Quick Install for Dry Contact Ringing
- Mount the unit and connect power to the 24VDC terminals. The power supply is typically located in the equipment room with power and control contacts provided through separate pairs in the cable from the equipment room.
- Press the test button (bottom right of unit). The warble should be heard on the speaker. Adjust volume and tone to suit (bottom left of unit).
- Connect telephone system night bell or auxiliary ring contacts to RELAY terminals.
- If loud or outdoor ringing is required, connect an 8 ohm speaker, such as the 1185, to the AUX SPKR terminals. The internal speaker may be disabled by removing the SPK shunt (refer to the inside diagram on page 7).
- Close cabinet and test.
About Duet Plus
Duet Plus is an auxiliary ringer compatible with most business telephone equipment and includes an audio amplifier for ring amplification or voice paging. This installation guide is included with the new plastic version of Duet Plus introduced in April 1995.
Mounting
Duet Plus must be mounted in a dry indoor location. Outdoor locations can be alerted with an external water-proof horn speaker such as the 1185. The Duet Plus cabinet is opened by inserting a screwdriver into the slot near the top of the cover and prying gently upwards while lifting the cover. Once open, the unit can be wall mounted with woodscrews using the two slot holes in the back.
Wiring
Connections to Duet Plus are made at the PC Board mounted terminal strip inside the unit. Connections depend entirely on the application. Duet Plus can be installed so that wiring is hidden by entering through the back of the cabinet from a mud ring, dedicated electrical box, or opening in the wall. For surface wired applications, wire can enter from the top, bottom, or left side. The power supply is often located in an equipment room and wired to Duet Plus using one pair of a 3 or 4 pair station cable, leaving additional pairs for dry contact closure and/or paging audio. Wiring to 8 ohm speakers should be low resistance for maximum audio power. If extra wire pairs are available, use them to reduce speaker wiring resistance. When an auxiliary speaker is used, the wiring is normally routed from Duet Plus directly to the speaker.
Inputs and Outputs
| Terminal Pair | I/O | Description/Function |
| 24VDC | Input | Power supply input. 12 to 27 volts DC, polarity insensitive. Idle current nominal 25mA. Maximum current with internal speaker 110mA, with typical 8 ohm horn speaker 320mA. |
| RELAY | Input | Trigger circuit to detect dry contact closure for connection to auxiliary ringing or night bell contacts (normally open). |
| AUX SPKR | Output | Output to loud speaker for full power performance. Provides both warble and amplified audio. This output can be selected at shunt J3 for high impedance output (10 kOhm) for connection to slave amplifiers. |
| AUDIO INPUT | Input | Balanced 600 ohm input for voice paging or ring amplification. |
| 10VAC | Input | Trigger circuit detecting foreign voltage. Isolated input detects 3 to 60 volts DC or AC. Input impedance approximately 4 kOhm. |
| T R | Input | Trigger circuit detecting 40 to 150Vac 16 to 68Hz ring signals from CO line or PBX station tip and ring. |
Inside Diagram
The inside diagram shows the printed circuit board (PCB) layout of the Duet Plus. Key components and connections include: Terminal blocks for 24VDC Power Supply, RELAY, AUX SPKR, AUDIO INPUT, 10VAC, and T R inputs. Jumpers J1, J2, and J3 are present for configuration. Controls include Warble Volume, Tone Control, and a Test Button. A PAG VOL control is also visible. The diagram illustrates how external devices like power supplies, telephone systems, and speakers connect to these terminals.
Option Jumpers
| Jumper | Setting | Description |
| J1 | HI | High level input paging signal (0 to +12 dBm) |
| J1 | LO | Low level input paging signal (-18 to 0 dBm) |
| J1 | DET | Maximum gain for very low input levels. Use for audio detection application only. |
| J2 | DET | Audio input signal routed to detection circuit |
| J2 | PAG | Audio input signal routed to amplifier. |
| J3 | PWR | Speaker output provided directly when shunt is in. With shunt out, signal is provided through 10K resistor. |
| J3 | SPK | When in, connects internal speaker. |
Block Diagram
The block diagram illustrates the internal signal flow of the Duet Plus. Audio input signals are processed through a pre-amplifier and then directed to either an audio detection circuit or an amplifier, controlled by jumpers J1 and J2. The unit features detection circuits for dry contact closure, low voltage, and 90V ring signals. A warble oscillator generates audible tones, controlled by volume and tone adjustments. The output stage, featuring a power amplifier, drives either the internal speaker (via J3 SPK shunt) or an auxiliary speaker (via J3 PWR shunt, with optional 10k resistor).
