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User Manual
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Studio Technologies ISS User Manual

User Guide
Issue 5, November 2014
This User Guide is applicable for serial numbers:
M233-01151 and later
Copyright © 2014 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50336-1114, Issue 5
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Table of Contents

Introduction ................................................................... 5
System Features ...........................................................
Installation and Setup ................................................... 12
Configuration ................................................................
Operation ...................................................................... 29
Advanced Operation ..................................................... 34
Technical Notes .............................................................
Specifications ................................................................
Appendix A .................................................................... 45
Block Diagram
6
17
35
44
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Introduction

What This User Guide Covers
This User Guide is designed to assist you when installing, configuring, and using the Model 233 Announcer’s Consoles with serial numbers of 01151 and later. Addi­tional background technical information is also provided. A product block diagram is included at the end of this guide.
System Overview
The Model 233 Announcer’s Console is designed to serve as the audio control “hub” for announcers, commentators, and production personnel. The tabletop unit is suited for numerous applications including on-air television and radio broadcasting. The Model 233 will also perform an out­standing role in stadium announce appli­cations. The Model 233 is compatible with essentially all broadcast and production audio system environments. Standard con­nectors are used to interface microphone, headphone, on-air, talkback, line input, and intercom signals.
Whether it’s the mic preamplifier, audio switching, talkback signals, intercom inter­facing, or headphone cue feed, superior audio quality is maintained throughout. A microprocessor provides the Model 233’s logic power, allowing precise control of the unit’s operation. With extensive flexibil­ity built in, creating the desired operating configuration is a simple matter. While the operating features of the unit can be care­fully tailored, the user is presented with an easy-to-use set of controls and indicators. A wide range of resources, great perfor­mance, and simplicity during use—these are the hallmarks of the Model 233.
The Model 233 is a truly “next-generation and then some” product. Exhaustive research into the needs and desires of field production personnel was integral to its creation. Providing a veritable “tool kit” of features, the unit supports a wide variety of applications that include on-air television and radio broadcasting, stadium announce­ment, and simultaneous interpretation. In addition, with the unit’s broad range
Figure 1. Model 233 front panel
Figure 2. Model 233 back panel
of capabilities many other specialized “behind-the-scenes” applications can also be implemented.

System Features

Microphone Input
A high-performance microphone preampli­fier circuit provides low-noise/low-distortion amplification over a 20 to 60 dB gain range. The gain is adjustable in 10 dB steps. The input is compatible with balanced dynamic and condenser microphones. The micro­phone power source is 48 volts nominal and meets the worldwide P48 phantom power standard. An LED indicator serves as an aid for optimizing the preamplifier’s gain setting. The output of the microphone pre­amplifier is used by the main output as well as being routed to the compressor circuit that supports the talkback functions.
Main Output
The Model 233 provides a main output that is designed to serve as the on-air, stadium announcement, or other primary audio feed. Nominally –2 dBu, it is designed as a fully professional interface with high output capability, low distortion, and low noise.
The output circuitry features a high-perfor­mance output transformer expressly de­signed for professional audio applications.
Talkback Functions
The talkback functions are intended to pro­vide personnel associated with production trucks, control rooms, live-performance, and sports venues with talent-originated cue signals. The Model 233 contains two pushbutton switches that control the talkback functions. Associated with each pushbutton switch is a dedicated line-level talkback output. Each pushbutton switch can also be configured to send audio to one specific channel associated with the Model 233’s dual-channel intercom interface.
The line-level talkback outputs are trans­former-coupled with a +4 dBu nominal signal level. They contain resistors in series with the output connectors, allowing line­level talkback outputs from multiple units to be directly “summed.”
For non-on-air applications, a special Model 233 feature set can be enabled by placing the unit in its “production” mode. This software-based mode allows the main output to be used as an additional talkback
output. This feature makes the unit even more powerful when used in live-event applications, such as serving as a master console for an orchestra conductor or production director.
With all the available talkback flexibility, the exact needs of many specific applica­tions can easily be met. And, of course, whatever configuration is implemented, the audio quality will be excellent.
Dynamic Range Control
To enhance the Model 233’s talkback func­tions, a studio-quality compressor circuit is provided to control the dynamic range of the signal coming from the microphone preamplifier. Far from a simple “clipper,” the circuit utilizes a sophisticated laser­trimmed voltage-controlled-amplifier (VCA) integrated circuit for quiet, low-distortion level control.
