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The Model SSA324 is a System to System Adapter (or interface). It interconnects the voice signals between different intercom systems. In addition, it can optionally interconnect "Calls" or tally signals between systems. Each SSA324 includes two two-wire to four-wire converters. The four-wire interface can deliver and accept high level signals such as those from the McCurdy intercom system. An SSA324 can also function as a two-wire to two-wire interface by interconnecting the two individual interfaces at the four-wire level. The SSA324 carries two voice channels when used as a dual two-wire to four-wire interface, and one voice channel when functioning as a two-wire to two-wire interface.

A front panel channel select switch for each of the two interfaces (A and B) will select one of two, two-wire channels. For Clearcom use, the switch will be in the Channel 2 position. For Audiocom use, a rear panel switch will select balanced two-wire operation.

Front panel controls include 1) adjustments for null, level, ducking, 2) switches for monitoring and channel select.

Rear panel controls include balance/unbalance switches for the two-wire connection of each interface. Rear panel connectors include two XLR3 connectors for two-wire, eight terminals for two four-wire interconnections, one 25 pin D connector for duplicate four-wire connections plus options connections. The terminals are useful for rapid field connections. The D connector aids rapid replacement where meantime-to-repair is an issue and also allows option swapping.

The SSA324 replaces the Model TWI224 and TWI222 interfaces where powering from the intercom is not required. Differences between the Model TWI224 / TWI222 interface and Model SSA324 include the following: 1) The SSA324 is self (locally) powered, the TWI224 / TWI222 is usually powered from the TW line or may be locally powered. 2) The SSA324 has a maximum output at the four-wire output port of +22 dBm, the TWI224 / TWI222 maximum output is 9 dBm.




The Model SSA324 consists of two two-wire to four-wire converter in a single package (converter A and converter B). If the two converters are interconnected, the Model SSA324 then functions as two-wire to two-wire converter. The method of interconnection is as follows: converter A's fourwire output is connected to converter B's four-wire input; converter A's four-wire input is connected to converter B's output.

Converter A's two-wire port is driven by an active balanced bilateral current source (an optional transformer may be added). Converter B's two-wire port is similar to Converter A's.

Converter A's four-wire output port is driven by an active balanced voltage line driver (or via an optional transformer). A build-out resistor (about 33 ohms) in each leg of the differential output maintains stability driving long cables. Converter B's four-wire output port is similar to converter A's.

The optional Transformers can be used to provide higher common mode voltage isolation between the four-wire System(s) and the two-wire systems.

Converter A's four-wire input port is active balanced, bridging, ten thousand ohms impedance. Converter B's four-wire input port is similar to converter A's. (An optional former is available for the four-wire input(s).


Ducking (bilateral)

Adjustable, 0 to 30 dB. Toggles from one direction to the other (threshold is factory set). There is one adjustment for interface A and one for interface B. Each interface has depth level adjustment (front panel).



Uses standard headset. Front Panel has six pin female XLR type headset connector.

Switch on frontpanel activates the monitoring function. User uses headset microphone or a built in oscillator to adjust for null in headset earphones (or via a built-in oscillator which is jumper selected by a jumper on the printed circuit board).



There are three null adjustments associated with each two wire port. These are resistive (medium), capacitive (high), and inductive (low) nulls. Medium, high, and low refers to frequency ranges; medium centers about 1 kilohertz, high, 3 kilohertz, low, 300 hertz.


Level Adjustments

There are two level adjustments for interface A (to-From two-wire) and two for interface B (to-from two-wire).



The Model SSA324 can be installed in 3 ways: a single unit mounted in a half rack space using an optional Model MCP2 Kit for rack mounting a single unit; or two SSA324 supplies mounted side by side using the optional MCPI Kit for rack mounting two units side by side; or free standing using the optional MCP8 Kit for adding side channels for non-rack mounting portable use.



The connection for the headset used to set-up the interface is on the front panel, all other connections are on the rear panel.

System A two-wire connection is at J101, System B, J102. These are XLR-3-31 (female) type connectors. System A and B fourwire connections are at both TB I and J103. J103 also contains connections to the option card, when installed. Low voltage alternating current power is applied to J104 (16 volts, AC).

