StudioTech 233 manual Microphone Preamplifier Gain and Phantom Power

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Figure3.Bottom view of Model 233 showing

configuration switches, trim pots, and compressor active LED

Microphone Preamplifier Gain and Phantom Power

Five switches are used to set the gain of the microphone preamplifier. One switch is used to select the on/off status of the phantom power supply.

Microphone Preamplifier Gain

Switches SW1-1 through SW1-5 are used to select the gain of the microphone preampli- fier. The choices are 20, 30, 40, 50, and 60 dB. Only one switch should be enabled at a time. There’s no problem changing the gain setting while the unit is operating. Audio clicks or pops might occur during gain tran- sitions, but this shouldn’t be a major issue as long as associated monitor loudspeak- ers are temporarily attenuated or muted.

Selecting the correct amount of gain for an application might take a little experimenta- tion. The goal is to bring the microphone’s

Figure 4. Microphone preamplifier gain switch settings

signal up to line level, nominally –2 dBu, on the Model 233’s main output. Operating at this signal level will help to ensure the delivery of “clean” audio to the connected device. The output of the Model 233’s mi- crophone preamplifier is used by both the main output and, by way of the compressor circuit, the talkback functions. So creating a nice “hot” signal will help maintain audio quality, specifically the signal-to-noise ratio, when driving the often-lengthy cable runs.

Unfortunately, there’s no “perfect” gain setting that this guide can recommend. The two issues that impact the setting are output sensitivity of the connected micro- phone and the acoustical output level of the microphone’s user. With some headset mi- crophones, such as the Sennheiser HMD25, selecting an initial setting of 40 dB is appro- priate. Users who speak loudly might need to have the gain reduced to 30 dB. Quiet users might need 50 dB of gain.

An LED indicator is provided as an aid in correctly setting the gain of the micro- phone preamplifier. Red in color, this LED is located adjacent to switch assembly 1.

Issue 1, September 2007

Model 233 User Guide

Page 18

Studio Technologies, Inc.

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Contents User Guide This page intentionally left blank Table of Contents Issue 1, September Model 233 User Guide Introduction What This User Guide CoversSystem Overview Main Output System FeaturesMicrophone Input Talkback FunctionsUser Controls and Status Indicators Dynamic Range ControlFlexibility Cue Sources SidetoneHeadphone Output Audio Quality and Protection Power SourcesIntercom Interface Auxiliary RelayAdditional Connector Locations ConfigurationConnectors Multi-Pin Headset ConnectorsInstallation and Setup OptionsSystem Components Headphone Output Line-Level Talkback Outputs Line Inputs External Power Input Configuration Pushbutton LabelingMicrophone Preamplifier Gain and Phantom Power Microphone Preamplifier GainPhantom Power On/Off Headphone Source SelectionLeft and right channel headphone source selection settings Headphone Output Mode Headphone output mode settingsMain Output Button Mode Operating ModesTalkback 1 Button Mode Talkback 2 Button ModeTalkback 1 Button Function Sidetone Mode Talkback 2 Button FunctionMain Output Source Dual-Channel or Stereo Mode Reverse Left/Right ModeHeadphone Output Operating Modes Minimum Level Mode Main Button ModeRelay Mode System ModeOperation Talkback 1 to Intercom Function ModeTalkback 2 to Intercom Function Mode ConclusionPushbutton Switches and Status LEDs Main Output Button and LED IndicatorsMain Output Button Modes Talkback 1 Button Modes Talkback 1 Button and LED IndicatorTalkback 2 Button and LED Indicator Talkback Output 2 Button ModesLevel/Level Mode Level/Balance ModeMonaural Headphone Output Level Control Operation Sidetone OperationAdjusting the Line Input Trim Pots Advanced OperationIntercom Interface Sidetone Adjustment Technical NotesGrounding and Shielding Intercom Channel Crosstalk Intercom Audio LevelsConnecting an IFB Circuit Phantom Power External Power SourcesSymptoms of Insufficient Power Additional Connectors LED ColorsTravel Case Issue 1, September Model 233 User Guide Pushbutton Backlighting Remote Control/Tally Connections P18Compressor Circuit P19Specifications General AudioAppendix a