Guitar Shop 101: The ABCs of Output Jacks | Premier Guitar Mar 25, 2016Guitar Shop 101: The ABCs of Output Jacks. John LeVan. March 25, 2016. A A A common use for a TRS jack is in an acoustic guitar that has an under-saddle pickup, as well as an onboard microphone or a body sensor. Photo 3 shows the wiring for a stereo open jack and Photo 4 is a stereo barrel jack. Photo 3Author: John Levan 1/4" Plugs, Jacks & Connectors | Markertek 1/4" Connectors Jacks & Plugs. 1/4" Connectors Jacks & Plugs are essential to any pro audio setup. The easiest explanation is that when manufacturers started selling amplifiers and speakers separately, speakers in one box and the amp in another.