.... Here's the story
I had just finished restoring a MCI JH110 1"
8 track tape machine, and my friend Larry wanted to bring his band
over to record some demo songs on it, we talked it over, and figured
out how we where going to fit everyone in my rec room and how we
were going to do everything, but we needed to be able to give everyone
thier own headphones, so I wired a bunch of jacks together and hooked
them up to a small Radio Shack amp I had, and it got us through
the session (impedence... what impedence?)
Afterwards I thought it would be handy to have a
real headphone distribution amp around, so I started playing around
with different circuit ideas, and after a couple of tries, I came
up with a circuit using a quad op amp (so I have 2 stereo channels
on each circuit board) that works great and is quiet.
I built two six channel boxes, the first one I made had two
1/4" mono jacks for inputs, but the second one uses a 1/4"
stereo jack for the input, so you can use the headphone out of your
mixer to feed the box, and each output has it's own volume control.
I am in the process of adding 6 amps to a blank channel strip in
my mixing console, and I am also building some rackmount versions.