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Author Topic: brain storm an optimal human safety system for back line  (Read 95567 times)

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #190 on: March 17, 2015, 12:19:29 pm »

If you place a relatively low impedance from a floating ground to neutral that should bleed off any phantom voltage-just like a low impedance VOM.  At least that is my thinking.
Yes, but if the line and neutral polarity are unknown, you may be connecting ground to hot.

One test involving micro control switches a load between hot and ground, then looks to see if neutral and ground show similar artifacts. I am not enthusiastic about making one of these and think a simpler way might be possible with an audio sniffer (just listen to ground and neutral.. they should sound subtly different when neutral is under load. )
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Yes, series components all have same current flow, and oder does not change that-but this is not a simple series circuit. If the neon lamps are connected to a touchpad they are interfering with each other.  Placing the ballast between the neon and the touchpad puts that impedance between the lamps so you get 2 times the ballast isolation-similar too, but more predictable than using three separate touchpads connected by your skin.

Sorry I still don't see much difference...

JR
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #191 on: March 30, 2015, 10:21:56 am »

Good news, I finally heard back from my serious guitar tester....To refresh everyone's memory since it has been a while, I modified a GFCI outlet strip with a 3 pos switch so the ground could be selected between, hard ground, open circuit, or cap coupled (my proverbial stinger cap throwback).  I used a 0.15uF cap to insure it would draw enough current from a fault to trip the GFCI (6 mA).

My tester was a guitar amp design engineer, who now runs his own company designing and selling guitar pedals (amptweaker). It took him so long to get around to testing this for me, because his business has been slammed with orders (just signed two new distributors overseas at NAMM show).

Long story short, the ground in "cap" position was identical for noise floor to the hard grounded position. An additional benefit that I didn't anticipate is that the cap position is quieter than the hard grounded position, if there is a ground loop (wrong name for what is going on) created by amp plugged into one branch circuit and pedals plugged into a different outlet (in another room).

He tested it with a very high gain amp (James designed the EVH 5150 while at Peavey so he knows high gain) and under typical use scenarios. 

So I am now satisfied that the GFCI + cap is a viable approach for back line. My main stipulation is that the ground cap be a "Y" cap (tested to not fail as a short). I was able to source some 0.1uF Y caps but no 0.15 yet. The larger cap is needed to insure the GDFI will trip if the fault path is through that ground cap.

JR

PS: I am kicking around a modification to the GFCI circuit that senses for current (or voltage) in the cap coupled ground path to trip the GFCI at less than 6 mA in that ground. 
« Last Edit: March 30, 2015, 10:25:16 am by John Roberts {JR} »
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frank kayser

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Re: brain storm an optimal human safety system for back line
« Reply #192 on: March 31, 2015, 12:04:26 am »

Good news, I finally heard back from my serious guitar tester....To refresh everyone's memory since it has been a while, I modified a GFCI outlet strip with a 3 pos switch so the ground could be selected between, hard ground, open circuit, or cap coupled (my proverbial stinger cap throwback).  I used a 0.15uF cap to insure it would draw enough current from a fault to trip the GFCI (6 mA).

My tester was a guitar amp design engineer, who now runs his own company designing and selling guitar pedals (amptweaker). It took him so long to get around to testing this for me, because his business has been slammed with orders (just signed two new distributors overseas at NAMM show).

Long story short, the ground in "cap" position was identical for noise floor to the hard grounded position. An additional benefit that I didn't anticipate is that the cap position is quieter than the hard grounded position, if there is a ground loop (wrong name for what is going on) created by amp plugged into one branch circuit and pedals plugged into a different outlet (in another room).

He tested it with a very high gain amp (James designed the EVH 5150 while at Peavey so he knows high gain) and under typical use scenarios. 

So I am now satisfied that the GFCI + cap is a viable approach for back line. My main stipulation is that the ground cap be a "Y" cap (tested to not fail as a short). I was able to source some 0.1uF Y caps but no 0.15 yet. The larger cap is needed to insure the GDFI will trip if the fault path is through that ground cap.

