User Guide

Issue 2, September 2007

This User Guide is applicable for serial numbers: M46-00180 and later and units upgraded with software version 1.3 and higher

Copyright © 2007 by Studio Technologies, Inc., all rights reserved www.studio-tech.com

50110-0907, Issue 2 This page intentionally left blank. Table of Contents

Introduction ...... 5 Installation ...... 10 Configuration ...... 16 Advanced Configuration ...... 18 Operation ...... 20 Advanced Operation ...... 25 Technical Notes ...... 26 Specifications ...... 28 Appendix A—Interfacing with Telex®/RTS® Matrix Intercom Systems ...... 29 Appendix B—Interfacing with Riedel® Artist™ Matrix Intercom Systems ...... 30 Appendix C—Interfacing with Clear-Com® Matrix Intercom Systems ...... 31 Block Diagram

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 3 This page intentionally left blank.

Issue 2, September 2007 Model 46 User Guide Page 4 Studio Technologies, Inc. The Model 46 mounts in one space Introduction of a standard 19-inch rack enclosure The Model 46 is designed to interface and requires 100-240 volts, 50/60 Hz for 2-wire full-duplex party-line intercom cir- operation. cuits with 4-wire audio circuits associated with matrix intercom systems. Other spe- 2-Wire Interfaces cialized audio system interfacing applica- The Model 46’s 2-wire interfaces are tions can also be supported. The Model optimized for direct connection with dual- 46 provides two independent full-featured channel party-line (PL) intercom circuits. 2-channel interfaces. Each interface con- In addition, single-channel party-line tains two hybrid circuits which include intercom circuits can also be connected. automatic nulling capability. The analog Many broadcast applications use the dual- circuitry, under software control, provides channel TW-series from Telex®/RTS®, excellent audio quality and high return- including their popular BP325 belt pack. loss. The interfaces are compatible with Other industry-standard single- and dual- powered and unpowered 2-wire party-line channel PL intercom systems, including circuits. They are capable of supplying DC those from Clear-Com®, are also directly power, allowing direct operation of devices compatible. To provide optimal signal such as user belt packs. Configuration set- matching and interface performance the tings allow the 2-wire and 4-wire interface nominal level of the Model 46’s 2-wire circuitry to be compatible with a range interfaces can be selected. Using DIP of nominal signal levels. Audio level me- switches, accessible on the front panel, ters provide user confirmation of system the nominal levels can be selected to be performance during setup and operation. either –10 or –14 dBu, settings that should Applications for the Model 46 include tele- allow compatibility with virtually all party- vision sports and special event broadcast- line systems. For example, for applications ing, theme park and theater installations, that use equipment from RTS the –10 dBu corporate events, and industrial testing setting is appropriate. For other equip- environments. Standard audio connectors ment, such as that from Clear-Com, the are used for all input and output signals. –14 setting is correct.

Model 46 Front Panel

Model 46 Back Panel

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 5 The Model 46’s 2-wire interfaces can intercom power source ensures that sys- correctly function with powered (“wet”) tems requiring long intercom cable runs or unpowered (“dry”) intercom circuits. will function correctly. The circuitry’s out- Powered circuits have a DC voltage pres- put regulation is such that little change in ent, typically provided by power supplies the output voltage will occur over its entire such as the RTS PS31 or Clear-Com rated output current. Also, the unique de- PS-232. This DC power, normally 30-32 sign of the power supply circuitry virtually volts, provides energy for connected eliminates the noise and “hiss” associated devices such as user stations or belt with typical intercom power supply perfor- packs. In this type of application the mance. Under software control the output Model 46 is configured to operate in its of the DC power supplies are monitored external 2-wire power source mode. In this for over-current and short-circuit condi- mode the Model 46’s circuitry maintains tions. This allows protection shut-down the required high-impedance load and, of the output DC, as well as providing an as in all cases, draws no power from the alert by way of a visual indicator. party-line circuit. An auto-terminate func- tion ensures that should a “wet” circuit not Analog Hybrids with Auto be connected, the Model 46’s interface Nulling circuitry will remain stable. This unique feature makes certain that objectionable A key reason that the Model 46’s inter- audio signals, including oscillations and faces achieve excellent audio performance “squeals,” will infrequently be sent to the is the design of the 2-wire-to-4-wire hybrid connected 4-wire device. circuits. They provide low noise and dis- tortion, good frequency response, and A significant capability of the Model 46’s high return-loss (“nulling”), even when 2-wire interfaces is their ability to supply presented with a wide range of 2-wire DC power and 200 ohm AC termination conditions. Unlike telephone-line (“POTS”) to the connected intercom circuits. Re- oriented DSP-based hybrid circuits, the ferred to as the Model 46’s internal 2-wire Model 46’s analog circuitry provides ex- power source mode, the 30 volt output tended frequency response. With a pass can power devices such as user stations band of 100 Hz on the low-end and 8 kHz and belt packs. In many applications this on the high-end, natural-sounding voice will eliminate the need for external inter- signals can be sent to, and received from, com power supplies. Besides reducing the 2-wire party-line circuits. total system cost, this feature can also lower system weight, reduce required A hybrid’s ability to isolate the transmit mounting space, and decrease the mains signal from the receive signal in the 2-wire- energy requirement. to-4-wire interface is critical. The quality of this isolation, technically known as With each 2-wire interface’s ability to sup- return-loss or trans-hybrid loss, is mea- ply up to 300 milliamperes of current, a sured in dB. A high value is important, typical broadcast application that uses two especially in applications where multiple sets of three BP325 belt packs can easily 2-wire-to-4-wire interfaces are used togeth- be supported. Each interface’s 30 volt DC er. Remote sports broadcast applications

Issue 2, September 2007 Model 46 User Guide Page 6 Studio Technologies, Inc. are especially sensitive to this requirement. 4-Wire Interfaces The Model 46’s sophisticated auto nulling Associated with the 4-wire portion of the function uses analog circuitry under mi- Model 46’s interfaces are analog line-level croprocessor control to achieve significant inputs and outputs. These are intended trans-hybrid loss. This return-loss “null” is to interconnect with a variety of 4-wire de- achieved by making a series of adjustments vices, including matrix intercom systems, to account for the resistive, inductive, and audio-over-fiber transmission systems, capacitive conditions that are present on and other specialized audio equipment. the connected 2-wire party-line circuit. The The input and output circuitry is transform- party-line’s conditions are the sum of the er-coupled to minimize the chance of impact made by the type and quantity of hum, noise, or ground “loop” issues. cable, the connected user-devices, and A key characteristic of the Model 46’s de- the intercom power source. sign is the ability to select the 4-wire input Whenever a user presses one of the Model and output nominal levels. This helps to 46’s “auto null” buttons digital circuitry ad- ensure compatibility with virtually all audio justs the analog hybrids to rapidly achieve equipment. Front-panel-accessible DIP their maximum return-loss. The nulling pro- switches allow the nominal levels to be cess takes less than 10 seconds for each configured from among four choices: 0, channel of an interface. However, it’s impor- +4, +6, or +8 dBu. The 0 dBu setting was tant to note that while the nulling process specifically provided for compatibility with is automatic, it only takes place upon user Clear-Com matrix intercom systems. The request. This can lead to more stable and +4 dBu setting allows “standard” audio consistent audio performance when a hy- signals to be directly connected. Digital brid is exposed to the varying 2-wire condi- matrix intercom systems from Riedel® can tions often found in broadcast applications. be effectively connected using the +6 dBu The parameters obtained during the nulling setting. And the +8 dBu setting allows process are stored in non-volatile memory; proper level matching with the popular mains power interruptions won’t require the ADAM™ series of matrix intercom systems auto nulling function to again be performed. from Telex/RTS. This setting also applies to the related RVON-I/O VoIP product. A sine-wave audio tone is generated for use during the auto nulling process. The The Model 46 contains eight 5-segment frequency is software-controlled to maxi- LED level meters. Four of the meters mize the ability of the hybrid circuits to are provided for each interface, with two reach a “deep” null. In addition, at the displaying the level of the signal being beginning of each auto null sequence a received from the 4-wire source and short period of 24 kHz tone is sent to the two displaying the level being sent to associated 2-wire party-line interface. This the 4-wire output. During installation and serves as a microphone disable (“mic kill”) setup the meters are invaluable in help- signal for user devices such as the RTS ing to confirm that the nominal level DIP BP325. By automatically disabling “open” switch settings have been properly made. microphones the auto nulling process can During normal operation the meters offer achieve better performance. rapid confirmation of audio signal flow in