The signal from the compressor is always used by the talkback functions. For flex­ibility, the audio source for the main output can be selected to be either the direct output of the microphone preamplifier or the output of the compressor. For on-air applications the signal coming directly from the microphone preamp would be correct. But having dynamic range control of the signal going to the main output can offer increased performance for selected applications. These could include stadium announcement locations, award show conductor positions, and use with non­professional announcers during sports events.
User Controls and Status Indicators
Three pushbutton switches, four LED indicators, and three rotary controls provide users with a clear, easy-to-use
interface. One pushbutton switch controls the status of the main output. This is the audio output intended for on-air, stadium announcement, or other primary uses. Two LEDs display the on/off status of the main output. Two additional pushbutton switches control the status of the talkback functions. These are the audio cue signals used to communicate with producers, directors, “spotters,” or other behind-the­scenes production personnel. A status LED is associated with each talkback button. Three rotary controls allow the user to adjust the level of the headphone output. Two of the controls are associated with externally connected cue signals. The third control is associated with the Model 233’s sidetone function, allowing the user to monitor the signal associated with the unit’s microphone input.
Flexibility
A large part of the Model 233’s unique power is the ability to configure the op­eration of the main output and talkback functions. To meet the needs of the many specific broadcast and production ap­plications, a variety of button operating modes is available. The main output button can be selected to operate from among four modes. In the “push-to-mute” mode the button performs a momen­tary mute of the main output. In this way a “cough” button function is created, something typically required for television sports broadcasting. In the “push-to-talk” mode the button provides a momentary active function for the main output. This mode would be appropriate for applica­tions such as stadium announcement. An alternate action “latching” configuration allows the button to enable or disable the main output as desired. This is useful in radio broadcasting, announce-booth, or
voice-over applications. The fourth mode provides a hybrid function, supporting both push-to-talk and tap-to-enable/tap-to­disable operation. This operation is similar to that found in many broadcast intercom system user stations.
The two buttons associated with the talk­back functions can be configured to oper­ate from either of two modes. One of the modes supports a “push-to-talk” function. This is typically used for on-air broadcast applications. The other mode provides a hybrid function, the operation of which is discussed in the previous paragraph. The hybrid mode is especially useful when the Model 233 is used in a production-support application.
The main button mode configures how the main output, when it is in the “latched” on state, responds to talkback activity. One choice momentarily turns off the main output when talkback is active, returning the main output to the on state when the talkback function has ended. The other choice “unlatches” the main output in response to a talkback function.
Cue Sources
The Model 233 supports the connection of up to four external audio sources, each of which can be selected for routing to the stereo headphone output. The sources are line input 1, line input 2, intercom channel 1, and intercom channel 2. Each source can be individually assigned to the left channel, the right channel, or both the left and right channels. This allows a wide variety of stereo and mono headphone mixes to be created.
For application flexibility, two line-level audio sources can be connected to the Model 233. Possible signal sources include off-air receivers, wireless IFB
systems, and audio consoles. The con­nected signals can be from two indepen­dent sources, or could be from a stereo audio feed such as would be associated with a broadcast music event. Two level trim potentiometers, located on the bottom of the unit, allow signals with wide nominal audio levels to be cleanly interfaced.
Audio signals associated with a single­or dual-channel intercom system can be routed to the headphone output. The Model 233’s intercom interface is com­patible with standard party-line intercom systems from manufacturers such as RTS™ and Clear-Com®. A broadcast-type IFB (interrupted foldback) circuit can also be connected to the intercom input. This “listen only” signal is often found in televi­sion broadcast applications.
Sidetone
The Model 233 includes an integrated sidetone function that allows the output of the compressor circuit associated with the microphone preamplifier to be routed to the stereo headphone output. This pro­vides a confidence signal to the user, al­lowing them to hear exactly what is being sent to the main and, if desired, talkback outputs. This sidetone signal can be a critical element when creating an effective communications environment.
In on-air television and radio broadcast settings the Model 233 user’s own micro­phone audio signal is typically returned to the headphone output by way of a cue audio source. But there are cases where this signal is not available, such as when “mix minus” cue feeds are utilized. This type of cue feed includes everything but the user audio, a requirement when sig­nificant time delays, typically associated with satellite transmission systems, are
present. In effect the Model 233’s sidetone function adds the “minus” part to a “mix minus” cue.
