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Thursday, June 14, 2012

Guitar Pedal Power Supply

Project Goals:

To design and build a reliable, high quality, heavy duty power supply
in a small size that can power 10 – 20 typical guitar pedals,
replacing 9 volt batteries and/or multiple wall-warts.

This would substitute for a typical $150.00 commercial unit,
available at music stores or on the internet.

Circuit Design:

A transformer-based supply was chosen, to reliably deliver the current and power required, rather than a lighter but less reliable and/or noisier 'switching supply'. The simplicity of the design, coupled with independent regulators will make a low-maintenance unit that delivers clean D.C. Power and very low noise. (See circuit diagram).

Full-wave rectification with de-rated parts and a wide safety margin for voltages and current was chosen, since consistency of voltage is needed, while the number of guitar-pedals and their power-needs will vary greatly and be out of the control of the designer. The unit must perform consistently under a wide variety of loads.

Important:  Each Regulator was mounted on a small heatsink to allow it to operate at high current values.

Guitar pedals range in current-draw from as little as 10 mA to as high as 100 mA.

Using a daisy-chain cable to connect them in parallel,
means the currents will simply add up.
Each regulator can handle a maximum of less than 1 Amp,
so load each branch accordingly.

Examples: (actual measured current draw)
Distortion + (BOSS) - 10 mA
Chorus Factory 7 (Digitech) - 90 mA
Main Squeeze (Digitech) - 80 mA
Accoustic Simulator (BOSS) - 20 mA
Noise Reducer (Behringer) - 30 mA
Ultra Temolo/Pan (Behringer) - 15 mA
Reverb RV600 (Behringer) - 90 mA
Digital Delay DD400 (Behringer) - 95 mA

Dual branches were chosen, to lessen the load on each branch, and further isolate various pedals from each other, when connected.
Also, in case of part-failure, one branch alone can easily drive at least 10 typical guitar-pedals so that the unit can continue in use until one branch can be repaired.

Long A.C. Mains chord and power-lines were chosen, to allow a physical distance of up to 3 feet from pedal area and/or signal cables, and to allow convenient connection to A.C. Supplies located anywhere on stage.

An indicator light was added to reveal power-on condition.
A heavy metal box which can endure abuse was also chosen, to support the weight of the transformer and protect circuitry.

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