Why pedals shouldn’t be powered by 9V batteries

When designing guitar pedal based on op-amps and/or discrete bipolar or FET transistors, the choice between symmetric and asymmetric power supplies can significantly impact your sound.

Symmetric (Dual) Power Supply:

A symmetric power supply offers several advantages. It allows for better headroom, enabling equal positive and negative voltage swings. This configuration simplifies biasing as there’s no need for voltage dividers to create a virtual ground. Symmetric supplies often result in reduced even-order harmonics, potentially leading to lower distortion. They also make AC coupling easier, which can sometimes be eliminated entirely, improving low-frequency response. Additionally, symmetric supplies often lead to quieter operation due to better common-mode rejection.

However, symmetric supplies also have some drawbacks. They require a more complex power supply design, needing two voltage rails and a center tap. This increased complexity typically results in higher costs due to the need for additional components. Symmetric supplies also demand more board space, which can be a constraint in compact designs. If not properly implemented, there’s also a potential for ground loops in symmetric supply configurations. They also needs higher voltage from power supply blocks : 15V is a minimum, 18V (which allows +9V/-9V) the best.

Asymmetric (Single-Ended) Power Supply:

An asymmetric power supply has its own set of advantages. It offers a simpler power supply design, requiring only one voltage rail. This simplicity often translates to lower costs, as fewer components are needed. Asymmetric supplies also allow for a more compact layout, reducing the required board space. They can be easier to integrate with digital circuits, as many digital ICs use single supplies.

On the downside, asymmetric supplies have some limitations : reduced voltage swing, with only half the total supply voltage available for signal and there’s a possibility of increased noise due to the virtual ground and biasing network.

The 9V battery is even worse :

• Variable voltage during the life cycle. As the battery drains, its voltage gradually decreases. This can affect the pedal’s performance, particularly in analog circuits that are sensitive to supply voltage.
• Limited current capacity, which may not be sufficient for more complex or power-hungry pedal designs.

Batteries have nevertheless two primary advantages : portability (no external power source nor cables) and noise reduction (ground loop hum or interference from AC power line with low cost external power supply units).

With your pedalboard, always use a premium external power supply unit (with or without power banks) and prefer pedals powered in 15V or 18V voltage.