Electronics for Audiophiles: Voltage and Current (Video)

[srkbear]

Oh? You know the NEC? How about "NFPA 70, NFPA 99 and NFPA 101?" The insurance code? The teach you these things in med school? I think not.

Come work for me as an electronic tech and I will teach you how to stay alive. If you violate that and listen to internet arguments about "it is current that kills you," then sadly your odds of needing the services from someone like you rises substantially.

I serve on the OSHA/Safety committee at my hospital and although I’m not familiar with the codes in detail, I’m fully aware of them. Certainly enough to understand his post. In medicine, we view electrical injuries and pathophysiology based on principles of current—I fully understand and respect that in your discipline you emphasize voltage.

In no part of this discussion did I ever denigrate your competency in your field of expertise. The university where I am on faculty feels differently enough to entrust me to teach young doctors how to practice medicine, and my patients don’t seem to share your point of view.

Why you assume that someone on here who is not an expert in your field cannot be an expert in another is unfathomable to me—but I can assure you that if you ever do have any life threatening mishaps with electrical current, the experts at any university hospital of the foremost prestige will speak in the same terms I have here, and you can tell them what idiots they are while they’re saving your life.

Sorry things went this way Amir. In another discussion we might have both learned something from each other. Hopefully another time, have a good night.

 

[KSTR]

Guys, this debate is ridiculous and reminds me to a story what was the first: the hen, or the egg?

Every oversimplification is wrong, and actually we have some standards to define safe voltage and safe current, under various conditions.

View attachment 221861

View attachment 221862

View attachment 221864

View attachment 221865

This!

The key point is to note the all-important difference between effective touch voltage and prospective touch voltage.

Prospective voltage is the voltage while you are not touching anything, basically the "open circuit" voltage of a circuit, vs. whatever point of reference.

Effective voltage is what remains present while you provide the current path through your body and that is what then establishes the harmful current, based on skin/body impedance. Your are the bottom leg of a voltage divider, the upper leg is the impedance of the source.

The most dangerours case obviously is zero/low source impedance which is the typical case.

This is why all those videos about "you can touch 100kV from an Graaf generator and don't get killed / birds don't fall off power lines / etc " are bullshit as the source impedance is so high that the effective touch voltage is reduced to effectively zero. The source impedance consist of two parts, the actual source resistance but the more important is the return path (which is going through an isolator like rubber mat, air etc).

Same goes for the partial mains voltage present on the case of EVERY non-earthed piece of gear. It doesn't kill you because the source impedance is very high at mains frequencies as the coupling mechanism is just a small capacitance.

It's all about Ohm's law in a closed circuit, in the end.

Thanks @Amir for the video.

 

[srkbear]

This!

The key point is to note the all-important difference between effective touch voltage and prospective touch voltage.

Prospective voltage is the voltage while you are not touching anything, basically the "open circuit" voltage of a circuit, vs. whatever point of reference.

Effective voltage is what remains present while you provide the current path through your body and that is what then establishes the harmful current, based on skin/body impedance. Your are the bottom leg of a voltage divider, the upper leg is the impedance of the source.

The most dangerours case obviously is zero/low source impedance which is the typical case.

This is why all those videos about "you can touch 100kV from an Graaf generator and don't get killed / birds don't fall off power lines / etc " are bullshit as the source impedance is so high that the effective touch voltage is reduced to effectively zero. The source impedance consist of two parts, the actual source resistance but the more important is the return path (which is going through an isolator like rubber mat, air etc).

Same goes for the partial mains voltage present on the case of EVERY non-earthed piece of gear. It doesn't kill you because the source impedance is very high at mains frequencies as the coupling mechanism is just a small capacitance.

It's all about Ohm's law in a closed circuit, in the end.

Thanks @Amir for the video.

You’re right, it truly was an unnecessary, petty exchange, which i believe I helped perpetuate, I’ve examined my part in it and what hooked me into it, and I’m willing to own it. That’s the best I can do, the rest is not in my hands.

 

[Holmz]

Both Edison and Westinghouse liked to make electric chairs using the other fellows technology.
Seemed like DC or AC both do a nice job of separating the soul from the flesh.

An electric fence, on the other hand, is a current limited high voltage device.
Whereas most amplifiers that are not total junk have enough capacitance in them to thump out joules of energy.

Eldest daughter was asking about changing a light switch. I mentioned that there is no dishonour in using a DMM to check the voltage before sticking screw driver to terminal.
She said later that she thought, “well I suppose I should even though I flipped the breaker off.”
And she said her next thought, was with raise eyebrows thinking, “WTF”… as it turned out it was the wrong breaker.

