User`s guide

Hardware

4.3.2.12 MICROPHONE GAIN CONTROL (R56)

MIC ADJ Potentiometer R56 (Ref A12) controls the gain of the Line/Microphone

Pre-Amplifier (U10:A). The default setting is with the arrow on the potentiometer

pointing to the arrow on the board.

4.3.2.13 LINE/MICROPHONE PRE-AMPLIFIER (U10:A)

The Microphone/Line Pre-amplifier (Ref A13) is implemented using one of the four

op-amps on the MCP6024 quad op-amp IC (U10). The output of this non-inverting AC

amplifier is biased at 1.65V. The gain of the amplifier is controlled by Potentiometer

R56, as given by Equation 4-1.

EQUATION 4-1: INPUT PRE-AMPLIFIER GAIN

4.3.2.14 ANTI-ALIASING LOW-PASS FILTER (U10:B,C,D)

The Anti-Aliasing Low-Pass filter uses three of the four operational amplifiers on the

MCP6024 quad op-amp IC (U10). The output of the Line/Microphone Pre-Amplifier

(Ref A14) uses an anti-aliasing low-pass sixth order Sallen-Key structure to filter the

signal and provide a cut-off frequency of 3300 Hz.

4.3.2.15 USER SWITCHES (S2 AND S1)

The starter kit features two press switches which are connected to the I/O ports on the

dsPIC33F device. The function of these switches is defined by the user application.

Note: Setting the gain too high can cause the output of the amplifier to saturate

and clip.

Gain 1

R56 R50+()

R44

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