Patrick wrote:

I have some vinatge headphones (Sennheiser HD424) and want to attach a new
plug.

Which color wires are the positive ones?

The colors in one of the leads are red & blue and in the other lead black
&
yellow. (No wire is used as screening - there's just two wires in each
lead.)

If they are the standard voice coil types, put them in front of a stereo
speaker and drive the amp with a sine wave. The headphone 'speakers' will
act as microphones. Use an oscilloscope on the pairs of leads to determine
phasing.

--
Paul Hovnanian
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Will code for food.