Basic Mechanical Connections

RCA

Traditionally, the signal is in the center. The outer part is the ground.

RCA connectors are used for audio, baseband video, and occasionally RF video.

When a pair of RCA connectors is used for stereo audio, they are usually color-coded as follows:

• Dual RCA, Red and white [most common]:
  • red connector = right channel
  • white connector = left channel
• Dual RCA, Red and black:
  • red connector = right channel
  • black connector = left channel
• Dual RCA, Black and white
  • black connector = right channel
  • white connector = left channel

1/4 Inch = 6.35mm

The contacts on the plug are named:

• Tip = End of plug
• Ring = Center band
• Sleeve = Third band

1/8 Inch = 3.5mm

1/4" and 1/8" connectors are similar in all but size. On top is a 1/4" plug. On the bottom is a 1/8" plug. On the right is Jefferson.

Like 1/4", the 1/8" connectors are also available in monophonic and stereo.

1/8" connectors are also called 3.5mm.

The contacts on the plug are named:

• Tip = End of plug
• Ring = Center band
• Sleeve = Third band

When used for stereo audio, 1/8" connectors are usually wired this way:

• Tip = left channel
• Ring = right channel
• Sleeve = common ground

Since 1/8" connectors are very commonly used for stereo connections, let's summarize:

physical position	name	usage
Tip	End of plug	left channel
Ring	Center band	right channel
Sleeve	Third band	common ground

These connectors are also commonly used on computer sound cards. When the manufacturer follows the PC99 standard, the jacks are color coded as follows:

• pink or red = Microphone input
• green = Line Output
• light blue = Line Input
• orange = Digital Output
• black = Line Out 2, analog, for rear speakers

3/32" = 2.5mm

It is most commonly called "2.5mm".

XLR

XLR connectors are frequently used for professional audio, especially microphones.

Binding Posts

Mechanical Adapters

I call a "jumper" a cable that has the same gender connector on each end.

This "barrel" lets you plug two male connectors into each other.

This adapter cable changes from one thing on one end to something completely different on the other end.

Here's an assortment of adapters:

1/4" stereo -> 1/8" stereo

two 1/8" stereo -> 1/8" stereo

two RCA -> 1/4" stereo

Basic Electrical Connections

Line-Level

Line-level signals don't obey the volume control. You pick, choose, and mix the line-level signals - then amplify them, which involves the volume control. [In the case of very low level signals, like phonograph cartridges, a "preamp" is used to get up to line level.]

Wolfstone reader Ralf Suckow was kind enough to add some details:

• Typical professional equipment uses level +4dBu (unloaded), which is 1.23V
• The German studio standard is +6dBu, which is 1.55V, but that does not mean all professional equipment provides such a high level
• Typical home/hifi equipment uses -10dBV, which is 0.316V
• For calculation of this type, see see http://www.sengpielaudio.com/Rechner-db-volt.htm
• The currents are very small because in audio equipment, for minimum distortions and best frequency response, you use low output impedance of sender and high input impedance of receiver.

Speaker-Level

Electrical Adapters

Special Topics

Helpful Formulae

Power = Current x Voltage

Voltage = Current x Resistance

These equations can be transformed in interesting ways:

Current = Voltage / Resistance

And then combined:

Power = Voltage^2 / Resistance

sqrt(Power x Resistance) = Voltage

Speaker Phasing

When using multiple speakers on a single amplifier channel, it is desirable that all the speakers push the same way at the same time (in phase), like a team of rowers in a boat.

Speakers that are out of phase work against each other.

If the speakers are pointed in the same general direction, as from the stage to the audience, the speakers are in phase when their diaphragms move in the same direction at the same time. To achieve this, speakers should be wired with the same polarity.

Series wiring of two speakers in phase, pointing in the same direction.

Parallel wiring of two speakers in phase, pointing in the same direction.

If the speakers face each other, they are in phase if the diaphragms move in opposite directions relative to the speaker housings. To achieve this, one speaker should be wired with reverse polarity.

Series wiring of two speakers in phase, pointing inwards.

Parallel wiring of two speakers in phase, pointing inwards.

In really large venues, speaker phasing is pretty much hopeless due to the different speeds at which sound and electricity travel. Correcting this requires additional amplifiers and audio delay circuits - expensive.

Related Pages