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 7 and out of the unit. Additional LED status circuits. This, along with other circuitry that indicators are also provided, offering a clear monitors DC voltages present on the view of the 2-wire DC power and auto null 2-wire circuits, ensures that audio instabil- functions. ity associated with unterminated circuits will rarely occur. As previously mentioned Pro Audio Quality the Model 46’s 2-wire DC power sources The Model 46’s audio circuitry was de- offer a unique level of performance. Their signed in the spirit of professional audio ability to deliver power while maintaining equipment, rather than that found in typical audio quality is simply unmatched. party-line intercom gear. High-performance components are used throughout, providing Special Applications low-distortion, low-noise, and high head- While the Model 46 is designed to directly room. Using passive and active filters, the integrate into typical applications, it’s frequency response is limited to approxi- ready to support the “one-in-a-million” mately 100 Hz to 8 kHz. This range was se- situations too. To accomplish this DIP lected to provide excellent performance for switches, accessible on the back panel, human speech, while maximizing the ability allow some of the automatic features to be of the hybrids to create substantial “nulls.” disabled. For example, one switch allows When the Model 46’s internal DC power the auto-terminate feature to be disabled. sources are selected to provide 2-wire While this feature can help maintain audio party-line intercom power, enhanced audio quality, advanced users might need to dis- performance can also be expected. The able it. This would allow full control over quality of the DC supply circuits is excellent, the Model 46’s four hybrid circuits, en- with very little noise, hum, or “hiss” being abling them to be used completely inde- added to the 2-wire connections. In addi- pendently. A second DIP switch changes tion, the impedance characteristics of each the way in which the front-panel auto null interface’s DC powered (“wet”) channels push button switches operate. Normally was tailored to be essentially identical to pressing one of the buttons begins the that of the unpowered (“dry”) channel. This process of auto nulling both channels unique situation allows the automatic null- associated with an interface. The alter- ing circuitry to provide excellent, consistent nate switch mode allows each auto null results for both the powered and unpow- sequence to be activated independently. ered channels. One tap of the auto null button will begin the auto null process for interface one. Attention to detail is a hallmark of the Model Two taps of the button will begin the auto 46’s design. For example, during the brief null process for channel two. For installer- auto nulling process an interface channel’s selected applications, three opto-coupled 4-wire input and output signal is muted, inputs allow selected Model 46 features preventing unwanted audio from reaching to be remotely controlled. These features the connected equipment. Associated with include remote auto nulling for each inter- the 2-wire interfaces is circuitry that, under face and remote “mic kill” activation. software control, applies 200 ohm termi- nating impedances to the 2-wire party-line

Issue 2, September 2007 Model 46 User Guide Page 8 Studio Technologies, Inc. Simple Installation apparent that installing and configuring existing 2-wire-to-4-wire interface units The Model 46 uses standard 3-pin XLR- was invariably a time-consuming, aggravat- type connectors to allow convenient inter- ing process that required the talent of an connection in most broadcast and general expert to achieve reasonable results. And audio environments. For flexibility, access even under those constraints the resulting to the 2-wire party-line intercom interfaces audio performance was often mediocre. can be made using the connectors pro- Any new design had to look at the applica- vided on both the front and back panels. tion in a different way. This led to the over- In permanent installations the back-panel riding Model 46 design goal: create a “new connectors will typically be utilized. In breed of cat,” fundamentally changing how other settings, such as field television pro- broadcast 2-wire-to-4-wire interface equip- duction, front-panel-access allows inter- ment fit into actual applications. com belt packs to be rapidly connected, without requiring access to the inside of a An important first step was to eliminate rack enclosure or necessitating the use of the requirement that a senior technician, a secondary input/output (I/O) panel. along with a screwdriver, be present dur- ing every installation. (It was universally The Model 46 is housed in a rugged steel acknowledged that their time can be better enclosure that is designed to be “road spent elsewhere!) The need to adjust trim tough.” It mounts in one space of a stan- potentiometers, fabricate special cabling dard 19-inch rack enclosure. The mains and connector straps, use nulling earpiec- input source can range from 100 to 240 es, etc. had to be eliminated. For example, volts, 50/60 Hz allowing direct operation in virtually all instances, input and output virtually anywhere in the world. A switch- levels fall within just a few dB of their nomi- mode power supply, contained within the nal values and, as such, could be support- Model 46’s enclosure, provides conver- ed with a limited number of configurable sion of the mains input power into the DC choices. In addition, it was acknowledged voltage required by the intercom power that in this application analog audio cir- supply circuits. Also contained within the cuitry was capable of providing excellent unit is a DC-to-DC converter that creates audio performance, but that the required the voltages required by the analog and manual nulling process was operation- digital circuitry. These efficient power sup- ally taxing. By adding digital control to the plies help to ensure cool, reliable opera- analog circuitry, automatic nulling couldbe tion in a variety of settings. performed—the best of both worlds! Design Philosophy The next step was to identify resources that While the “bits and pieces” that make would improve the installation process and up the Model 46 have been described in make operation more reliable. This led to conventional terms, the real strength of the inclusion of multiple LED level meters, the unit rests in how it integrates and per- allowing continuous monitoring of the input forms in the “real world.” Before beginning and output signals. It also turned out that the Model 46’s design process, conversa- in many applications only a small number tions with industry experts quickly made it of user devices, such as belt packs, are

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 9 typically connected to 2-wire party-line link the unit with the connected devices. circuits. By adding DC power sources to This is really only a factor in relation to the the Model 46’s 2-wire interfaces, the need 2-wire party-line intercom circuits. These for external intercom power supplies could circuits carry unbalanced audio which often be eliminated. can be susceptible to interference and crosstalk issues. Intercom circuits also The final step was to create a physical carry DC power which may make resistive package that would provide significant re- losses come into the picture. In general, sources in a form that allowed simple and shorter intercom cable lengths will as- reliable integration with other equipment. sure more reliable and consistent system This was accomplished by including two performance. Another location criterion is 2-channel interfaces in a one-rack-space access to the Model 46’s front panel. An enclosure. Using standard 3-pin XLR-type optimal location will allow convenient use audio connectors would enable rapid of the auto null push buttons and easy installation and troubleshooting. And by observation of the status and level meter making the Model 46 “universally” pow- LEDs. ered, installation in any locale could be directly supported. Mounting the Model 46 Once a mounting location has been se- lected installation can begin. The Model Installation 46 requires one space (1.75 vertical In this section you will be installing and inches) in a standard 19-inch (48.3 cm) interconnecting the Model 46. The one- equipment rack. Secure the unit into rack-space unit will be mounted in an the equipment rack using two mounting equipment rack. Audio input, audio out- screws per side. put, and party-line intercom connections will be made by way of 3-pin XLR-type 4-Wire Audio Inputs and connectors. AC mains power will be con- nected by means of a detachable cord Outputs set that is compatible with the Model 46’s Two audio line input and two audio line 3-pin IEC 320 C14-type inlet connector. output signals are associated with the 4-wire section of each of the Model 46’s System Components two interface circuits. Connections are The shipping carton contains the Model made using standard 3-pin male and 46 Interface and associated user guide. female XLR connectors. Refer to Ap- Units destined for North America and pendices A, B, and C for details on inter- Japan also include an AC mains cord. connecting with Telex/RTS, Riedel, and Your dealer or distributor should provide Clear-Com matrix intercom systems. an AC mains cord for other destinations. 4-Wire Line Inputs Locating the Model 46 As previously mentioned, each of the Model 46’s two interfaces allows two The Model 46’s mounting location will dic- analog line-level audio sources to be tate the length of the cable runs needed to