 

[diaolodoro]

Once more, with high impedance of body, the only way to get sufficient current into body is to push the voltage up: I = V/R. You usually have no control or idea of current in the supply. But you know with very higher certainty the voltage. A 120 volt AC mains will absolutely cause more danger than 12 volt coming out an AC adapter. As a result, a person dealing with these situations only needs to look at the voltage to determine level of danger.

This is the advice that is followed by electricians, EE, my professors and every professional I know that tinkers with electronics. Why this important advice is good enough for professionals, but some think it's not good enough for the general public is beyond my understanding.
I don't know the background of the people who disagree with the above, but I've never met a professional who calculates how much current is going to flow through their body every time they touch a circuit. We just glance at the voltage and continue our work in seconds (this is usually safer as well). I've never in my life had to think about my body impedance and calculate things that way. It's insanely impractical, can lead to more mistakes and do more harm than good.

I'm pretty sure we are not over-simplify things, but people who say we're "wrong" they're unnecessarily over-complicate things. Maybe they'll suggest to stop driving our cars unless we understand exactly how every single part of them works, because oversimplification is wrong and dangerous, right....? And then people overloaded with information will think they can fix their cars and they'll end up in a ditch.
Amir, I can almost feel how frustrating this conversation can be for you, but I'm almost certain that if those people who disagree continue to learn, or better, work with electronics as enthusiastically as they're commenting, they'll come full circle and will understand why we're so focused on voltage.

 

[tomtoo]

This is the advice that is followed by electricians, EE, my professors and every professional I know that tinkers with electronics. Why this important advice is good enough for professionals, but some think it's not good enough for the general public is beyond my understanding.
I don't know the background of the people who disagree with the above, but I've never met a professional who calculates how much current is going to flow through their body every time they touch a circuit. We just glance at the voltage and continue our work in seconds (this is usually safer as well). I've never in my life had to think about my body impedance and calculate things that way. It's insanely impractical, can lead to more mistakes and do more harm than good.

I'm pretty sure we are not over-simplify things, but people who say we're "wrong" they're unnecessarily over-complicate things. Maybe they'll suggest to stop driving our cars unless we understand exactly how every single part of them works, because oversimplification is wrong and dangerous, right....? And then people overloaded with information will think they can fix their cars and they'll end up in a ditch.
Amir, I can almost feel how frustrating this conversation can be for you, but I'm almost certain that if those people who disagree continue to learn, or better, work with electronics as enthusiastically as they're commenting, they'll come full circle and will understand why we're so focused on voltage.

"....I'm pretty sure we are not over-simplify things, but people who say we're "wrong" they're unnecessarily over-complicate things..."

No there is no over-compilcation to tell how things realy work. Ever thouched a electric pasture fence? Ever got a shock from a static? Ever got taserd? Man why are you not dead, if voltage is what you kills, and not the current through your body? See its not that i say amirs video is wrong, its ok. But i wished he had gone just a littel deeper into the basics.

 

[diaolodoro]

"....I'm pretty sure we are not over-simplify things, but people who say we're "wrong" they're unnecessarily over-complicate things..."

No there is no over-compilcation to tell how things realy work. Ever thouched a electric pasture fence? Ever got a shock from a static? Ever got taserd? Man why are you not dead if voltage is what you kills, and not the current through your body?

I've said in my previous comment that current flow is what kills you, but this can be very misleading. We don't care about current unless there's a high voltage. I've touched low voltage ~130A circuit and I'm still not dead and most importantly didn't even feel a thing while doing so. If 1A can fry you, how was I able to touch >100Amps without being in any danger? See how these examples like yours can be way more misleading? And by the way high voltage shocks always hurt. Also, you're only mentioning irrelevant things that are designed to hurt or aren't even electronic devices. Nobody here is going to get tased or start roaming around cows and electric fences. We're talking about how to handle electronic devices, not ways to escape from the police.

 

[tomtoo]

I've said in my previous comment that current flow is what kills you, but this can be very misleading. We don't care about current unless there's a high voltage. I've touched low voltage ~130A circuit and I'm still not dead and most importantly didn't even feel a thing while doing so. If 1A can fry you, how was I able to touch >100Amps without being in any danger? See how these examples like yours can be way more misleading? And by the way high voltage shocks always hurt. Also, you're only mentioning irrelevant things that are designed to hurt or aren't even electronic devices. Nobody here is going to get tased or start roaming around cows and electric fences. We're talking about how to handle electronic devices, not ways to escape from the police.

