Emax

Hey guys...I'd recently purchased an emax HD keyboard as a back up to my rack. I'd decided to sell it because it simply took up too much space in my apartment. To test it I sampled it and played the samples back via the mono out. No problem. That said, when I hooke up the second /stereo out I noticed that every 8th key was louder. With the filter and resonance in play as well I noticed the resonance seemed to jump on every 8th key as well. 

Any thoughts? Sadly I just sold this on ebay and I don't want to send this guy a partially functioning machine. 

Thanks!

Joel