Rane TTM 52i User Manual download pdf (Page 7)

Manual-7

Rane’s policy is to accommodate rather than dictate.

However, this document contains suggestions for external

wiring changes that should ideally only be implemented by

trained technical personnel. Safety regulations require that all

original grounding means provided from the factory be left

intact for safe operation. No guarantee of responsibility for

incidental or consequential damages can be provided. (In

other words, don’t modify cables, or try your own version of

grounding unless you really understand exactly what type of

output and input you have to connect.)

THE ABSOLUTE BEST RIGHT WAY TO DO IT

Use balanced lines and tie the cable shield to the metal

chassis (right where it enters the chassis) at both ends of the

cable.

A balanced line requires three separate conductors, two of

which are signal (+ and –) and one shield. The shield serves

to guard the sensitive audio lines from interference. Only by

using balanced line interconnects can you guarantee (yes,

guarantee) hum-free results. Always use twisted pair cable.

Chassis tying the shield at each end also guarantees the best

possible protection from RFI [radio frequency interference]

and other noises [neon signs, lighting dimmers].

THE NEXT BEST RIGHT WAY TO DO IT

The quickest, quietest and most foolproof method to

connect balanced and unbalanced is to transformer isolate

all unbalanced connections. Your audio dealer can recom-

mend such a transformer.

The goal of transformer adaptors is to allow the use of

standard cables. With these transformer isolation boxes,

modification of cable assemblies is unnecessary. Virtually

any two pieces of audio equipment can be successfully

interfaced without risk of unwanted hum and noise.

Another way to create the necessary isolation is to use a

direct box. Originally named for its use to convert the high

impedance, high level output of an electric guitar to the low

impedance, low level input of a recording console, it allowed

the player to plug “directly” into the console. Now this term is

commonly used to describe any box used to convert unbal-

anced lines to balanced lines.

THE LAST BEST RIGHT WAY TO DO IT

If transformer isolation is not an option, special cable

assemblies are a last resort. The key here is to prevent the

shield currents from flowing into a unit whose grounding

scheme creates ground loops (hum) in the audio path (i.e.,

most audio equipment). Do not be tempted to use 3-prong to

2-prong “cheater” adapters to lift grounds. This is a dangerous

and illegal practice.

It is true that connecting both ends of the shield is theo-

retically the best way to interconnect equipment – though this

assumes the interconnected equipment is internally grounded

properly. Since most equipment is not internally grounded

properly, connecting both ends of the shield is not often

practiced, since doing so can create noisy interconnections.

A common solution to these noisy hum and buzz problems

involves disconnecting one end of the shield, even though one

can not buy off-the-shelf cables with the shield disconnected

at one end. The best end to disconnect is a matter of personal

preference and should be religiously obeyed; choose inputs or

outputs and always lift the side you choose (our drawings

happen to disconnect the outputs). If one end of the shield is

disconnected, the noisy hum current stops flowing and away

goes the hum — but only at low frequencies. A one-end-only

shield connection increases the possibility of high frequency

(radio) interference since the shield may act as an antenna.

Many reduce this potential RF interference by providing an

RF path through a small capacitor (0.1 or 0.01 microfarad

ceramic disc) connected from the lifted end of the shield to

the chassis. The fact that many modern day installers still

follow this one-end-only rule with consistent success indi-

cates this and other acceptable solutions to RF issues exist,

though the increasing use of digital and wireless technology

greatly increases the possibility of future RF problems.

See the following page for suggested cable assemblies for

your particular interconnection needs. Find the appropriate

output configuration from either your mixer output or the MX

22 output (down the left side), and then match this with the

correct balanced or unbalanced input to the MX 22 or the

amplifer (down the right side.) An “off-the-shelf” cable may

be available or modifiable. Soldering should only be at-

tempted by those trained in the art.

SUMMARY

If you are unable to do things correctly (i.e. use fully

balanced wiring with shields tied to the chassis at the point of

entry, or transformer isolate all unbalanced signals from

balanced signals) then there is no guarantee that a hum free

interconnect can be achieved, nor is there a definite scheme

that will assure noise free operation in all configurations.

WINNING THE WIRING WARS

• Use balanced connections whenever possible.

• Transformer isolate all unbalanced connections from

balanced connections.

• Use special cable assemblies when unbalanced lines cannot

be transformer isolated.

• Any unbalanced cable must be kept under ten feet (three

meters) in length. Lengths longer than this will amplify

the nasty side effects of unbalanced circuitry's ground

loops.

This information was condensed from Rane Note 110,

“Sound System Interconnection”. If you would like the

complete note, call or email the factory, download it from

Rane's web site http://www.rane.com, or ask your dealer for a

copy.

SOUND SYSTEM INTERCONNECTION

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Rane TTM 52i User Manual Page 7

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