This is the simplest way to use a combo amp as a speaker cabinet for a separate amp head. I am using a Line 6 Spider IV combo here but most combos will work this way. The required parts only cost £8.50 ($13) and this project can be undertaken by someone with little to no electrical skills like myself.
Make sure you match the impedance (Ω) of your new head and the speaker in the combo.
• 2x 1/4 inch mono jacks
• Speaker cable (1/4 female to female, like a guitar lead but higher impedance)
• Pliers / cable stripper
• Soldering iron and solder
• Philips head screwdriver
Step 1: Remove the Back of the Amp
Loosen all screws on the back of the amp then remove them all evenly. This step may vary according to your amp. My back panel was secured in with some glue so took some force to remove it. I removed it by simply lifting up the amp slightly holding onto the back panel and the amp fell away (common sense alert: only do this over a soft surface such as a bed/sofa). Removing the back panel should expose the speaker.
Step 2: Remove the Amp and Speaker From the Amp Cabinet
This is simply a case of removing screws and lifting them out - it will vary lots from amp to amp. Keep in mind that your amp probably won't have been disassembled before and things may be hard to remove. Keep a mental note of what you're doing as it will be helpful when you come to reassemble the amp.
Step 3: Cut the Wire Connecting the Amp and Speaker and Strip the Ends
With a pair of pliers cut the wire connecting the amp and speaker. It's a good idea to leave more length on the speaker end as this wire will need to reach further if you're to easily access the jack. With the sharp part of the pliers carefully strip the wires like shown in the photo and twist the ends so it doesn't fray. Strip both the wires emanating from the speaker as well as those coming from the amp.
Step 4: Connect a Jack to Each Side
Solder a jack to the amp wires and the speaker wires. Do the following steps for both the amp wires and the speaker wires.
- Connect the positive wire (white on my amp) to the tip of the jack and the negative (black) onto the sleeve.
- Solder the join. My soldering is terrible but just put enough on to kind of secure it in place.
- Wrap the join in electrical tape to secure it and seal it. This is especially useful if you aren't the best at soldering.
Step 5: (Optional) Secure the Jacks Into a Certain Place or Tidy Them Up.
This step is optional, you can drill holes for the jacks to sit securely in or leave them dangling about.
Luckily, on my amp there was a hole pre-drilled where I could secure the jack, securing it in place with a washer and nut. If there isn't on yours you can leave the jack loose or drill some holes (they should probably be just over 1/4 inch in diameter).
Step 6: Test Your Amp
Use the speaker lead, such as the one pictured to connect the two freshly installed jacks together. Make sure to use a speaker cable like the one pictured as the load will be much higher than a guitar cable. Plug the amp section back in, connect your guitar and play. You should here it just as you did before the mod and everything is fine.
Step 7: Reassemble Your Amp
Now just reassemble your amp, basically doing the reverse of step 1&2. Make sure to loosely screw in all screws then tighten them.