Issue 2, September 2007 Model 46 User Guide Page 10 Studio Technologies, Inc. connected. The source for these signals remove a potential ground current path will typically be ports on a matrix intercom from the Model 46’s earth/chassis ground system. It’s also possible that the signals point through the shield of a cable. Also, if will come from other devices, such as a a hum or noise issue does arise be certain fiber optic or copper-based audio trans- to confirm that, unless absolutely neces- mission system. The 4-wire input circuitry sary, the mating connector’s “shell” isn’t is balanced, capacitor coupled, transform- connected to the cables’ shield or pin 1. er isolated, and has an impedance of 13 k Termination of this “fourth” pin of a 3-pin ohms. The line inputs are compatible with XLR connector is often the cause of seem- signals that have a nominal level of 0, +4, ingly inexplicable noise issues. +6, or +8 dBu. Configuration switches, With an unbalanced source connect located on the Model 46’s front panel, al- pin 2 to signal high (+ or hot) and both low the circuitry to be adjusted to match pins 1 and 3 to shield. If connecting an the connected nominal level. The switches unbalanced source in this manner results work in tandem to control both the input in hum or noise, connect pin 2 to high and output nominal levels. (+ or hot) and pin 3 to shield; leave pin 1 Audio sources are connected to the line unterminated. inputs by way of 3-pin female XLR-type connectors which are located on the unit’s 4-Wire Line Outputs back panel. Refer to Figure 1 for a detailed Each of the Model 46’s two interfaces view. Note that pin 1 of these connectors provides two analog line-level audio out- is internally connected to the Model 46’s puts. These outputs are intended to be earth/chassis ground point. connected to inputs on the devices asso- ciated with the 4-wire audio signals. The Prepare the mating connectors (males) outputs are capacitor coupled, transform- so that pin 2 is signal high (+ or hot), pin er balanced with a nominal level of 0, +4, 3 is low (– or cold), and pin 1 is shield. If +6, or +8 dBu. As previously mentioned, connecting a source in this manner results the 4-wire nominal level configuration in hum or noise it’s possible that remov- switches, located on the Model 46’s front ing the shield connection from pin 1 can panel, control the level of both the line eliminate the issue; “floating” pin 1 will outputs and the line inputs. The 4-wire line

Figure 1. Detail of back panel showing line inputs and outputs

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 11 outputs are capable of driving inputs that and two on the front. They are organized have impedances as low as 600 ohms, in groups of two connectors per interface, however connecting to loads of 2 k ohms one on the back and one on the front. or greater is preferred. The line outputs They are wired in parallel (“multed”) and are connected by way of 3-pin male XLR- provide access to the identical signals. type connectors which are located on the Model 46’s back panel. Refer to Figure 1 Dual-Channel Intercom Systems for a detailed view. If compatibility with RTS TW systems is desired the mating connectors (females) The mating connectors (females) should should be wired so that common is on be prepared so that signal high (+ or hot) pin 1, DC with channel 1 audio is on pin is expected on pin 2. Signal low (– or cold) 2, and channel 2 audio is on pin 3. This should be expected on pin 3. The cables’ wiring scheme is correct whether the con- shields can be connected to pin 1. How- nected devices are to be powered by an ever, in order to minimize the chance that external source or by means of the Model ground-interaction problems will arise, 46’s internal power sources. pin 1 on each of the line output connec- tors is isolated from all Model 46 circuitry Single-Channel Intercom Systems and ground points. “Floating” pin 1 virtu- There are two ways of connecting to the ally eliminates the chance that a “ground Model 46’s 2-wire PL intercom connec- loop” problem will occur. tors when compatibility with Clear-Com single-channel intercom devices is de- 2-Wire Party-Line Intercom sired. The most direct method is to pre- Connections pare the female XLR mating connector so The Model 46’s 2-wire party-line (PL) that common is on pin 1, power is on pin intercom interfaces are designed to di- 2, and audio is connected on pin 3. With rectly connect with standard single- and this connection scenario only audio chan- dual-channel party-line intercom devices. nel two, associated with pin 3 of the Model Each of the two 2-channel PL interfaces is 46’s 2-wire PL intercom interface connec- compatible with intercom circuits that have tors will be utilized. Pin 2, the Model 46’s their own DC power sources. Alternately, audio channel one, will only be used for the Model 46 can provide the DC power connecting DC power to the connected required by connected intercom user devices. While the audio resources pro- devices. The internal 30 volt DC intercom vided by channel one will not be used, the power source is limited to 300 milliam- Model 46 can still be used to supply DC peres of current. This moderate amount power on pin 2. As previously mentioned, of power requires that the type and num- the maximum current draw on the 30 volt ber of connected user devices be selected DC output is 300 milliamperes. Alternative- appropriately. ly, an external intercom power supply can support the connected devices. For convenience, the 2-wire PL intercom circuits can be connected to the Model 46 In some single-channel PL intercom sys- by way of four 3-pin male XLR-type con- tem applications it may be desirable to nectors; two are located on the back panel take full advantage of the two channels

Issue 2, September 2007 Model 46 User Guide Page 12 Studio Technologies, Inc. associated with each Model 46 interface. Refer to the Configuration and Advanced In these applications one might want Configuration sections of this user guide to view the Model 46 as providing four for details. 2-wire-to-4-wire interface circuits. The Model 46 can certainly be used in this Remote Control Inputs fashion, but adapter cables will have to be The Model 46 allows connection of three prepared. These adapters will “split” the externally provided DC signals. These Model 46’s 2-wire PL intercom connectors signals can provide remote control opera- into two 3-pin male XLR connectors, one tion of three functions: auto nulling for for each audio channel. Pin 1 of the female interface 1, auto nulling for interface 2, and 3-pin XLR intended to mate with the Model a special “mic kill” function. Remote con- 46 will connect to pin 1 of both 3-pin male trol of the auto nulling functions provides a XLR connectors. Pin 2 of the female XLR resource identical to that of the front-panel will go to pin 3 of the male XLR designated pushbutton switches. The exact manner in as channel 1. Pin 3 of the female XLR will which the buttons and the remote control go to pin 3 of the male XLR designated as inputs operate depends on the setting of channel 2. Refer to Figure 2 for details. Us- auto null button mode configuration DIP ing two adapter cables the Model 46 can switch. The “mic kill” function is unique, be directly interconnected with four Clear- only being available using the remote Com intercom circuits. However, power for control input. It causes a 500 millisecond the connected devices must be provided “burst” of 24 kHz signal to be sent se- by external power sources. The Model quentially to both of the 2-wire partly-line 46’s ability to supply intercom power will interface channels associated with each not be utilized. of the Model 46’s two interfaces. To clarify, a “mic kill” signal is sent to a total of four intercom channels whenever the func- tion is activated. Independent control of sending “mic kill” signals to interface 1 or interface 2 is not supported. User intercom devices compatible with this 24 kHz “mic kill” signal include RTS TW-series belt- packs such as the BP325. Figure 2. Adapter cable wiring diagram The opto-coupled remote control inputs are designed for direct connection with Note: It’s critical that the correct con- 3.3 and 5 volt DC logic signals. An internal figuration settings be made when using 475 ohm resistor, in series with each opto- the Model 46’s interfaces to support four coupler’s photodiode, acts to limit the independent intercom circuits. Specifically, current flow. Signals of up to 32 volts DC the 2-wire power source configuration DIP can be safely connected as long as the switches must be set for external. In addi- current is limited to 20 milliamperes maxi- tion the auto terminate disable DIP switch mum. If necessary, an external resistor must be placed in its on (up) position. can serve to limit the current. For example,