".. If 1A can fry you, how was I able to touch >100Amps without being in any danger?.."

We can kid arround if you like to. Iam absolutly sure that 100A did not go through your body. You would look like a Bratwurst. See questions like this show me missing understanding of the basics. Thats why iam so behind teaching the basics right even it needs more efford. There is a easy explanaition why high voltages are more dangerous, they enjoy to drive higher currents thru your body, that enjoy to kill you. So is it the high voltage? Not exactly. Simplify it and say so, is usually not dangerous. But it also not realy helps to understand cirquets.

 

[Audiofire]

Thanks, although you either misquoted me or spoke incorrectly—DC current typically causes a single muscle contraction that throws one from the source of the shock; AC current is what prevents a hand from letting go. May I ask what discipline you’re writing this technical article from?

Thanks, I believe in your statement. My discipline is construction, so I perused a lot of references in order to write the article. I also posted the link, so that others get a chance to read it, and maybe post some constructive feedback.

I would suggest that our statements about whether the current will repel are compatible, since the voltage, contact resistance and contact area vary with real situations. If the voltage is brought up from a safe value to the breakdown voltage whatever the current is, then thermal energy will be felt more as well.

 

[Robbo99999]

I've said in my previous comment that current flow is what kills you, but this can be very misleading. We don't care about current unless there's a high voltage. I've touched low voltage ~130A circuit and I'm still not dead and most importantly didn't even feel a thing while doing so. If 1A can fry you, how was I able to touch >100Amps without being in any danger? See how these examples like yours can be way more misleading? And by the way high voltage shocks always hurt. Also, you're only mentioning irrelevant things that are designed to hurt or aren't even electronic devices. Nobody here is going to get tased or start roaming around cows and electric fences. We're talking about how to handle electronic devices, not ways to escape from the police.

Hey, as a kid I used to hang onto electric fences for fun! (cow field) We worked out through experience that if you link hands with someone whilst the first person touches the electric fence then only the second person feels the shocks. Ha, well I was very young kid and this was only after accidentally touching the electric fence that we experimented with it. Don't do it kids!

 

[Mutagen]

Thank you, Amir. This was very well done.
I'd love to see you continue through the (audio-specific) issues of voltage along the device chain - that is, a practical walkthrough of matching (or not?) input voltages vs. output voltages on devices, and the relationship to clipping, volume, and quality.

 

[Ajax]

Hi Amir,

As you are no doubt well aware you will never include the right amount of information to please everybody, as you are speaking to such a diverse knowledge base.

I am an engineer (civil) and have run small business supplying products to the building industry for many years and I was always astounded at the range of knowledge of both my staff and my customers. I could walk into one Architect's office and start explaining my product and watch his eyes close over while the next guy wanted to get into it and for me to explain the most minuscule detail. Ditto with my staff.

My favourite expression became "You don't know what you don't know".

I believe the art of teaching is to clearly state what it it is you wish people to learn/understand and then YOU decide how best to do that. You simply cannot accomodate the huge variation of knowledge (or lack of).

The other side of the coin is you end up with people focusing on an irrelevant point such as how voltage/current kills you. This is not what your mission is, which is to explain the basics of audio, and they inadvertantly cause confusion and block the sharing of knowledge.

Bloody hard but very rewarding for both you and us if you can get the balance right. Keep at it.

 

[DualTriode]

You can throw away all of that as soon as you open a piece of equipment. There is not a shred of regulation that applies to that situation. And per my repeated post, any mention of "current being the hazard" is totally wrong with respect to what is and is not dangerous inside some audio gear.

But I will humor you. Go ahead and explain what you can, or cannot touch given your claim that "hazard is the current." This is the second time I am asking.

We do agree that there is not an enforcement agency that will come out to your house as long as you are alive.

If you end up killing yourself the M.D.'s and P.E.'s will determine that it was the current that killed you.

In the City where I live if you electrocute yourself they send out the Electrical Inspector to see how you did it. You know for the personal and or product liability law suits that often happen.

What I do is is hook up everything with terminal blocks , mini-grabbers or mini-alligator clips, close everything in a large grounded locking electrical panel box. The same type of practices you often see in the FLUKE and or other safety videos.

If it is large switch gear I step outside the door down the hall and put on my PPE.

