I've been given two audio headsets to repair, of the same but unidentified brand. On each, the moulded-on 3.5mm TRRS plug was damaged, so I chopped both off, stripped back the insulation on the free cable ends, and tinned the ends.
Each cable has only three 'wires'; one each for the Left and Right signals and a screened one for the Mic.
My DMM shows low Ohms (~16 on one headset, 25 on the other) between the L and R wires and ~1.8k between the Mic and its screen (Gnd). The mystery is that there is a DC open circuit between L and Gnd and between R and Gnd, on both headsets. So how are the L and R circuits completed? Coupling capacitor?
The headset schematic seems to be this:
Each cable has only three 'wires'; one each for the Left and Right signals and a screened one for the Mic.
My DMM shows low Ohms (~16 on one headset, 25 on the other) between the L and R wires and ~1.8k between the Mic and its screen (Gnd). The mystery is that there is a DC open circuit between L and Gnd and between R and Gnd, on both headsets. So how are the L and R circuits completed? Coupling capacitor?
The headset schematic seems to be this: