Im following this instructable http://www.instructables.com/

The output of a headphone jack can only power the very small speakers found in headphones.

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>>1048308
Strange since it works when I attach the wires to this.

>>1048326
Then you fucked something up.

i had one of those dollar-store radios where the 3.5mm jack was purposely wired without a ground, such that the output was mono, effectively putting the 2 headphone speakers in series.

i'm not suggesting this is your case, it's just one of the possibilities that you can figure out much quicker by doing trial an error than asking strangers for help.

Alpha toss

They are mono speakers running stereo which is why it works with the adapter. Take one speaker out and it will work without the adapter. get a y jack male female female from radio shak snip ends wire problem solved.