DT

Edit:
I use one of these to prototype tube circuits on my bench.
https://www.keysight.com/zz/en/product/N5752A/dc-system-power-supply-600v-1-3a-780w.html
I close everything up in the panel box. Exploding capacitors make me pucker up a bit

 

[pma]

If one sticks with the explanation that only voltage is important, regardless current, source impedance, energy, voltage shape (ESD, surge), then please explain a simple example from real life of the audio consumer. Let's have 230/50Hz mains and two instruments, one is class I, the second one class II. They are plugged in and turned on, but not interconnected by a signal cable. Voltage difference between the metal cases of this two instruments may get as high as 115Vac (half of the mains voltage), depending on stray capacitances. From a simple voltage view, this would be a lethal voltage level. But, this voltage is generated just through the transformer stray capacitance, and when the circuit loop to ground (= case of the class I instrument) is closed, the maximum ac current would be usually less than 0.3mA. So, from the simplified voltage view, we have a "lethal" voltage of 115Vac, but from the current view we have a safe current of 300 microamperes maximum. The result is that the system is safe.

 

[Audiofire]

If one sticks with the explanation that only voltage is important, regardless current, source impedance, energy, voltage shape (ESD, surge), then please explain a simple example from real life of the audio consumer. Let's have 230/50Hz mains and two instruments, one is class I, the second one class II. They are plugged in and turned on, but not interconnected by a signal cable. Voltage difference between the metal cases of this two instruments may get as high as 115Vac (half of the mains voltage), depending on stray capacitances. From a simple voltage view, this would be a lethal voltage level. But, this voltage is generated just through the transformer stray capacitance, and when the circuit loop to ground (= case of the class I instrument) is closed, the maximum ac current would be usually less than 0.3mA. So, from the simplified voltage view, we have a "lethal" voltage of 115Vac, but from the current view we have a safe current of 300 microamperes maximum. The result is that the system is safe.

You explained already, because the system is safe and the average audiophile might not even notice "lethal" voltages there.

 

[Endibol]

If one sticks with the explanation that only voltage is important, regardless current, source impedance, energy, voltage shape (ESD, surge), then please explain a simple example from real life of the audio consumer. Let's have 230/50Hz mains and two instruments, one is class I, the second one class II. They are plugged in and turned on, but not interconnected by a signal cable. Voltage difference between the metal cases of this two instruments may get as high as 115Vac (half of the mains voltage), depending on stray capacitances. From a simple voltage view, this would be a lethal voltage level. But, this voltage is generated just through the transformer stray capacitance, and when the circuit loop to ground (= case of the class I instrument) is closed, the maximum ac current would be usually less than 0.3mA. So, from the simplified voltage view, we have a "lethal" voltage of 115Vac, but from the current view we have a safe current of 300 microamperes maximum. The result is that the system is safe.

Better safe than sorry. This was the whole point of Amir's presentation!

 

[DMill]

Better safe than sorry. This was the point of Amir's presentation!

That’s how I took it too. I shocked the hell out of myself once screwing around with a lamp. I will be thankful never to feel anything like that again. Lucky I didn’t kill myself. How I took it was don’t go screwing around in your amp unless you know what you’re doing. EDIT: or your L(amp)s either

 

[diaolodoro]

If one sticks with the explanation that only voltage is important, regardless current, source impedance, energy, voltage shape (ESD, surge), then please explain a simple example from real life of the audio consumer.

I'll throw the question back at you with 3 very realistic scenarios.
1) You open an amplifier and see a few big fat capacitors. How do you know it's safe to touch them?
2) Between two power supplies 12V 2A and 60V 2A which one could be more dangerous. What are the parameters are YOU looking for?
3) If in question 2) you changed the first power supply with a 12V 10A, would it be more dangerous?

 

[Doodski]

1) You open an amplifier and see a few big fat capacitors. How do you know it's safe to touch them?

You don't know if they are safe unless you have metered them and discharged them.

2) Between two power supplies 12V 2A and 60V 2A which one could be more dangerous.

60VDC would be the more dangerous jolt.

3) If in question 2) you changed the first power supply with a 12V 10A, would it be more dangerous?

No. The skin resistance needs to be lower for a lower voltage jolt. So 60VDC is danger zone de jour.

 

[diaolodoro]

You don't know if they are safe unless you have metered them and discharged them.

60VDC would be the more dangerous jolt.

No. The skin resistance needs to be lower for a lower voltage jolt. So 60VDC is danger zone de jour.

So there you have it. Three practical examples for audio consumers were the only parameter that's needed to understand if something's dangerous is the voltage.