Understanding electrical ground is critical when dealing with electrical systems (including amplifiers, preamplifiers and the like).
What is amplifier ground, and where should we ground an amp? Amplifier ground refers to the ground wire that safely provides the least amount of electrical resistance to earth ground or chassis ground to minimize the chance of electrocution. Amps are typically grounded via power mains outlet connections and/or power supplies or to the car chassis.
In this article, we'll discuss electrical ground in more detail, its importance to various audio amplifiers, and how to connect amplifiers to ground if they are not already connected.
What Is Electrical Ground?
Electrical ground, in circuit design, is the reference point in which all voltages within the circuit are measured (typically set to 0 V). Ground acts as a common return path for electrical current.
The term “electrical ground” (or its other term “electrical earth”) is in reference to the fact that the actual earth/ground is usually idealized as an infinite source or sink for an electric charge. Ground, in a perfect world, will absorb an unlimited amount of current without changing its potential.
In electronics, we often refer to 3 different electrical “grounds”:
All three ground “types” indicate a connection to a [theoretical] point of zero voltage. In reality, ground will usually have a varying (but negligible) voltage due to the inevitable resistance of the ground return path.
However, each refers to electrical ground within a different context:
- Signal ground: defined as the 0 V (zero potential) reference point within a circuit.
- Chassis ground: defined as a ground point that connects to the metal chassis of an electrical device.
- Earth ground: defined as a path to “earth”, typically through the ground connection of the wall plug and power mains.
Let's dig in with a bit more detail here and add details about amplifier ground as we do so.
The signal ground is the reference point from which a signal is measured. In the case of amplifiers, this is the audio signal, which is an AC that has frequencies between 20 Hz and 20,000 Hz (or more). It also acts are a reference point for power supply voltages and the like.
A clean signal ground is required for audio devices so as not to induce noise into the signal. Many audio signals are of low voltage levels and require clean circuits to maintain high signal-to-noise ratios.
Amplifiers typically deal with relatively low-voltage audio signals (particularly at their inputs) and relatively high-voltage power supplies. Having a distinct signal ground for each distinct amplifier circuit is possible and even suggested to keep ground-induced noise to a minimum in the signal.
Though perhaps counterintuitive, the signal ground should, at a single point, be connected to the chassis ground of the amplifier.
Let's say some interference noise is induced directly on the chassis or indirectly on the ground wire of an audio cable (which would connect to the chassis ground). To keep the relationship between signal and chassis ground, it's actually beneficial to have the signal ground fluctuate along with the chassis ground.
Though fluctuation is not necessarily a wanted occurrence, it happens, and amplifiers should be designed to deal with it effectively.
This signal ground may be connected to earth ground through the chassis ground. A system where the signal ground is not connected to another circuit or earth is often called a floating ground or “double-insulated”.
The chassis ground is the point that connects to the metal enclosure of the electrical device (amplifier).
Chassis ground presents a common point for the signal ground and earth ground (via the ground wire of a signal connection and the power mains connection, respectively). The chassis ground is useful for shielding and prevention of electrical shock.
The chassis ground of an amplifier is typically made at a single point and works to prevent two undesirable occurrences:
- A return current path through an available but undesirable path
- Current circulating through the chassis
Current flowing through the chassis of an amplifier (or another audio device) can, and most often will, induce a ground loop. Therefore, the chassis should be ground to earth at a single point only.
Ground loops are the dreaded 60 Hz hum (or 50 Hz, depending on the geographical location of the power mains). This is caused by having two or more different ground potentials connected to the chassis that cause current to flow through and be induced in the chassis and audio device.
Note that it is rare for two separate grounds to have exactly the same electrical potential.
Since the chassis can also connect to the signal ground at the audio connections, it can further add unwanted electromagnetic interference noise in the amplifier's input and/or output signals.
Ground loop is discussed in greater detail in my article What Causes Speaker Hum & Hiss (How To Eliminate Them Both).
Earth ground is more or less a safety precaution. The designed earth ground return path for amplifiers will be provided from the ground wire of the amp's power supply (on the 3-prong power mains connector).