Applications
Dry Contact Office Ringer
This is the most common application. Night bell or auxiliary ring contacts connect to the RELAY terminals. When contacts operate, Duet Plus provides a warble sound from the internal speaker. Volume and tone are adjustable. The TEST button activates the unit for testing. For multiple units connected to the same contacts, ensure all RELAY circuits are wired with the same polarity to prevent mutual activation. This setup is suitable for offices, quiet warehouses, and common areas. The power supply can be located in an equipment room. Note: The warble volume cannot be turned completely off.
Loud or Outdoor Dry Contact Ringer
An 8 ohm horn speaker is added for significantly improved output volume. The AUX SPKR terminals provide access to 100% of the unit's power, while the internal speaker receives only 25%. For outdoor applications, a weather-proof horn speaker (like Algo's 1185) can be mounted outside while the Duet Plus remains indoors. This also simplifies maintenance. The internal speaker can be enabled or disabled using the J3 (SPK) shunt. The TEST button activates the warble through the horn speaker.
Loud Ringer and Paging
Once installed as a loud ringer with an external speaker, voice paging can be added by connecting the dry page port from the telephone system to the AUDIO INPUT terminals. Duet Plus will then provide loud ringing and paging through the same speaker. A 3-pair cable can supply power, dry contacts for ringing, and paging audio. Minimize wiring resistance for maximum output power. The PAG VOL control on the PC board adjusts paging volume independently. With a typical 8 ohm horn speaker, the unit provides sufficient ring and paging volume for warehouses up to 10,000 square feet.
Norstar Station Set Ringer
Duet Plus can detect audio signals and activate warble tones when a threshold is reached. This is commonly used to detect ringing on Northern Telecom Norstar station sets via the headset jack. Jumpers J1 and J2 are set to DET mode, with the monitored audio connected to the AUDIO INPUT terminals. The PAG VOL control adjusts detection sensitivity. Algo provides 2501 and 2502 modular cords for connecting to Norstar station sets (M7208/M7310/M7324 and M7100 respectively). Due to high sensitivity requirements, wiring should be kept short. Adjust the station set's ring volume high, then set Duet Plus sensitivity. Excessive sensitivity in noisy environments can cause false ringing.
Norstar Station Set Strobe Light
Duet Plus can provide a visual indication of ringing by connecting a 1126 strobe light to the AUX SPKR terminals. The strobe light flashes approximately once per second when activated. This is useful for visual alerting in noisy or noise-free environments, triggered by 90V ringing, dry contact, or Norstar station set ringing. Strobe lights are available in various colors. For bright environments or when the strobe is not in line of sight, Algo offers a high-powered strobe light kit. The 'Volume' control must be set to maximum for proper strobe operation. The speaker can be enabled or disabled as needed.
Telephone Speaker Amplifier
In some cases, amplifying the electronic telephone speaker signal is beneficial for loud ringing or voice paging. Duet Plus amplifies any signals present on the telephone speaker, providing loud ringing specific to the phone and loud paging with talkback if the phone supports hands-free answerback. This is useful when additional wiring for paging or ringing is difficult. Connecting to speaker leads may void the telephone manufacturer's warranty; test the phone first. Connect wires to the speaker wires (preferably using insulation displacement crimps) and to the AUDIO INPUT terminals of Duet Plus. For talkback paging, speaker location is critical; avoid directing the speaker towards the telephone.
