Studio-technologies 47A Instrukcja Użytkownika Pobierz pdf (Strona 18)

Issue 1, September 2014 Model 47A User Guide

Page 18 Studio Technologies, Inc.

pins 2 or 3. This function is directly com-

patible with RTS TW-Series intercom ap-

plications in which the three conductors of

a cable support both DC power and two

channels of audio. It’s also compatible in

situations where all three conductors of a

Clear-Com single-channel intercom circuit

are connected to the Model 47A. In this lat-

ter case only one of the Model 47A’s audio

channels will be used.

There may be situations where it’s neces-

sary for the two channels associated with

each Model 47A interface be used with

separate 2-wire party-line circuits. An ex-

ample of this might be where two “loops”

of single-channel beltpacks, such as units

from Clear-Com, need to be connected.

Adapter cables as shown in Figure 2 would

be used. In this case the intercom circuit’s

DC power will not be connected to the

Model 47A, but only to the user devices. In

this scenario, a DC voltage won’t be pres-

ent on pins 2 or 3. Another example of this

might be where adapter boxes with DC

blocking are used to interconnect intercom

circuits with the Model 47A. In both these

cases a DC voltage won’t be present on

either pins 2 or 3 and the Model 47A will

automatically apply 200 ohm terminations.

In both these cases the termination will be

in error and will result in incorrect audio lev-

els due a “double-termination” condition.

To prevent this problem the auto termi-

nate function can be disabled. Referring

to Figure 7, when DIP switch 1 is in its off

(down) position the auto terminate func-

tion is active. When DIP switch 1 is in its on

(up) position the auto terminate function is

disabled. Repeating for clarity, the auto ter-

minate function applies to both interfaces

1 and 2. With the auto terminate function

disabled the two interfaces, when set for

external power, will operate normally with

the exception that pins 2 and 3 will never

be terminated by the Model 47A’s circuitry.

The auto terminate function should be

disabled only when absolutely necessary;

it’s possible that a signiﬁcant downside

could be experienced. With auto terminate

disabled it’s important that properly ter-

minated 2-wire party-line intercom circuits

be connected to pins 2 or 3 on the Model

47A’s 2-wire PL connectors. If they are not

connected, it’s likely that audio oscillations,

noise, and distortion will be generated in

the Model 47A’s 2-wire-to-4-wire converter

circuitry. These audio artifacts will not

cause any damage, but will be sent out the

4-wire line output connectors. Users of the

4-wire equipment may be less than pleased

with what they hear!

Figure 7. DIP Switch 1—Auto Terminate

Figure 6. Detail of back panel showing the

advanced mode DIP switches

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 32 33

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