The MixPre-D features two transformer balanced analog inputs. Each input provides enough gain to amplify a variety of signals from low-sensitivity ribbon and dynamic microphones, medium-level wireless and condenser microphones, and “hot” line level signals.
The XLR inputs of the MixPre-D are transformer-balanced. The isolation characteristics of transformers are superior to other balancing techniques and are ideal for the hostile and uncontrolled environments of field production. Transformers provide galvanic isolation from the driving source, meaning there is no direct electrical connection. Signals are “transformed” magnetically. The input transformers in the MixPre-D use premium magnetic core material to achieve high signal handling capability (especially at low frequencies) while keeping distortion to a minimum. Because of their inherently high common mode impedance, transformers are unrivaled by any other type of input for commonmode noise rejection.
The inputs of the MixPre-D can be used as balanced or unbalanced. When unbalancing, ground pin-3 to pin-1 of the XLR connector. There is no change in gain between unbalanced and balanced connections into the MixPre-D.
Before plugging a source into an XLR input on the MixPre-D, set the Mic/Line and phantom powering switch to the correct position:
Phantom powering is a fixed DC voltage at either 12 or 48 volts. This voltage is resistively applied to pin-2 and pin-3 of an XLR connector relative to pin-1. There is no voltage difference between the signal pins-2 and -3. Dynamic microphones will operate as normal when phantom power is applied to them.
The MixPre-D can provide up to 10 mA to each input at 48 V, sufficient for the most power-hungry condenser microphones. Many phantom powered microphones do not require 48 V and can be properly powered with 12 V. When acceptable, use 12 V phantom to extend the MixPre-D’s battery life.
The phantom voltage level can be set to either 12 V or 48 V and is applied across all inputs where phantom power is selected.
To change the phantom voltage between 12 V and 48 V, hold down the Headphone Controller and slide the Slate switch into the slate position. The 12 V Phantom LED on the left side panel illuminates green when the phantom voltage is set to 12 V.
The amount of gain applied to an input is adjusted with the Input Gain Control. A fully clockwise position results in no signal passing from the input to the output bus (muted).
Up to 66 dB of gain is available from for microphone inputs.
Each input of the MixPre-D has a two-position high-pass filter. High-pass (or low-cut/low frequency roll-off) filters are useful for removing excess low frequency energy in audio signals. Wind noise is a common unwanted low frequency signal and a high-pass filter is effective for reducing wind noise.
For most audio applications engaging the high-pass filter is beneficial, since little usable audio information exists below 80 Hz, especially for speech reproduction.
The MixPre-D’s high-pass filters feature a 6 dB/octave slope with either 80 Hz or 160 Hz corner (-3dB) frequencies. The 160 Hz setting is used when aggressive filtering is required. The MixPre-D’s high-pass circuit is unique because of its placement before any electronic amplification. Most mixer’shigh-pass circuits are placed after the mic preamp, where all of the high-energy low-frequency signals get amplified. Because the MixPre-D’s circuit cuts low-frequency signals before amplifying, higher headroom is achieved in presence of signals with a high amount of low-frequency energy.
When possible, attempt to equalize at the sound source with microphone selection, use of windscreens, microphone placement, and on-board microphone filtering. Many microphones have onboard high pass filters, and the high-pass filters on the MixPre-D can be used in conjunction with the microphone’s filters to increase the filter’s slope. The three available high-pass filter settings are switched for each input by pressing the Input Button for the adjacent input. The two blue High-pass Filter LEDs for each input indicate the setting of the high-pass filter for the adjacent input.
The MixPre-D Limiters act solely as “safety” limiters. Activate the Limiters using the front panel“LIM” switch. Both input and output limiters are active, with input limiters preventing overload of the input stage and output limiters preventing the MixPre-D from overloading the next device in the signal chain.
In normal operation, with a properly set gain structure, the limiter threshold is only occasionallyreached. In the presence of extremely high input signal levels, such as in high SPL environments, the limiter(s) activate to prevent the input signal from clipping. The limiters have no effect on audio below the set threshold.
When Inputs 1 and 2 are linked as a stereo pair, the limiters also link; gain reduction is equal for both
To change the threshold of the limiters, hold down both the Input 1 Button and the Input 2 Button and turn the Headphone Controller.
The pan switches assign inputs to the channels of the output bus. Inputs can be sent to the left, right, or both outputs equally. The MixPre-D features excellent “off-attenuation” in the left and right positions. With the use of the pan switches, separate mixes can be sent to the left and right outputs. For example, a summed mono mix of both inputs can be sent to the right output while a single input can be sent to the left output.
Each channel of the Tape Return input can be routed to various locations. When additional inputs are needed (such as when multiple wireless receivers are used) the Tape Return channels can be
independently routed to the main output bus of the MixPre-D to act as additional inputs (3 and 4).
v1.0 Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.
To cycle between the available routings of the Tape Return signal, hold down the Input 1 Button (for Channel 3) or the Input 2 Button (for Channel 4) and press the Headphone Controller. An LED in the right meter will illuminate to represent the destination of the routing:
When any channel of the Tape Return input is routed to the main output bus, the RTN Monitor Source is disabled.
The TAPE RTN (Input 3 and 4) Input is an unbalanced stereo input that is suitable for tape or line level devices only. There are no microphone preamps on Inputs 3 and 4.
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