Connectors and Adapters

Why Use Balanced Connections?

Balanced vs Unbalanced Connections

An Unbalanced connection has one signal wire and one ground wire that serves as a voltage level reference and often also as a shield against interference. Any noise induced in the signal wire will appear in the terminating circuit.

A Balanced connection has two signal wires, with the second signal being of opposite polarity (180 degrees out of phase) to the first. Any noise induced in the connection will appear on both signals. At the receiving circuit, the second signal is inverted and added to the first signal. This doubles the level of the signal and subtracts out all the noise.

Unbalanced Audio

These types of cables are generally used to connects line-level devices to each other or to a mixer. At the top are RCA plugs. Below that are quarter-inch (6.35 mm) phone plugs, and then eighth-inch (3.5 mm) mini-stereo plugs. Most devices that use these generate stereo audio, and mixers that have jacks for them are always stereo channels.

Balanced Audio

These connectors are used for microphones as well as some line-level devices, where noise pickup must be kept to a minimum. The upper two are Female and male XLR, the lower two are quarter-inch TRS phone plugs. A TRS cable can also be used for Unbalanced Stereo connections.

Speaker Connectors

These connectors are used where higher current levels are required. The top is a standard quarter-inch phone plug, below that a Speakon plug, and finally an adapter that connects a standard phone plug to a Speakon jack. You will seldom see any other type of speaker connection in Pro audio.

Some helpful resources about audio connectors

Some Common Adapters

There are many adapters that come in handy from time to time for an audio tech. Some are direct adapters, that just switch from one type of connector to another. Others are impedance-matching adapters, that use a transformer to permit connecting a device with one impedance to another with a different impedance.

Four common adapters are pictured below.

XLR Male to Quarter-inch Female Transformer Adapter

With a quarter-inch unbalanced male/male cable, this adapter lets you connect a line-level device to an XLR microphone input.

XLR Female to Quarter-inch Male Transformer Adapter

This adapter is used to connect a low-impedance microphone to a High-Z input device. It could also be used to connect a line-level quarter-inch output to a Low-Z input, if an XLR male gender-changer is used.

Quarter-inch TRS Male to XLR Female Direct Adapter

This adapter is used to connect a XLR output from one device to another device that has Balanced TRS inputs, typically using a standard M/F XLR cable.

XLR Male to TRS Male Direct Adapter

This adapter is used to connect a TRS output from one device, such as the Aux Out from a mixer, to another device that has XLR inputs, such as a powered speaker, using a standard XLR cable.

Circuit Diagrams

A Few Examples

The ability to read circuit diagrams, also called Schematic Diagrams, is a very helpful skill for an audio tech, as these diagrams can consolidate a tremendous amount of information in a rather basic picture. A few simple examples are given here.

The picture to the left shows that a single line stands for an audio signal or DC circuit path. The diagram does not actually represent how the signals physically flow in the device itself. On a diagram, lines often cross without there being an actual connection. Three ways this is typically shown are given here. A solid dot or circle where the lines cross means an actual connection is made.

Next are a couple of ways that phone jacks may be pictured. The top one shows a jack for a single signal with a closed-circuit switch and a local or circuit-board ground. The other shows a stereo jack with an earth or chassis ground connection.

The figure to the right shows some common symbols used for electronic components in circuit diagrams. These may vary slightly from one author to the next, but they usually are slight variants of these symbols. Of course, there are quite a number of other circuit components not shown here. These are the most common.

The link below is to a site that gives a comprehensive description of circuit symbols.

As an example of what one can determine from a circuit diagram, consider the simplified flow diagram shown here. This is a partial diagram of the inputs of an audio mixer. This is not a complete circuit diagram, just the audio flow diagram, so electronic components are not shown. Here are the things this diagram shows:

  1. This shows three different types of inputs:
      a. The upper one is a Balanced Monophonic input. Either an XLR or quarter-inch TRS plug connector can be used. The XLR is intended for a low-level mic signal, while the TRS input is for a line-level signal.
      b. In the middle is a Balanced Stereo input that uses quarter-inch TRS plugs only
      c. The lower one is an Unbalanced stereo input that uses a 3.5 mm stereo mini-plug.

