John Curl's Blowtorch preamplifier part III

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#30,144
simon7000 said:
Then there was the time we were replacing the sound system at a small American football field, the guys did a final hookup in a Monday and none of the far side loudspeakers worked properly. They had tested fine on Friday.

Turns out the folks who had installed the buried cable had grounded one wire. So when the weekend storm came in the loudspeakers worked quite nicely as lightning arresters. The inductors in the crossover were quite literally blown apart.
Just in case anyone was curious as to what happens to an inductor that passes a lightning surge.
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I have seen Cat 5 blown apart/shredded, also plastic watering controller two wire line terminating/protection box blown off a wall and leaving imprint of the box lid embossed text on the opposite plasterboard wall !.
I have also seen Fulgurites after the same storm 😱.

I assume the bolt only hit one of the loudspeakers and it was the induced voltage that did in the rest.
Max don't use an umbrella when climbing the nearby tallest tree during a lightning event!
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I have read if you are out fishing and one's hair is standing on end, immediately lift anchor and GTFOOT.
Trees already act as umbrellas, why would anybody climb a tree in a storm ? :tongue:


Dan.
 
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#30,145
simon7000 said:
Probably. But it does apply to the discussion as to why one should not add inductors to power mains.
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My experiment is to keep spikes/noise on the street Neutral out of the house PE network, the house PE network is connected directly to the well earthed grounding electrode.

Where I live is low risk for lightning strikes, and in any case there is about sweet FA that can be done to prevent damage due to a direct hit.


Dan.
 
#30,147
no crosstalk here, eh?

emanations in all directions
 

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#30,148
Here's something for someone else to test: if caught outdoors and exposed in a lightning storm, no ditches to get into, squat with feet close together and arms wrapped around knees, hands not touching the ground. Voltage gradients across the ground's surface can be hundreds of volts per meter before the strike.


If you're really flexible you might want to bend your head further down and kiss your sweet butt goodby.


All good fortune,
Chris
 
#30,151
Yah, that thought came to mind long after I posted. Sadly, it is indeed trajectory..the constant battle between metabolism, pizza, and beer.

I am losing that battle.

However I am winning the tool battle. Just picked up a set of pin gauges from .011 to .250 inches in .001 inch increments (.0002" under), and a set of micrometers 0-1", 1-2", and 2-3".

No matter how good your machinery is, you can never make something of extreme precision if you cannot measure it.

On that note... Q..

By comparing amplifier output (at the terminals and also at the load) to input differentially, how deep a null has anybody achieved?
Also, what level of null is required at 1kHz to discern a time shift of 1 uSec assuming the level is dead on accurate? IOW, if the load, amp, and cable conspire to shift some frequencies of the signal by 1 uSec, can it be measured?

Ps. I know we cannot discern 1uSec, but we must be able to measure beyond our capabilities if we wish to be accurate.

Jn
 
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#30,152
Apply a sinewave input at frequency f. Use one of those zippy fast Linear Technology voltage comparator ICs (7ns prop delay) to detect zero crossings of the input. Attach oscilloscope probe for Channel A to voltage comparator IC output. It's a square wave.

Connect a second voltage comparator IC to detect zero crossings of the output. Attach oscilloscope probe for Channel B to second voltage comparator output. It's another square wave.

Measure the time delay between zero crossing at input, and zero crossing at output. Plot time delay versus frequency f. Done.
 
#30,153
Mark Johnson said:
Apply a sinewave input at frequency f. Use one of those zippy fast Linear Technology voltage comparator ICs (7ns prop delay) to detect zero crossings of the input. Attach oscilloscope probe for Channel A to voltage comparator IC output. It's a square wave.

Connect a second voltage comparator IC to detect zero crossings of the output. Attach oscilloscope probe for Channel B to second voltage comparator output. It's another square wave.

Measure the time delay between zero crossing at input, and zero crossing at output. Plot time delay versus frequency f. Done.
Click to expand...

many dual channel oscilloscopes will do all that for you and measure/display delay time.


-RNM
 
#30,155
If desired, you could also connect a phase locked loop after the voltage comparator and before the scope probe, at both input and output. The flywheel-like behavior of the PLL's VCO will attenuate cycle-to-cycle jitter, giving a more stable chan1_to_chan2 delay measurement.
 
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