Seventh Circle Audio success

standard psu

Power supplies are not a cheap addition to an item, especially in something like sca's kits. A power supply has a lot to do with the amount of noise on a circuit and should be expensive or else its probably crappy. And the fact that you can chain up eight units to one supply is great.

So why build one? if you just want to learn about something, you could build a power supply for a royer tube mod.
 
well, i asked about the soldering thing, and he says he's quite good with it...

MY biggest problem is that i'm shaky...and i don't see shakiness and precision soldering working out for the best
 
I'll agree with sonic that any kit that is based on thru hole parts will not be difficult to build with a proper soldering iron and some decent solder (as any kit should be). I would get a cheaper kit to practice with first since the SCA kit does have a number of expensive parts that you don't want to mess up practicing your solder skills on.

Power supplies are not a cheap addition to an item, especially in something like sca's kits. A power supply has a lot to do with the amount of noise on a circuit and should be expensive or else its probably crappy. And the fact that you can chain up eight units to one supply is great.
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very, very true. I spent the better part of this summer designing and building linear power supplies for mixed analog and digital circuits and its a lot math, going over spec sheets, testing stuff on the bench but the results can be very impressive (Noise floor inproved from about -40 dB to about -90 dB!) but if it was between doing all the work myself or buying something that someone already did the work on, i would always go with the latter.
 
eh, not exactly

altitude909 said:
5 mA is not a lot of current, you would probably need hundreds of thousands of volts for this to be lethal (ala stun gun)
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Last I remember 0.75 mA was about prime to kill you when passing through your heart. This will upset the normal pacemaker cells and you heart will fibulate.

Voltage is important in that it is required to overcome your skin resistance (which than allows the current to flow through you). You might think that 12 volts is too low of a voltage to be a problem but let me suggest that you do not soak your hands in salt water and then grab the terminals of a car battery.

The current that will flow through you is defined by ohms law: I = E/R So with 1600 ohms through the body resistance, 12 volts will pass .75 mA (12/1600=0.0075) Checking by stabing myself with my multimeter probes gave 16k ohms So I could expect 0.075 ma from 12 volts.

Gotta try that next time I have an open cut or two.

Once skin resistance is overcome it gets interesting. THe current flow causes a further breakdown in the barriers along the path. This leads to lower resistance and thus more current flow.

The real killer of 120 (240) volts is not so much defibulation but rather the burning of the tissue along the paths of current flow. Large currents through you heart cause the muscle to contract hard and then to release when the current is removec. This does not really kill too often. But the cooking along the way and in the heart tissue does. You are fried!

Current kills, voltage overcomes skin resistance.
 
When I was a child

I was in about 3rd grade when I started working on AC/DC radios (now they were dangerious!) In the summer between 4th and 5th grade I aquired a Deforest electronic kit. What an education. This kit has hundreds of bakelite squares with resistors, capacitors and tube sockets and all the wire you needed to hook them up. Along with a 300v power supply (plus filament voltages) This was the electronics teaching kit of the day.

The docs were wonderful. They showed how to connect it all to make am radios, fm radios, amps, am transmitters and fm transmitters (both freq and phase modulation but not sterio). I built them all. The more complex projects were spread out over a 3 by 4 foot area.

Very cool and very instructional.

So my point is that here I was at what 12 years old working with a 300v, 100 mA supply on an open wired project that took up square feet. Did I get shocked? You bet, more than once. But even then I knew not to hold on to a water pipe at the same time I was putting my hand in the circuit.

Unless things have changes 16 is plenty old enough.

Best advise I've ever had? Put your left hand in your pocket when reaching into some equipment. The next best is to hold the power plug in your left hand when working on something.
 
Ventricular fibrillation - A low-voltage (110 to 220 V), 50 or 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA. With DC, 300 to 500 mA is required.
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0.75 mA is nothing unless connected directly to your heart. Kits for kids powered on batteries and tested for safety is one thing, tinkering around with mains voltages and currents is another.

So my point is that here I was at what 12 years old working with a 300v, 100 mA
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Thats still only 30 watts and i'm sure it was fused for shorts, a wall socket is capable of putting out 1725 watts before blowing a breaker.


Anyway..

My whole point here is to be careful, if you dont know what is dangerous and whats not, find out the easy way, look it up, take a class, ask someone. The hard way is not a good way to find out how to hook up high voltage devices
 
Sorry no fuse

That was from the top of my head.... To quote a wiki: http://en.wikipedia.org/wiki/Electric_shock

- A low-voltage (110 to 220 V), 50 or 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA. With DC, 300 to 500 mA is required. If the current has a direct pathway to the heart (e.g., via a cardiac catheter or other electrodes), a much lower current of less than 1 mA, (AC or DC) can cause fibrillation. Fibrillations are usually lethal because all the heart muscle cells move independently. Above 200mA, muscle contractions are so strong that the heart muscles cannot move at all.

And sorry no fuse in that supply....
 
Ever read that chain email "It's a miracle any of us survived" or something like that? It talks about all the things we did as kids that should have killed us, given all the hysterical laws and warnings protecting us from such madness today. To be sure, electricity is potentially dangerous, but so is driving a car.
 
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