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Shock
May 23, 2009 0:29:44 GMT -5
Post by angelodp on May 23, 2009 0:29:44 GMT -5
I wonder if Leo Fender and others in the vanguard of amp & guitar design worried about the possibility of shock from their instruments. I assume they believed that their designs would withstand a considerable degree of use and abuse. Still.... the other night at a friends house I happened to touch a Bassman amp while holding on to my guitar which was powered up through my rig which is all three prong and grounded properly. I got a momentary shock and quickly pulled my hand back. This old Bassman ( 60's ) is two prong. I have been imploring my friend to let me do the conversions to several of his old amps to three prong. So what was that shock... full 120v ?? It was unpleasant and surprising but it did not feel like it might kill me. The bass player went ahead and played through that amp, but I stayed well clear of that rig.
Ange - still kicking LOL
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Shock
May 23, 2009 0:45:49 GMT -5
Post by newey on May 23, 2009 0:45:49 GMT -5
Sure, that's why they started putting polarity switches on 'em. While it might be nice to rewire to three-prong, the polarity problem can be solved with one of those three-prong adapters. Just check for correct polarity, reversing the plug if needed, then tape the adapter/plug connection securely so someone can't come along and easily redo it. That's what I used to do with my old Harmony two-prong amp (w/o a polarity switch). Of course, if you move the amp to another location, you still need to check that the mains polarity was wired correctly when the crew of yahoos originally slapped the building together.
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Shock
May 23, 2009 3:09:16 GMT -5
Post by sumgai on May 23, 2009 3:09:16 GMT -5
I wonder if Leo Fender and others in the vanguard of amp & guitar design worried about the possibility of shock from their instruments. Nope. Weren't so damned many cotton pickin' weasels lawyers back then, so the courts weren't infested with fake liability lawsuits. Nope, again. The equipment itself was well able to withstand that "abuse" of an occasional shock of this nature. Players, on the other hand....... Reminds me of a famous ChrisK saying: "Someone's got to be the fuse! Try to not let it be you!!" newey's suggestion has merit. If the three-prong adapter is too tightly attached for anyone to monkey with it, then it preserves a vintage amp's vintageness. As to checking house wiring, a "real" three-prong power cord can't correct for problems there either, so one really should, at all times, carry a 5 dollar outlet tester, available at most anyplace that sells electrical stuff. Nope, yet again. It's actually half of the mains supply voltage. Figure 55 to 60vAC, in your neck of the woods. This is why most players that get bit survive with nothing more than a short-term piss-off. The one death that occured in an actual live stage performance was supplied by 240vAC, meaning that he got about 120vAC across his feet and lips.... which didn't do his heart any good at all, to say the least. For more details (a bit macabre), go here: Fuller UpHTH sumgai
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Shock
May 23, 2009 8:39:17 GMT -5
Post by newey on May 23, 2009 8:39:17 GMT -5
I learned early on- 8th grade garage band, hot humid summer day, sweaty bare feet on a concrete garage floor. As we broke for lunch, the lead guitarist ended up holding his guitar by the neck as the other guitarist handed him his guitar, a brand-new Gretsch, to hold for a sec.
He was debating with himself on which one of the 2 to drop as the current coursed through, when I noticed his distress and grabbed one guitar away from him (grabbing it by the body).
I'm sure SG will correct me (properly so!) if I am wrong, but my understanding is that, while the voltage determines whether one will get a shock, the amount of current, and the time over which it is applied, dictate the amount of damage that will be done. Grabbing a spark plug wire subjects one to a pretty sizable voltage, but it's a fairly low current so not likely to do much damage. Household AC is certainly enough to kill you, however.
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Shock
May 23, 2009 10:55:39 GMT -5
Post by sumgai on May 23, 2009 10:55:39 GMT -5
newey,
No corrections will be necessary at this time! ;D
sumgai
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Shock
May 23, 2009 12:33:57 GMT -5
Post by angelodp on May 23, 2009 12:33:57 GMT -5
Can you explain how it ends up being 60v? How do i get my pig headed friend change out his gear to a safe version LOL.
