Ingram Engineering MPA685, Owner'S Manual

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MPA685 Owner’s Manual
3/2012
10
A ¼” phone jack for each pre-amplifier audio channel output is also provided on the rear
panel. The ¼” jack is wired for Tip = Hot, Ring = Cold and Sleeve = Ground.
Direct Inject (DI) instrument input is made with a standard ¼” phone jack on the front
panel. The ¼” jack is wired for Tip = Hot, Ring = Cold and Sleeve = Ground.
A second ¼” TRS phone jack is provided on the front panel. This second jack can be
used as a DI loop-through. This allows the instrument signal to be simultaneously
tracked through the DI and also amplified. The two jacks are hardwired together, so
either jack may be used as the input or loop-through.
The DI inputs are loaded with a FET buffer that has an input impedance of 1 Meg
Ω .
Note: the impedance of a circuit connected to the direct instrument loop-through will be
in parallel with the FET buffer 1 Meg
Ω impedance. The load impedance of the device
connected to the loop-through may therefore dominate the instrument load if the loop-
through load is less than 1 Meg
Ω . If excessive signal loading is experienced when
using the loop-through connection, remove the loop-through connection and check the
specifications of the device that was connected to the loop-through.
4. Using the Audio Input / Microphone Impedance Selector
Use the leftmost knob on the selected channel to choose either front panel Direct Input
(DI) or rear panel microphone input.
Impedance presented at the rear panel microphone connection can be chosen as
“Low”, “Medium” or “High”. Audio tones are affected by the load presented to the
microphone, so the microphone impedance selector may be used as a tool to tweak the
audio quality so that it matches the recording situation. Some microphone
manufacturers have explicit requirements for the load presented to the microphone, so
the MPA685 impedance selector can also be used to guarantee that the microphone
manufacturer’s requirements are met.
The specific impedances installed are described in the Specifications section and at the
beginning of this manual.