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Well, yeah, again, electric shocks from mics !!

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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Sat Dec 08, 2018 4:45 pm

There's lots of stuff on the interweb about this, such as:

Image

https://jmkengineering.com/electric-shock-human-body/

Although an American article, it is the current that matters, not the voltage... and not the difference between 50 and 60Hz either!

H
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Re: Well, yeah, again, electric shocks from mics !!

Postby wireman » Sat Dec 08, 2018 5:15 pm

The c1 curve in one of the figures contained in the document I linked to earlier is relevant and there was a mention of the IEC 60479 standard it came from.

Anyone with some spare cash could get the latest standard which seems to be PD IEC/TS 60479-1:2005+A1:2016 Effects of current on human beings and livestock. General aspects.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Trevor Johnson » Sat Dec 08, 2018 7:53 pm

As my old dad, (and others), used to say, "its volts that jolts, but mills that kills"!
He worked on radar during WWII, both on land and sea, and was seconded to the Royal Canadian Navy because of his expertise: one of his teachers was the great Watson-Watt. He knew the dangers and potential lethality of voltages.

Anyway, I followed him and became a radio amateur, growing up with some EHT power supplies, (>2KV), to power valved linear amplifiers. Clearly you make a mistake only once at 2KV, so I was taught safety at all times. In fact I was taught to regard any voltage as potentially hazardous.

In terms of audio, the voltage and current on the output capacitors of a powered up Quad 303 are more than capable of putting you into VF, depending on the circumstances (e.g. your right hand is connected to positive and your left is grabbing onto something earthed. Golden rule: put your non-working hand firmly away in a pocket. And back to the OP; if you feel a tingling sensation from your mics don't ignore it as your mic maybe looking for a new owner sooner than expected!
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Re: Well, yeah, again, electric shocks from mics !!

Postby Sam Spoons » Sat Dec 08, 2018 10:26 pm

Trevor Johnson wrote: Golden rule: put your non-working hand firmly away in a pocket.

Something I learned early in my amateur electronics (failed) career and have adhered to ever since. Good advice, obviously, as I'm still here :thumbup:
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Re: Well, yeah, again, electric shocks from mics !!

Postby ef37a » Sun Dec 09, 2018 12:06 pm

Trevor Johnson wrote:As my old dad, (and others), used to say, "its volts that jolts, but mills that kills"!
He worked on radar during WWII, both on land and sea, and was seconded to the Royal Canadian Navy because of his expertise: one of his teachers was the great Watson-Watt. He knew the dangers and potential lethality of voltages.

Anyway, I followed him and became a radio amateur, growing up with some EHT power supplies, (>2KV), to power valved linear amplifiers. Clearly you make a mistake only once at 2KV, so I was taught safety at all times. In fact I was taught to regard any voltage as potentially hazardous.

In terms of audio, the voltage and current on the output capacitors of a powered up Quad 303 are more than capable of putting you into VF, depending on the circumstances (e.g. your right hand is connected to positive and your left is grabbing onto something earthed. Golden rule: put your non-working hand firmly away in a pocket. And back to the OP; if you feel a tingling sensation from your mics don't ignore it as your mic maybe looking for a new owner sooner than expected!

Microwave ovens similarly take no prisoners. 2kV at at least an amp. We were told at an Hitachi traing course that you NEVER fire up the oven and make voltage tests, diagnosis was to be indirect and by "cold checks".
Problem was if the magnetron was the suspect (almost always was) they were 30 quid a pop and had to be ordered in. Hanging an Avo 8 on 2.5kV range then firing up from a discrete distance proved the 'tron. If the volts went to 2kV+ and stayed there it was pulling no current and thus borked (it paid however to check the heater supply!)

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Re: Well, yeah, again, electric shocks from mics !!

Postby wireman » Sun Dec 09, 2018 2:29 pm

It seems that there is a whole load of health-and-safety-free MO transformer fun to be had out there video1 video2.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Trevor Johnson » Sun Dec 09, 2018 8:29 pm

Problem was if the magnetron was the suspect (almost always was) they were 30 quid a pop and had to be ordered in. Hanging an Avo 8 on 2.5kV range then firing up from a discrete distance proved the 'tron. If the volts went to 2kV+ and stayed there it was pulling no current and thus borked (it paid however to check the heater supply!)

The magnetron, specifically the cavity magnetron, was critical to the development of radar during WWII.

An Avo 8 on the 2.5kV range, wow! I do all my HV testing remotely with a master switch close at hand and in the vicinity of an AED. I remember a couple of years ago a well known HiFi magazine developed a kit with 300Bs in the output stages. But they were encouraging builders to prod around the valve bases with a multimeter to check voltages. I thought how insane they were!
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Re: Well, yeah, again, electric shocks from mics !!

Postby ef37a » Sun Dec 09, 2018 9:03 pm

Trevor Johnson wrote:
Problem was if the magnetron was the suspect (almost always was) they were 30 quid a pop and had to be ordered in. Hanging an Avo 8 on 2.5kV range then firing up from a discrete distance proved the 'tron. If the volts went to 2kV+ and stayed there it was pulling no current and thus borked (it paid however to check the heater supply!)

The magnetron, specifically the cavity magnetron, was critical to the development of radar during WWII.

An Avo 8 on the 2.5kV range, wow! I do all my HV testing remotely with a master switch close at hand and in the vicinity of an AED. I remember a couple of years ago a well known HiFi magazine developed a kit with 300Bs in the output stages. But they were encouraging builders to prod around the valve bases with a multimeter to check voltages. I thought how insane they were!