This earth-ground connection ensures a safe path for any stray current to run to ground (rather than through a person's body, for example, when the person touches an exposed part of the power (or audio) circuits).
Any potentially dangerous/lethal current will be safely dissipated to the earth and will, hopefully, trip a fuse to turn off the equipment to avoid any damage.
The signal ground is the reference point (typically 0 volts) for the audio signal in an amplifier circuit/connection that carries audio signals.
The chassis ground is the point that connects to the metal enclosure of the electrical device (amplifier) and presents a common point for the signal ground and earth ground. It helps with shielding and the prevention of electrical shock.
This earth-ground connection provides a safe path for any stray current to run to the earth.
Why Amplifiers Should Be Grounded
To continue on the points listed above, let's discuss why an audio amplifier should be grounded?
First, the amplifier should be grounded to earth for safety reasons. More importantly, the amplifier should be connected to the same ground potential as all the other audio equipment in the system.
By properly grounding the amplifier (and other audio equipment) to the same earth potential, we provide a safe path for any stray current to flow toward. This should be a major safety consideration when setting up studios and PA systems. More on this in the section Grounding A Guitar/Bass Amplifier.
Poor wiring and grounding can lead to personal injury if someone touches the amplifier circuits and effectively becomes the shortest path to ground. Improper grounding can also lead to malfunctioning and damage of the amplifier and its connected audio devices.
Note that the danger of an amplifier is not so much a product of the AC audio signal, which has a relatively low voltage. Rather, the risk comes from the power supply and power circuitry that powers the amplifier with higher voltages.
Relating the entire system to a single ground potential also works to eliminate (or at least reduce) ground loop hum, which makes itself apparent in audio systems as the dreaded 50 or 60-cycle hum.
The audio circuits of the amplifier should be grounded to a zero-potential signal ground to reduce noise in the signal further. This is especially important in amplifiers since they are designed to amplify the signal and any noise within the signal.
Note that, for optimal results, balanced signal transfer is suggested. All balanced signals work with the signal ground. More on balanced signals in the section A Note On Balanced Audio Connections.
Amplifiers should also have a chassis ground to connect to the signal and earth grounds at a single point.
The chassis ground is useful for shielding the amplifier's audio signal and preventing electrical shock. It also helps to prevent current from flowing to an undesired location, further improving the amplifier's safety.
Grounding A Car Power Amplifier
Car amplifiers should be grounded via a single wire that connects the amplifier chassis to a bare metal area of the car's body.
A general rule of thumb is to make this connection to the car body less than 18 inches from the amplifier's location.
A common ground connection location is at any bolt connected to the car's metal chassis. Similarly, the strut tower in the car's trunk is a useful connection point if the amplifier is positioned in the trunk.
Ensure the ground wire touches bare metal rather than any rust. An adhesive may be required to hold the ground wire in place. Just ensure that the adhesive does not separate the wire from the car's metal chassis.
Grounding A Live Sound Power Amplifier
When grounding a live sound power amplifier, it's best to connect it to the same power mains source (wall plug or power conditioner) as the mixer.
Using a power amplifier in a PA system generally means the speakers and the mixer are passive. This means that the speakers will not need to plug into any wall sockets (that eliminate a few connections to possible different ground potential connections in the system).
The mixer will still require a power source for its preamps and active circuitry. Therefore, plugging both the power amplifier and the mixer into the same power source (same ground potential) will reduce any ground hum and the possibility for shock.
Note that the amplifier chassis ground should be connected to the mixer chassis ground.
The instruments (if active) that connect to the mixer should also be grounded, even though reaching the same power source (ground potential) as the amp and mixer is unlikely.
Grounding A Home/Studio Power Amplifier
To avoid the possibility of ground loop hum and shock hazards, a home/studio power amplifier should be connected to the same wall plug as the mixer and/or other audio source devices.
Again, this helps mitigate any risk of shock while also reducing the likelihood of hum in the connected speakers.