Several configurable parameters allow the sidetone function to be tailored to the needs of a specific Model 233 installation. The sidetone function can be configured to route audio to the left, right, or left and right headphone outputs. It can also be completely disabled. Sidetone can also be configured to be active only when the main output is active, or to be active anytime the main output or either of the talkback outputs is active.
Headphone Output
Three rotary controls are provided for user adjustment of the headphone output. Two of the controls adjust the levels of the externally connected sources. The third control is used to set the level of the side­tone function.
For flexibility the actual functioning of the two controls associated with the external sources is configurable. For traditional on-air sports applications they can be selected to the dual level control mode which provides independent control of the left and right channel volume. For use with stereo cue signals, or to support user preference, the level/balance mode can be selected. In this mode one control adjusts the overall level of both the left and right channels, while the other allows adjust­ment of the left/right level balance. To help minimize the chance of broadcast cues being missed, both level control modes can be configured so that a minimum headphone output level is maintained. Alternately, the headphone output can be set to fully mute when these controls are at their minimum position.
A headphone control reverse mode is provided specifically for on-air television applications where a headset with boom microphone is used. The reverse mode ensures that no matter which headset orientation is used by the talent, the two “pots” controlling the external sources will always work intuitively. This will result in a comfortable work environment, allowing the “left” control to impact the level to the talent’s left ear while the “right” control impacts the right.
The sidetone level control is dedicated to adjusting the level of the mic audio signal that’s routed to the headphone outputs. Configuration switches allow which of the headphone outputs—left, right, or both— will receive the sidetone signal. When the sidetone level control is set to its minimum position the sidetone level is always set to be fully muted.
Provision has been made to support ap­plications where a monaural cue feed is desired. A configuration switch allows the summing (combining) of the selected left and right headphone sources. In addition to creating a dual-channel mono output it also allows the level controls to be config­ured as a simple 3-channel mixer.
The headphone output is optimized to meet the needs of contemporary head­phones and headsets. Specifically, the output circuits act as voltage, rather than power, drivers. In this configuration they can provide high output levels with very low distortion and noise, along with mini­mal current consumption. The output cir­cuits are configured to safely drive stereo or mono loads. This ensures that all types of headphones, headsets, and earpieces can be directly connected.
Intercom Interface
Of special note is the Model 233’s sophis­ticated intercom interface. It’s designed to work correctly with industry-standard single- and dual-channel party-line intercom systems, including those from RTS and Clear-Com. An intercom line connected to the Model 233 can serve three functions: providing cue audio signals to the head­phone output, allowing talkback audio to be sent to intercom users, and acting as a Model 233 power source. Audio signals present on the single- or dual-channel intercom line can be flexibly routed to the stereo headphone output. Talkback audio, controlled by the two talkback pushbutton switches, can be sent to either or both of the intercom channels. Trim potentiometers, located on the bottom of the unit, allow adjustment of the talkback-to-intercom sidetone (null) level.
The ability to listen to one or both pins of a connected intercom circuit will only be available when the intercom interface circuit detects DC voltage on pin 2. This feature minimizes the chance that objectionable audio content (i.e., “howls” or “squeals”) will be routed to the headphone output when an intercom circuit is not connected.
Audio Quality and Protection
The Model 233’s circuitry is carefully tailored to provide excellent audio performance. Professional-quality components are fea­tured throughout. For reliability all audio routing is performed using solid-state devices under microcontroller direction. In all critical audio paths, “clickless” elec­tronic switches provide noise-free control. All audio inputs and outputs make extensive use of protection components. This limits the chance of damage from ESD and other undesirable, yet real-world, hazards.
Power Sources
The Model 233 can derive its operating power from an intercom line or an external 24 volt DC source. For redundancy, both power sources can be connected simul­taneously. An internal switch-mode power supply ensures that all Model 233 features are available, including phantom power, when the unit is powered by either source.
Auxiliary Relay
Model 233 resources include a general­purpose relay, allowing specialized configu­rations to be created. Under software con­trol, the relay can be configured to follow the state of the main output, talkback 1, or talkback 2 buttons. Taking advantage of the back-panel locations provided for additional XLR connectors, a technician may easily create functions such as an “on-air” indica­tor or implement loudspeaker muting dur­ing talkback function. Special configuration modes are even included to allow direct control of the relay using the talkback 1 or talkback 2 buttons without impacting any of the Model 233’s audio signals.
