StudioTech 233 manual Microphone Preamplifier Gain and Phantom Power

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.