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Shock
May 23, 2009 22:02:46 GMT -5
Post by ChrisK on May 23, 2009 22:02:46 GMT -5
Explanation requested for post #2 please.
While I may be mistaken, I'm not sure that the firing voltage for an NE-55 neon bulb and half the mains voltage are related in this continuum.
Yes.
Regardless, I'm going to stop discussing the isolation cap concept since I do not feel that, even when implemented correctly, it gives more that an illusion of safety. When implemented incorrectly, it gives the delusion of safety.
Use wireless.
While I understand the intent of the isolation cap from an electrical engineering perspective, as a practicing electrical design engineer, I have never used it.
I use wireless.
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Shock
May 23, 2009 22:45:42 GMT -5
Post by newey on May 23, 2009 22:45:42 GMT -5
And, so far as we know, the safety cap has never been empirically tested.
I was wondering the other day whether it was primarily vintage (or "vintage-wired") tube amps that are subject to giving one a large DC voltage up the cable. Do the more modern tube designs, many of which use a PCB based circuit, exhibit the same hazards?
If the risk is confined to only the truly vintage tube amps (or the vintage pretenders) then ChrisK's advice makes even more sense. When you buy an amp presenting this risk, mentally figure the cost of a good wireless system into the purchase price.
And for one's other amps, don't obsess about it.
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Shock
May 23, 2009 23:47:35 GMT -5
Post by ChrisK on May 23, 2009 23:47:35 GMT -5
It may have been, but no one talking....
One might ask what the cap is intended to protect against. If it's a high potential DC voltage, then a cap will give some protection against such steady-state potential. However, until the cap is charged to that high potential (at which point no additional loop current will flow), the charging current will flow thru, yep you guessed it, the operator. This is a fault usually limited to tube amplifiers.
The safest way to prevent this is to use wireless.
If there is an AC potential impressed on the cable thru faulty safety grounding at the mains supplying the amp, then the isolation cap will charge and discharge at the 120 HZ rate (once for each half-cycle). At 60 Hz, a 0.33 uF cap has a reactance of 8,000 Ohms. This means that, at the mains AC peak voltage of 169 volts, there is potentially 21 mA of current available to flow thru the operator's body. At high line conditions of 130 VAC, we will have about 23 mA available. Pointlessly, the r.m.s current will be 15 mA.
Some operators enhance the effect of this possible current by playing barefoot on cement floors, with or without chewing on microphones. This is called "natural selection", which is a fundamental component of the theory of evolution (assuming that said selection naturally occurs prior to the operator's breeding).
Mains faults are not limited to tube amplifiers, but are more likely in amplifiers that do not have a three prong grounding plug, with a safety ground.
The leakage current thru a wireless link is zero. At high line conditions it is zero. Under DC fault conditions on an amp, it is zero. Under AC safety ground failure it is zero.
Take aways;
Use wireless on guitars and microphones.
Use gear that has a properly connected three prong mains cord.
Use wireless.
Do not use any gear that does not have a properly connected three prong mains cord. I don't care how vintage it is, change the cord. If you don't want to change the cord, don't use it. If you insist, this is dumb stupid "natural selection".
Use wireless.
Don't defeat the three prong mains cord with a grounding adapter. This device, contrary to its name, is a grounding dis-adapter, which negates the safety of the safety ground. Using one is dumb stupid "natural selection".
Purchase an outlet tester. Test every outlet before you use it. If the outlet fails the test, don't use it.
Use wireless.
Current agency listed amplifiers (UL, CE, etc) use three prong plugs and safety grounds because they're necessary. Vintage amps did not since no one then cared much about operator safety.
UL (Underwriter's Laboratories) was primarily a testing lab for insurance purposes (uh, underwriter's...). They originally cared more about fire hazards than operator safety. It was far cheaper/easier to make more people than more buildings.
Agency listings now address safety as well as fire hazards. But remember, while you're operating that plugged-in guitar, you're connected to an amp plugged in to the mains that is connected to your location thru miles of an above-ground lightening antenna. While I use many mains-powered devices, I rarely walk around holding them while they're plugged in.