Tally Output
Another unique Model 233 feature is the tally output. It provides an indication, in the form of a current-limited DC signal, of the status of the main output. Whenever the main output is active the tally output is active. This 3.5 volt nominal, 12 milliam­peres maximum, signal is capable of direct­ly lighting an LED indicator or triggering an external control system. The tally output is provided specifically for specialized ap­plications such as television award show broadcasts where remote monitoring and control of the main output is required.
Configuration
Model 233 configurations are made using a number of DIP switches and four trim potentiometers. One 8-position switch assembly is used to set the gain of the microphone preamplifier, the on/off status of phantom power, and control of the head­phone output mode. A 12-position switch assembly configures which of the four cue audio sources, as well as the sidetone au­dio, are routed to the headphone outputs. In addition, the last two sections of the 12­position switch assembly are used to select whether talkback audio will be routed to the intercom interface. Two 8-position switch assemblies communicate the desired oper­ating modes to the microprocessor.
Two rotary “trim pots” are used to adjust the sensitivity of the line inputs. Two addi tional rotary trim pots are provided to adjust the sidetone (null) level for the intercom interface’s talkback functions.
All switches and trim pots are accessible via the bottom of the Model 233’s enclosure; the unit does not have to be disassembled. Changes made to any of the configuration parameters become active immediately. To prevent access to the configuration controls a security plate, included with each unit, is attached to the bottom of the enclosure.
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Connectors
The Model 233 uses standard connectors throughout. The microphone input, line inputs, and intercom interface functions use 3-pin female XLR connectors. The main and line-level talkback output func­tions use 3-pin male XLR connectors. The headphone output utilizes a ¼-inch 3-conductor jack. The external source of 24 volt DC power is connected by way of a 2.1 x 5.5 mm “locking” coaxial power jack.
Additional Connector Locations
In the world of broadcast, production, and public address audio it’s fair to say that applications vary widely. To this end, up to three additional XLR connectors can be easily mounted into the Model 233’s back panel. Multiple 3-position “headers” located on the Model 233’s circuit board provide technician-access to literally every input and output connection. Moreover, some additional features, including the remote control inputs and tally output, are accessible using 3-position headers. Using a factory-available interface cable kit, these headers allow a Model 233 to be optimized to meet the exact needs of specific applica­tions. For example, some applications may prefer to use a multi-pin XLR connector to interface with a headset. This could be eas­ily accomplished by adding the appropriate 6- or 7-pin XLR connector and making a few simple connections. Other applications may benefit from having “mult” or “loop­through” connections, something easily incorporated into a Model 233.
Multi-Pin Headset Connectors
As previously mentioned, some applica­tions are best supported using headsets that interface using a multi-pin connector. In most of these cases the desired connec­tors are 6- or 7-pin male XLRs wired to an industry-standard pinout scheme. Studio Technologies offers headset connector as­semblies that allow fast and painless instal­lation into a spare connector location in the Model 233’s back panel. Details about these optional assemblies are available on the Studio Technologies website.
Options
The Model 233’s standard resources are more than sufficient to directly support a large number of applications. But in the “real world” of audio and intercommunica­tions special needs always seem to arise. To that end, Studio Technologies offers a number of option cards. In addition to passive or active components, each card contains an integral connector, allowing simple installation into a spare connector location on the Model 233’s back panel. For interest, the resources provided by some of these option cards are worth describing.

Installation and Setup

In this section interconnections will be made using the input and output con­nectors located on the Model 233’s back panel. Microphone, line-level audio sourc­es, intercom, main output, and line-level talkback output signals are interfaced by way of 3-pin XLR connectors. A ¼-inch 3-conductor phone jack is provided for the headphone output. A 2.1 x 5.5 mm coaxial jack allows connection of an exter­nal 24 volt DC power source.
• The direct microphone output card provides access to the dynamic or con­denser microphone that is connected to the Model 233’s mic input. Passive components, along with the auxiliary relay contact, create a “click-free” micro­phone-level audio signal.
• The remote switch input card uses a 4-pin XLR connector to provide access to the Model 233’s remote switch inputs.
Other general-purpose option cards provide 3-pin XLR, 4-pin XLR, and 8-pin EtherCon® connectors. With the range of option cards available it’s hard to imag­ine an application that can’t be served. But you’re welcome to try to “stump the chumps” in the Studio Technologies tech­nical support department! But first please check the complete list of the available option cards listed on the Studio Technol­ogies website.
System Components
The following is included in the shipping carton: Model 233 Announcer’s Console, user guide, button label sheet, and 24 volt DC power supply.
