Arrakis Systems X-mixer-14-22 Specifications download pdf (Page 9)

THE X-MIXER DIGITAL CONSOLE

PERIPHERAL DEVICE LOGIC

CONNECTIONS

Starting and Stopping Peripherals

All logic outputs for the console are high cur-

rent open collector logic sinks to ground. The

open collector logic in the console can sink up to

50 milliamps and 12 VDC into ground.

This type of open collector logic output can

directly connect to many peripheral devices with-

out an interface. Because this direct logic connec-

tion requires the grounds between the console and

the peripheral to be connected, then a potential of

a ground loop is created. If the cable is short and

the studio has a good ground system, then the

noise can be inaudible.

If the peripheral device logic requires higher

voltages or currents than the console open collec-

tor logic is rated ...OR... if it is important to not

have a ground reference through the control logic,

then an interface circuit is required. Examples of

isolated interfaces would be a powered mechani-

cal relay, solid state relay, or optoisolator.

The circuit on this page illustrates how to use

the console logic output to drive an external relay.

Because an independent power source is used and

the dry relay contacts are the only logic connec-

tions to the peripheral device, there is no current

path between the console and the peripheral. That

means there is no connection through the logic

that can create half of a ground loop.

+12VDC

Logic

Output

(maximum

12VDC, 50mA)

Ground

Peripheral Device Logic Interface

VDC

Relay

to Peripheral

Logic Input

VDC

Power

Supply

Pin Signal Description

1 High (+), left channel

2 Low (-), left channel

3 High (+), right channel

4 High (-), right channel

5 Audio & Logic ground

6 Shield Ground

7 Source Start output logic

8 Source Stop output logic

9 Channel On-off control logic

Analog Inputs (stereo line)

(9-pin connector signals)

(example: starting or stopping a source)

NOTE: about Ground Loops

A ground loop is created when more than one ground path exists between two pieces of electronic audio equipment in a signal chain. This

creates an efficient low frequency loop antenna which receives energy from stray 60 cycle power fields. The 60 cycle current induced in the anten-

na creates a voltage difference between the two pieces of equipment due to the finite impedance of the ground loop. This 60 cycle voltage is then

added to the audio signal as a low frequency hum. The only way to eliminate the possibility of a ground loop is to design the system in such a way

that there is only ONE ground path between the two pieces of audio equipment.

The most common ground loop is created with the AC power ground as one half of the loop and the audio ground in the shield wire as the sec-

ond half of the loop. Because AC power ground is almost always connected between two pieces of equipment, the audio shield ...OR... a ground

through the console logic interface can easily provide the second half of a ground loop.

It is interesting to note that consumer stereo systems are designed with an AC power/audio shield wire ground loop built in, and yet they can be

extremely high performance. This demonstrates that studio systems with short cable lengths and very low resistance grounds can perform very

well without any audible hum.

GROUND PATH #1

SHIELD

GROUND PATH #2

THROUGH AC GROUND

EARTH

GROUND

CHASSIS

GROUND

EARTH

GROUND

SIGNA;L

GROUND

TYPICAL

GROUND

LOOP

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 28 29

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Arrakis Systems X-mixer-14-22 Specifications Page 9

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