No Trev' I was not "poking about"! The magnetron has -2kV or so on its cathode/heater, anode is bolted to chassis. I used to hook a crock lead from heater to chassis, oven off! Then attach the Avo, remove the eathing crock then switch on. The no load volts pushed Avo over FSD slightly but if it did not start to fall after 30 secs or so I knew the magnetron was dedded.

One thing scared me though. Do you remember the huge wide screened CRT TVs? They did not last long before Plasma came in but we had to change a tube in one. The CRT came in a monster crate with two special handling hooks. It took two of us to change it and so great I think was the capacitance twixt inside and outer dags that if you copped the residual volts it would have been curtains. Had we dropped the CRT I reckon the implosion would have shredded us and flattened the building!

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Re: Well, yeah, again, electric shocks from mics !!

Postby Folderol » Sun Dec 09, 2018 9:26 pm

but... but... they were 'only' about 35kV. What's a little 'k' between friends :tongue:

P.S.
We had a safety earthing strap that was always used when removing a tube... before disconnecting anything. At the 'top' end it had a 100k 10W resistor and a very thin blade that could slip under the the rubber cup. It was left in place for about 1/2 hour to ensure that the somewhat high resistance internal graphite coating was completely discharged.
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Re: Well, yeah, again, electric shocks from mics !!

Postby ef37a » Mon Dec 10, 2018 9:45 am

Just under 25kV pretty sure Will otherwise punters get dosed with X rays.

Yes, you can dump it but an hour later the dielctric stress builds it back up again and the energy stored in that huge CRT was something I did not want across me!

But also, handling something THAT big under atmospheric pressure was most unnerving.

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Re: Well, yeah, again, electric shocks from mics !!

Postby funky54 » Tue Sep 03, 2019 3:28 pm

I didn’t read 11 pages. This thread is a little over my head.

For 30 years I have done a few things to protect myself.

First, I have two really good power conditioners with surge. One for PA and One for my guitar amps.

Second, I try to plug PA, guitar amps into the same circuit if at all possible

Third, I never plug lighting in on the same circuit with anything else band related (and in truth I’m about to go all LED anyway)

Last, this one may seem like voodoo... I have a bag full of large “O” shaped strong magnets that open in the center. Each and every cable near the user end is wrapped 3-4 times through the magnets and then are sealed wrapped in twine.

Now make fun if you like, but I’ve set up my 6600 watt PA, Wet Dry Wet guitar rig in every Victorian Home converted to biker bar, tavern, bar, wedding, school gym, County Fair, State Fair imaginable, and have never experienced ground loops or a shock through a mic.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Tue Sep 03, 2019 4:48 pm

funky54 wrote:....and have never experienced ground loops or a shock through a mic.

It's nothing at all to do with your weird magnet voodoo* ;) or even your (pointless) power conditioners... and everything to do with having properly maintained and grounded equipment, with balanced connections and all plugged into the same mains outlet...

H

* It might be worth reading up on the very well understood physics of static wires carrying alternating currents wrapped around magnets (Flemings left hand rule), and also the effect of coiling wires carrying alternating currents around metal cores (inductance).
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Re: Well, yeah, again, electric shocks from mics !!

Postby ef37a » Tue Sep 03, 2019 7:15 pm

Hugh Robjohns wrote:
funky54 wrote:....and have never experienced ground loops or a shock through a mic.

It's nothing at all to do with your weird magnet voodoo* ;) or even your (pointless) power conditioners... and everything to do with having properly maintained and grounded equipment, with balanced connections and all plugged into the same mains outlet...

H

+ 1 and FFS get an RCD! Preferably one that is hard wired into the main supply cable so you cannot forget it.

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Re: Well, yeah, again, electric shocks from mics !!

Postby cyrano.mac » Thu Sep 05, 2019 5:10 pm

I've lost a dear friend to this kind of foolery, so I learned the hard way...

If you're in doubt about anything mains related, don't play. That's my rule.

A good solution is to buy an isolation transformer. If your amp is connected through it, you still might get shocked, but at least you won't die from it. Unless you're foolish enough to put one hand on one side of the transformer and the other on the other end.

You'd still have to hope the rest of the setup is ok, but seeing that tube guitar amps are the worst offenders, it's a big advantage.

Our entire live setups are connected through big isolation transformers. These were installed for safety, but also solved a problem of magnetic interference. There's a 750 KVA - 500V transformer across the street, feeding the trams. It was there already before our old building was constructed, so not much reason to complain. It resulted in a hum in some equipment. Nobody could solve it, until the decision was made to invest in isolation transformers everywhere. The hum was only a problem in one place and there it depended on equipment used. It could be horrible and it could be hardly noticeable.

The main argument was safety, but it also solved the other problem. Everybody's real happy now.

And since it's legal in the UK to "steal ground", it's even more important than elsewhere.
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Re: Well, yeah, again, electric shocks from mics !!

Postby funky54 » Sat Sep 07, 2019 4:55 am

Hugh Robjohns wrote:
funky54 wrote:....and have never experienced ground loops or a shock through a mic.

It's nothing at all to do with your weird magnet voodoo* ;) or even your (pointless) power conditioners... and everything to do with having properly maintained and grounded equipment, with balanced connections and all plugged into the same mains outlet...

H

* It might be worth reading up on the very well understood physics of static wires carrying alternating currents wrapped around magnets (Flemings left hand rule), and also the effect of coiling wires carrying alternating currents around metal cores (inductance).

Gotta ask, why do you feel power conditioners are pointless? They do a great job at removing hum and static sounds. Not to mention smooth voltage. Mine might even serve as the very transformers your talking about. They also have indicator lights to let you know if your grounded, out of phase, hot neutral wire, and a few other responses that I can’t remember.
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