  2. The XLR mic input can use 48-volt phantom power that can be switched on or off. (A condenser microphone requires a polarizing voltage that typically is supplied by the mixer. It is called “phantom” power because because it is applied in a way that microphones that don't need it do not ”see “ it.) Capacitors are used to couple the audio signal to the input amplifier and block the DC coming from the power supply.

  3. Both the Line-in and Mic-in inputs feed a differential amplifier whose Gain can be adjusted. The differential circuit inverts the signal at the Minus (-) input and adds it to that at the Plus (+) input, doubling the size of the input signal and subtracting any noise picked up by the connecting cable.

  4. Each of the input signals feeds an Analog-to-Digital Converter that sends a digital signal to the mixer.

  5. Notice the switches incorporated into the jack for the Right channel of ST1. The Left jack is labeled L/M, which indicates that it can be used as the Left input or as a monophonic signal that can be fed to both channels, if no jack is connected to the Right input jack. When a plug is inserted into the Right channel jack, the switch opens, and that signal goes to the Right channel.

Hum and Noise

Ground Loops

Hum is one the most frequently encountered types of noise in an audio system. The cause is usually a Ground Loop connection between two devices, such as a CD/DVD player and a mixer. It is very common when PC audio is connected to a mixer.

For safety reasons, every device powered from a standard electrical outlet must be properly grounded. Typically, the metal chassis of the device is connected to the electrical ground connection. The metals jacks used by the connectors on the device are usually grounded to the chassis. When two devices are connected together, their chassis connections must be at the same voltage potential, something very close to zero volts. If this is not the case, a very small electrical current can flow in the ground connection between the two, creating an 60-Hz signal in the connection. Typically, this signal is very small, but if the audio signal is also very small, the hum can be very noticeable, and its level is amplified every time the audio signal is amplified. Mike Sokol has an article om the Serious Business of proper grounding.

There are several common steps that can be taken to eliminate or minimize hum in an audio system. The following list is from a 5-minute YouTube video:

  • Connect all devices to the same breaker, preferably to the same outlet.
  • Use Balanced Connections wherever possible
  • With Unbalanced connections, use a transformer isolator.
  • Use audio chokes when needed and if effective.
  • Use audio filters (EQ) to minimize the effect of the noise

Hum and crackling noise can results when there is an intermittent break in the signal wire of a cable or plug, or in the shield. The break must be identified and repaired or replaced. Sometimes, the hum can come from the power supply in a device. If the supply has inadequate filtering, or if its filter capacitors have deteriorated, hum can result. Due to DC rectification, this hum is now at 120 Hz. This can be very difficult to remove. Repair the power supply, replace the device, or try some EQ to minimize the noise.

Three Tools for Eliminating Ground Loop Hum

An XLR Cable
Ground Lifter

This handy device can eliminate some ground loop issues by breaking the ground connection in the XLR cable between two devices.

A Passive DI Box

A Direct Injection (DI) Box is a good way to connect an unbalanced source to a mixer. A passive DI box uses a transformer and is preferred when possible, but an Active DI Box can often be used when needed to match impedances. Both should have a ground lift switch to open the ground connection between the two devices. (Circuit Diagram and more details.)

Audio Isolator

An Audio Isolator is similar to a DI Box, but it typically has no ground lift switch, because the two grounds are not connected. A transformer is used to couple the two audio signals. The one shown above is intended for stereo, but single-channel versions are common. Some pro audio techs just use bare audio transformers to save money; they work just as well

(Circuit Diagram).

Some additional causes of noise and their cure can be found in the following TechHive video:

Larry Robinson has a good article on eliminating ground loops

Audio Networks

In recent years, as audio systems have increased in complexity. and numerous components have been added, the necessity for connecting them together with a central control system has increased. For example, a large line array speaker system can have eight or more amplifiers installed in a high ceiling, and it is important to be able to monitor and control these amps from a remote location. To take advantage of the benefits of Category cable and the facts that such cables have been previously installed in some instances, various protocols for sending audio over IP networks have evolved. At present, three protocols have emerged as the most common.

