Our very first version of the EPS001 had a design flaw in which the output cable and jack from the preamp module was mono, but should have been stereo. There were only a handful of these first versions, so it’s unlikely that your unit has this issue. To check, you can look at the wire that goes from the preamp “Out” socket to the guitar cable socket. This wire should be a stereo wire as shown as wire “A” (which features two black bands on the male connectors) in the picture below. If your wire has only one black band on the male connectors as shown in wire “B” then you need to replace this cable along with the guitar cable jack connector shown below. Simply reach out to us on our contact form and request for the cable and connector and provide us with your address and phone info, and we’ll send the replacements at no charge.