Shure SR105 Bridging Connections, Adding Headphone Jack to Speaker Connections, Coil

duce approximately 28.3 volts at the DIRECT OUTPUT terminals (8,9), or 70 volts at the 70V OUTPUT terminals (11) when the 70-volt input line is supplying 70 volts.

70-VOLT
	LINE
*				3 - PIN MALE
	.		ATTENUAm	AUDIO CONNECTOR
		r - - - i
lr		I	I
	- I
g	=8
I			- I
5	b
u				INPUT

FIGURE 10. 70-VOLT SYSTEM ATTENUATOR

BRIDGING CONNECTIONS

If greater power or optimum system reliability becomes extremely important, two Amplifiers may be connected in series (never in parallel!) to obtain an output of 400 watts into an 8-ohm load, or 200 watts into a 16-ohm load (6 ohms minimum load). To determine available power, divide the actual load impedance by two and, referring to Figure 6, Page 7, double the output power shown on the graph. This connection also provides a fail-safe, or redundant, system: if one Amplifier fails, the second remains functional at its normal power output. This series connection of amplifier outputs is commonly referred to as a bridged configuration.

Connect the Amplifier balanced inputs out of phase as shown in Figure 11, Page 11, with the speaker load con- nected between the two 28V terminals of the DIRECT OUT- PUT Terminal Strips (9). Connect the two GND terminals together.

If a 140-volt output is required (SRlO5A Amplifier only), two SR105A Amplifiers may be connected in series as described above, except that the 70-volt outputs are used. Connect the speaker load to the 70V terminals (11) of the two SR105A Amplifiers and connect the COM terminals together. Use Class 1 wiring.*

ADDING HEADPHONE JACK TO SPEAKER CONNECTIONS

If it is desirable to monitor the Amplifier direct output through headphones, a headphone output may be fabri- cated as follows. Obtain parts listed below or their equiva- lent.

'As def~nedby U.S. Nat~onalElectrical Code

PHONE PLUG TRANSFORMER

	I W OR LESS	8 OHM
SPEAKER	-3 1	COIL
TERMINALO		COM
	COM

NOTE: USE JUMPER FOR STEREO

HEADPHONES ONLY.

Qty.	Part	Recommended Type
1	Phone Jack	Switchcraft 12-8
1	Phone Plug	Switchcraft 280
1	Volume Control	Switchcraft 666Pl or 656
	(L-Pad)
1	Transformer, 25V	Essex-Stancor A-8095
	Line to Voice Coil	or A-8096

Connect the parts as shown in Figure 12, Page 11. Make certain the "hot" speaker lead (28V) is connected to a one- watt or less tap on the 25-volt transformer; this connection sets the maximum headphone volume. If only stereo head- phones are to be used, interconnect the tip and sleeve contacts of the headphone jack. If it is desired to monitor the 70-volt output of an SRlOSA Amplifier, substitute a 70- volt line to voice coil transformer for the 25-volt transfor- mer listed above.

IMPEDANCE.. ..8n NOM

6 f i M I N

POWER TO e n . . .. 4oo w

POWER TO 1 6 n . . . 2 0 0 W

VOLTAGE OUT.....5 6 . 6 V

SR105 AMPLIFIER

BA ER

FIGURE 11. BRIDGED AMPLIFIER CONNECTIONS

VOLUME CONTROL (%-OHM L-PAD)

-		PHONE JACK
		-TIP
-
-	NOTE	-
		RING
		SLEEVE

FIGURE 12. HEADPHONE JACK FOR

SPEAKER CONNECTIONS