Have you ever had this experience? You’re playing a show. You pick up your guitar, strum a few chords, and give a “Check one, two…” to the microphone. Everything seems fine until you feel a powerful shock from the microphone.
Why Do Microphones Shock You?
If a microphone shocks you, your equipment (such as a guitar amp or mixer) is poorly-grounded, putting an electrical voltage onto your body. When you touch a properly grounded microphone or another grounded surface, your body discharges. This has the potential to be very dangerous, so it’s important to understand why it happens and how to fix the problem.
If a microphone shocks you, your equipment (such as a guitar amp or mixer) is poorly-grounded, putting an electrical voltage onto your body. When you touch a properly grounded microphone or another grounded surface, your body discharges.
How Can a Microphone or Guitar Shock You?
If your getting shocked when you touch your microphone or guitar, there are a few things happening. Once you understand how the equipment is shocking you, it will be easier to determine what is the cause and how to fix it.
1. Your Equipment is Improperly Grounded
In most cases, the microphone or guitar is not actually the problem. It’s more likely that the equipment they plug into is improperly grounded.
Electrical Fault Inside Equipment
Your guitar amplifier, pedalboard, audio mixer, or microphone preamp is usually the culprit in situations like these. Something on the inside of the device is malfunctioning. A variety of things can go wrong inside your equipment. Whatever it may be, this malfunction is creating a voltage on the device’s chassis, or enclosure.
Two-Prong Adapter Plugs
The electronics within these devices are designed in a way that should protect you from any voltage applied to the chassis. Devices with three-pronged plugs connect the third, round prong to the chassis of the device so that any voltage will be drained to ground.
Using a two-prong adapter, or “cheater” plug for these devices will disable this safety feature. If voltage is present on the chassis of a device that is plugged in using one of these adapters, it will have no place to go. This can be very dangerous, as you’ll see in the following sections.
2. Your Body Becomes Charged
If the chassis of the equipment your instrument or microphone is plugged into has voltage applied to it, it is important that that voltage has a place to go. The purpose of the safety ground circuit inside your equipment is to provide a pathway for any voltage to be discharged. Removing this pathway means that the voltage will have to find another path. It’s possible that your body will become that path!
You’re Connected to Your Equipment
Although you may feel safely isolated from the electrical components of your guitar amplifier or mixer, this is not the case. Even while standing several feet away from these devices, you are still directly connected to them through the guitar or microphone in your hand.
Just as the chassis of the amplifier and mixer are connected to ground, so are the hardware of your guitar and the grill of your microphone.
The following images show this:
The bridge of your guitar is connected to the sleeve, or shield, of your instrument cable. The sleeve of your cable also connects to the amplifier chassis. Therefore anything that is metal and touching the bridge is connected, too. Your tremolo bar, tail piece, strings, and tuners are all directly wired to the chassis of your guitar amp.
The grill of your microphone is connected to pin 1 (ground) of your XLR microphone cable. This is a direct connection to the chassis of your microphone preamp, or mixer.
There is no need to be concerned by these connections. When functioning properly, these connections are actually a safety measure, in place to allow voltage to find a pathway to ground. When your equipment is not properly grounded, however, these safety measures become a safety hazard.
Your Body’s Capacitance
Capacitance is an object’s ability to store electric charge. Capacitance doesn’t describe the intensity of a charge, but rather an object’s ability to resist voltage from being discharged. The capacitance of the human body is relatively limited, maxing out around 100pf, or pico-farads. In the following equation, you can see that the maximum charge an object can store is limited by its capacitance.
When you touch a guitar or microphone that is connected to an ungrounded system, the voltage on the chassis of that system will be transferred to you. If you are not touching another conductive surface, the voltage will be stored to your body as electric charge. The body’s low capacitance prevents a dangerous charge from forming.
The situation becomes dangerous when you simultaneously touch both the ungrounded equipment and a grounded surface, creating a conductive pathway from the ungrounded equipment to ground.
3. Touch Something That is Grounded
When you walk on a carpeted floor, your body can become charged. However, you don’t notice the charge until you touch something, such as a door knob, that allows the voltage on your body to discharge. This can be somewhat painful, but is not life threatening. That’s because even though up to 30kV can be transferred to your skin from the carpet, the body’s low capacitance limits the maximum intensity of the charge.
