Dangerous Current?

[MR.MAGOO]

Being a total noob about electricity (volts, watts, amps, hertz, etc), how deadly is the current flowing from a receiver or amplifier to the speakers? As kids with a little AM transistor radio with a 9 volt battery, we'd stick the battery terminals to our tongues to find if the battery was 'dead' or not.

 

[Johnny2Bad]

It depends on the amplifier power and topology, plus exactly how it is connected to a human body; the more powerful amplifiers are delivering more than less powerful ones.

By "more" I mean this is determined by the topology; a voltage Power Amplifier (most) would be delivering more voltage (volts), a current topology Power Amplifier (rare, but they do exist) would be delivering more current (amps).

You could connect the terminals to areas of the body more sensitive to electricity than others, for example if you were to hold each terminal (one positive, one negative, for one channel of a Power Amplifier's output) in each hand, you would need a very powerful amplifier to have some risk, while there are definitely areas of the body that are far more sensitive to electricity that would have greater risk.

Also there is always the possibility of a Power Amplifier operating in one or another failure mode, where the normal limits on output power ... that is an amp working properly into an expected speaker load .... are no longer in effect, and, basically, "anything goes".

Most commercial Power Amplifiers have protection circuitry designed to limit or eliminate problems, but they are not 100% reliable and some, especially those built to extract the last bit of resolution, may have limited or no protection circuit. This would be a situation where damage to the speaker would result, except you are connected to a human body, not a speaker.

In the end you must keep in mind that you are connected, through the Power Amplifier, to the household current of 120V/60Hz AC, which is definitely dangerous. Abnormal conditions means all bets are off, basically.

Broadly speaking the specific risk as your question describes is low, because the natural impedance of dry skin on the human body is high ... typically 100,000 Ohms (the Power Amplifier expects perhaps 2 to 16 Ohms; higher impedance means less power is delivered).

However it would be wrong to say the risk is zero; and the impedance of the body is not fixed. It varies from person to person, time of day, and whether dry or wet. Again, another example is on the same part of the body where impedance with dry skin would be 100K Ohms it might be only 1,000 Ohms (1K Ohms) if wet.

From the above you can see that you could detect electrical charge on a 9V battery on your toungue (wet, sensitive, internal) but not on the back of your hand (dry, insensitive, external). Things like that affect the risk.

There is no "black and white" answer to electrical shock questions; in some cases very low currents can be dangerous while in others very high voltages could be relatively safe (for example, tesla coils). Far better is to adopt "best practices" when dealing with electricity, which could be summed up as "don't take chances".

It's something I would not worry about, personally, as far as they typical home audio system is concerned, but do try to avoid connecting yourself to electrical devices; it is not a good idea.

 

[tyhjaarpa]

Are you trying to test your cables if they work or not? If that is the case you can do the battery trick with the wire as well.

 

[KenM10759]

My understanding is that amps are more dangerous than volts, and as such you can have 3 volts at 400 amps that'll kill you, or 10,000 volts at 1mA that you wouldn't even feel.

Or is it the other way around?

 

[herbu]

how deadly is the current flowing from a receiver or amplifier to the speakers?

Have you ever looked at the back of a speaker? The terminals are right next to each other and ARE NOT insulated or isolated from touch. That means there are millions of homes around the world with their speaker wires exposed for babies, kids or adults to touch.

Would the speaker manufacturers build speakers like that if it was dangerous? Would the govt's allow it? Have you ever heard of anyone injured by touching their speaker wires?

Johnny2Bad says above, "Broadly speaking the specific risk as your question describes is low". In fact, it is SO LOW that manufacturers of AVRs, amps and speakers invite you to touch the wires by the very design of their products... and have for years. No organic injuries so far. The only danger is possibly to your equipment, not you.

 

[highfigh]

Being a total noob about electricity (volts, watts, amps, hertz, etc), how deadly is the current flowing from a receiver or amplifier to the speakers? As kids with a little AM transistor radio with a 9 volt battery, we'd stick the battery terminals to our tongues to find if the battery was 'dead' or not.

The current from the terminals of a 9V battery tingles because your tongue is wet and the distance is very small- if you touch each terminal with a wet finger from both hands, not much current will pass. Ohm's Law states that I (Current) =E (Voltage)/R (Resistance) and if we use the resistance mentioned before, 9V/100K Ohms=9 micro Amperes. The problems occur when the current passes through the heart, causing disruption or stopping the heart beating. The power supply is where the danger is located but if an output transistor shorts and the amp has nothing to protect the speakers, the speakers will be destroyed and if that doesn't destroy the amplifier, the voltage present could be dangerous.