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 13 with a 12 volt DC signal using a 560 ohm, onto a piece of 10-conductor flat ribbon ¼-watt resistor in series with the connec- cable. This ribbon cable can safely exit tion would be appropriate. With a 24 volt the Model 46 by laying flat between the DC control signal a series resistor of 1.8 k chassis and the cover. The ribbon cable (1800) ohm is recommended. For correct can then “fan out” to loose wires or, better operation a minimum current of 2 milliam- yet, be terminated onto another connector peres is recommended. such as a 9-pin D-subminiature type. Access to the remote control inputs There are several ways of preparing to is provided by means of a 10-pin male connect to the remote control inputs. The “header” connector which is located on easiest means is to purchase an inter- the Model 46’s circuit board. Refer to connecting cable assembly from Studio Figure 3 for a view of the connector’s Technologies, Inc. The cable assembly location. The “keyed” and “shrouded” consists of a length of ribbon cable with header follows a common industry- a 10-pin socket on one end and a 9-pin standard specification: 2 rows of five pins D-sub female on the other. Contact the each with 0.1 inch between rows and pins. factory or check the website for details. The mating connector is intended to be Alternately, a competent technician can an insulation-displacement (IDC) socket easy fabricate an appropriate remote con- connector such as the AMP 746290-1. The trol input interconnect wiring assembly. An connector would be “crimp” terminated example of a partially pre-made assembly

Figure 3. Location of 10-Pin male header connector on the Model 46 printed circuit board

Issue 2, September 2007 Model 46 User Guide Page 14 Studio Technologies, Inc. is part number A1AXH-1036G-ND which is It’s important that a competent techni- available from Digi-Key (www.digikey.com). cian be available to perform the actual remote control input connection process. It’s important to ensure that the source As expected, mating the interconnecting of the remote control signals can meet cable assembly with the Model 46’s 10- the Model 46’s logic-state and timing re- pin “header” requires removing the unit’s quirements. The Model 46 recognizes an cover. As such, this must be done only idle remote control input as one that has after confirming that all sources of mains no current flowing through it. An active power have been disconnected from the remote control input is one that has current unit. flowing through it for a minimum of 30 milliseconds. A special case arises when the auto null button operating mode has AC Mains Power been set to independent. This requires The Model 46 operates directly from AC one front-panel button “tap” to auto null mains power of 100 to 240 V, 50/60 Hz. channel 1 and two button “taps” to auto As a “universal mains input” device, there null channel 2. The remote control equiva- are no switches to set or jumpers to install. lent for one “tap” is current flowing for a A 3-pin IEC 320 C14-type inlet connector minimum of 30 milliseconds. The equiva- on the Model 46 mates with a detach- lent for two “taps” is current that flows able mains cord set. For units shipped to for 30 milliseconds, then a minimum no- North America and Japan a cord is sup- current period of 30 milliseconds, followed plied that has a North-American (NEMA by current flow for a minimum of 30 milli- 15L) standard plug on one end and an seconds. The second period of current flow IEC 320 C13-type connector on the other. must come within one second of the start Units bound for other destinations require of the first. that the appropriate cord set be obtained. The wire colors in the mains cord should Once the interconnect method and the conform to the internationally recognized source of the control signals have been color code and should be terminated selected, refer to Figure 4 for connection according to the following chart: details. Ensure that the connected signals follow the specified polarity or damage to the opto-coupled inputs may occur.

10-Pin 9-Pin D-Sub Function Header (P9) Interface Cable Remote Auto Null Interface 1 + 7 4 Remote Auto Null Interface 1 – 9 5 Remote Auto Null Interface 2 + 2 6 Remote Auto Null Interface 1 – 4 7 Remote “Mic Kill” + 6 8 Remote “Mic Kill” – 8 9 Figure 5. Detail of back panel showing AC mains power connector Figure 4. Remote control input pin-out chart

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 15 Connection Wire Color Configuration – Interface 1 Neutral (N) Light Blue Line (L) Brown and 2 Earth/Ground (E) Green/Yellow The DIP switch assemblies associated with interface 1 and 2 are accessible on the Model 46’s front panel. They provide identi- Safety Warning: The Model 46 does cal capability for their respective interfaces. not contain an AC mains disconnect Refer to Figure 6 for a detailed view. In this switch. As such, the AC mains cord section the four switches associated with plug serves as the disconnection de- interface 1 will be covered in detail. This vice. Safety considerations require that information applies to interface 2 as well. the plug and associated inlet be easily The four switches allow selection of the accessible to allow rapid disconnec- 2-wire party-line power source, the nominal tion of AC mains power should it prove level for the 2-wire party-line channels, and necessary. the nominal level of the 4-wire inputs and outputs. As soon as AC mains power is applied the Model 46 will begin its power-up sequence. As a “boot up” indication the power LED and each of the status LEDs will momentarily light. After the sequence has completed the power LED will again light and remain lit. The unit is now fully functional.

Configuration Figure 6. Detail of front panel showing four DIP For the Model 46 to support the needs of switches specific applications a number of operat- ing parameters must be configured. These 2-Wire Party-Line Power Source include the 2-wire party-line power source, the nominal 2-wire level, and the nominal DIP switch 1 is used to select whether or 4-wire level. Three 4-position DIP-type not the Model 46 provides DC power to switch assemblies are used to establish pin 2 of connectors associated with the the desired configuration. One DIP switch 2-wire party-line intercom channels. Two assembly is associated with interface 1, a 3-pin male XLR-type connectors, one second is associated with interface 2, and located on the Model 46’s front panel a third associated with advanced operat- and one on the back panel, are used to ing features that apply to both interfaces. interconnect the Model 46 with the inter- com user devices. When switch 1 is in its off (down) position the Model 46 will not provide DC power. This switch setting is appropriate when an external intercom

