Installation guide

ManualsBrandsRane ManualsAudio MixerMOJO MM 8z

Interconnection-2

Ground Loops

Almost all cases of noise can be traced directly to

ground loops, grounding or lack thereof. It is important

to understand the mechanism that causes grounding

noise in order to eﬀectively eliminate it. Each compo-

nent of a sound system produces its own ground in-

ternally. is ground is usually called the audio signal

ground. Connecting devices together with the inter-

connecting cables can tie the signal grounds of the two

units together in one place through the conductors in

the cable. Ground loops occur when the grounds of the

two units are also tied together in another place: via

the third wire in the line cord, by tying the metal chas-

sis together through the rack rails, etc. ese situations

create a circuit through which current may ﬂow in a

closed “loop” from one unit’s ground out to a second

unit and back to the ﬁrst. It is not simply the presence

of this current that creates the hum—it is when this

current ﬂows through a unit’s audio signal ground that

creates the hum. In fact, even without a ground loop, a

little noise current always ﬂows through every inter-

connecting cable (i.e., it is impossible to eliminate these

currents entirely). e mere presence of this ground

loop current is no cause for alarm if your system uses

properly implemented and completely balanced inter-

connects, which are excellent at rejecting ground loop

and other noise currents. Balanced interconnect was

developed to be immune to these noise currents, which

can never be entirely eliminated. What makes a ground

loop current annoying is when the audio signal is af-

fected. Unfortunately, many manufacturers of balanced

audio equipment design the internal grounding system

improperly, thus creating balanced equipment that is

not immune to the cabling’s noise currents. is is one

reason for the bad reputation sometimes given to bal-

anced interconnect.

A second reason for balanced interconnect’s bad

reputation comes from those who think connecting

unbalanced equipment into “superior” balanced equip-

ment should improve things. Sorry. Balanced inter-

connect is not compatible with unbalanced. e small

physical nature and short cable runs of completely

unbalanced systems (home audio) also contain these

ground loop noise currents. However, the currents in

unbalanced systems never get large enough to aﬀect

the audio to the point where it is a nuisance. Mixing

balanced and unbalanced equipment, however, is an

entirely diﬀerent story, since balanced and unbalanced

interconnect are truly not compatible. e rest of this

note shows several recommended implementations for

all of these interconnection schemes.

e potential or voltage which pushes these noise

currents through the circuit is developed between the

independent grounds of the two or more units in the

system. e impedance of this circuit is low, and even

though the voltage is low, the current is high, thanks to

Mr. Ohm, without whose help we wouldn’t have these

problems. It would take a very high resolution ohm

meter to measure the impedance of the steel chassis or

the rack rails. We’re talking thousandths of an ohm. So

trying to measure this stuﬀ won’t necessarily help you.

We just thought we’d warn you.

Figure 1a. The right way to do it.

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BLACK 2-CONDUCTOR SHIELDED CABLE

2-CONDUCTOR SHIELDED CABLE

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CHASSIS

GROUND

CHASSIS

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SIGNAL

GROUND

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BALANCED OUTPUTS BALANCED INPUTS

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