I just bought one and i plugged the cable into the headphone jack but the audio is only coming out of the left side of the speaker.

is this the way it is? is the jack messed up? or do i need adjust some setting within the synth to make it stereo?

It should be stereo or at least mono with both ears playing same signal.

This could be due to your headphones being slightly bent, bad solder connection inside or the headphone jack's insides are bent from previous having bent plug inside it, pushing out the metal contact.

Try different cans first, after that, open up the unit and try to take push in the outer connector so it makes contact unless you notice the jack is loose, in which case it's the soldering.

If it's new, just trade it in.

thanks