JR

PS: I am kicking around a modification to the GFCI circuit that senses for current (or voltage) in the cap coupled ground path to trip the GFCI at less than 6 mA in that ground.
Cool beans!  Good test.  I like the added benefit of the quieting the "ground loop" misnomer. 
frank
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #193 on: April 09, 2015, 12:22:51 pm »

I am about ready to stick a fork in this KISS version... A GFCI power drop with "Y" cap in series with ground. My testing has satisfied me that this would provide another degree of human safety for back line use, while providing the additional benefit in reducing "ground loop" noise issues. Besides that probably not being an accurate description for what is causing the ground related hum, if a pedal or preamp in front of the protected guitar amp is plugged into a different grounded power outlet (or why would there be hum), that other ground is not cap isolated so again a shock hazard from rouge external mains voltage faults.

I believe there is merit in somebody (not me) making and selling a GFCI power drop with stinger cap. While this might finesse UL requirements by labeling the ground differently, it would be really nice for UL to bless this, or at least not discourage it.

=========

Part deux is the smart GFCI drop and this would have enhanced features beyond the KISS version. An additional power disconnect relay could test for RPBG and never power up, if outlet wiring is rogue. Further it could sense for voltage/current in the ground path and use that to trip the GFCI and/or disconnect power/ground relay.

Perhaps this could even measure mains voltage and not turn on if voltage too high (or too low).

I DO NOT BELIEVE THIS IS A SELLABLE PRODUCT.... musicians are not suitably motivated by human safety to pay what this would cost... and it would probably come with some liability if people still manage to get hurt.

The KISS version has a much better chance of commercial success and seem hard to screw up.

JR
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #194 on: April 24, 2015, 08:30:33 pm »

I've finished my side project so I'm back on this for now.

I am reluctant to put a microprocessor inside because debugging a hot chassis design could be shocking. 

To build upon the KISS (tm) GFCI power drop, I have another enhancement-work around to protect the ground.

I am uncomfortable with making the ground carry 6mA to trip the GFCI and leaving it always connected even after a fault.  My improved approach uses a 3 pole relay to disconnect Line, Neutral, and ground after a fault. The relay goes in series with the GFCI and mains power. The relay coil is powered from the output side of the GFCI. The relay is momentarily bypassed to latch the system on, and once the GFCI comes up the relay is powered and supplies continuous power to the GFCI. If there is a fault and the CFCI opens, the relay opens too, opening up the ground.

Now I can improve the sensitivity of ground current and use a fault detected there to imbalance the GFCI and trip it off.

I have other possible enhancement to pursue, but this should allow us to increase the sensitivity of ground fault currents and open up that path completely.

Of course the devil is in the details, but I'm soaking this idea in beer right now.... I'm optimistic.  8)

JR
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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #195 on: April 24, 2015, 11:17:19 pm »

Since commercial GFCIs disconnect both hot and neutral when they trip, in theory you could use a SPDT relay to connect the ground-disconnecting the ground if the GFCI is tripped.  Using a second GFCI with adjustable sensitivity in in series to monitor current on the EGC would complete the protection.
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #196 on: April 26, 2015, 08:42:06 am »

Of course the devil is in the details, but I'm soaking this idea in beer right now.... I'm optimistic.  8)

Per your recommendation I soaked this in beer last night, and came up with a slightly different spin. Rather than creating a bunch of extra circuitry to disconnect the EGC feeding the stinger cap, why not just add a neon bulb with its own series resistor in parallel with the stinger cap? That way, if there was a hot ground for whatever reason (RPBG, line-to-chassis fault, etc...), and touched the guitar strings, the neon bulb would light up indicating a "hot ground".

So by adding just three parts to a standard GFCI receptacle (Stinger cap, neon bulb, 100K ballast resistor) you would not only protect musicians from a hot guitar or hot mic, you would add an extra indicator light that told them what to look for when troubleshooting why the GFCI tripped.

