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Old 11th June 2009, 11:10 PM   #51
cbdb is offline cbdb  Canada
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Don't worry, it's my fault: I spoke wrong language when used visual and audial predicates. Now I know how to explain you my feelings about amplifier distortions: where they are coming from, how do they go, and how to approach the solution of the problem.
Not your fault, Iwasnt thinking. Look forward to more "great amp" thread, see you over there later. now I have to pick up kid and finish this bad movie!
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Old 12th June 2009, 06:11 AM   #52
1audio is offline 1audio  United States
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To measure the current make a current transformer with a ferrite donut and a few turns on the secondary loaded with a resistor. Calibrate it with an audio generator. Should be good from 1 KHz to something very high and well insulated. Use it on the low side for safety.

The ionized air is the Ionovac / Hill Plasmatronics approach. Dr. Hill explained that its a thermal-acoustic transducer actually. He described plans to me make one working down to 100 Hz that would be enormous. Never happened.

The length of the spark may create a phase difference between the ends but the discharge will be well faster than the speed of sound across the gap. I would expect that it would have a cylindrical radiation pattern and should be pretty planar when parallel to the gap.

The magnetic field might register in the output if the shielding isn't effective. Could be tested by discharging into a shorted gap.
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Old 12th June 2009, 07:52 AM   #53
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Does it have to be a spark?

Can a similar short impulse be generated by exploding a short length of fuse wire by discharging a large capacitor through the wire?
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Old 12th June 2009, 04:06 PM   #54
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Quote:
Originally posted by Ouroboros
Does it have to be a spark?

Can a similar short impulse be generated by exploding a short length of fuse wire by discharging a large capacitor through the wire?
Yes, and pistol shots have been used too. It's just that it's nice to not have to reload.

I picked an old electronic starter for a residential stove off of a discarded one the other day. This looks like it could be rigged to trigger automatically.
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Old 13th June 2009, 06:34 AM   #55
1audio is offline 1audio  United States
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We have been talking about a spark in free space. What about a surface gap spark plug flush mounted on a flat plane? The spark on the surface won't have a reflection, nothing can vibrate with the energy, etc.

The frequency range of interest is above 1 KHz so a 1M diameter disk or minimum rectangle should be enough to get good info.
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Old 13th June 2009, 03:03 PM   #56
KSTR is offline KSTR  Germany
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Demian,

Excellent idea, it seems... like on a piece of clean(!) sheet of glass or other suitable material? This would also lessen the impact from the mechanical noise from actuating a piezo stack when we feed the gap from "behind" that pane.

- Klaus
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Old 13th June 2009, 05:24 PM   #57
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Click the image to open in full size.Click the image to open in full size.

FWIW, I experimented with spark recordings about 3 years ago.
The device on the left was made with a surplus 7.5 kV "air ionizer"
It was a form of spark gap relaxation oscillator.
The voltage would build up on the caps until a spark occurred and the process would repeat about once a second.
Very loud but -- the recordings were useless for getting a response curve.

The device on the right was a line powered dual gas stove igniter.
I wired the output coils in series.
This works by charging a cap and then discharging it through a primary coil. Repeats at about once a second.
I got very consistant sparks and was able to get useful response curves from the spark recordings.

Cheers.

ZAP
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