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This is a real stab in the dark, but is anyone familiar with the precise schematics of the Sennheiser cable used on the PXC350?

The stock cable has a volume attentuater but furthermore, it terminates in a 4 pin configuration at the headphone, even though just the left, right and ground are the only outputs from the attenuator itself to the 4 pin plug.

I'd like to replace the stock cable and ditch the attenuator as I don't need it, but this is easier said than done. I tried simply cutting out the attenuator and bypassing it altogether and the sound from the headphone was terrible.

Further testing of an original cable with my multimeter just leaves me further confused, as this 4th pin on the connector has me bewildered.

 

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I have it figured out. You need to run a 2Kohm resistor from the left to common and another 2kohm resistor from the right to common. So if you test the resultant cable with the multimeter you should get 0 ohms resistance from tip to tip, centre to centre and common to common. Then you should get 2kohms from left to common, 2kohms from right to common and 4kohms from left to right.

Without this resistor network in the cable this headphone sounds truly horrific. With the resistors it sounds superb. It is always nice to get rid of a completely redundant potentiometer in a circuit.

Anyway, here is the cable I made. Unfortunately the connector to the headphone itself is super, super proprietary, so there is no choice but to cut and solder.