If you do, the signal from your guitar won’t be loud enough to be heard and it won’t sound its best because the Eris E3.5BT or Eris E4.5BT inputs require a much “hotter” signal than most guitars produce. To use a guitar with the Eris E3.5BT or Eris E4.5BT speaker, you will need to plug your guitar into a DI (Direct Injection, or “direct”) box, then plug the output of the DI box into the Eris E3.5BT or Eris E4.5BT TRS input.
PreSonus makes the TubePre V2, a high-quality preamp that also serves as a DI box. More information can be found here.
Please contact PreSonus Technical Support by creating a Support Ticket at My.PreSonus.com for further assistance.