Stompbox power supply : Things to know

In a precedent post , we tried to spot different ways to power a pedal or any active circuit for guitars. The situation is not that simple and easy as one would like, but one can nevertheless get some sure benchmarks, usefull or problematics.

We also will have to remember that hum may sometimes not be caused by supply voltage, but by faulty connections …


A couple of things usefull to know

Batteries and stabilized power supplies ensure most often an absence of noise.
•  It is essential for distorsion boxes, three transistors fuzz and other high gain stompboxes.
•  It is best for buffers, preamps, compressors placed at the head of chained stompboxes.
•  Downstream connected equipments will appreciate their silence.

Digital pedals can work well with a noisy power supply.
•  It can be a simply filtered DC power supply, provided it can supply the needed current.
•  It can be an ordinary switching power supply, which in this case should not cause hiss.
•  The pedal contains an internal filter that will smooths the external power supply.
•  But nothing beats a well stabilized device.

Analog pedals sometimes work correctly with a succinct power supply.
• It depends on their gain, the power voltage routing, presence of découpling cells.
• Cheap pedals, or poorly built models, are generaly senstive to hum and hiss.
• If they work properly or not can be verified only under real conditions.

All Guitar Poppa’s stompboxes are equipped with an active supply filter.
• It is there to eliminate hum and hiss brought by external power supplies.
• But it can prevent only from noises coming through the power supply.

Last words on hum

Hum may be not caused by the power supply !
(And often it’s the worse that could happen)

• Some are caused by messy ground connections in the guitar, the wiring…
• They come into the amplification system through the guitar input of the first pédal.
• They are all the louder than the ground connections of the building’s installation is poor.
• They typically vary with the guitar volume control, and are generally louder halfway.
• No filters, no stabilization in the power supply can do anything drastic against such a hum.
• Using batteries avoids aggravating the problem, but is not a solution in itself.

The solution should be found by improving ground connections inside the guitar, in plugs and cables, and by avoiding ground loops into the pédal. Not easy…

Guitar Poppa


Links  : 

Stompbox Power Supply : Overview (article)
Stompbox Power Supply : Poppa’s tricks (article)

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