Microphone Input
The Model 233 is compatible with balanced dynamic and condenser microphones. Depending on the application, the micro­phone may be part of a headset, or be an independent handheld or stand-mounted model. The Model 233’s 48 volt nominal power source will support essentially all phantom-powered microphones. The qual­ity of the Model 233’s microphone pream­plifier and associated circuitry is such that special applications may benefit from using “high-end” microphones. If selected appro­priately, models from manufacturers such as AKG, Beyer, Neumann, Sennheiser, and Shure will perform very well in Model 233 applications.
The microphone input is also compatible with line-level audio sources. This allows the output of an external microphone pre­amplifier, microphone processor, or audio
console to be directly connected. When the configuration DIP switches are set for 0 dB (no gain) the nominal level of the source audio signal should be approxi­mately –2 dBu.
Microphone interconnection is made by way of a 3-pin female XLR connec­tor which is located on the Model 233’s back panel. The mating connector (male) should be wired so that pin 2 is signal high (+ or hot), pin 3 is signal low (– or cold), and pin 1 is shield. It’s possible that an unbalanced microphone will also work correctly. In this case, the mating connec­tor (male) should be wired so that pin 2 is signal high (+ or hot), and signal common/shield is connected to both pins 1 and 3.
The Model 233 is not compatible with unbalanced “electret”-type microphones that require a source of low-voltage DC for operation. These microphones, some­times found in low-cost headsets, are not generally suitable for on-air or other demanding applications.
As of the writing date of this user guide, the Sennheiser HMD 26 headset is very popular for on-air sports broadcasting use. A fine product, it works very well with the Model 233. Note that adding the suffix “-XQ” to the headset’s full part number (HMD 26-600-XQ) specifies a 3-pin male XLR connector for the dynamic micro­phone and a ¼-inch 3-conductor plug for the stereo headphones. This configura­tion is very useful, allowing the headset to work directly “out of the box” with the Model 233.
If the writer may digress for a moment to recount a story… an audio dealer once shared a secret with me concerning headsets. He loved selling the “lower-end”
(less expensive) models of name-brand headsets, which he did by the veritable “boatload.” Why? Because these usually broke soon after going into service! He knew that on a regular basis he’d receive orders for more of them. Had these users, from the beginning, purchased only premium-quality headsets, their total cost of ownership would have been much less. Enough said…
Headphone Output
The Model 233’s headphone output is compatible with stereo or mono head­phones, headsets, or earpieces. Connect­ing devices with a nominal impedance of 100 ohms or greater is preferred. This shouldn’t be an issue as essentially all contemporary devices already meet this condition.
Devices are connected to the headphone output by way of a ¼-inch 3-conductor phone jack located on the Model 233’s back panel. As is standard for stereo headphones, the left channel is connected to the “tip” lead of the ¼-inch headphone jack. The right channel is connected to the “ring” lead of the jack. Common for both channels is connected to the “sleeve” lead.
Devices with ¼-inch 2-conductor “mono” plugs can also be used with the Model 233’s headphone output. In this arrange­ment only the tip lead (left channel) will be active. The 2-conductor plug will physically connect (“short”) the ring lead (right channel) to the sleeve lead (com­mon). Technically this won’t damage the circuitry associated with the right-channel headphone output. (100 ohm protection resistors are electrically in series with the headphone output circuits.) However, energy will be wasted if an audio signal
coming out of the right channel goes into a “dead” short. There is a simple means of eliminating this issue; when configuring the headphone sources simply do not as­sign any to the right channel headphone output. Refer to the Configuration section of this user guide for details.
Main Output
The Model 233’s main output is intended to be the “on-air” or primary signal that typically connects to the input of an audio console. The output is transformer balanced with a nominal signal level of –2 dBu. The actual level will depend upon the gain setting of the microphone pream­plifier, sensitivity of the microphone, and how loudly the user speaks into the micro­phone. The transformer used in the main output is intended for professional audio applications. Its source impedance is very low and can drive lengthy cable runs without difficulty. It is capable of driving loads as low as 600 ohms but performs best with loads of 2 k ohms or greater. (This should not prove to be an issue as virtually all contemporary audio equipment has a relatively high input impedance.) As the secondary winding of the output transformer connects directly to the main output connector, care should be taken so that a DC voltage is never present on the interconnecting cable.