Issue 2, September 2007 Model 46 User Guide Page 16 Studio Technologies, Inc. power supply is providing power to the 4-Wire Nominal Audio Level intercom circuit. In addition to power, it’s DIP switches 3 and 4 are used to config- expected that the external power supply ure the nominal level of the input and out- will also provide the required 200 ohm ter- put circuitry associated with interface 1’s minating impedance to both pins 2 and 3. two 4-wire input and output connections. When switch 1 is in its on (up) position the Four level settings are available: 0, +4, Model 46 will provide a 30 volt, 300 mil- +6, and +8 dBu. Prior to setting these DIP liamperes maximum source of DC power switches it’s important to determine the to pin 2 of the 2-wire PL intercom connec- nominal audio level of the equipment con- tors. The Model 46 will also provide 200 nected to the Model 46’s 4-wire input and ohm terminating impedances for both pin outputs. This may take a little investigation 2 and pin 3 of the party-line connectors. but is important for obtaining the best pos- The DC power and termination capabili- sible Model 46 performance. ties allow direct powering of dual-chan- The 0 dBu setting is provided specifically nel intercom belt packs, such as the RTS for use when a Model 46 is interconnected BP325. In addition, listen-only belt packs, with a Clear-Com matrix intercom system. such as the Model 34 from Studio Tech- The +4 dBu setting is appropriate when nologies, Inc. can be directly connected. standard audio lines with “+4” nominal There’s also no problem connecting levels are interconnected. The +6 dBu single-channel intercom belt packs or user setting can be appropriate when intercon- stations. necting with equipment manufactured in Europe, such as the digital matrix intercom 2-Wire Nominal Audio Level systems from Riedel. The +8 dBu setting DIP switch 2 allows adjustment of the is provided specifically when interconnect- nominal audio level for the two 2-wire ing the Model 46 with audio signals asso- party-line channels associated with inter- ciated with an RTS ADAM-series of matrix face 1. When the switch is in its off (down) intercom system. This includes the related position the nominal level is –14 dBu. RVON-I/O unit. This level is compatible with intercom belt packs from manufacturers such as Clear- When DIP switches 3 and 4 are in their Com. When the switch is in its on (up) off (down) position the nominal level is position the nominal level is –10 dBu. This set for 0 dBu. When switch 3 is on (up) setting is appropriate when belt packs and switch 4 is off (down) the nominal from RTS, such as the BP325, or listen- level is +4 dBu. When switch 3 is off only talent amplifier units from Studio (down) and switch 4 is on (up) the nomi- Technologies, Inc. are connected. For best nal level is +6 dBu. When both switches Model 46 performance it’s important that 3 and 4 are in their on (up) position the the 2-wire nominal level selection be made nominal level is configured for +8 dBu. correctly.

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 17 are connected to the Model 46. In this lat- Advanced ter case only one of the Model 46’s audio channels will be used. Configuration There may be situations where it’s nec- Four DIP switches are provided on the essary for the two channels associated Model 46’s back panel. They allow the two with each Model 46 interface be used interfaces to be configured for several ad- with separate 2-wire party-line circuits. vanced operating modes. Refer to Figure An example of this might be where two 7 for a detailed view of these DIP switches. “loops” of single-channel belt packs, The available modes include auto termi- such as units from Clear-Com, need to be nate disable, auto null button operation, connected. Adapter cables as shown in refresh disable, and factory test. Figure 2 would be used. In this case the intercom circuit’s DC power will not be connected to the Model 46, but only to the user devices. In this scenario, a DC volt- age won’t be present on pin 2 or pin 3. Another example of this might be where adapter boxes with DC blocking are used to interconnect intercom circuits with the Model 46. In both these cases a DC volt- age won’t be present on either pin 2 or 3 and the Model 46 will automatically apply Figure 7. Detail of back panel showing the 200 ohm terminations. In both these cases Advanced Mode DIP switches the termination will be in error and will re- sult in incorrect audio levels due a double- Auto Terminate Disable termination condition. The auto terminate function is designed to To prevent this problem the auto termi- ensure that each 2-wire-to-4-wire interface nate function can be disabled. When DIP circuit remains stable under most oper- switch 1 is in its off (down) position the ating conditions. Specifically, 200 ohm auto terminate function is active. When impedances are automatically applied to switch 1 is in its on (up) position the auto both pins 2 and 3 of a Model 46 2-wire terminate function associated with each party-line interface when that interface is interface is disabled. Repeating for clarity, configured for external power and no ex- the auto terminate disable function applies ternal source of intercom power is detect- to both interfaces 1 and 2. With the auto ed on pins 2 or 3. This function is directly terminate function disabled the two 46 compatible with RTS TW-series intercom interfaces, when set for external power, applications in which the three conductors will operate normally with the exception of a cable support both DC power and two that pins 2 and 3 will never be terminated channels of audio. It’s also compatible in by the Model 46’s circuitry. situations where all three conductors of a Clear-Com single-channel intercom circuit

Issue 2, September 2007 Model 46 User Guide Page 18 Studio Technologies, Inc. The auto terminate disable function should This is provided specifically for cases be used only when absolutely necessary; where the Model 46’s 2-wire party line it’s possible that a significant downside interfaces will be used with dual channel could be experienced. With auto terminate intercom user devices. As an example: the disabled it’s important that properly ter- RTS TW-series provides two independent minated 2-wire party line-intercom circuits audio channels, as well as power, over a be connected to pins 2 or 3 on the Model single 3-conductor cable. In a case such 46’s 2-wire PL connectors. If they are not as this it’s useful for both of the hybrid connected, it’s likely that audio oscilla- circuits associated with an interface to tions, noise, and distortion will be gener- be auto nulled at approximately the same ated in the Model 46’s 2-wire-to-4-wire time. The dual auto null mode allows a converter circuitry. These audio artifacts single “tap” of the button to initiate nulling will not cause any damage, but will be of both hybrid circuits. sent out the 4-wire line output connectors. When DIP switch 2 is in its on (up) posi- Users of the 4-wire equipment may be less tion the independent auto null mode is than pleased with what they hear! selected. This would be appropriate for applications in which the two audio paths Auto Null Button Operation associated with each interface are used One pushbutton switch is associated with independent party-line intercom with each of the Model 46’s two interface circuits. This situation might arise when circuits. An advanced configuration pa- two Clear-Com single-channel intercom rameter allows selection of the button’s circuits are connected to one of the Model operation. The choices are dual auto null 46’s dual-channel interfaces. The hybrid mode and independent auto null mode. circuit associated with each channel can When dual auto null mode is selected a be auto nulled as desired. Another exam- single “tap” (press and release) of one of ple would be in an RTS TW-series applica- the two front-panel pushbutton switches tion that uses source assignment panels. initiates a routine that begins with chan- The “SAP” panels would be used to route nel 1’s auto null sequence taking place multiple intercom channels to various sets followed immediately by channel 2’s auto of user devices as desired. In this case, null sequence being performed. Note that the two channels associated with each the mode selected for auto null button op- Model 46 interface will often end up not eration will also apply to the remote auto routed to the same user device; indepen- null inputs. dent auto nulling is certainly desired. The independent auto null mode allows the auto null function to be initiated for Refresh Disable each channel as desired. A single “tap” While testing the Model 46 as part of the will start the auto null routine for channel development process it was found that 1. Two “taps” will start the routine for in cases of extreme ESD (electro-static- channel 2. discharge or “static”) an integrated circuit in the audio signal path could “latch up.” When DIP switch 2 is in its off (down) posi- This would result in the audio signal no tion the dual auto null mode is selected.

