Audio Polarity of Shure Wireless Bodypack Transmitters

FAQ #4414 Updated September 13, 2017

Question:

Please clarify the audio polarity from a Shure bodypack transmitter input to the receiver XLR output?

Answer:

1) Positive signal voltage on pin 3 of the transmitter TA4M input will produce a positive signal voltage on pin 2 of the receiver XLR male output.

2) Positive pressure on the Shure lavalier microphone diaphragm will produce a positive signal voltage on pin 2 of the receiver XLR male output.  Shure lavalier microphones do not invert the signal voltage.  Shure employs a three-wire FET circuit.  The FET is used as a non-inverting buffer amplifier, known as a "Source Follower" or "Common Drain."  The gain is unity, or close to unity.

Note: Non-Shure lavalier microphones often use a two-wire circuit, known as a "Common Source." This circuit inverts the signal. If used with a Shure wireless system, positive pressure on the microphone diaphragm will produce a negative signal voltage on pin 2 of the receiver XLR male output.

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