A Beginner’s Guide To Audio Connections

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by Bruce Bartlett

An audio system has so many cables and connectors, it’s easy to become confused.

What plugs into what?

This article will help you sort out the various types of audio cables and connectors.

Cables are assemblies of wires; they carry electric signals from one audio component to another.

Connectors link together to form a temporary path for the signal to flow from one component to another.

Cable Construction

Audio cables are usually made of one or two insulated conductors (wires) surrounded by a wire-mesh shield which reduces hum.

Outside the shield is a soft plastic or rubber insulating jacket (Fig. 1).

Cables are designed to carry signals that are either balanced or unbalanced.

Fig. 1. Cutaway view showing the parts of a cable for balanced signals

Cables For Balanced And Unbalanced Signals

A cable for a balanced signal (Fig. 1) uses two conductors to carry the signal, surrounded by a shield.

An cable for an unbalanced signal has a single conductor surrounded by a shield (Fig. 2). In this case, both the center conductor and shield carry the signal.

An example of a cable for balanced signals is a mic cable.

Fig. 2. Cutaway view showing the parts of a cable for unbalanced signals.

 

An example of an cable for an unbalanced signal is a guitar cord. A cable for a balanced signal (Fig. 1) is usually called a balanced line.

A balanced line rejects hum better than an unbalanced line, but an unbalanced line under 10 feet long usually provides adequate hum rejection and costs less.

Signal Levels
A cable carries one of these four signal levels or voltages:

• Mic level is a weak signal. A microphone puts out a mic-level signal. It’s typically about 2 millivolts or .002 volt.

• Instrument level is a fairly weak signal. An electric guitar or synth puts out an instrument-level signal. It’s about 50 millivolts, or .050 volt.

Fig. 3. A 1/4” phone plug

• Line level is a moderately strong signal. An electronic device puts out a line- level signal. Some electronic devices are a mixer, recorder, effects device, and a mic preamp Geek speak: In unbalanced equipment, line level is 0.316 volt (also called – 10 dBV). In balanced equipment, line level is 1.23 volts (also called +4 dBu).

Fig. 4. A 1/4” phone jack

• Speaker level is a strong signal. A power amplifier produces a speaker-level signal. It’s about 1 to 1000 watts, or about 3 to 90 volts.

Cable Connectors And Chassis Connectors
Some connectors are part of cables; they are called cable connectors. Other connectors are built into equipment chassis; they are called chassis connectors.

Cable connectors mate with (plug into) chassis connectors. Several types of connectors are used in audio.

The 1/4-inch phone plug (Fig. 3) is used to connect unbalanced line-level or instrument-level signals.

This plug is part of a cable used with guitar amps, mixers, electric keyboards, electric guitars, and some power amplifiers.

A guitar cord has a phone plug on each end.

The tip of the plug is soldered to the cable’s center conductor; the sleeve or long cylinder is soldered to the cable shield.

Fig. 5. An RCA or phono plug

 

You plug a phone plug into a phone jack (Fig. 4).

The plug is on a cable; the jack is in the chassis of a piece of audio gear.

Note that a jack is a receptacle; a plug goes into a jack to make a connection.

The RCA or phono plug (Fig. 5) is also used to connect unbalanced line-level signals. It’s commonly seen in stereo equipment.

Fig. 6. RCA jack in a chassis

The center pin is soldered to the cable’s center conductor; the cup is soldered to the cable shield.

An RCA plug connects to an RCA jack (Fig. 6). The plug on a cable; the jack is in the chassis of a piece of audio gear.

The 3-pin professional audio connector (XLR) is used with cables for balanced mics and balanced equipment.

Fig. 7. Female XLR cable connector

 

The female connector (with holes) plugs into equipment outputs. The male connector (with pins) plugs into equipment inputs.

A female XLR cable connector plugs into a male XLR chassis connector (Fig. 9).

A male XLR cable connector plugs into a female XLR chassis connector (Fig.10).

Fig. 8. Male XLR cable connector

An XLR connector has 3 pins (male) or 3 holes (female).

The pins or holes are numbered 1, 2, 3. In any XLR connector, pin 1 is soldered to the cable shield; pin 2 is soldered to the “hot” lead (usually red), and pin 3 is soldered to the remaining lead.

The stereo phone plug (Fig. 11) is used with stereo headphones and with balanced line-level cables.

A stereo phone plug connects to a stereo phone jack (Fig. 12).

Fig. 9. Male XLR (left) and Fig. 10. Female XLR (right)

How do you know if a 1/4” phone jack is balanced or unbalanced, mono or stereo? You need to look at the specifications in the equipment manual.

For example, if the jack is labeled “Aux Send”, look up the specification for the Aux Send connector in the manual.

It will tell you if it’s balanced or unbalanced.

Fig. 11. Stereo phone plug (also called a TRS or tip-ring-sleeve connector)

For headphones, the tip is soldered to the left-channel lead (wire); the ring (just behind the tip) is soldered to the right-channel lead, and the sleeve is soldered to the common lead.

For balanced line-level cables, the sleeve is soldered to the shield; the tip is soldered to the “hot” lead, and the ring is soldered to the remaining lead.

Some mixers have Insert jacks that are stereo phone jacks; each jack accepts a stereo phone plug.

Fig. 12. Stereo phone jack

The tip is the send signal to an audio device input; ring is the return signal from the device output, and sleeve is ground. These signals are unbalanced.

If your recorder or mixer has unbalanced mic inputs, but your mic and mic cable are balanced, you might be able to buy an adapter cable with a female XLR on one end and a 1/4” phone plug on the other end. It’s called a female XLR to 1/4” adapter cable.

For more connection basics, like cable types, stay tuned for part two of this article.

AES and Syn Aud Con member Bruce Bartlett is a recording engineer, audio journalist, and microphone engineer. His latest books are “Practical Recording Techniques 5th Ed.” and “Recording Music On Location.”

From: prosoundweb.com

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