Connector Pin-outs are listed below.

Two-Wire (1101- J102)

Audiocom Clearcom RTS RTS

Bal Unbal** Bal-* Unb


CHI 2,3 3 2,3 2


CH2 - - - 3


Com 1 1 1 1



*S 101 (System B) and/or S 102 (System A) set to in position for balanced operation.


If option board installed and Clearcom call light operation is required, move jumper W103 (System A) and/or jumper W203 (System B) on motherboard to 2,3 position. Jumper J103- 7, 20 for System A, and/or J103- 12,25 for System B.

TB1 Four-Wire Connection.-,


System A System B


Audio In Hi 1 5

Audio In Lo 2 6

Audio Out Hi 3 7

Audio Out Lo 4 8


J104 Power Input


Earth 1

16VAC 2

16VAC 3

No Conn. 4

J103 I/O

1 Earth


2 4-Wire Audio In Hi, System A

15 4-Wire Audio In Lo, System A

3 4-Wire Audio Out I-ii, System A

16 4-Wire Audio Out Lo, System A

4 4-Wire Audio In Hi, System B

17 4-Wire Audio In Lo, System B

5 4-Wire Audio Out Hi, System B

18 4-Wire Audio Out Lo, System B

6 Call Send GND (A)

19 Call Send I-Ii (A)

7 DC Call Sig En GND (A)

20 DC Call Sig En Hi (A)

8 Relay Contact NO (A)

9 Relay Contact COM (A)

21 Relay Contact NC (A)

22 Relay Contact NO (B)

23 Relay Contact COM (B)

10 Relay Contact NC (B)

11 Call Send GND (B)

24 Call Send IE (B)

12 DC Call Sig En GND (B)

25 DC Call Sig En Hi (B)


Front Panel Dym- Mic- Headset Connector

1 Mic Lo

2 Mic Hi

3 Headphone Com

4 Left Headphone Hi

  1. Right Headphone Hi

6 No Connection

Motherboard Test Signal Jumper

Place jumper on W2 for tone test signal, W3 for voice test signal. Test signal used with headset and front panel nulling adjustments to null return two-wire signal.




Front Panel




1. Channel Select switch, CHI out / CH2 in, Sys. A.

2. Presses momentary switch for nulling System A Two-wire.

3. Channel Select switch, CHI out / CH2 in, Sys. B.

4. Press momentary switch for nulling System B Two-wire.



5. XLR6-31 Female 6 pin headset connector



6. Monitor headphone level (VOLUME).


7. Indicator (Power) Green LED.


8. LEVEL TO RTS, System A.

9. LEVEL FROM RTS, System A.

10. DUCK Level, System A.

II. Inductive (LOW) null, System A.

12. Resistive (Medium) null, System A.

13. Capacitive (High) null, System A.

14. LEVEL TO RTS, System B.

15. LEVEL FROM RTS wire, System B.

  1. DUCK Level, System B.

17. Inductive (LOW) null, System B.

18. Resistive (Medium) null, System B.

19. Capacitive (High) null, System B.


Rear Panel Switches


20. Unbalance (Out) Balance (In) / Select Two-Wire, System A

21. Unbalance (Out) Balance (In) / Select Two-Wire, System B





Preset Controls as Follows:

To/From RTS Set to Midway

Duck Level Set to CW

LOW Set to Midway

Med Set to Midway

Hi Set to CCW

Volume 10 o'clock


Press Test Switch

If test signal tone, adjust Med for null, then Hi, then Low.

If test signal voice, say ahhh into microphone, adjust Med for null, then Hi, then Low.

Release Test Switch




Have Talkers 1 and 2 on Four-Wire System, Talkers 3 and 4 on Two-Wire System. Adjust To/From RTS Controls so that all Talkers can hear other at about the same level regardless of which system the other talkers may be on.


Duck level

Adjust Duck Level only if full duplex operation is not possible because of feedback. Adjust Duck Level carefully from CW towards CCW. Only a very small amount of ducking should be used.



Last Modified : 09 February, 2006