Telex TR-825, TR-800 Dual Listen Functionality, Parts to be Removed by User to Enable Dual Listen

Dual Listen Functionality

The base stations's main audio board has the option of placing additional parts to enable dual listen. Dual listen allows the mixing of the intercom channels. The mixing will occur lo- cally, within the base station, and is only heard on that base station's beltpacks. The user will have the ability to enable/dis- able the mix of I/C A into I/C B or vise versa. If you have TR-825 beltpacks, there is no need to install this base option. The level of the mix can be controlled at the TR-825 via the two volume controls.

They will also have the ability to control the level of the mix (-4 dB to -24 dB down from main channel). Removing two surface mount resistors and installing two SPDT switches and two potentiometer enables dual listen. The parts to be installed are shown in Table 1. The two resistors on the board to be re- moved are in Table 2.

Board
Designator	Description and Function		Value		Manufacturers, Part No.
VR5, VR6	Potentiometers		20kW - 25kW	Bourns, 3309P-1-203
	VR5 = Controls I/C A into I/C B Mix			CTS, U262R253B
	VR6 = Controls I/C B into I/C A Mix			Piher, PT10LV10-203A2020
S6, S7	Switches		SPDT	E-Switch, 500ASSP1M2RE
	S6 = Enable/Disable I/C A into I/C B Mix			E-Switch, EG1218
	S7 = Enable/Disable I/C B into I/C A Mix			Alcoswitch, TSS11DGPC
		Table 1
	Parts to be Installed by User to Enable Dual Listen
	Board
	Designator	Description and Function			Value
	R295	Resistor, Default if mix components not installed			10k
	R296	Resistor, Default if mix components not installed			10k

Table 2

Parts to be Removed by User to Enable Dual Listen

The listed manufactures and part numbers in Table 1 are those that the audio board was laid out for and thus the hole pattern used. Several of these parts may be found at Digi-Key and other distributors. Trim the leads on the parts so they can not hit the metal case. Locations to place these components are provided on audio board part number 750608.

The audio board part number is located on the lower left hand side of the board if facing the front of the unit. The locations where the components can be installed are on the upper right hand side of the board. See Figure 22 for the locations. Board part number 750541 does not have locations to place compo- nents, however, modification documents may be obtained from Telex Communications for those who wish to modify older audio boards for dual listen.

BACK					B INTO A
			MIX
					MIX
		LEVEL
			VR6		ON
					OFF
	B INTO A				S7
	MIX		R298	R296	IF PARTS INSTALLED
	ON
	OFF				REMOVE R296
	ON		MIX		S6
	OFF	LEVEL
	A INTO B				ON
	MIX
			VR5
					OFF
			R297	R295	A INTO B
					MIX
					IF PARTS INSTALLED
					REMOVE R295
750608	REV X	750608	REV X
879416- 1 REV J		879416- 1 REV J
FRONT

Figure 22

Audio Board Part Number and Dual Listen Component Locations

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