4.45v at the center leg and .54v and the other leg and one well it is grounded.
Registered Member #1524
Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38
Austin wrote ...
K Daniel here is another photo of pin 2 at U4. everything seems to be working smoothly up to this point, however I still get nothing out of pin 3. I am going to drive down to frys and pick up another 555 timer, just in case I fried the others. Thank you for your patience with me.
500hz @ 1.4volts
I have the same trigger to the 555 timer U4 and no out put from the ic. But I don't have more then 5.75v at pin 5 ether. I'm not too sure how to get a higher voltage from U2a.
As i follow the audio signal:
input is 827mV 500hz (from a tone generator I was able to down load)
out from U1a-1 is 7.82 p-p
in at U1b-5 is 6v p-p
out at U1b-7 5.96v p-p
in at U2a-3 6.08v rms
out from U2a is 6.48 rms
meter reading across R10 is 5.75vdc max as I have tested and examined the monostable function of the 555 timer my battery voltage has dropped to around 3.5 vdc at U4-5.
But it looks like my troubles are after the op-amp and comp U2a with a low output voltage. I'm not sure how to address this low voltage. Can anyone see where I'm going wrong. Im a little confused what to expect out of the second stage of op-amp U1.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Okay, so the function of U2A is simply a buffer. The same voltage going in should be coming out. Which it appears it does.
Now, at the output, you have a voltage divider with R9 / R10. This is one of those circuits added in just case you might need it. In most cases, this isn't needed. I'd remove R9 and R10 and then put like a 10-100 ohm resistor in place of R9. Just something to act as a short although the resistance really isn't too critical.
Also, this volume foldback circuit isn't necessary. You can simply disable it by removing R9 and R10 and C10 completely.
Also, check to ensure your trigger voltage into the 555 meets the specs. You should have a 1000pF capacitor for C14. If C14 is too large, you won't get a low enough voltage to trigger the 555.
U1B is your volume duty foldback control. Its basically a low pass filter and is a simple way to control duty cycle as frequency increases. Basically, for low frequencies, the input and output voltage of this op-amp should be the same as its before the cut-off frequency of the filter. But as you increase in frequency, you want to maintain a constant duty cycle otherwise you'll blow your coil skyhigh. So, as frequency increases, the amplitude will start decreasing at the output of this op-amp, which is then fed into the control pin of the 555 to act as a voltage feedback control to reduce pulsewidth.
I've been meaning to update the manual, but just haven't had time to get to it lately.
Registered Member #1524
Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38
Dr. GigaVolt wrote ...
Okay, so the function of U2A is simply a buffer. The same voltage going in should be coming out. Which it appears it does.
Now, at the output, you have a voltage divider with R9 / R10. This is one of those circuits added in just case you might need it. In most cases, this isn't needed. I'd remove R9 and R10 and then put like a 10-100 ohm resistor in place of R9. Just something to act as a short although the resistance really isn't too critical.
Also, this volume foldback circuit isn't necessary. You can simply disable it by removing R9 and R10 and C10 completely.
Also, check to ensure your trigger voltage into the 555 meets the specs. You should have a 1000pF capacitor for C14. If C14 is too large, you won't get a low enough voltage to trigger the 555.
U1B is your volume duty foldback control. Its basically a low pass filter and is a simple way to control duty cycle as frequency increases. Basically, for low frequencies, the input and output voltage of this op-amp should be the same as its before the cut-off frequency of the filter. But as you increase in frequency, you want to maintain a constant duty cycle otherwise you'll blow your coil skyhigh. So, as frequency increases, the amplitude will start decreasing at the output of this op-amp, which is then fed into the control pin of the 555 to act as a voltage feedback control to reduce pulsewidth.
I've been meaning to update the manual, but just haven't had time to get to it lately.
You also mentioned looking at the trigger signal comparing it to spec. From what I picked up from the link on the 555 timer the trigger is about 1/3 of pin 8 the V+ input. and a negative going pulse is detected the 555 timer executes the RS pulse determined by R18+R19 and C15.
I do not understand why my trigger negative going pulse needed to reach such a low voltage 788mV in order to get output from the U4 timer.
As long as the pulse width is not over 200us I should still be ok on the drsstc igbts. So I will continue on and see what else is preventing me from getting modulator output.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Yeah, something doesn't sound right. Do you have the diodes oriented correctly in that trigger path? You should be getting almost the Vcc voltage (9V) for your high on the trigger and then dipping down to below 1/3 Vcc. Also, a larger cap should make the valleys not as low as it takes longer to discharge the cap during the trigger pulses. I'd double check your components, in that area.
Almost 99.99% of the problems people have had so far have been incorrectly installed components.
Registered Member #1524
Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38
After removing one leg at a time of every component on the board and changing the C14 cap from a 1000pf to a 4700pf I fing every thing operational. The high freq fold back and PW based cut off all work perfect. I was using the bar option from the display and that was really killing the battery. I have since started using a wall wart for testing and that made things easy as the voltage would remain the same as I followed the inputs through the board.
Next thing I would life to do is make an optical input circuit so I can feel a little safer connecting my laptop.
Registered Member #1524
Joined: Sun Jun 08 2008, 05:25PM
Location: Grand Junction, Colorado
Posts: 38
Well I am using a few applications on my mac to drive the xenosonic modulator and I am more interested in saving the computer from the tesla plus I have several other optical outputs in audio side. Not much adjustment is required after the modulator is in use and operational. I was even thinking about mounting it on the coil in a copper box and using the logic power connection to power the xenosonic board.
As far as the uv meter I just switched it to dot per the instructions.
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XenoSonic Construction / Troubleshooting