Use wireless.
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Shock
May 24, 2009 1:43:35 GMT -5
Post by sumgai on May 24, 2009 1:43:35 GMT -5
Hay-soos Kristus, that was some diatribe! Enjoyed every minute of it!! ;D But down to the nitty-gritty...... Wireless is the correct solution, but is it acceptable? Consider: The very reason we, or most of us anyways, and the more-often-encountered "tone-mongers" are using vintage equipment is, what else, tone. Easy, you say. Yes, but what about "the rest of the story"..... Yes, now you begin to see it all, grasshopper. Tone-nazi's tend to emulate every bit of lore and legend as passed down from Mount Olympus, presumably by those who were there at the time. (And you all know what they say about the 60's, right? ) So, this means that if you use a '63 Strat or a '59 LP, and an FTR-BF or an FSR-BF (or even a 5F6 Bassman), you don't use a wireless setup, because it ain't got the mojo, baby! You suck it up, plug it in (remember, curly cords are de reigeur for the elite), and make sounds like your heroes. At least that's the way your mind interprets what's coming out of the speakers. To this crowd, wireless is for wussies!! Now, that said, I use wireless for my bass, but my Strat currently has only one output jack, and that's a 13-pin Roland jobbie. With all the isolation going on, thanks to various circuits, I'm safe enough with my FTR, should I choose to use it, and providing the thing ups and goes Ge-Fooey © (copyright CEKikta, 2005). Wireless is good for more than safety, IMHO. I use it for stage cleanliness, and occasionally pandering to the crowd. Too bad no one has come out with a 8 or 10 channel transmitter-receiver combination for the Roland. Onwards...... ( EDIT: Part way down from here is some arithmetic, which I blew. In retrospect, I actually took a shortcut for which I must now atone. The numbers were correct, but the nomenclature left something to be desired. The names have now been changed to protect the guilty. ) Unklmickey (may he R.I.P.) once straightened us all out, when this very same discussion cropped up a few years ago. (I think I was here then, don't recall now though.) The bottom line is that the only protection you get from this magical capacitator is prevention against a large charge should the amplifier decide to short a power supply filter capacitor - no mention need be made about line frequency. When this particular failure happens, which is more often than a blue moon, but not as often as Hell freezing over, then the entire DC output of the supply, including any ripple, will be dumped to chassis ground for a moment. That last part is important. This sudden appearance of a positive charge at ground will blow the fuse, but as we all know, fuses take time to blow. Specifically, in most tube amps, it can take appreciably longer than the charge/discharge cycle of a capacitor at line frequency. By all that, I mean that the time it takes a capacitor to go from zero volts to it's nominal maximum charge is something like a little over one half cycle of the frequency present. Thus, the power line frequency being 60Hz in most of North America, the time is a little bit more than the period of one cycle, or 16.666 msec., for most simple rectifier circuits. (But that number is cut in half for a full-wave rectifier, which actually doubles the frequency.) Fuses that can carry the necessary amperage just don't blow that fast, period. So, what happened to all those accumulated electrons that were dumped on the chassis ground? You guessed it, they followed the path of least resistance. Can you see where this is headed? Do I need to remind you of that famous ChrisK saying, the one about not being the fuse? Yep, you surely don't want to be touching that chassis ground, even if you're not standing in a naturally selected puddle of water. But just in case, the magical capacititator will act to reduce (and only reduce, not eliminate) the effects of this large charge dump. It does so not be presenting a resistance, but by reacting (Chris did use the term 'reactance'. If you read that as 'resistance', go to the back of the class. ) in a time-controlled manner. Reactance is defined as rate of charge over time, which is another way of saying frequency. And all that boils down to the capacitator stretching out the time it takes for the charge to build up within your body. That slowness should make the difference between a nasty shock and a whole new "out of body" experience. But as pointed out by newey, no one's reported back yet on whether or not this "effectiveness" is truly... well, effective. IOW, the jury is still out, and probably will be for the foreseeable future. As Chris puts it, the take away for me is, I don't use such a device. I change the