This tutorial describes how a microphone with a balanced output is properly connected an audio recorder. There are generally two different types of recorder microphone inputs:
This is quite simple as there is a straight 1:1 connection between the microphone output and the recorder input:
The advantages of this type of connection is the rugged physical construction of the XLR connectors with their thick cables and reliable strain reliefs, the immunity to electromagnetic interferences and the option to power the microphone through the recorder via the P48 phantom power.
This is a bit more complicated because the balanced microphone output needs to be adapted to the unbalanced microphone input:
If you use one microphone only, the microphone output (XLR pin 2) can be connected to both the left (tip) and right (ring) input channels of the recorder. In case the recorder has a mono 1/4″ TS input, the microphone output (pin 2) is connected to the tip of the phone plug. The negative microphone output (XLR pin 3) should be left open when the microphone has a transformerless output. Otherwise, the grounded negative output could potentially cause trouble in the electronic microphone circuit. Though, most microphones can also tolerate such a grounded output.
For stereo recording, the left microphone must be connected to the tip and the right microphone to the ring of the TRS plug.
However, if the microphone has a transformer-coupled output (such as the old Sennheiser K3/ME8x series), pin 3 must be connected to ground in order to close the electric signal circuit:
If you are unsure whether the microphone employs an output transformer or not, you could measure the resistance between the XLR pins 2 and 3 by using a multimeter while the microphone is switched off. If the resistance is around 50 Ohms, then there is a transformer in it. If the resistance is several mega ohms, then it is a transformerless model.
In case the microphone requires an external phantom power supply (no internal battery), an additional phantom power supply unit is required to connect such a microphone to an unbalanced 3.5 mm microphone input:
Depending on output circuit of the microphone (with or without transformer), the XLR pin 3 must be connected to ground via an electrolytic capacitor or it can be left open (transformerless output).
Unfortunately, the tiny 3.5 mm connectors with their thin cables are prone to physical damages under rough field conditions. In addition to that, the small sized contacts can sometimes cause unreliable electrical connections that cause crackling noise.
