SLEEVE TIP SLEEVE TIP
Figure D: RCA plug

1⁄4" TS PHONE PLUGS AND JACKS

“TS” stands for Tip-Sleeve, the two connections available on a “mono” 1⁄4" phone jack or plug (Fig- ure C). TS jacks and plugs are used in many

SLEEVE

SLEEVE TIP

TIP

 

 

TIP

Figure C: TS plug

SLEEVE

different applications, always unbalanced. The tip is connected to the audio signal and the sleeve to ground (earth). Some examples:

•Unbalanced microphones

•Electric guitars and electronic instruments

•Unbalanced line level connections

NOTE: All the unbal-

anced 1⁄4" inputs on the

LM-3204 have the ring con-

ductor wired to the shield

(ground), so that you can plug in a balanced cord with no loss of level.

ANOTHER NOTE: All the unbalanced 1⁄4" outputs on the LM-3204 implement “imped- ance balancing”. When you plug a balanced cord into one of these, both the tip and ring conductors have equal impedance, significantly improvings common mode characteristics. In other words, although unbalanced, a balanced input receiving this cord will “think” it’s getting a balanced signal!

SWITCHED 1⁄4" PHONE JACKS

Switches can be incorporated into 1⁄4" phone jacks which are activated by inserting the plug. These switches may open an insert loop in a cir- cuit, change the input routing of the signal or serve other functions. The Mackie LM-3204 uses switches in the channel insert and bus insert jacks, input jacks, AUX sends and AUX returns labeled “(MONO) Left.” See Special Mackie Connections farther on. We also use these switches to ground the line level inputs when nothing is plugged into them.

In most cases, the plug must be inserted fully to activate the switch. Mackie takes

advantage of this in some circuits, specifying circum-

stances where you are to insert the

plug only partially. Once again, see Special Mackie Connections, later in this section.

RCA PLUGS AND JACKS

RCA-type plugs (also known as phono plugs) and jacks are often used in home stereo and video equipment and in many other applications (Figure D). They are unbalanced, and electrically identical to a 1⁄4" TS phone plug or jack. Connect the signal to the center post and the ground (earth) or shield to the surrounding “basket.” Tape In and Tape Out are available on RCA jacks on the Mackie LM-3204.

UNBALANCING A LINE

In most studio, stage and sound reinforcement situations, there is a combination of balanced and unbalanced inputs and outputs on the various pieces of equipment. This usually will not be a problem in making connections.

• When connecting a balanced output to an

unbalanced input, be sure the signal high

 

(hot) connections are wired to each other,

 

and that the balanced signal low (cold) goes

APPENDIX

to the ground (earth) connection at the

 

unbalanced input. In most cases, the

 

balanced ground (earth) will also be

 

connected to the ground (earth) at the

 

unbalanced input. If there are hum or radio

 

frequency ground-loop problems, this

 

connection may be left disconnected at the

 

balanced end.

 

•When connecting an unbalanced output to a balanced input, be sure that the signal high (hot) connections are wired to each other.

The unbalanced ground (earth) connection should be wired to the low (cold) and the ground (earth) connections of the balanced input. If there are ground-loop problems, try connecting the unbalanced ground (earth) connection only to the input low (cold) connection, and leaving the input ground (earth) connection disconnected.

In some cases, you will have to make up special adapters to interconnect your equipment. For example, you may need a balanced XLR female connected to an unbalanced 1⁄4" TS phone plug.

SPECIAL MACKIE CONNECTIONS

The balanced-to-unbalanced connection has been anticipated in the wiring of the Mackie LM-3204 jacks. A 1⁄4" TS plug inserted into a 1⁄4" TRS balanced input, for example, will automatically unbalance the input and make all the right connections. Conversely, a 1⁄4" TRS plug inserted into a 1⁄4" unbalanced input will automatically tie the ring (low or cold) to ground (earth).

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