The power supply technologies for effect pedals

In this article, we will explore pedal power supply technologies in more detail. To understand their differences, how they work, and the advantages and disadvantages of each of them. And if you want to know which power supply is the most adapted to your board, we also made this other article to guide you!

the 9v battery

The battery was the first solution to power pedals that need a small current draw. We find them in a lot of pedals. And except its quick discharge, it has all the advantages of a good power supply. With batteries, we’ve got a nice isolated power supply for each pedal, no ground loop that could pick up external interferences, a perfectly continuous voltage, no 50/60 cycle coming from the mains that could radiate close to the pedals… The perfect solution in noise terms!

Some manufacturers like Danelectro even had fun making battery-powered power supply units. It seems not useful at first, but it allows you to have a board that doesn’t move. Avoiding to snatch and open the pedals to change the batteries, or unplug the cables to save batteries when you’re not playing. While avoiding the noise problems of power supplies connected to the mains!

power supply in the pedal

To avoid the use of batteries, some manufacturers have chosen to power their pedals directly from the wall plug. At that age, effect pedals were much more voluminous. And we didn’t see many huge pedalboards with dozens of pedals either. As a result, the pedals of this era also integrated all the power electronics. All you had was a cable coming out of the pedal, to be connected directly to the mains socket.

The problem with powering the pedal from the mains is that it requires additional electronics. We have to convert the high AC voltage from the mains into a lower DC voltage to power the pedal. But this avoids having a discharged battery, and creates other voltages than the usual 9V, to bring more headroom and keep a better dynamic along the chain of effects.

Finally, with the miniaturisation of the components, the power supply circuit was taken out of the pedal, including all the electronics directly in the plug housing. That’s how we have power supplies like the 1 Spot today. And at least, if the power section is broken you only need to replace it by a 1 Spot which is way less expensive than having to replace the whole pedal.

from the mains plug to the effect pedal

Let’s get into the theory. We are going to see step by step how to go from the mains 230V AC (or 110V AC) to a few volts DC to create a simple power supply.

the transformer

This is the first step! It will lower the voltage coming from the mains. The mains is an alternating voltage, i.e. it varies and reverses periodically over time, oscillating 50/60 times per second (the famous 50/60 cycle).

The transformer is an iron ring, around which the input and output are coiled up. The voltage that goes into the first coil, which is connected directly to the mains, will create a magnetic field that circulates through the iron ring. On the other side, the opposite effect will occur: the magnetic field passing through the second coil will generate a voltage at its terminals.

The magnetic field only occurs when the voltage changes, so a transformer only works with alternating voltage. If both coils are identical, then the output voltage will be exactly the same. But by adjusting the number of turns of the coils, you can lower the voltage!

the rectifier

We’ve lowered the voltage, now we’ll have to make it continuous! We do this in several stages, and the first one is rectification. By using diodes that only let the signal flow in one direction, we obtain a voltage that will be always positive, by rectifying the negative portions of the signal.

filtering

Then we apply filtering, to approach a DC signal as close as possible. We can use a simple capacitor, which will store and restore charges, or much more complex and efficient filtering.

the voltage regulator

Finally, a regulator is used to obtain a perfectly smooth voltage. It is a component that will lower and maintain a constant output voltage, evacuating the excess in heat. Nevermind the current draw the device asks to the system!

We finally have a perfectly continuous voltage! In the end, we have converted the mains voltage in 4 steps to be able to power a pedal.

multiple power supply units

We have seen how to create a power supply to power a pedal. But if you want to power several of them, you can choose between several technologies.

the daisy chain

The simplest solution is to connect all the pedals in parallel to the power supply output. This works very well for 3 or 4 analog pedals, but you will quickly get noise problems if you use more of them, or if you have digital pedals.

With a daisy chain, there is no isolation between the pedals. Digital pedals can generate slight perturbations on their power supply. And these perturbations will be transmitted to the other pedals connected to the same daisy chain.

In addition, there are loops on the ground and the 9V between each pedal. Each loop acts as an antenna, so electrical devices near to the pedals can generate perturbations that will be picked up and transformed into noise.

Finally, as the voltage regulator cannot supply very high currents either, the number of pedals can be quickly limited.

the fx power source: the pseudo-isolated power supply

The FX Power Source works on the same principle, but with filter stages and a voltage regulator for each output stage.

Having a regulator on each output will isolate them from each other on the 9V. This avoids the noise problems associated with a digital pedal that generates perturbations. In addition, the AC/DC conversion is done in an external housing. This avoids having the audible 50/60 cycle of the mains, responsible of the ” hum ” noise, passing close to the pedals.

We also remove the loops on the 9V, but we still have a ground loop between the pedals. And we still have limited currents on each output because of the regulator, even if it is sufficient for the majority of the pedals. With up to 200mA by output, this power supply can supply properly up to 90% of the pedals from the market.

the cioks: galvanic isolation

The solution to completely isolate each output and avoid ground loops: put a transformer on each output! This is what Cioks does on most of their power supply units.

But as mentioned, a transformer needs an alternating voltage to work. So we’re going to have 50/60cycle running through the power supply, which can interfere with the outputs by electromagnetic radiation. And there is still a current limitation on the outputs.

This solution is necessary if you have positive ground pedals which cannot work with the common ground.

the K+: the switched-mode power supply

We come to the last solution, and the one we decided to integrate into the K+, the switched power supply! Instead of the regulator, we are going to use a switching technology, which will cut and leave the signal pass at a very high frequency (several dozen of kHz so that it is not audible). This will create a high frequency square wave signal.

Then, by controlling the ratio between the time the signal passes and the time it doesn’t, we can vary the output voltage. Which will be filtered again to convert it again to constant voltage.

The advantage of this technology is that it allows to lower and keep stable the voltage simply by controlling the switching. No heat dissipation like the regulator, and that’s how we can offer up to 1A at the output!

As with the FX Power Source, the whole 50/60 cycle section of the mains supply is converted in an external housing to prevent interference. There is therefore no interference inside the K+ unit. The outputs are also isolated on the 9V thanks to the switching chips. But a common ground is conserved which doesn’t create a lot of noise even in very complexe systems. A very intense attention has been paid to the filtering of any 50/60 cycle and its harmonics to avoid any noise inside your devices.

conclusion

We have seen the different technologies, and the advantages/disadvantages they have.
None of them are perfect, but they each have their own utility according to the kind of board you want to build.

If you need a power supply adapted to your board, you can have a look at our article about choosing your power supply.
To make sure you choose the model and technology that suits your needs!