Hi new member here, this is my first post 🙂
so I play in a band and we get shocked by the microphones while singing and playing guitar. I thought it might be a grounding issue.
I noticed the problem persisted with different guitar amps and guitars, and I tested all sockets and they do have a ground.
Thinking it might be a problem with our PA system, I used a multimeter and noticed that the pin 1 on XLR entries are not connected (no continuity) to the ground prong (same for input jack entries).
I opened the Mixer (a Phonic Powerpod 750RW) and noticed the following:
Here are my questions:
1) Does this seem normal to you ? / Is this why I'm getting shocked by the microphone ?
2) Would it be a problem to connect a wire from the front panel chassis to the wire attached to the back panel chassis (and thus connected to the ground prong) ?
Thanks a lot for your help ! I hope it's clear, please tell me if it's not or if I'm using wrong terminology !
Best,
Teemb
so I play in a band and we get shocked by the microphones while singing and playing guitar. I thought it might be a grounding issue.
I noticed the problem persisted with different guitar amps and guitars, and I tested all sockets and they do have a ground.
Thinking it might be a problem with our PA system, I used a multimeter and noticed that the pin 1 on XLR entries are not connected (no continuity) to the ground prong (same for input jack entries).
I opened the Mixer (a Phonic Powerpod 750RW) and noticed the following:
- The XLR pin 1 are connected to the front panel chassis, but the chassis itself is not connected to the ground prong.
- The connections on the back panel are connected to the chassis, which is itself connected to the ground prong.
- The front and back chassis are not directly connected to each other.
Here are my questions:
1) Does this seem normal to you ? / Is this why I'm getting shocked by the microphone ?
2) Would it be a problem to connect a wire from the front panel chassis to the wire attached to the back panel chassis (and thus connected to the ground prong) ?
Thanks a lot for your help ! I hope it's clear, please tell me if it's not or if I'm using wrong terminology !
Best,
Teemb
It seems like you might have found the problem but I don't know if your methodology will solve it, but it is worth a try. You will certainly void any warranty on the mixer. Have you contacted Phonic about it to see what they say? Has this happened in different venues or does it only happen in only one place? (I ask this because if you are connected to bad power then that might be the problem.........the ground and neutral must be bonded in the power that you're connected to).
Getting shocked in this way IS dangerous. Have you measured the voltage between the guitar pickups and the microphone? It's good to know.
One other temporary solution is to use wireless guitars as that will break the possibility for ground.
Getting shocked in this way IS dangerous. Have you measured the voltage between the guitar pickups and the microphone? It's good to know.
One other temporary solution is to use wireless guitars as that will break the possibility for ground.
The ground must always be connected to the chassis by law. Period. If it isn't connected it will not have passed any electrical safety.
So that unit is either not approved for use in your (any) country, or someone modified it and exposed everyone to danger. People have been killed on stage for all to see in your situation.
So that unit is either not approved for use in your (any) country, or someone modified it and exposed everyone to danger. People have been killed on stage for all to see in your situation.
Thanks a lot for your quick replies !
@anatech I bought the unit new on Thomann, never modified it. I expected to find a faulty connection, maybe something disconnected, but no it seems that it was designed on purpose with the front chassis not connected to the ground, but the back chassis connected ! On the front panel I don't see anywhere a place where a wire would be connecting to the ground... (for exemple if the wire was forgotten). I contacted Phonic but haven't received a reply yet.
@ThatSoundsGood: I brought the mixer home for testing and have measured 70mV between the metallic parts of the guitar and the microphone, I don't know if it's a lot or not... We only use the mixer in our rehearsal space, so I haven't tested elsewhere. Anyway, it seems if the ground and neutral were bonded in a bad power, I probably wouldn't get shocked, as the ground is not connected to the microphone, right ?
The mixer is not under warranty anymore, so no problem here, I think I will simply connect a wire from the front chassis to the wire on the back chassis, that's pretty easy and that should fix it. In the mean time, yes we used wireless guitars !
@anatech I bought the unit new on Thomann, never modified it. I expected to find a faulty connection, maybe something disconnected, but no it seems that it was designed on purpose with the front chassis not connected to the ground, but the back chassis connected ! On the front panel I don't see anywhere a place where a wire would be connecting to the ground... (for exemple if the wire was forgotten). I contacted Phonic but haven't received a reply yet.
@ThatSoundsGood: I brought the mixer home for testing and have measured 70mV between the metallic parts of the guitar and the microphone, I don't know if it's a lot or not... We only use the mixer in our rehearsal space, so I haven't tested elsewhere. Anyway, it seems if the ground and neutral were bonded in a bad power, I probably wouldn't get shocked, as the ground is not connected to the microphone, right ?
The mixer is not under warranty anymore, so no problem here, I think I will simply connect a wire from the front chassis to the wire on the back chassis, that's pretty easy and that should fix it. In the mean time, yes we used wireless guitars !