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 19 longer passing through this component ESD-induced audio path problem could and on to the 4-wire audio output. When- occur. A good “rule of thumb” is that if a ever this situation arose the component Model 46 is mounted in an equipment rack was not damaged, but restoring the flow of with a known-good ground connection, audio required either a power down/power disabling refresh shouldn’t pose any risk up sequence, an auto null operation, or a to reliable operation. But if a unit is mount- change to one of the level configuration ed in a portable rack, or used loose as a DIP switches to take place. While it is very single device, refresh should always remain unlikely that this type of ESD event would enabled. The reasoning is quite simple: occur during normal field operation it is of the latter condition is much more likely to concern for critical Model 46 applications. allow an ESD “hit” to dissipate into the To minimize the chance that the audio Model 46’s enclosure, while a substantial path could experience this problem a rack enclosure will offer a low-impedance “refresh” routine was added to the Model path for ESD energy to dissipate into. 46’s operating software (“firmware”). To ensure that the ESD-sensitive component Factory Test always remains functioning correctly the Back-panel DIP switch 4 is used to select software resends its operating instructions between normal mode and factory test four times each second. With this imple- mode. When switch 4 is in its off (down) mentation the worst case scenario would position the Model 46 operates in its stan- result in an audio loss of 250 milliseconds dard fashion. When switch 4 is in its on (up) or less in the event of an extreme ESD position the factory test mode is selected. “hit” being experienced. As expected, when the Model 46 is de- But nothing comes without a price and in ployed in the field switch 4 should remain this case the refresh routine adds a very in its off (down) position. No damage to slight audio “tick” to the 4-wire output and the Model 46 or connected equipment will 2-wire party-line signals. During typical occur when factory test mode is active. applications these refresh “ticks” will not be noticeable. But there may be situa- tions where any added audio artifact may Operation simply not be acceptable. To address this Technician intervention is typically not possible, but highly unlikely, case back- required during normal Model 46 operation. panel DIP switch 3 can be used to disable The unit is designed for continuous opera- the refresh routine. When switch 3 is in its tion with no routine maintenance necessary. off (down) position the Model 46 operates Activating the auto null functions may be in its standard fashion. When switch 3 is warranted should connected user devices in its on (up) position the refresh routine or wiring associated with the 2-wire party- is disabled. The Model 46 will continue to line intercom be changed. Upon power-up function normally with the exception that the Model 46 will go through a short initial- the four-times-per-second component ization sequence before normal operation refresh routine will not occur. Goodbye will begin. The power and status LEDs “click” but hello to the possibility that an will each light sequentially and, upon

Issue 2, September 2007 Model 46 User Guide Page 20 Studio Technologies, Inc. completion, the power LED will light an excessive level condition, but it does steadily. The settings for the four hybrid provide a warning that at some stage circuits are stored in non-volatile memory reducing the signal level may be prudent. and will be recalled during the power-up Normal operation with normal signal levels process. should find the meters lighting near their 0 dB point. Signal peaks may cause the Level Meters yellow LEDs to flash. But a yellow LED that The Model 46 contains eight 5-segment lights fully during normal operation will LED level meters. These meters are pro- typically indicate a signal level or configu- vided as a support aid during installation, ration problem. configuration, operation, and trouble- If the “from 4-wire” meters display consis- shooting. The meters represent the sig- tency lower or higher levels than their 0 dB nals coming in from, and going out to, points it’s possible that a configuration is- the 4-wire connections. The meters are sue exists. One potential problem is incor- organized in four groups each represent- rectly set 4-wire nominal audio level DIP ing one input and one output. They are switches for one or both of the Model 46’s calibrated to reflect the level in dB rela- interfaces. If the nominal level is set too tive to the configured nominal operating low then sufficient audio headroom might level. This is similar to the way in which not be available. It can also result in ex- now-legacy VU meters functioned. As an cessively-high audio signals being sent to example let’s take the situation where the 2-wire party-line circuits. Setting the nomi- nominal operating level of an interface is nal level for too high a value will reduce configured for +4 dBu and an output (“to the signal-to-noise performance. And, as 4-wire”) LED labeled “0 dB” is lit. (For this expected, it may also result in audio sig- example, the level on the 2-wire PL circuit nals being sent to the 2-wire circuits at is just large enough to light the “0” LED.) too low a level. Begin a review by confirm- This indicates that a signal with an approx- ing that the two 4-wire level DIP switches imate level of +4 dBu is present on the as- associated with each interface are set as sociated 4-wire output connector. Another required. example would be a Model 46 interface configured for +8 dBu operation and a If the Model 46’s 4-wire nominal levels –12 dB LED is lit. This indicates that a are set correctly but the meters still reflect signal with audio level of –4 dBu is sub-optimal levels, the issue may be relat- present on its associated output. ed to incorrect settings on the equipment connected to the 4-wire inputs and out- Each level meter contains four green puts. It’s possible that although a connect- LEDs and one yellow LED. The four green ed 4-wire device’s nominal level matches LEDs indicate signal levels at or below the the Model 46’s level setting, its actual configured nominal level. The top LED is nominal level may be significantly differ- yellow in color and indicates a signal that ent. With a digital matrix intercom system is 6 dB or greater than the nominal level. this problem could be due to an incorrect An audio signal that causes the yellow configuration having been made to a spe- LED to light doesn’t necessarily indicate cific channel or port. For example, the RTS

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 21 ADAM system has a published nominal of at least 6 dB. Removing the unwanted level of +8 dBu, but using its configuration termination is really the only valid means software it’s possible to set panels or ports of correcting the problem. to a level different than nominal. The best solution in this case is to adjust the inter- Connecting Party-Line com system so that its levels comply with Devices its own published nominal. This should, at least in theory, lead to the best system The Model 46’s two dual-channel interface performance, including correct interfacing circuits allow two sets of user devices to with the Model 46. But often it’s impos- be connected. Depending on the setting sible to “clean up” the levels of a existing of the configuration DIP switches, either system. In this case it may be necessary an external intercom power source or the to revise the Model 46’s 4-wire nominal Model 46’s internal 2-wire power source level settings to match the reality of the has been designated for supporting the connected signals. connected user devices. The “to 4-wire” meters display the level External Power Source of signals that come from the 2-wire party- When set for an external 2-wire power line circuits and go out the 4-wire inter- source, the Model 46 will not provide faces. An issue may arise if the signals power on pin 2 of the 2-wire connectors, coming from the connected party-line nor will the Model 46 use any power from user devices aren’t at a sufficient level a connected intercom circuit. As expected, so that a normal meter display can be audio signals will be sent from, and re- reached. This could be the result of an ceived by, each interface’s two audio cir- incorrectly configured 2-wire nominal cuits. In this mode of operation the Model audio level. Confirm that the DIP switch, 46 acts as a typical user station on the associated with each interface, is set to connected intercom circuit. match the nominal level of the connected devices. RTS user devices have a nominal As a connection confirmation, hardware level of –10 dBu; Clear-Com devices typi- and software in the Model 46 monitors cally have a –14 dBu nominal level. pins 2 and 3 of the 2-wire PL intercom connectors for the presence of DC volt- It’s also possible that an error is pres- age. A level greater than approximately ent on the 2-wire party-line circuit. Signal 18 volts DC on pin 2 will cause the status levels associated with 2-wire party-line LED labeled pin 2 to light. A level greater circuits depend on a single termination than 18 volts DC on pin 3 will cause the being present. This termination, typically pin 3 status LED to light. 200 ohms, is almost always made at the power supply source. But it’s possible The author is aware that user intercom that another device, such as a second devices almost always draw power from active power supply on the same circuit, pin 2 rather than pin 3. However, in many will cause a “double-termination” condi- broadcast applications, power is provided tion. This leads to a nominal 100 ohm line on all intercom paths so that flexible chan- impedance which will result in a level drop nel assignments can be made. In the

