I was recently asked by a friend to modify their old-school Russian Electro-Harmonix Big Muff π, with a standard 2.1mm, switching, DC power input socket (often known as a ”Boss style” power jack), for use with a 9v battery. It was a fairly straight forward job, but I thought I would do a short blog post about it, as knowing how to add a DC input socket is super useful for a whole range of projects. These DC sockets let you switch automatically between battery and adaptor use, while conserving the battery when the adaptor, is plugged in.
Before we go through the mod, let me say something about safety
This project and modification are designed only to be used with the standard 2.1mm ”Boss Style” switching DC input socket that takes a 9v, centre negative DC power adaptor.
Power from the mains AC power supply (the electricity from the plug in the wall) WILL, AND WANTS, TO KILL YOU. Never mess with anything that plugs into a wall socket unless you are 100% confident with the power adaptor, that you know what you are doing, and the circuit you are working on. Absolutely NEVER mess with a device WHEN IT’S PLUGGED INTO the wall. Please be careful, and always put your and others’ safety first.
Now… let’s take a look at the layout of the 2.1mm DC input socket:
Lug 1 – Ground (All ground connections)
Lug 2 – Power (From battery)
Lug 3 – Power (To board)
BE VERY CAREFUL- Check, double check, and triple check your soldering and the pinout of the socket before connecting a power adaptor, or you risk frying your board.
When running on battery, lugs 2 & 3 are connected. When a power adaptor jack is plugged in, the connection between the lugs is broken, saving the battery, and power is only drawn from the adaptor via lug 3.
So here is how the mod went:
1. I opened up the Russian Big Muff:
2. I drilled a 12mm hole for the DC socket. The metal is steel and quite tough but I managed to get through it:
3. The old 9v battery snap was broken so I’m gonna use a new one:
4. I inserted the DC Socket:
5. I then soldered the black wire from the new battery snap and the black wire from the old battery snap (that was still connected to the board) to lug 1 on the socket:
N.B. if there wasn’t already a wire soldered to the board (from the old battery snap), I would have had to add one from lug 1 to a ground point on the board).
6. Then I soldered the red wire from the new battery snap to lug 2 on the socket:
7. The red wire from the old battery snap was still connected to the board so I soldered it directly to lug 3 on the socket (I also added a small piece of insulating mounting tape to prevent the lugs accidentally touching the board):
8. Finally I remounted the board, and added a fresh battery:
9. And here she is working away:
– Thom Conaty
thom@maker.ie
maker.ie 
thanks for this post, specifically for the info on what goes to what on the dc socket lugs! just added 9v Jack to mine and it’s working great!
You’re very welcome! Thanks for the kind words. Glad it was useful 🙂