NOTE: THIS MOD WILL VOID YOUR WARRANTY!! DO NOT PERFORM THIS MOD UNLESS YOU ARE WILLING TO VOID YOUR WARRANTY!!

Here's how to defeat the speaker output mute when plugging into the Headphone/Line output of Spider IV amps. Do not attempt this unless you are familiar with soldering and are comfortable working on the inside of amplifiers that have high voltages inside! You will need: soldering iron, hookup wire, a spst mini switch, a drill.

1. remove back back panel of amp
2. unhook speaker wire(s) noting their position
3. remove screws on top of the amp
4. carefully slide chassis out of back of amp
5. remove plastic nut around headphone jack
6. remove 5 screws on circuit board that hold the headphone jack/ ethernet jack, etc.
7. carefully pull circuit board up to expose bottom side
8. note the two lugs of the headphone jack closest to the edge of the circuit board. Now, you are going to solder one wire to each one of these lugs, and the the other end of each wire to a lug of the mini switch Basically, you are using the switch to short these two lugs together.(the headphone jack is a switch and breaks the connection when a plug is inserted.) Make the wires long enough to reach a hole you are going to drill on the back panel for the switch. I made mine about 5 inches which allowed convenient placement of the switch close to the ethernet jack.
   
9. Drill a hole slightely larger than the threaded shaft of the switch
10. Insert switch in hole, and tighten nut to mount switch on the back panel
11. Optional- at this point you can hook up the chassis to the speakers, plug in guitar and cable to headphone jack, test that the switch allows you to hear speakers when jack is inserted.
12. reverse disassembly instructions, replace circuit board, install 5 screws, etc.
13. There you are, a line out which doesn't defeat the speakers unless you flip the switch.

THIS VIDEO SHOWS HOW IT WAS DONE ON A SPIDER III, WATCH IT, BECAUSE IT'S ALMOST IDENTICAL TO THE SPIDER IV.