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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

Summary of Contents for MLM82S

Page 1: ...rtant Safety Instructions MLM82S Manual MLM82S Data Sheet Sound System Interconnection Warranty Declaration of Conformity 22356 10 0 2 4 8 6 10 0 2 4 8 6 10 0 2 4 8 6 10 0 2 4 8 6 10 0 2 4 8 6 10 0 2...

Page 2: ...he power cord is the AC mains disconnect device and must remain readily operable To completely disconnect this apparatus from the AC mains disconnect the power supply cord plug from the AC receptacle...

Page 3: ...r le courant alternatif AC et doit absolument rester accessible Pour d connecter totalement l appareil du secteur d branchez le c ble d alimentation de la prise secteur 16 Cet appareil doit tre branch...

Page 4: ......

Page 5: ...front panel Internal switches allow setting output signal levels for MIC or LINE The factory default setting is LINE If the MLM82S is connected directly to a power amplifier equalizer or recorder inpu...

Page 6: ...A and B Inputs for that channel have exactly the same level 6 OUTPUT OverLoad LED illuminates within 3 dB of an approaching overload condition To avoid this the associated OUT PUT LEVEL control may be...

Page 7: ...andle either balanced or unbalanced signals In most cases an unbalanced signal may use a mono plug Tip Sleeve See the Sound System Interconnection RaneNote included with this manual for proper connect...

Page 8: ...ue to clipping is occurring or imminent Check these conditions A The LEVEL control may be turned too high B The Output of the preceding device may need to be reduced C The Input may be switched to MIC...

Page 9: ...output signal to Mic level The factory default is Line level Features Four balanced Mic Line Inputs XLR with 15V Phantom Power Bi Color Signal Present Overload indicators Trimless Mic Stage Preamplif...

Page 10: ...Stereo Line Input Impedance 20k min Gain Range off to 12 1 dB Signal To Noise Ratio 90 typ dB Unity gain output 4 dBu 22 kHz BW Frequency Response 10 Hz 35 kHz 3 dB THD Noise 0 007 max 4 dBu at 1 kHz...

Page 11: ...TPUT A OUTPUT B LEVEL LEVEL LEVEL LEVEL LEVEL LEVEL LEVEL LEVEL 40 dB PAD RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI FILTER RFI F...

Page 12: ...able for the B mix A and B mix outputs shall feature overload indicators independent A B level controls internally selected 40 dB pad for microphone level output and XLR output jacks Security features...

Page 13: ...onnections Grounding and EMC practices Shields of connectors in audio equipment containing active circuitry Rane s policy is to accommodate rather than dictate However this document contains suggestio...

Page 14: ...connect is not compat ible with unbalanced The small physical nature and short cable runs of completely unbalanced systems home audio also contain these ground loop noise currents However the currents...

Page 15: ...CTICE 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...

Page 16: ...ounded and therefore immune to ground loop hums and buzzes Ground lifts are simply another Band Aid to try in case of grounding problems It is true that an entire system of properly grounded equipment...

Page 17: ...guarantee that a hum free intercon nect can be achieved nor is there a definite scheme that will assure noise free operation in all configurations References 1 Neil A Muncy Noise Susceptibility in An...

Page 18: ...20 24 24 19 18 17 B B B B A A A A A A FEMALE BALANCED XLR NOT A TRANSFORMER NOR A CROSS COUPLED OUTPUT STAGE FEMALE BALANCED XLR EITHER A TRANSFORMER OR A CROSS COUPLED OUTPUT STAGE BALANCED TRS NOT A...

Page 19: ...RED SHIELD RED SHIELD SHIELD RED RED BLACK N C N C N C RED BLACK RED SHIELD N C BLACK RED BLACK RED 3 NC 2 RED 1 SHIELD 2 RED 1 SHIELD 3 BLACK 2 RED 1 NC 3 BLACK 2 RED 1 NC 3 BLACK 2 RED 1 SHIELD SHIE...

Page 20: ...3 BLACK 2 RED 1 SHIELD 3 BLACK 2 RED 1 SHIELD SHIELD BLACK SHIELD RED BLACK SHIELD RED BLACK RED SHIELD SHIELD BLACK RED SHIELD BLACK RED SHIELD BLACK RED SHIELD BLACK RED SHIELD BLACK RED SHIELD RED...

Page 21: ...ECTS IN MATERIAL OR WORKMANSHIP THE SPECIFIC PERIOD OF THIS LIMITED WARRANTY SHALL BE THAT WHICH IS DESCRIBED TO THE ORIGINAL RETAIL PURCHASER BY THE AUTHORIZED RANE DEALER OR DISTRIBUTOR AT THE TIME...

Page 22: ...IN THE USA If the product is being sent to Rane for repair please call the factory for a Return Authorization number We recommend advance notice be given to the repair facility to avoid possible need...

Page 23: ...for compliance with the LV directive and EMC directive in the event that the equipment is modified without written consent of the manufacturer This declaration of conformity is issued under the sole r...

Page 24: ...LINE LINE 15V PHANTOM POWER MLM82S 5 B A 6 B A 7 B A 8 A B OUTPUTS 1 3 4 2 LINE INPUTS MIC LINE INPUTS BALANCED PIN 3 PIN 2 PIN 1 G CLASS 2 WIRING BALANCED PIN 3 PIN 2 PIN 1 G CLASS 2 WIRING 100 240...

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