Rane CP 52S, Installation Manual

Interconnection-3

Standards Committee (SC-05-05) working on this subject. 

He tirelessly tours the world giving seminars and dispens-

ing information on how to successfully hook-up pro audio 

equipment

2

. He makes the simple point that it is absurd that 

you cannot go out and buy pro audio equipment from sever-

al different manufacturers, buy standard off-the-shelf cable 

assemblies, come home, hook it all up and have it work hum 

and noise free. 

Plug and play.

 Sadly, almost never is this the 

case, despite the science and rules of noise-free interconnect 

known and documented for over 

60 years

 (see References for 

complete information).

It all boils down to using balanced lines, only balanced 

lines, and nothing but balanced lines. This is why they were 

developed. Further, that

you 

tie the shield to the chassis, at 

the point it enters the chassis, and at both ends of the cable

(more on ‘both ends’ later).

Since standard XLR cables come with their shields tied to 

pin 1 at each end (the shells are not tied, nor need be), this 

means equipment using 3-pin, XLR-type connectors 

must 

tie pin 1 to the chassis 

(usually called chassis ground) — not 

the audio signal ground as is most common.

Not using 

signal ground

 is the most radical departure 

from common pro-audio practice. Not that there is any ar-

gument about its validity. There isn’t. 

This is the right way 

to do it

. So why doesn’t audio equipment come wired this 

way? Well, some does, and since 1993, more of it does. That’s 

when Rane started manufacturing some of its products with 

balanced inputs and outputs tying pin 1 to chassis. So why 

doesn’t everyone do it this way? Because life is messy, some 

things are hard to change, and there will always be equip-

ment in use that was made before proper grounding prac-

tices were in effect.

Unbalanced equipment is another problem: it is ever-

where, easily available and inexpensive. All those RCA and 

¼" TS connectors found on consumer equipment; effect-

loops and insert-points on consoles; signal processing boxes; 

semi-pro digital and analog tape recorders; computer cards; 

mixing consoles; et cetera. 

The next several pages give tips on how to successfully 

address hooking up unbalanced equipment. Unbalanced 

equipment when “blindly” connected with fully balanced 

units starts a pattern of hum and undesirable operation, 

requiring extra measures to correct the situation.

Figure 1b. Recommmended practice.

CASE

(+)

(–)

COMMON (WRONG) PRACTICE

RECOMMENDED PRACTICE

(–)

(+)

OPTIONAL

CASE

1

2

3

3

1

2

CHASSIS

GROUND

SIGNAL

GROUND

CHASSIS

GROUND

CHASSIS

GROUND

The Next Best Right Way To Do It

The quickest, quietest and most foolproof method to con-

nect balanced and unbalanced is to 

transformer isolate all 

unbalanced connections

. See Figure 2.

Many manufacturers provide several tools for this task, 

including Rane. Consult your audio dealer to explore the 

options available.

The goal of these 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 un-

balanced 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).

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 usually creates noisy 

interconnections.

A common solution to these noisy hum and buzz prob-

lems 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 the 

receiving end. 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 ground-sending-end-only 

shield connection minimizes the possibility of high fre-

quency (radio) interference since it prevents the shield from 

acting as an antenna to the next input. Many reduce this 

potential RF interference by providing an RF path through 

Figure 2. Transformer Isolation

NOT CONNECTED

AT CHASSIS

(PLASTIC JACK)

EARTH GROUNDED

METAL ENCLOSURE

CHASSIS IS

GROUNDED TO PIN 1

1/4”

TIP-SLEEVE

CASE LUG MAY

CONNECT TO 

CHASSIS

(NOT REQUIRED)

TRANSFORMER

UNBALANCED

BALANCED

3

1

2