filter caps in my FTR every 15 or 20 years, so they shouldn't go bad from aging. (insert crossed-fingers smilie here) Even so, my feeling is that if one wishes to insert the device, one should be my guest - I won't dissuade them. But if one relies on this thing to protect them from all manner of evil spirits from Indiana, then one is certain to fall to some other means of bedevilment, I can state that with authority. Paraphrasing the above, try to not be the Beta Tester here, eh. Next up..... clean up in Isle #2 If I recall correctly, the half-voltage scenario was due to the "floating ground" found in amplifiers of dubious design, such as early Fenders, etc. A capacitor of relatively large value was connected directly from one side of the AC cord to the chassis. (Why? To reduce hum and other undesirable interference. It was a common practice from the very early days of radio and TV. Remember what Leo started out as?) When this didn't work so well for some folks, a so-called polarity switch was installed, which simply switched the capacitor to the other side of the incoming AC power cord. Even later editions gave the polarity switch a third position, off in the center.... the capacitor was not connected from the chassis to either side of the cord. When one side of the incoming line is connected to the chassis like this, the chassis/ground is said to be floating - it's not truly at earth ground potential. In most cases, all other things being equal, it works out to about half of the full mains voltage. And no, I don't usually take a meter into the field with me, and test for a potential (voltage) difference between the mic and my guitar. One, I have a lot of circuitry between me and the incoming mains/ground. (Or if I'm on bass, then I'm also on my wireless system.) Two, I use the $5 tester, all the time. In fact, I have two of them, it's easy to temporarily misplace one, but Mr. Murphy can't count to two, so I'm usually well prepared. And three, I don't sing, so I don't give a tinker's damn about any microphones! OK, what else...... Say what? I'm out of time? I can't be, there's still some characters left in my counter. But.... but..... but...... HTH sumgai
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Shock
May 24, 2009 12:31:26 GMT -5
Post by ashcatlt on May 24, 2009 12:31:26 GMT -5
I used to glibbly state that I didn't have this problem since my amps (all virtual) are powered by low voltage DC wallwarts. I've found a problem with this recently, having begun playing in an actual band with other people. The problem is that these virtual amps don't actually make any sound. They're fine for jamming through headphones, or even recording. Now that I need to be heard by other people, and sometimes over acoustic drums, I have to plug this into an actual amplifier. And guess what. The shield of every cable between that amp (a Peavey keyboard amp right now) and my guitar is at the same potential as the third prong on that amp's power cable. Apparently, this is not the same potential as the concrete floor in the basement in which we're practicing. I'm kind of embarassed to admit it , but I discovered this in about the most "naturally selective" way possible - wearing socks in a puddle of spilled beer (there's carpet atop the concrete). Luckily the leakage isn't enough to cause any real harm, but it sure did affect my performance that day. I have mentioned to the owner of the house that this is a concern which he should have adressed, but I don't currently have the option of just not using this outlet, and he doesn't currently have the budget to have it fixed. In the meantime, I'm wearing shoes while we practice. Our vocalist, who also plays the "Bono guitar" found out about this yesterday. Luckily the mic is plugged into the same amp, so he shouldn't get the arcing between his nose/lips and the mic, but I forgot to tell him to wear rubber soled shoes, and he got a little jolt out of his guitar.
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Shock
May 24, 2009 13:29:50 GMT -5
Post by ChrisK on May 24, 2009 13:29:50 GMT -5
Yeah, I know, them cables add their own vintage tone. Well, just use your cable adapted to the wireless transmitter unit. Or, measure the capacitance of your favorite cable, and wire in a crapacitor of the same value.
"Ground" is a misnomer. While a steel or aluminum chassis can provide a good, even-potential local ground, the actual ground is anything but even or good.
The safety ground in a modern house wiring implementation is relatively consistent with the ground spike driven into the Earth near the power entry point. It is not the same point as the deck in the back yard or the cement slab (which is an excellent absorber of moisture and hence conductor of electricity).
