IF YOU BREAK YOUR AMP, WHICH THERE IS A GOOD CHANCE OF, DON'T BLAME ME! YOU HEARD IT FROM ME FIRST, IT'S BEST TO TRY THIS OUT ON A CHEAP AMP THAT YOU DON'T PARTICULARLY CARE ABOUT IN THE EVENT THAT YOU DO BREAK IT! ALSO, BE ABSOLUTELY SURE BEFORE YOU DESOLDER OR SOLDER.
Step 1: What You Need
1 Guitar Amp (I'm using a Kay GA20K, very cheapo)
Some bits of wire
2 1/4" phono jacks, aka guitar jacks.
Some Soldering skills.
Also drilling skills and a drill
Step 2: The Concept
Step 3: Disassembly
Now examine your amps guts, see if you can unplug anything else off of the main amp board thing. It turned out I could unplug the power supply and the speaker outs/headphone jack.
Now carefully remove the knobs (some amps have knobs that just push on, others have a set screw) and their nuts, also the input jack's nut. Then proceed to remove any other screws holding the board down, mine had two on the little heat sync thing connected to that black thing there. Essentially, just get it out.
NOTE: Be careful with your wires, I broke one of the connectors for the power supply, this provided me with much anger/annoyance because I thought it was a problem with something I had meant to do. I think it was when I was testing it that I did this. So be careful! (As you always should anyhow).
Step 4: Finding the Division Aka the Hard Part
Look for ominous looking chips, then google their numbers. In my case, I found two ominous looking chips that turned out to be two op amp chips, one smaller than the other (smaller one is the pre amp chip!). This made it easy for me, because I just looked up the pin out for my big chip, found the input and that was my power amp in.
Master volume knob. Some amps have the master volume knob right before the power amp in. For example, look at this Pignose G40V tube amp's schematic, you can see (as I've circled it) the master volume pot is pretty much the only connection to the power amp stage (the one with the 6L6 tubes). But I don't recommend following that directly from me, as I haven't tried it! (EDIT!!: I did try it. And it didn't work, I'm in the process of making it though).EDIT AGAIN!!: (I tried it after the master volume and it works, although you can't do a compression pedal or anything like that, because that makes it go full volume! haha and auto wahs don't work.
Be careful! If you find something you might think is it, be careful when desoldering it. Clip an alligator clip onto the component as a heat sync, and try to keep the heat out of it. And when you try to start it up with your wires attached, keep them either hooked up to the pedal, or touching each other when you start it up. I had some times when I didn't and the noises I heard didn't indicate a happy amp. You may not know what I'm talking about with the wires, but we'll get to that in the next steps.
Step 5: Soldering on the Wires!
Step 6: Moment of Truth
Get your least favorite effects pedal (as you might blow it up if you inadvertently picked a place that's like +10248236 volts or something) and plug in two guitar cables to it. Now connect the wire that is coming from the pcb, the send wire, to the tip of the cable that goes in to the "in" hole on your pedal. Connect the wire going into the power amp to the tip of the cable coming from the "out" hole in your pedal. Connect both the "sleeve" parts of the cables to ground. Now strum the guitar and turn it on, you should have effectage! If you didn't (like I didn't) then you picked the wrong place to splice in. Try again! If its an op amp, look over the pin outs that it shows on the datasheet (you can find those via google) and if you're like me, you slap you face with the palm of your hand and realize your mistake.
Step 7: Wiring Up the Jacks
Step 8: Drill!
Step 9: Re-Assembly!
Step 10: Plug It in and See If It Works!
Now there are a few tricks with this thing. The first and foremost is always have something plugged into the loop, otherwise it makes a nasty noise that quickly gets louder and gives me a bad feeling of "this thing might blow" So just play it safe and keep something plugged in. The other thing is, if you want to not have anything plugged in, just plug both ends of a cable into the loop.