 

[rsharp]

My understanding is that amps are more dangerous than volts, and as such you can have 3 volts at 400 amps that'll kill you, or 10,000 volts at 1mA that you wouldn't even feel.

Or is it the other way around?

In general, the answer is actually both. There's a good summary with examples here: http://www.madsci.org/posts/archives/aug98/899698536.Eg.r.html

 

[3db]

I remember when I was 17.... I disconnected the leads from one of the speakers, flipped the balance over to the free leads, grabbed them and cranked the voulme of my 25Watt/per channel integrated amp and I did feel a mild tingling sensation. That didn't hurt compared to the time I accidently slipped my finger off the piece of metal that was supposed to short out the spark plug on the lawnmower to turn it off. That spark plug shock hurt more then the time I accidently touch a fuse socket in the barn.

 

[TLS Guy]

I remember when I was 17.... I disconnected the leads from one of the speakers, flipped the balance over to the free leads, grabbed them and cranked the voulme of my 25Watt/per channel integrated amp and I did feel a mild tingling sensation. That didn't hurt compared to the time I accidently slipped my finger off the piece of metal that was supposed to short out the spark plug on the lawnmower to turn it off. That spark plug shock hurt more then the time I accidently touch a fuse socket in the barn.

That's because it was 2000 volts at least!

 

[3db]

That's because it was 2000 volts at least!

multiply that by 10 .. Dumbest design I've ever seen..

 

[fmw]

Being a total noob about electricity (volts, watts, amps, hertz, etc), how deadly is the current flowing from a receiver or amplifier to the speakers? As kids with a little AM transistor radio with a 9 volt battery, we'd stick the battery terminals to our tongues to find if the battery was 'dead' or not.

Not deadly at all.

 

[TLS Guy]

My understanding is that amps are more dangerous than volts, and as such you can have 3 volts at 400 amps that'll kill you, or 10,000 volts at 1mA that you wouldn't even feel.

Or is it the other way around?

It takes volts to create the current and that is solely determined by the voltage and the resistance to ground. So it is the power liberated in the event which is calculated as the square of the current X the resistance, or the square of the voltage divided by the resistance. The number is the same which ever way you calculate it. That gives you the wattage involved in the event. Time is also obviously a factor as that determines the total energy for the event. That is the number in that determines the damage done. I watt/sec is 1 Joule.

 

[TLS Guy]

multiply that by 10 .. Dumbest design I've ever seen..

Sorry yes, I left off a zero. An older lawnmower with breaker type ignition will have 20,000 volts or thereabouts, a solid state magneto, 30,000 volts or thereabouts.

 

[TLS Guy]

Being a total noob about electricity (volts, watts, amps, hertz, etc), how deadly is the current flowing from a receiver or amplifier to the speakers? As kids with a little AM transistor radio with a 9 volt battery, we'd stick the battery terminals to our tongues to find if the battery was 'dead' or not.

To answer you question it depends when you touch them.

100 watts in into an 8 ohm speaker will give you 28 volts RMS but peak to peak around 33 volts.

A 250 watt amp driving 8 ohms will give you 44 volts RMS and about 54 volts peak to peak.

I can assure that is enough to give you a nasty nip. However you are only likely to encounter that sort of voltage power testing an amp, unless you put your fingers in the wrong place at the wrong time during a loud musical peak.

However there is one caveat. You should never mess with connection when an amp is live.

If you got hold of the speaker connector and disconnected the speaker holding the connector while the speaker was under power, then you could get a nip of may be a few thousand volts, due to the back EMF generated by the series inductors to the woofer in the crossover. This high voltage spark would jump the gap and likely fry the output transistors.

So always shut equipment down for all connects and disconnects.

 

[highfigh]

multiply that by 10 .. Dumbest design I've ever seen..

But it works. Hey, it was designed when men were men and a little pain was part of everyday life. If you really want to have a good time, grab the top of an HEI distributor on a GM while your hand is on a grounded part of the engine or vehicle. Now THAT'S livin'! Those are usually in the 50KV range and if the plugs or plug wires are old, the added resistance makes getting zapped easier.

Not quite as bad as this, though.

 

[Johnny2Bad]

(snip) ...

Would the speaker manufacturers build speakers like that if it was dangerous? Would the govt's allow it? Have you ever heard of anyone injured by touching their speaker wires?


Johnny2Bad says above, "Broadly speaking the specific risk as your question describes is low". In fact, it is SO LOW that manufacturers of AVRs, amps and speakers invite you to touch the wires by the very design of their products... and have for years. No organic injuries so far. The only danger is possibly to your equipment, not you.