The same thing is true for musical equipment. When you pick up an instrument connected to ungrounded equipment, any voltage on the chassis will be transferred to your skin. Voltages within the circuits of various amplifiers range widely, but typically range from a few millivolts to 500V. Due to the low capacitance of your body, charges from these devices are very low.
If you set the instrument down and then touch a grounded surface, the charge on your body may be so small that you do not even feel the discharge. However, if you touch a grounded surface while still holding the instrument connected to ungrounded equipment, you’ll find yourself in a very dangerous situation.
The following two diagrams are useful to understand why this is the case:
This diagram shows a simplified image of what is happening when you touch ungrounded equipment without touching anything else. The second you touch the ungrounded equipment, or an instrument connected to it, the voltage quickly charges your body to its maximum capacity until you are fully charged.
You can imagine it’s like filling up a balloon, because once your body is fully charged, the voltage has nowhere else to go.
This diagram shows a much more dangerous situation. This is what happens when you touch both ungrounded equipment and a grounded surface. The voltage from the ungrounded chassis now has a pathway through your body and into the grounded surface. That creates the potential for a very strong electric current to indefinitely flow through your body.
This is because your body is no longer simply storing an electric charge, so the limited capacitance of the body is irrelevant. Instead, the electricity is flowing through you to the grounded object. This can be deadly.
Touching a grounded object can mean a variety of things. You could touch a properly-grounded microphone system while holding an improperly grounded guitar system, or vice versa. You could be standing on a damp basement floor with bare feet. If there is moisture from rain, a microphone stand or your shoes could become conductors to the ground.
How to Test for Poor Grounding
If you’re experiencing this, you should really find the source of the problem and fix it. This section will help you to determine where the voltage is coming from, so that you can take action on resolving the issue.
Testing with a Multimeter
If you don’t have a multimeter, you might want to have one. They are useful for a lot of troubleshooting situations. I recommend getting one with a digital display, like this one.
Set your multimeter to test for continuity. This setting measures resistance and is often marked by an omega symbol (Ω). Run the following tests:
Testing Your Guitar Rig
1. For this, the guitar amp will be unplugged from power. Place one probe on the input of your guitar amplifier. Place the other probe on the ground prong of the guitar amplifier’s three-pronged power cable. You should see the needle jump. This indicates that these points are properly connected. If this test passes, move on to step 2.
2. Keep your guitar amplifier unplugged from power. Plug your guitar into the amplifier with an instrument cable. Place one probe on your guitar’s bridge. Place the other probe on the metal chassis of your guitar amplifier. You should see the needle jump. This indicates that these points are properly connected. If these two tests pass, your guitar rig is properly grounded.
Testing Your Microphone System
1. For this, the mixer will be unplugged from power. Place one probe on pin 1 of the microphone input of your mixer. Place the other probe on the ground prong of the mixer’s three-pronged power cable. You should see the needle jump. This indicates that these points are properly connected. If this test passes, move on to step 2.
2. Keep your mixer unplugged from power. Plug your microphone into the mixer with an XLR cable. Place one probe on the chassis of your microphone. Place the other probe on the metal chassis of your mixer. You should see the needle jump. This indicates that these points are properly connected. If these two tests pass, your microphone system is properly grounded.
How to Fix the Problem
Don’t Touch Grounded Surfaces
As mentioned above, it is possible to hold a charge from your ungrounded guitar amplifier or mixer and not even notice, so long as you don’t touch the device and a grounded object simultaneously. You should always wear shoes when using these devices. If you ensure that you do not touch both your ungrounded instrument and a microphone, water pipe, floor, or other grounded object at the same time, you will probably not be harmed. However, the risk of electrocution is very serious, so I would recommend servicing your equipment.
Service Your Equipment
If you have determined that ungrounded audio equipment is the cause of the shocks, you should definitely take your equipment to a service shop to be repaired or modified.
If your amplifier does not have a three-pronged power cable, take it to a guitar amplifier shop to have one installed. This is an important safety measure that is worth the money.
If your amplifier does have a three-pronged power cable, but you suspect it is not properly grounded, take it to a professional to search for any electrical faults that might exist inside.
Some may recommend using a three-to-two-prong “cheater” adapter, but this is extremely dangerous. Do not use these adapters with audio equipment under any circumstances.
Although wired connections are always superior to wireless connections for sound quality, electric current can not travel through wireless connections. This might be an option worth looking into if you are not willing to have your equipment repaired.