Some old guitar effects used -9V DC.[1] And the convention with guitar effects power adapter is the barrel is center negative (which is motivated with facilitat

Some old guitar effects used -9V DC.[1] And the convention with guitar effects power adapter is the barrel is center negative (which is motivated with facilitating easy wiring of the socket's switch to connect to a 9V battery inside). [1] https://www.analogisnotdead.com/article26/what-is-going-on-with-positive-ground https://www.analogisnotdead.com/article26/what-is-going-on-w...