Grounding A Guitar/Bass Amplifier
Having proper grounding is incredibly important when playing through a guitar amplifier and other audio systems simultaneously.
There are countless accounts of guitarists getting shocked, seemingly from touching a microphone as they play through their amplifier.
Essentially, some piece of equipment in the overall system is grounded to a different potential than another.
Let's say a powered mixer that takes in a microphone's signal, amplifies that signal and sends it to a PA speaker is grounded at a certain potential (wall plug A).
The guitar is plugged into a guitar amp that is either ungrounded or grounded at a different potential (wall plug B).
As the guitarist is playing, he or she may touch (or even get close to) the microphone. This can cause a circuit to form when the electricity of the system flows through the performer to ground, resulting in an electric shock or far worse.
Having all equipment grounded is important and ensuring the grounds (various wall plugs) are equal is even more important to the safety of the performers.
For more information on this topic, check out my article Why Do I Get An Electrical Shock When I Touch My Microphone?
Preamplifiers should be grounded, too.
Preamp chassis should be connected to the signal ground of the connected audio cable. They should also be grounded to the output connection.
To properly ground a preamp to earth, ensure it's plugged into its proper power supply and make sure that power supply is connected to a wall plug that is common among the other pieces of audio equipment in the audio system.
A Note On Balanced Audio Connections
It's worth mentioning that an amplifier's audio connections (inputs and outputs) may also be “grounded”.
Balanced audio transferring/connections have two signal wires (positive and negative polarity) and a common ground wire.
How do balanced connections work? Let's have a look at a few diagrams to better our understanding.
First, balanced audio is usually carried via XLR cables (though it can also be carried via TRS and other connections). Let's have a look at a simple diagram of an XLR connector with its pins.
- Pin 1: Ground
- Pin 2: + Signal (Positive Polarity)
- Pin 3: – Signal (Negative Polarity)
Pin 1 of a balanced XLR connection (the sleeve of a TRS connection) provides a common ground for the signal conductors (pins 2 and 3 or tip and sleeve of a TRS). This ground wire will also shield the cable, helping to reduce noise and interference while also connecting to the ground chassis of the source and/or input.
The input of a balanced connection is generally grounded and has a differential amplifier that sums up the differences between the two signal conductors.
As the differences are summed together, the common noise/interference on both signal wires is cancelled out. This cancellation is known as common-mode rejection, which is generally measured in decibels and listed on specifications sheets as CMRR (common-mode rejection ratio).
Can an amplifier drain your car battery? Car amplifiers plug into and get their power from the car's battery. Proper wiring and matching of power ratings will keep things safe, and the alternator should keep things running without issue. Improper wiring and matching could lead to the amp draining the battery completely.
How do I choose an amp for my speakers? When choosing/matching an amplifier and speakers, it's good to do your research. There are a few important specifications to consider:
- Compare the speaker's nominal impedance to the *rated output impedance of the amplifier. Speakers with lower impedances are more difficult to driver (more power-hungry and lower damping factors) so look for an amp with a low enough *rated output impedance.
- Compare the speaker's power handling spec and the amp's output power specs to see if the amp is powerful enough to drive the speakers. Amps with too much wattage can be used but must be kept at lower levels to avoid damaging the speaker and/or the amp itself.
- Look at the sensitivity rating of the speaker and determine how much power is required to achieve the desired listening sound pressure levels.
*The rated output impedance of an amplifier is not its actually output impedance (which is much lower). The rated output impedance allows us to compare better and match impedances between the amp and the speaker.
For more information on speaker impedance, power handling and sensitivity, check out the following My New Microphone articles respectively:
• The Complete Guide To Speaker Impedance (4Ω, 8Ω, 16Ω & More)
• Complete Guide To Speaker Power Handling & Wattage Ratings
• Full Guide To Loudspeaker Sensitivity & Efficiency Ratings
Choosing the best power amplifier for your car, home sound system, or pro audio application can be a complicated assignment. For this reason, I've created My New Microphone's Comprehensive Power Amplifier Buyer's Guide. Check it out for help choosing the best power amp for your applications.