Connecting to a Paging Amplifier
The AUX SPKR output of Duet Plus can connect to a paging amplifier to send the warble tone to existing speakers. This is advantageous when speakers are already installed. Pull the J3 PWR shunt for this application. When the shunt is installed, the AUX SPKR output is direct. When pulled, it provides a 10K OHM resistor output. Into a 600 ohm load, Duet Plus delivers approximately 0 dBm signal. It can also parallel an existing connection between a telephone system page port and amplifier. Caution: Ensure Duet Plus operates from a ground-isolated power supply (e.g., 1223 adaptor) to avoid ground loops.
90 Volt Loud Ringing
The 90 Volt ring detection circuit is used behind analog station ports on PBX and EKT systems, or for direct connection to CO telephone lines. Inputs T and R are not polarity sensitive. This application shows Duet Plus as a loud ringer activated by CO line voltage and dry contact closure, demonstrating that multiple detection circuits can be used. It can replace a 90V loud bell and a separate dry contact ringer. The dry contact could be a push button. For FCC/DOC approved installation on a telephone line, connect using an approved connector like Algo's 2502 modular cord. Duet Plus will warble according to the 90V ring cadence or when activated by dry contact closure.
90 Volt Ring Generation From Norstar Station
Duet Plus detects ringing on a Norstar station set via the headset jack and activates the Algo 3012 Ring Generator. The 3012 Ring Generator detects the warble signal from Duet Plus and provides 90 Volt 20 Hz sinewave ringing for up to five mechanical bells. The 3012 can be activated directly by dry contact or low voltage detection, but Duet Plus provides the interface for telephone line ringing or Norstar station set ringing. This is useful where 90V bells exist but the new telephone system does not provide ringing. The 3012 Ring Generator was originally designed as a replacement for Nortel's NT0B17 ring generator.
Multiple Speakers
The number of speakers that can be attached depends on the required power, speaker impedance, and wiring resistance. Duet Plus was intended for one speaker, typically a horn speaker for warehouses or machine shops, or a wall baffle cone speaker for quieter indoor areas. An auxiliary speaker is often connected for improved power and bass response in voice paging applications. The diagrams show maximum power capability with 8 ohm speakers, a 24Vdc power supply, and no wiring losses. Output capability is reduced by approximately 30% for voice paging to avoid clipping. Wiring resistance is critical, especially with low impedance loads like 8 ohm or 4 ohm speakers. For a 4 ohm load, 50% of the power is lost after 75 feet (23m) of 24 gauge wire. Use spare wires in parallel to reduce resistance.
Speaker Wiring Arrangements and Typical Output Power
The diagrams illustrate various speaker wiring configurations, showing how multiple speakers can be connected in series or parallel to achieve different impedance loads and power outputs. For example, configurations are shown with speakers rated at 4.9W, 1.2W, 0.6W, 2.3W, and 1.25W, demonstrating how total power output is distributed across connected speakers based on their impedance and the Duet Plus's output capabilities.
Application Hints and Suggestions
- Duet Plus provides sufficient ring volume for most office environments and is often used in warehouses and noisy locations without external speakers. For LOUD ringing, connect an 8 ohm speaker to the AUX SPKR terminals, as the internal speaker does not receive maximum power.
- Duet Plus contains a protective device that clamps power supply voltages above 27 volts. The Algo 1223 adaptor is recommended. If an alternate power supply is used, ensure it does not supply more than 27 volts at a load of 50 mA, otherwise the protective device may overheat and fail.
- Multiple Duet Plus units can share a common set of dry contacts for activation (up to 50 units). The TEST button is designed to trigger only the unit being tested for singular testing. If relay terminals on two or more Duet Plus units are wired in reverse to each other, they may warble continuously. Connect units one at a time to avoid this condition.
- If Duet Plus is mounted over a drywall mounting plate that protrudes above the wall surface, the ribs on the bottom of Duet Plus near the mounting holes may be cut to provide a flush fit. These ribs normally prevent the plastic case from being deformed by over-tightening mounting screws.
- When shunts are pulled from option jumpers (e.g., the SPK shunt to disable the internal speaker), park the shunt back on one pin only so it is not lost if the speaker needs to be reactivated.
Need a different sound? Algo has developed a "Talking Duet Plus" which provides a user-programmed audio signal instead of a warble. Refer to www.algosolutions.com/1826 for more information.
