User's Manual

GC864 Hardware User Guide

1vv0300733 Rev. 0 - 12/06/06

7.5 Microphone buffering

As seen previously, a microphone shall be connected to the input pins of the GC864 through a buffer

amplifier that boosts the signal level to the required value.

Again the buffered microphone circuitry can be balanced or unbalanced : where possible it is always

preferable a balanced solution. The buffering circuit shall be placed close to the microphone or close

to the microphone wire connector.

7.5.1 Buffered Balanced Mic.

A sample circuit can be:

This circuit has a gain of 10 times (+20 dB), and is therefore suited for the “Mic_MT “ input if you have

a microphone with a sensitivity close to the suggested one (-45 dBV

rms/

Pa). If your microphone has a

different sensitivity or if the buffer is connected to the “Mic_HF “ inputs , then a gain adjustment shall

be done by changing resistors R604 and R606 ( if the required value is not a standard one , you can

change R605 e R607 ) and as a consequence the capacitors C636 and C637 to maintain the

bandwidth 150-4000Hz (at -3dB).

GC864

270pF