Pedal Power: Why Center Negative?
by Jerry Catanescu, December 2024
updated March 2026
Why do guitar pedals use center-negative DC adapters instead of the much more common center-positive design? Is there a real technical reason, or is it just a way to push proprietary DC adapters?
There is, in fact, a practical reason rooted in how pedals handle battery power. Many pedals are designed to run on either a 9V battery or an external DC adapter. To make this work efficiently, the battery must be disconnected from the circuit in two situations:
When a DC adapter is plugged in, and
When the guitar input cable is unplugged (this doubles as the pedal’s “off” switch to save battery life)
To handle the first case, standard female DC jacks include a normally closed switch on the sleeve (outer) terminal. The battery's positive is connected to the circuit through this switch. When a DC plug is inserted, this switch opens, disconnecting the battery.
For the second case, the battery’s negative terminal is connected to the ring of the pedal’s TRS input jack. When a standard guitar cable is inserted (mono, or TS), it shorts the ring to the sleeve, connecting the battery negative to ground and powering the circuit. Removing the cable breaks this connection, effectively turning the pedal off.
Because the battery negative is already committed to this switching scheme, only the positive terminal remains available for the separate switching mechanism via the DC jack (see illustration below) As a result, the external power supply must provide positive voltage on the outer sleeve and negative on the center pin.