I am absolutely shocked by the fact it passed any electrical certification. Standards are very strict, all metallic surfaces that can be touched must be connected to the safety ground. Try and find a place to ground the front panel. The audio common is normally connected to the chassis through a resistor 10 ohms to 100 ohms in value. It shouldn't pass any current.
Place a 1K0 resistor between the two devices, then again each to ground individually. Measure the AC voltage drop and that tells you what the leakage current is for each device (E/R=I). Compare with the standard in your country and in the service manual for that device.
Static can give you a shock, pretty common in dry weather. AC current leakage is something you have to be careful of. Yup, ground it!!!
Place a 1K0 resistor between the two devices, then again each to ground individually. Measure the AC voltage drop and that tells you what the leakage current is for each device (E/R=I). Compare with the standard in your country and in the service manual for that device.
Static can give you a shock, pretty common in dry weather. AC current leakage is something you have to be careful of. Yup, ground it!!!
Here is a picture for illustration. Next to the red arrow you can see the wire with a screw on the metallic chassis from the back panel (painted black here). The other wires just connect one logic board to the other. I figured I could just connect a wire from this screw located on the back panel to one of the screws that you can see at the top of the front panel (screws visible at the bottom of the photo). Wouldn't that work @anatech ?
The ground is not connected to the microphone, but you are connected to the ground and microphone. When you get shocked, you become the ground and it is because you are the path of least resistance to ground. But if you're only seeing 70 millivolts between the microphone and the guitar then I think you're getting static shocks. And if you are using wireless guitars and still getting shocked then the problem is most likely static since the wireless is breaking the loop between the guitar amplifier and the mixer.
70mV is very little. I've seen as much as 60 volts in a bad power situation. I don't think the mixer is the problem. I would not modify it. I think you might be getting static electricity shocks. I don't think you would even feel 70mV. You would see something like 10-50 volts if there was a grounding problem in your system. is the air dry where you are at? I've experienced some pretty bad static shocks on microphones. The way to know if it's static is that it will also happen to people who do not play guitar (unless you have a massive grounding problem). Windscreens can help this. I have also used something called "Static Guard". It's made to keep clothes from wrinkling but I spray it under the feet of the artist singing and it helps to ground the static.
I am going to say that this is all on purpose by design and you're missing something about their design. That panel is either non-conductive or connected somewhere that you can't see. You could be causing a bigger issue by modifying it.
Are you getting shocked with wireless guitars being used? Then it's static.
I would contact Thomann about this as it is both a safety and a product liability issue and they may be interested to hear about it. (I buy gear from Thomann and they seem conscientious)
It's not entirely surprising in a mic circuit that pin 1 is not directly grounded to chassis since it is used as the return for phantom power, but the design should make provision to provide a connection to safety earth for the audio GND (and pin 1) somewhere on that board.
Something else to check is ground integrity at the venues where you play, there are approved devices to quickly check for that.
I would measure leakage current from mic pin 1 to earth GND, technically speaking there should not be any. It could be that there is something wrong with your particular board. Using wireless to the guitars certainly helps but it is possible that your PA is actually hazardous. Just because the device has a CE mark does not mean it was actually tested, it is the manufacturer's assurance that it has been, and self certification is permitted (whether or not you have a qualified test lab at your disposal - however if there is a problem and they found out it was not properly tested there would be he11 to pay.) Does it have a CE mark and a TUV or other European compliance agency symbol by the AC power connection?
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Hi Kevin,
Absolutely!
A conductive front panel must be earthed. Any touchable metallic surface must have a solid bond to earth.
Absolutely!
A conductive front panel must be earthed. Any touchable metallic surface must have a solid bond to earth.
The devices has a CE mark and also a QC checked... But good idea, I will contact Thoman to see if the had similar issues from other clients.
I don't think this is a static problem. The issue is not present when we use a wireless system on our guitars. (Actually it might have happened a couple of times, but the shock was way milder...). Also the air in our rehearsal space is far from dry, it's actually a quite damp basement (over 65% humidity if we don't use a dehumidifier).
The 70mV I measured was at home, I'll try to measure it in our practice space on Monday, and will check again the ground on the sockets and the guitar amps.
If it's just an audio problem, I guess I will hear it and it will probably indicate that the design is on purpose...
That said, I don't see how it would be normal that the microphone grill has no continuity with the ground prong...
thanks again to all for your replies !
I don't think this is a static problem. The issue is not present when we use a wireless system on our guitars. (Actually it might have happened a couple of times, but the shock was way milder...). Also the air in our rehearsal space is far from dry, it's actually a quite damp basement (over 65% humidity if we don't use a dehumidifier).
The 70mV I measured was at home, I'll try to measure it in our practice space on Monday, and will check again the ground on the sockets and the guitar amps.
