Eighty year old SX-28 headphones and modern $300 headphones are not the same.
This is a little adaper box to permit the use of the new with the old. I bought a little one foot headphone extnesion cord (really? one foot?) from Amazon for $7, cut it in half and wired it into a little project box.
From the plug, the tip (in this case the white wire) is the 'hot'. The red is the little ring for the other channel‐it gets connected to ground so the stereo plug more closely resembles a mono plug. The braid (shown unbraided and twisted) is the ground.
To the socket, the white and red get twisted together so both earpieces work.
The grounds get connected together.
Put a 200Ω resistor between the incomming white and outgoing red+white. I used a 5W mostly because I had one. 1 or 2 should work as well. Not sure I'd go smaller.
Put a 22Ω resistor from the headphone end of the 200Ω resistor to ground.
It works well with my Sennheiser HD-595 phones. When I was using the speaker, I frequently had the volume up to 8 or 9. With this, it's a comfortable 2.
Page: /Headphones/Headphones.shtml
Last modified: Thursday, 27 Aug 2026