Regulatory Notices
Industry Canada
The Industry Canada label identifies certified equipment that meets telecommunications network protective, operational, and safety requirements. The Department does not guarantee user satisfaction. Users must ensure equipment connection is permissible to local telecommunications company facilities and use an acceptable connection method. Compliance may not prevent service degradation. Repairs should be made by an authorized Canadian maintenance facility. User alterations may lead to disconnection requests. Ensure electrical ground connections (power utility, telephone lines, internal metallic water pipe system) are connected together, especially in rural areas. Contact an electrician for these connections. The Load Number (LN) indicates the percentage of total load on a telephone loop; the total LN of all devices must not exceed 100.
FCC Part 68
This equipment complies with Part 68 of the FCC rules. The label on the back contains the FCC registration number and Ringer Equivalence Number (REN). This information must be provided to the telephone company. FCC compliance depends on using a FCC compliant modular cord and plug assembly into an FCC compliant jack; Algo offers cord PN 2502. The REN determines the quantity of devices allowed on a telephone line; excessive RENs may prevent devices from ringing. The sum of RENs should not exceed five (5.0). Contact the local telephone company for REN limits. If the equipment causes harm to the telephone network, the telephone company will notify you for temporary discontinuance of service. Advance notice may not always be practical. You will be advised of your right to file a complaint with the FCC. The telephone company may make changes to its facilities that could affect equipment operation; advance notice will be provided for necessary modifications. For USA repair or warranty information, contact Algo's service center at (800) 457-4287. If the equipment causes harm, the telephone company may request disconnection until the problem is resolved.
Warranty and Repair
Duet Plus is warranted to be free of defects in material and workmanship for 18 months from the date of manufacture. A label on the back identifies the manufacture code (e.g., 9503 for the third week of 1995). To return a product for repair, contact the repair center for a Return Authorization Number and instructions. Ship product freight prepaid. Product will be returned freight collect for out-of-warranty repairs and freight prepaid for warranty repairs in Canada or the USA. For shipping to Canada, use the following address: Algo Communication Products Ltd, Repair Center, 4500 Beedie Street, Burnaby, B.C., Canada V5J 5L2. Tel: (604) 454-3790, Fax: (604) 437-5726, www.algosolutions.com. For locations outside Canada, contact Algo for the nearest repair center.
Additional Products (Partial List)
- 1071 Norstar™ Press To Talk: Nortel handset with PTT switch.
- 1070 Norstar™ Press To Mute: Nortel handset with PTM switch.
- 2502 Modular Cord: Provides connection between headset jack of Norstar™ M7100 and Duet Plus or Talking Duet Plus.
- 4100 AuxBox: Monitors the digital signaling between a Norstar or M1 system and a Meridian telephone.
- 1826 Talking Duet Plus: Auxiliary ringer and paging amplifier with recorded message. Visit www.algosolutions.com/1826.
- 1826P Talking Duet Plus with Power Supply: Talking Duet Plus packaged with 1223 power supply. Visit www.algosolutions.com/1826.
- 3012 Ring Generator: Develops 20Hz 90Vrms sinewave ring signal. Triggered by dry contact or low voltage.
- 4102 USB AuxBox: Digital desktop voice recording. Stores telephone conversations as call records on a customer-supplied PC using Algo Call Recording Software. Visit www.algosolutions.com/4102.
- 1185 Horn Speaker: 8 Ohm 20 Watt horn speaker, water-proof white plastic. Visit www.algosolutions.com/1185.
- 1223 Power Supply: 22 Vdc 350 mA output; 110 Vac 60 Hz Input; CSA and UL approved.
- 1127P Visual Indicator: A desktop or mountable visual indicator that can be activated by Duet Plus. Visit www.algosolutions.com/1127.
- 1126 Strobe Light: Provides a visual flash indication when connected to the auxiliary speaker terminals of Duet Plus. Visit www.algosolutions.com/1126.
- Application Notes: Visit www.algosolutions.com/appnotes for a detailed listing of Algo product Application Notes.