Hey, it was really good beer... ;D
« Last Edit: April 26, 2015, 10:20:06 am by Mike Sokol »
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #197 on: April 26, 2015, 10:41:35 am »

Per your recommendation I soaked this in beer last night, and came up with a slightly different spin. Rather than creating a bunch of extra circuitry to disconnect the EGC feeding the stinger cap, why not just add a neon bulb with its own series resistor in parallel with the stinger cap. That way, if there was a hot ground for whatever reason (RPBG, line-to-chassis fault, etc...), and touched the guitar strings, the neon bulb would light up indicating a "hot ground".
Nice, but I bet the musician can probably feel the 6mA or so. :o  While more lights are always good.  ;D


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So by adding three parts to a standard GFCI receptacle (Stinger cap, neon bulb, 100K ballast resistor) you would not only protect musicians from a hot guitar or hot mic, you would add an extra indicator light that told them what to look for when troubleshooting why the GFCI tripped.

Hey, it was really good beer... ;D
With the KISS(tm) approach or KISS+Neon, the hot ground does not automatically trip the GFCI, so for RPBG the stinger cap coupled ground is still connected. It will only draw 6 mA through the ground cap if hard path to ground exists (like muso holding mic and guitar strings.) Six mA is not life threatening and safe as is, while not very pleasant.

KISS+Relay in minimum complexity configuration is relay with coil powered from output side of GFCI so ground path is also lifted whenever GFCI trips. I am not sure that this adds benefit commensurate with cost.

KISS+Relay+smart glue.  My goal, is to add some extra logic to enhance the GFCI trip modes. Sensing the voltage/current in the ground path, and when above some arbitrary threshold trip the GFCI, which removes power from the relay so opens up the ground. This way adds detection and protection against a different fault vector hopefully with even more sensitivity than the GFCI's 5mA +/-1mA.

In addition to adding a disconnect on ground fault, I can add some more glue logic, to turn on the relay (with one or two relay poles supplying mains power to the GFCI when on to latch the circuit powered up. The jump start power to turn on the GFCI + relay is switched via a touch switch that only works if the outlet Line lead is hot. This way if Line and Neutral leads are reversed (like in a RPBG), the unit will not latch power on when the on switch is touched.  Neon bulbs can be added for various passive indication. A neon lamp across the relay ground pole could indicate voltage present input/output ground. Another neon lamp could confirm that miswired outlet has voltage present, just not the correct polarity if power switch is unresponsive.

I need to do some testing, but i suspect I might be able to operate the touch switch automatically from the output side of the GFCI (neutral) with products plugged into the strip. Even better if the GFCI and power drop output side had enough capacitance to provide the low reference to turn it on. Having to re-latch the power strip if power is interrupted may be undesirable.

JR   

PS: I need to be careful that my intentional imbalance of the GFCI when it detects ground current does not accidentally correct an imbalance in the GFCI especially if that is the original source of the ground current. IMO this is unlikely but something to anticipate. 
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Tim Padrick

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Re: brain storm an optimal human safety system for back line
« Reply #198 on: April 26, 2015, 02:06:57 pm »

Design it.

Patent it.

Sell it to Whirlwind to add to their extensive line of power goodies.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #199 on: April 26, 2015, 04:15:54 pm »

Design it.
already in process
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Patent it.
Not worth the time and $5-10k. All a patent does is give you the right to sue... and you can still lose in court after you sue (ask me how I know that  >:( ).
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Sell it to Whirlwind to add to their extensive line of power goodies.
My work effort in this is published (here) and free for anybody to use. To do this right for production somebody has to invest several $k into establishing a UL file to test and prove that the concept is solid, while i have no doubt.

I don't see a huge commercial market for this. The external or secondary hot ground seems to be a music industry specific problem mostly affecting live performers. 

JR
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