@ThatSoundsGood, what kind of issue are you thinking about? My only worry would be a safety issue, but I don't see how a simple wire connecting the chassis on the front panel to the wire on the back panel chassis would bring any safety problems ? Am I missing something?
If it's just an audio problem, I guess I will hear it and it will probably indicate that the design is on purpose...
That said, I don't see how it would be normal that the microphone grill has no continuity with the ground prong...
thanks again to all for your replies !
I have seen a problem like this a couple of times before. One time it was caused by a Mesa Boogie guitar amp which had a 3-position on/off/on power switch (for hum reduction). The two "on" switch positions connected a cap from chassis ground to either line or neutral. If the amp wasn't properly grounded and if the switch was set to the wrong position, the guitarist could get a shock from touching something like a PA mic which is grounded to AC line ground.
The other occasion was at a Frank Zappa concert. Frank was getting a shock when he touched his PA mic. Problem in that case was traced to improper grounding of the PA system.
The other occasion was at a Frank Zappa concert. Frank was getting a shock when he touched his PA mic. Problem in that case was traced to improper grounding of the PA system.
I'm not familiar with this mixer, but some mixers have specific faders that are sensitive to grounding because they will only move when a finger touches them. I believe the SSL live consoles are like this. Might not apply to your mixer. But I think modifying the mixer is the wrong path here. You haven't even determined that the problem is the mixer. I would take a look at the voltage between the microphone and person getting shocked. Check to see what else is plugged into the same power as your mixer (lights, tea kettles, etc.). Unplug them and see if the problem goes away. Plug one thing in at a time until you figure out what is dumping voltage down the ground and causing the shocks. It's likely to be a guitar amplifier, light or random piece of gear. You might have a wiring problem with something. I've seen this many times before and it has never had anything to do with the mixer. It's almost always something else plugged into the power causing the problem. It could be a bad extension chord. You can use your volt meter to check the power running through every cable and make sure that it's consistent and there's zero (or near zero) voltage to the ground.
Well i continued my investigation and i still thing something is wrong with this PA system.
If you look at the picture (metal plate separating the front and back of the PA system box), there are TWO screws with paint removed around (I guess to facilitate electric contact) and the black wire (connected to the back panel chassis on the other side which is itself connected to ground) is not even connected to one of these screws !
So my guess is that the back panel chassis is connected to the middle metal separation plate, and the front panel chassis SHOULD be connected to this separation plate as well, to have a common ground (but isn’t !).
Also, the way it is now, I see no reason why a wire connects the back panel chassis to this separation metal plate. It makes absolutely no sense to me.
If you look at the picture (metal plate separating the front and back of the PA system box), there are TWO screws with paint removed around (I guess to facilitate electric contact) and the black wire (connected to the back panel chassis on the other side which is itself connected to ground) is not even connected to one of these screws !
So my guess is that the back panel chassis is connected to the middle metal separation plate, and the front panel chassis SHOULD be connected to this separation plate as well, to have a common ground (but isn’t !).
Also, the way it is now, I see no reason why a wire connects the back panel chassis to this separation metal plate. It makes absolutely no sense to me.
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My guess is that the plate is there to provide some shielding between the frontend circuitry and the higher power amplifier components. Only one side of a shield needs to be grounded.
In that case, the front plate is probably not connected to the same earth as the power circuitry to prevent hum or problems with the digital side of the amplifier.
However, you're not getting shocked when touching the front plate, and no high voltage runs through it, so it's probably not your problem.
Your Guitar, Amplifier, the PA, and the microphone need to be connected to the same ground for there to not be a voltage potential between them. You said that they're all connected to ground, but are they all connected to the same ground? There isn't a faulty connection in a power strip or something?
In that case, the front plate is probably not connected to the same earth as the power circuitry to prevent hum or problems with the digital side of the amplifier.
However, you're not getting shocked when touching the front plate, and no high voltage runs through it, so it's probably not your problem.
Your Guitar, Amplifier, the PA, and the microphone need to be connected to the same ground for there to not be a voltage potential between them. You said that they're all connected to ground, but are they all connected to the same ground? There isn't a faulty connection in a power strip or something?
You can measure with a DVM set to AC volts from the PA chassis (or wherever someone gets a shock) to a cold water pipe or another known good ground. However, a DVM is 10Megohm input impedance. You can put a loading resistor of 1meg or something like that if you measure some voltage and see how far it gets pulled down with some more loading. That type of measurement strategy can probably pin down where the problem is fairly quickly.
Musicians being electrocuted is tragically common. More so in the past, but still in recent times also. =( Easy to find plenty of examples on goog. Watch out!
Could it be that you're feeling the phantom voltage? Some microphones require a +48 V bias voltage (commonly: phantom voltage). It's often supplied through a significant resistance so it shouldn't kill you, but I have heard of musicians getting 'buzzed' on the lips if they get a bit too close to the mic on a damp day.
Tom
Tom