Tag Archives: Circuits

Stompbox power supply : An overview

Stompboxes power supply is both a trivial issue and a relevant subject. There are some basic points behind banality that can help make a good choice — and avoid troubles — when organizing a pedalboard. This overview on the current situation will bring some classic issues, such as polarity of old pedals, consumption orders of magnitude according to types of stompboxes. The big issue remains choosing between traditional transformer power supplies and switching power supplies, that nowadays begin to impose their technology, but are not always appropriate to analog circuits…

A second article will expose points on which ensure personal choices … A third will be devoted to the system that equips my Guitar Poppa pedals, in order to power them silently through any types of DC power supply respecting the negative to ground standard.

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Stompbox Power Supply : Poppa’s tricks

Early stompboxes were exclusively powered by batteries. Their low consumption made it possible. When most demanding stompboxes came around 1978, external power supplies, less or more stabilized, were necessary. Today, current switching power supplies are widespread because they are cheap for the manufacturer and reliable for the user. The problem is they are often noisy when used on analog equipment.

So I had to integrate the issue of power supply in my Guitar Poppa project : My products had to operate as silently as possible with any negative grounded DC power supply, and providing 7 to 12V in charge. As I moreover use both silicon NPN and germanium PNP transistors, the question of polarity was added to the problem.

From these objectives came a specific supply circuit that is in all my effects pedals. It uses an active noise filtering and decoupling cells.

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Stompboxes : True Bypass

This article is devoted to one of the best known switching system : the True Bypass, which is generaly said to be the best, although it has some not so known limits … We shall see that the big question is that TrueBypass keeps a high impedance bypass routing, which makes this circuit not so efficient as usually said when many pedals are chained.

This introduces to a classical quarrel among guitarists : Pro and cons buffering…
Input buffering will be the subject of a second article.

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Input buffers

Buffers are devices that are interposed between a signal source and an active circuit. The most simple ones do not provide signal amplification but operate impedance matching. This prevents from signal losses, espacially concerning the level and the bandwith.
They are technically very useful but little known, and sometimes badly regarded by vintage electronics purists under the pretext that historical circuits do not have any of them — and that Japanese equipment is stuffed with.

Guitar Poppa could not stay indifferent to this electronico-aesthetic quarrel…

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