Issue 2, September 2007 Model 46 User Guide Page 22 Studio Technologies, Inc. external 2-wire power mode the Model 46 mount component technology and have is simply an observer; whether intercom a lower maximum current draw of 65 mil- power is present on pin 2, pin 3, or both liamperes. Four of these “modern” BP325 pins 2 and 3 is not significant. units can easily be supported. So that the Model 46’s 2-wire-to-4-wire The Model 46’s intercom power supply interface circuits remain stable and don’t circuits operate under software control. generate audio artifacts, an auto terminate This allows detection of fault conditions feature is implemented. This maintains a and protection of both the Model 46’s 200 ohm termination on both pins 2 and 3 circuitry and connected intercom user so long as neither of the 2-wire power sta- devices. Upon initial Model 46 power tus LEDs is lit. To clarify, if either, or both, up no monitoring of the intercom power the LEDs are lit then both terminations output takes place for a period of five are removed. It was felt that this method seconds. This allows the Model 46’s would provide a fairly accurate indication circuitry and the connected intercom user that an active intercom circuit is connect- devices to stabilize. The LED associated ed. In this case the 200 ohm termination is with pin 2 will light to indicate that the expected to be provided elsewhere, typi- output is active. After this initial 5-second cally as part of the external power supply, period monitoring becomes active. A fault and the Model 46’s termination is “lifted.” condition is detected if the power on pin 2 falls below 24 volts for a continuous one Internal Power Source second interval. The hardware and soft- When an interface’s front-panel DIP switch ware responds to this condition by turning is set for internal 2-wire power the Model off the power source to pin 2 and flashing 46’s 2-wire party-line interface supplies the pin 2 LED as a warning. After a five 30 volt DC on pin 2 of the output con- second “cool down” interval the output re- nector. A maximum current draw of 300 turns to the same condition as upon initial milliamperes is available. This current is power up: power is again applied to pin 2, sufficient to power various intercom user the pin 2 status LED will light, and moni- devices such as small user stations and toring won’t begin for another five sec- belt packs. A common broadcast appli- onds. A full short-circuit condition applied cation would be to use RTS BP325 belt to the Model 46’s 2-wire connectors will packs. Select the connected devices so result in a continuous cycle of 6 seconds that their total current doesn’t exceed 300 on (5 seconds for start up and one second milliamperes. That’s not always the easiest for detection) and 5 seconds off. figure to calculate but a web search will As a diagnostic aid the 2-wire power generally find specifications for all com- status LED associated with pin 3 remains monly used devices. For example, active in the internal power mode. When- a search finds that the original version ever DC in excess of approximately of the BP325 consumes a maximum of 18 volts is present on pin 3 the LED will 85 milliamperes of current. According to light. This condition will normally never this figure up to three of these units can exist but could prove useful in special be connected to each Model 46 interface. circumstances. Newer versions of the BP325 use surface

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 23 Auto Null An actual auto null sequence starts by muting the 4-wire input and output signal Each of the Model 46’s dual-channel inter- paths associated with the specific channel faces has circuitry to automatically null the to be nulled. Then a short period of 24 kHz two 2-wire-to-4-wire interfaces. Normally signal is sent out the 2-wire PL intercom this process is performed at the time of interface channel. This will turn off micro- initial Model 46 configuration but there’s phones on those connected user devices no reason why “auto nulling” can’t be initi- that are compatible with the RTS TW- ated anytime one desires. The only time series “mic kill” protocol. The actual auto that auto null must be performed is if con- nulling process will next be performed. A ditions have changed vis-à-vis the inter- series of tones will be sent out the 2-wire com user devices and wiring connected to interface. Other Model 46 circuitry, un- a Model 46 2-wire PL interface connector. der software control, will rapidly perform Even a slight change to an intercom cir- adjustments to achieve the best null pos- cuit, such as adding or removing a section sible. After the adjustments are made the of cable, is sufficient to require that the results are stored in non-volatile memory. auto null process be performed. Once the process has completed the Two buttons, one associated with each 4-wire input and output paths are again interface, are provided to activate the activated. auto null process. Refer to Figure 8 for a Advanced configuration DIP switch 2, detailed view. To initiate auto null simply located on the back panel, allows an requires pressing and releasing (“tap- independent auto null button mode to ping”) a button. The process begins by be selected. If switch 2 is in its on (up) nulling channel one of an interface and, position, the front-panel pushbuttons will when completed, moves on to channel function in quite a different manner. In the two. Two LEDs provide a visual indication independent mode, a single “tap” to a of the auto null process, flashing when the switch will cause channel 1 to auto null. auto null process for its respective chan- Two “taps” will cause channel 2 to auto nel is active. null. By observing the operation of the two auto null status LEDs it will become readily apparent which of the button modes has been selected. If possible, prior to performing an auto null it’s polite to warn all personnel who are actively using the connected intercom devices. The tones sent to the 2-wire inter- com circuit during the nulling process are not excessively loud or obnoxious, but most users might want to remove Figure 8. Detail of front panel showing auto null section their headsets during the process. In addition to warning users, it might be a good time to ask them to mute any

Issue 2, September 2007 Model 46 User Guide Page 24 Studio Technologies, Inc. active microphones. While the automatic As a visual aid, LEDs on the front panel “mic kill” signal will apply to many user will display the DC power status of pins devices it may not apply to all. Muting 2 and 3. But when auto terminate disable microphones is significant as obtaining a mode is active the LEDs will no longer “deep” null requires that no extraneous indicate the intercom circuit’s termination signals be present on the intercom circuit. status. For special externally powered 2-wire ap- plications the auto terminate function can Advanced be disabled. This primarily will come into play when “splitting” the Model 46’s re- Operation sources into four separate single-channel The Model 46 allows several of the operat- interfaces. Moving advanced configuration ing parameters to be configured to meet DIP switch 1, located on the Model 46’s the needs of specific applications. The back panel, to its on (up) position disables following paragraphs provide details about the auto terminate function. To someone the auto terminate disable and factory observing only the Model 46’s front panel test modes. this change would not be readily appar- ent. The front-panel LEDs will continue to Auto Terminate Disable display the DC power status of pins 2 and 3. But whether or not either or both LEDs As previously discussed in this user guide, are lit, the Model 46 will never apply 200 the auto terminate function can come into ohm terminations to pins 2 or 3. For the play when a 2-wire interface is configured hybrid circuits to remain stable termina- for external power. Using a combination tion impedances must be provided by the of hardware and software, pins 2 and 3 connected circuits. If these are not pres- of each 2-wire PL intercom connector are ent one should expect the hybrid circuits monitored for the presence of DC voltage. to generate a very impolite noise. This If a level of greater than approximately condition, caused by the 2-wire output 18 volts DC is not detected on either pin, circuitry being in an “unloaded” state, will 200 ohm terminating networks are applied not damage the Model 46’s circuitry. But to those same pins. This ensures that the errors in cable “patching,” a disconnected Model 46’s hybrid circuitry remains stable, cable, or other real-world issues, can lead preventing objectionable audio signals users listening to signals that originate in from being sent to the 4-wire output con- the Model 46’s 4-wire outputs from being nectors. One caveat does apply; there presented with a rude surprise! may be a few seconds of severe noise whenever an interface moves from a DC In conclusion, it’s important that technical present condition to a DC not present personnel working with the Model 46 be condition. But other than that period, the informed when the auto termination func- audio paths will remain “clean.” tion has been disabled. They will then be aware of the potential noise issues and be ready to make corrections should a prob- lem arise.

