Immediately after the Mic / Line switch is the – 20 dB pad switch (# 9 ). It ’ s important that the pad circuit is engaged before the signal gets to the transformer , preamp , and EQ circuits to avoid distortion from strong transients and overly loud sources .
10 . Isolation balanced input transformer . Immediately after the – 20 dB pad is the isolation transformer (# 10 ). Transformers are common electrical circuit components because they can perform multiple functions , depending on how they ’ re wired . They can step up and step down the voltage from input to output , match impedances , and in the case of this channel signal path , isolate the ground between the input and the output . Isolation transformers use magnetic induction to send the audio signal through the transformer . Notice that the transformer symbol consists of two coils with a space between them . They aren ’ t connected , yet the audio signal is passed through . There are two coils of copper wire around the same magnet but isolated from touching in the magnet . The incoming signal is connected to the incoming coil and as the AC signal varies the magnetic field in the magnet , the outgoing coil is induced with the identical variations in magnetism . So , the incoming signal passes through the transformer relatively unchanged ; however , because the electrical connection has been broken between the input and output of the transformer , any ground-connection noises have also been disconnected .
11 . Phase switch . The phase switch is extremely important in some very specific sound operating tasks . The phase switch is sometimes simply called , polarity . Pressing this button inverts the phase of the audio signal , flipping the audio wave upside down so that the crests become troughs and the troughs become crests . By definition , that is the same as reversing the polarity . Anytime two microphones are pointing at each other or when they ’ re positioned on opposing sides of an instrument , such as a snare drum , the sound they capture is 180 degrees out of phase so , in order to get the two mics to work together , the