I work in (and helped pioneer) the automated building control industry. We use galvanically isolated comms means between controllers, and recommend separate transformers to isolate the local control equipment from the overall building power distribution scheme. In some medical buildings (buildings with medical equipment), there can be ground bounce effects of well over 100 Volts. I have seen PCs and other coordinating controllers set ablaze from the lack of attention (cheap stupidity) related to isolation.
The problem is that we and the equipment makers view what we're doing as the center of the universe. We are not such emanating outwards, but just the last stop in the mains grid distribution system, where the focus is to deliver as much billable energy as possible to us.
This requires an exceptionally low impedance distribution system as possible, and sometimes finds our high impedance body conveniently in the way.
It is true that we don't often hear of electrocutions from musical gear. This speaks well of the current safety regulations and practices. I said current. This does not mean that that vintage amp with the two prong unpolarized plug should ever be plugged into the mains ever. You know, the one with the switchable cap to minimize hum since no one could be sure which wire in the mains was even connected to the neutral or the hot.
Gee, what about the concept of connecting the chassis to a safety ground first (thereby eliminating the screaming), and worrying about the humming later. There's a reason why the unpolarized two prong power cord is no longer permitted on most equipment; it's unsafe.
If you want to use that vintage unsafe amp, get a registered electrician to sign off on your using it with specific outlets.
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Shock
May 25, 2009 0:20:39 GMT -5
Post by sumgai on May 25, 2009 0:20:39 GMT -5
Ya know..... Chris's story above reminds me, I used to run across various installations of "isolated ground systems", in the early days of computerdom. I learned that hospitals have had to do that since the very early days of fancy diagnostic equipment. (Who was to know - I hadn't been to a hospital since JC was a messcook on the Merrimac. ) Anyways, this was the only way to make sure that all systems were grounded to the same point in the basement, via this "star" grounding system. IOW, there were no common grounds (I'm talking about the third prong here, same as Chris) from one outlet to the next, it was every outlet going directly to the connection in the basement (and thence to the collection of steel rods driven into the earth, and partially covered with the concrete pad). One of the main benefits of this was nearly no noise between equipment. Which of course means a steady reading on the monitoring screens for the folks in the operating room, a comforting thought to the loved ones of the operatee, I'm sure. But I digress........ One of the things I'm somehow remembering just now (must have overdosed on my Ginko Biloba) is that when I was in the Army in Germany, a lot of us GI's had American amplifiers, but absolutely all US Army bases used local power. That's right, it was (and still is) 220vAC/50Hz, available for everyone and his brother. Of course this lead to the guaranteed sale of a step-down transformer just about every time a GI was transferred into the country. New or used, he had to buy one (or more), or buy all new stuff on the local economy. No brainer there. Recall that in the vast majority of transformers, the two windings are isolated from each other. (An autotransformer would be one exception to this rule.) How does this do us any good, you ask? Essentially, through the modern miracle of magnetics. ;D Magnetism is what allows us to induce energy in one coil that is in close proximity to another coil which is carrying a current flow. Now, imagine if you will, the primary coil of a transformer is carrying household current (the mains). One side is "hot", the other side is grounded, perhaps via the outlet to a cold-water pipe, whatever. Now take a close look at the other coil - it has two leads, and if a load is hooked across them, then transferred energy flows through that load, right? Well, who says we need to hook one side of that coil to ground? If a complete circuit exists, then all of our electrical requirements have been met, have they not? Indeed, they have, and this does work as advertised. Witness the hundreds of thousands of units as earlier described, belonging to GI's in various parts of the world. Voila, you have now achieved a veritible isolation for your playing safety. ;D ;D ;D Of course, you now have a two-fold albatross aroond your neck - it costs quite a bit more than your lunch money, and it weighs like a beeyotch. One more thing..... if you are thinking "Variac" here, be aware that many, if not most, Variacs made today are really autotransformers in hiding. No isolation there, pardner! Double check before you lay out your cash, or make sure you can return it if you find that it does not have two entirely separate coils. Happy trails indeed! sumgai
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Shock
May 27, 2009 18:07:58 GMT -5
Post by ChrisK on May 27, 2009 18:07:58 GMT -5
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