Let's just say that some people find pleasure in unusual ways, and those people have injured themselves via Power Amplifiers deliberately connected to their bodies. There is a risk of death if, while connected to the power amplifier, they touch an ungrounded device (say, a lamp with a 2-conductor AC cord); the AC from the wall socket via the lamp cord can find a ground path through the body.*

No point in elaborating, since this is a family-friendly forum, but people do strange things sometimes. Like I said, it is wrong to say the risk is zero.


* Which raises another issue, in that there are some amplifiers that do use an ungrounded AC cord. Such an amplifier cannot pass current CSA or UL regulations, but they were legal in the past and certainly someone can come across them.

There is a genuine chance of electric shock with such an amplifier if operating with speaker terminals touching the human body (or by touching the amplifier chassis itself, for that matter).

At one time it was standard practice to connect one wire of the AC line directly to the chassis. Certain inexpensive table top vacuum tube radios sold up to the early 1960's (and which sound fabulous, most of the time), would not use a relatively expensive transformer for AC power, and are notorious for such shock or electrocution risk.

 

[herbu]

Let's just say that some people find pleasure in unusual ways, and those people have injured themselves via Power Amplifiers deliberately connected to their bodies.

You gotta be kiddin me!
I had no idea, and don't think I can add anything further to that subject... other than Come On Darwin!

 

[3db]

But it works. Hey, it was designed when men were men and a little pain was part of everyday life. If you really want to have a good time, grab the top of an HEI distributor on a GM while your hand is on a grounded part of the engine or vehicle. Now THAT'S livin'! Those are usually in the 50KV range and if the plugs or plug wires are old, the added resistance makes getting zapped easier.

Not quite as bad as this, though.

This is the lawn mower I used as a kid.... Iron Horse. (Marauder) the red one) ....lasted 20 years .. notice the open flywheel which you had to wrap a cord around to pull start it... none of this whimpy safety poop and no way of shorting out the plug..ours broke off.

 

[highfigh]

No point in elaborating, since this is a family-friendly forum, but people do strange things sometimes. Like I said, it is wrong to say the risk is zero.


* Which raises another issue, in that there are some amplifiers that do use an ungrounded AC cord. Such an amplifier cannot pass current CSA or UL regulations, but they were legal in the past and certainly someone can come across them.

There is a genuine chance of electric shock with such an amplifier if operating with speaker terminals touching the human body (or by touching the amplifier chassis itself, for that matter).

At one time it was standard practice to connect one wire of the AC line directly to the chassis. Certain inexpensive table top vacuum tube radios sold up to the early 1960's (and which sound fabulous, most of the time), would not use a relatively expensive transformer for AC power, and are notorious for such shock or electrocution risk.

Some radios and amplifiers didn't even have a power transformer- I can't imagine how many people were injured or killed by those.

Most electric devices made before the mid-'60s had an un-grounded power cord and one example of dangerous was guitar amps, which not only were un-grounded, they sometimes had a switch for reversing the polarity of the power connections. The switch had a capacitor on the polarity switch that's usually called the "death cap" because it could fail shorted and cause the chassis to be electrically 'hot'. When these amps are restored/serviced, a grounded cord is installed, the polarity switch is disconnected and the amp is usually safe but people have died or almost died because of this, including Keith Richards (Rolling Stones) and Keith Relf (The Yardbirds). I don't know what these switches have against people named 'Keith', but.....

A good indicator that something is wrong comes when touching the chassis of audio equipment and feeling a slight tingle or strange vibration when sliding a hand or finger along a metal piece, like the face plate of a receiver, pre/power or integrated amp when standing on concrete, especially without shoes. With a guitar amp, touching the strings, the cord or the amp can result in tingling when on concrete and it could be the amp or the electric wiring. I have experienced this in both cases and it's no picnic. If a guitar player has one hand or forearm across the strings and grabs a mic or touches it with their mouth when singing, arcing can be seen and grabbing it can cause the current to pass through the person's heart.

 

[highfigh]

This is the lawn mower I used as a kid.... Iron Horse. (Marauder) the red one) ....lasted 20 years .. notice the open flywheel which you had to wrap a cord around to pull start it... none of this whimpy safety poop and no way of shorting out the plug..ours broke off.

How did you shut it off- screwdriver from the plug to something that shorted the stator?

Outboard motors were the same- open flywheels catching a sleeve when someone would reach over it. Nasty!

Nice washing machine- must have been a weird link.