Aphex EXCITER Instruction Manual download pdf (Page 24)

Aphex Systems Ltd. Model 204Page 24

204

instruction Manual

7.0 Appendices

Appendix A: Balanced and Unbalanced Lines and Operating Levels

Interfacing all types of equipment with balanced and unbalanced lines and can sometimes be troublesome.

First you have to somehow connect balanced to unbalanced and then you have to deal with different levels.

This tutorial will teach you about the principles of balanced and unbalanced lines, wiring standards, and how

to effectively interface them.

Standards

Professional audio equipment usually comes equipped with inputs and outputs that are balanced using 3-pin

XLR connectors and sometimes 1/4 inch phone jacks as well. This equipment most often is designed to oper-

ate at +4dBu, a professional industry standard. That translates to a magnitude of 1.23 volts RMS (Root-Mean-

Squared).

Consumer gear has unbalanced I/O as standard, usually on RCA jacks. The normal operating signal level follows

the IHF (Institute of High Fidelity) standard of -10dBV, or 0.316 volts (316mV) RMS. Converting to dBu dimen-

sions, this works out to be the same as -7.79dBu. There is therefore a difference of 11.79dB between pro and

consumer operating levels.

Grounding

There is the notion that some king of earthly “ground” exists out there that sinks all the noise and acts as

some kind of a shield. You see wires connected to ground rods and water pipes that are supposed to get a

good ground. This is not a correct interpretation of grounding from an audio standpoint. Proper grounding of

equipment and wiring is important and you will gain a better understanding of that as you read along.

Balanced -vs- Unbalanced

Every audio signal is connected through a circuit. The circuit must contain two conductors to create a complete

return path. In other words, a signal voltage is conducted to a piece of equipment by injecting a current into a

wire. That current has flow though to the destination through the wire and return back to the source through

another wire. Since audio is an alternating voltage, swinging through negative and positive polarity, the current

through the two conductors changes direction each alternate half cycle. Which wire is the source and which is

the return alternates accordingly. In this regard, balanced and unbalanced lines are the same. They both need

two conductors.

What makes a system unbalanced is when one of the wires is formed into a tube that wraps around the other

conductor, without touching it, such that the outer conductor can be said to “shield” the inner conductor. This

describes all of the coaxial cable used for video, cable-TV and radio as well as most of the high fidelity audio

cables.

Balancing

If both conductors are identical insulated wires that are twisted together, then they form a balanced line.

This describes telephone lines, microphone cables, and most professional audio cables. Typical balanced cables

include an additional shield wrap around the twisted pair, but this is not strictly required for balanced lines to

work properly.

Many people, because they have more experience with unbalanced wiring, think that balanced is confusing.

Believe it or not, balanced lines are really easier to understand than unbalanced. There is no grounding issue

with balanced, and the way it works is perfectly natural and simple. Balancing naturally rejects hum and noise

and eliminates all sorts of complications in interfacing.

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