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 25 Factory Test Mode Technical Notes Back-panel DIP switch 4 allows a factory test mode to be enabled. During normal Software Version Display operation switch 4 should remain in its off A special Model 46 power-up sequence (down) position. When switch 4 is in its on allows the unit’s software version number (up) position factory mode is active. En- to be displayed. This is useful when work- abling this mode will result in the following ing with factory personnel on application operating condition: during an auto null support and troubleshooting situations. sequence the associated 4-wire output The four status LEDs associated with channel will remain active. This will allow interface 1 are used to display the major the tones associated with the nulling pro- release number with a range of 1 through cess to be present on the 4-wire output. 4. The four status LEDs associated with While not appropriate during actual Model interface 2 are used to display the release 46 use, it is interesting to “hear” the null- sub-number which again ranges from 1 ing process take place. But unless direct- through 4. Refer to Figure 9 for a detailed ed by factory personnel switch 4 should view of the status LEDs and the corre- remain in its off (down) position. sponding software version numbering scheme. The Model 46’s initial software release is version 1.1 which is represented by the bottom LEDs of each status column being lit.

Interface 1 LED Section Interface 2 LED Section (Major Release Number) (Release Sub-Number)

O 4 .4 O O 3 .3 ● O 2 .2 O ● 1 .1 O

Figure 9. Detail of front panel showing the status LEDs that display the software version. In this example, the software version is 1.3.

Issue 2, September 2007 Model 46 User Guide Page 26 Studio Technologies, Inc. To display the Model 46’s software version tasks. But it’s not intended to act as a is very simple. From the powered-down “universal” 2-wire-to-2-wire interface such state, press and hold the auto null button as is provided by the venerable Clear-Com associated with interface 1. Apply mains TW-12B. The Model 46’s 2-wire inter- power while continuing to press the but- faces are not isolated from each other; ton. The normal power-up sequence will they share the Model 46’s internal power not occur but instead one LED will be lit in supply’s common connection. (The power the column associated with interface 1 and supply common point is DC isolated from one LED will be lit in the column associated chassis and earth ground.) Specifically, with interface 2. As previously described, pin 1 on the XLR connector associated these two LEDs represent the unit’s current with interface 1’s 2-wire party-line inter- software version. While the software version face is electrically connected to the pin 1 number is being displayed the LED level connection on interface 2. This is due to meters will likely display random readings. the fact that both 2-wire party line inter- This is not a problem and can simply be faces are capable of supplying DC power ignored. After the software version number to connected devices. They also use the has been “read” the auto null button can resources of a single set of logic circuitry. be released. At this time the unit will begin And as such they each require access to its normal power-up sequence. the Model 46’s common power supply circuitry. There’s no doubt that a Model 46 Note that while it’s easy to determine which could be used to create a 2-wire-to-2-wire software version is loaded into the Model party line “bridge” by cross-linking the 46 a trip back to the factory is required to 4-wire inputs and outputs using standard update it. The 8-bit microcontroller that XLR-type audio cables. But it’s likely that provides the unit’s logic “horsepower” also a significant “ground loop” would be cre- includes internal FLASH memory. This non- ated through pin 1 of each of the Model volatile memory is used to store the operat- 46’s 2-wire interfaces. While it’s possible ing software (“firmware”). Re-programming to use a set of special isolation transform- this memory requires using a specialized ers to eliminate the ground loop, that’s programming unit. While not outrageous in best left to the brave of heart! price, it still costs in the range of US$500. The “programmer” uses a ribbon cable and socket to interface with a 6-pin “head- Model 72 Interface er” on the Model 46’s printed circuit board. And now for a shameless “product plug.” And, as you would guess, once connected, Studio Technologies, Inc. manufactures reprogramming takes only a matter of sec- a nifty product called the Model 72 Level onds. But unfortunately the programmer Meter/Interface. A compact, standalone is not something that would be found in unit, it can prove very useful when setting a typical “field shop” or repair facility. up, maintaining, and troubleshooting inter- com circuits. It will give a direct indication Not a TW-12B Replacement! of signal levels at any point in a single- or dual-channel intercom circuit. Check The Model 46 will provide a high level of it out! performance over its range of intended

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 27 Specifications General Audio: 4-Wire Inputs: 4, 2 per interface Frequency Response: ±2 dB 100 Hz to 8 kHz Type: transformer-coupled, capacitor isolated Distortion (THD+N): <0.5%, measured at 1 kHz, Impedance: 13 k ohms 4-wire input to 2-wire interface pin 2 Nominal Level: 0, +4, +6, or +8 dBu, selectable Signal-to-Noise Ratio: >55 dB, measured at 1 kHz, in tandem with nominal output level 4-wire input to 2-wire interface pin 2 Maximum Level: +22 dBu Connectors: 4-Wire Outputs: 4, 2 per interface Inputs from 4-Wire: 3-pin female XLR-type Type: transformer-coupled, capacitor isolated Outputs to 4-Wire: 3-pin male XLR-type Impedance: 50 ohms nominal 2-Wire Party-Line Intercom: 3-pin male XLR-type Nominal Level: 0, +4, +6, or +8 dBu, selectable Remote Control: 10-pin header, requires optional in tandem with nominal input level 10-pin ribbon connector assembly Maximum Level: +20 dBu into 2 k ohms AC Mains: 3-blade, IEC 320 C14-type (mates with Meters: 8 IEC 320 C13) Function: displays level of 4-wire inputs and 2-Wire Party-Line Intercom Interfaces: 2 outputs Type: 2-channel party-line (PL), unbalanced Type: 5-segment LED, modified VU ballistics (pin 1 common; pin 2 DC with channel 1 audio; pin 3 channel 2 audio) Remote Control Inputs: 3 Compatibility: single- and dual-channel intercom Type: optically coupled systems such as from Telex®/RTS® and Input: 3-32 volts DC; 2 milliamperes minimum for Clear-Com® operation, 20 milliamperes maximum Impedance, External Power Mode: >10 k ohms Functions: auto null interface 1, auto null interface Impedance, Internal Power Mode: 200 ohms 2, and “mic kill” Nominal Level: –10 or –14 dBu, selectable AC Mains Requirement: 100-240 volts “Mic Kill” Signal: square wave, 24 kHz, ±1% (–15/+10%), 50/60 Hz, 0.7 amperes maximum @ 0.4 amperes maximum @ 240 volts Internal Power Source: 30 volts DC nominal, 300 100 volts, milliamperes maximum Dimensions (Overall): Hybrids: 4, 2 per interface 19.0 inches wide (48.3 cm) 1.72 inches high ( cm) Topology: 3-section analog circuitry compensates 4.4 8.5 inches deep (21.6 cm) for resistive, inductive, and capacitive 2-wire party- line loads Mounting: one space in a standard 19-inch rack Nulling Method: automatic upon user initiation, Weight: 7.75 pounds (3.5 kg) processor implements digital control of analog cir- cuitry; null settings stored in non-volatile memory Nulling Line Impedance Range: 120-350 ohms Nulling Cable Length Range: 0-3500 feet, typical Specifications and information contained in this Trans-Hybrid Loss: >40 dB, typical at 800 Hz User Guide subject to change without notice.

Issue 2, September 2007 Model 46 User Guide Page 28 Studio Technologies, Inc. Appendix A

Interfacing Telex®/RTS® Matrix Intercom Systems with the Model 46 Interface

ADAM™ Matrix Intercom System Analog Ports to Model 46 Interface

RVON-I/O I/O Connections to Model 46 Interface

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 29 Appendix B

Interfacing Riedel® Artist™ Matrix Intercom System Analog Ports with the Model 46 Interface

Issue 2, September 2007 Model 46 User Guide Page 30 Studio Technologies, Inc. Appendix C

Interfacing Clear-Com® Matrix Intercom System Analog Ports with the Model 46 Interface

Model 46 User Guide Issue 2, September 2007 Studio Technologies, Inc. Page 31