Dante

Developed by Audinate, Dante (Digital Audio Network Through Ethernet) is an uncompressed multichannel digital media networking technology that combines software, hardware, and network protocols. It uses standard Ethernet technology to allow for the transfer of large numbers of audio channels among multiple locations, over long distances, and with low latency. Dante’s specs include up to 1,024 channels per network node with no limit on the number of nodes, a minimum latency of 150 microseconds, sample rates up to 192kHz, and resolution up to 32 bits.

One significant advantage of Dante is that it uses standard ethernet routers and switches, which makes it easy and relatively inexpensively to expand the system, but use of Dante requires that manufacturers license the technology from Audinate. Many manufacturers have done so, including most of the major pro audio firms.

RedNet

RedNet is a family of audio interfaces developed by Focusrite that connect via Audinate’s Dante digital audio networking protocol. With a single network connection per box, hundreds of channels of 24-bit audio can be easily transmitted among multiple locations and over long distances. Focusrite’s RedNet interfaces allow many different options for interfacing with the audio world, including analog I/O, MADI, AES3, and other formats. RedNet also facilitates interconnection with Mac and PC, compatibility with Avid Pro Tools, and easy interconnection with other Dante-based products.

AVB

AVB (Audio Video Bridging) is a set of standards developed by the Institute of Electrical and Electronics Engineers and promoted by the AVnu Alliance. AVB is an “open” protocol and does not require manufacturers to license the technology. Manufacturers including PreSonus, MOTU, Avid, and more have developed products compatible with AVB. AVB works by reserving and dedicating a portion of the Ethernet bandwidth for AVB media use. The benefits are said to be precise synchronization, data management for media streams, “admission controls” (control over transmitters and receivers in the system), and identification of participating devices in the AVB network, which assures the quality of the audio system. All of the “nodes” in the networked system share the same clock, and data is carefully managed to ensure low latency and to prevent “data collisions.” There are no limitations on how small or large an AVB network can be. Minimum latency is 250 microseconds, with sampling rates up to 192kHz and resolution up to 32-bit floating point. One difference between Dante and AVB is that AVB requires a dedicated AVB network switch

The Evolution of Transport Protocols

In November 2021 Steve Harvey published an article using the above Heading in his title. He describes the constant change that has been going on in network protocols, applications, and customer needs. Manufacturers have been releasing new products and up-grades to meet these demands. He indicates that "there are as many as a dozen different ecosystems supporting the transport of audio and video over an IP network." He suggests that Dante seems to have the lead, "with more than 3000 Dante-enabled devices from more that 500 different manufacturers."

Audinate decided to leverage the standards on which Dante was based to more easily create subnet crossings and introduced the Dante Domain Manager (DDM) to create subnets that enable networks to scale over greater distances while remaining transparent to users. The increased use of software makes these improvements possible. The user can have separate things going on in separate groups - domains, or separate Dante networks - that cannot interfere with each other. The increased use of software means that products powered by Linux and ARM processors could be added to the mix along with Intel. With software-based Dante, integrators are not constrained as much by hardware

Various manufacturers have worked with the various protocols to allow their products to be networked. Harvey discusses the QSC Q-Sys Ecosystem with Audinate as a prime example. "Dante is now fully integrated into the Q-Sys audio, video, and control workflow, offering device discovery, synchronization, control, and management for Dante audio alongside native Q-Lan, AES67, and other generic media streams."

Thus, it behooves an AV technician or engineer to develop some awareness and expertise in the application of these various networking protocols.

Online Resources

Sweetwater has an excellent article that covers audio networking in some detail. Much of the above text is from this article.

Avnetwork.com is a good source of information on Network protocols and various other AV technologies.

So far, I have elected not to get into wireless communications, which includes wireless microphones, AV over IP networks (AVOIP), Bluetooth, and WiFi. Here, I will suggest a few resources on these topics where one can go for details.

Dan Leafblad has several articles on topics related to wireless communications. See Wi-Fi 101: Cracking The Code On What It Is (And Isn’t), As Well As How It Works, Wi-Fi 201: Applications & Deployment Of Wi-Fi For AVL Systems,

Other resources on wireless communications can be found on the ProSoundWeb Study Hall.

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