The main output is interfaced by means of a 3-pin male XLR connector located on the Model 233’s back panel. The intercon­necting cable’s mating connector (female) should be wired so that signal high (+ or hot) is on pin 2 and signal low (– or cold) is on pin 3. The cable’s shield can be con­nected to pin 1, but it will have no func­tion. Also, the cable’s shield must not be terminated on the metal “shell” connec­tion of the mating connector. To limit the
chance of grounding interaction between the Model 233 and connected equipment, pin 1 on the main output’s connector is isolated from any point in the Model 233. The fact that pin 1 “floats” will minimize the chance of hums, noises, or buzzes be­ing present on the equipment connected to the main output.
Line-Level Talkback Outputs
The two line-level talkback outputs are intended to be connected to control rooms, production trailers, or other loca­tions where talent-originated voice cues are required. The outputs are transformer balanced with a nominal level of +4 dBu. To enhance talkback audio quality, a com­pressor circuit controls the dynamic range of the signal coming from the microphone preamplifier.
For protection against accidental connec tion to cables that have DC power present, the line-level talkback outputs are capaci­tor coupled. In series with the talkback output leads are 300 ohm resistors, mak­ing the effective output impedance ap­proximately 600 ohms. These resistors create a passive summing network, allow­ing talkback outputs on multiple Model 233 units to be connected (“bridged”) together.
The line-level talkback outputs are con­nected by way of two 3-pin male XLR con­nectors which are located on the Model 233’s back panel. The mating connectors (female) should be prepared so that signal high (+ or hot) is provided on pin 2. Signal low (– or cold) should be provided on pin 3. The cables’ shields can be con­nected to pin 1. But, like the main out­put, in order to minimize the chance that ground-interaction problems will arise, pin 1 on the line-level talkback output
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connectors are isolated from the Model 233’s chassis and circuitry. By making pin 1 “float,” often-feared “ground loop” problems shouldn’t arise. Note that the metal shell of the mating connector must also be “floating.”
In most cases this attenuation won’t pose a problem. Typically a device that receives the talkback signal, such as an amplified loudspeaker, will have an adjustable input sensitivity so this attenuation won’t prove to be a problem.
The line-level talkback outputs are in­tended to drive the lengthy cable runs that are often part of broadcast and produc­tion audio applications. While the output circuitry is not intended to be “on-air” quality, overall audio performance should be very good. Devices connected to the line-level talkback outputs can range from amplified loudspeakers, analog inputs on intercom systems, and input channels associated with audio consoles. Connect­ing the outputs to devices that allow easy control of the signal level can be helpful. For example, connecting to an input on an audio console provides the flexibility to add gain or attenuate as required. A dedicated talkback-associated output on the audio console can then be routed to the final destination.
As previously mentioned, the line-level talkback outputs on multiple Model 233 units can be directly connected together. Using a simple “Y” or “W” cable, this pas­sive summing (adding together or “bridg­ing”) of talkback signals allows one audio cable to serve as a master talkback path. A side effect from using this passive sum­ming technique is that signal attenuation will occur. The audio quality won’t suffer, but an audio “pad” is created. If two line­level talkback outputs are connected to­gether, a signal attenuation of 6 dB can be expected. Connecting three talkback out­puts together will result in 9.5 dB of atten­uation. And four talkback outputs “multed” together will lead to 12 dB of attenuation.
Line Inputs
The Model 233 allows two line-level audio sources to be connected. These sources can be individually routed to the left chan­nel, right channel, or both the left and right channel of the headphone outputs. The inputs are balanced, transformer-coupled with a nominal impedance of 10 k ohms. Capacitors, in series with the transformer’s input leads, prevent a DC voltage present on a connected source from impacting performance. The line inputs are compat­ible with signals that have a nominal level of –12 dBV to +6 dBu. Two trim potentiom­eters, located on the bottom of the Model 233’s enclosure, allow signals over this wide nominal level range to be effectively utilized.
Audio sources are connected to the line inputs by way of 3-pin female XLR connec­tors which are located on the unit’s back panel. Prepare the mating connectors (males) so that pin 2 is signal high (+ or hot), pin 3 is low (– or cold), and pin 1 is shield. If connecting a source in this manner results in hum or noise, it’s possible that removing the shield connec­tion from pin 1 can eliminate the issue. With an unbalanced source connect pin 2 to sig­nal high (+ or hot) and both pins 1 and 3 to shield. If connecting an unbalanced source in this manner results in hum or noise, con­nect pin 2 to high (+ or hot) and pin 3 to shield; leave pin 1 unterminated.
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