Working With Voltage

Most guitar effects pedals run on a 9VDC power source, which allows for a wide choice of pedalboard power supplies, wall warts, or batteries to run them on. However, there always seems to be one or two pesky pedals in the collection that complicate the issue requiring some other voltage; say 12V, 15V or 18V. Although it may seem like these pedal designers are trying to make life difficult, the reason is usually that some components used in the device require the higher voltage. It’s possible to have a boost converter in the pedal itself that would raise 9V to the level required, but there may be reasons to leave this out; such as space, thermal, noise, and cost constraints.

So, it’s easily fixed, right? Just use a pedalboard power supply with all the necessary voltage outputs, or use one of the myriad cheap boost converters available. Well, maybe, but there are a few things to keep in mind.

There are several pedalboard power supplies with different voltage outputs. The MXR MC 403 is a 16-output supply that has 9V and 18V outputs as well as two adjustable outputs, and a 9V AC output. It’s a very flexible supply (I have three of them in the lab as bench test sources) but the large size, weight and cost (almost $300) limits the demand for most people using smaller boards. I believe it now has to be special ordered, or you’ll have to search around for old stock or used items.

The Strymon Zuma is a 9-output supply with two outputs switchable between 9V, 12V, and 18V. It’s also a great unit, but again is quite large and heavy, is around $250, and requires a 24V wall wart to power it.

So, purpose built power supplies can be an option but may be large and costly. What if you are trying to build something small and low cost? There are plenty of boost converters available online at quite low cost. Pay a few $, plug 9V in, get 18V out, problem solved. Hmm, let’s take a quick look.

Xotic Effects make a nice and popular device called the Voltage Doubler. It sounds straightforward enough, but check the documentation and it clearly indicates that it’s designed for use with some specific Xotic pedals and the current limit is 80mA. Try to power a higher current digital device and it is not going to be able to deliver enough power. Also keep in mind that voltage boosting is not free, and some power from the input source is used by the booster itself. Depending on the design and the voltage difference, this can be quite significant. A charge pump like the Voltage Doubler can be drawing over 250mA at the 9V input to provide 80mA at the 18V output, so make sure your power supply can provide enough current to power the pedal AND the voltage booster.

There are a substantial number of off-the-shelf switching converters available from internet sellers. Many of these are quite low cost and support a range of different features such as variable output voltages and digital voltage displays. While more efficient than charge pumps, even a good switching converter will still use power itself.

As an example, I used a generic adjustable switching converter PCB from Amazon and measured the current at a 9V input connected to an Eventide H9 at 12V at the output. Steady state current draw was around 450mA, but it momentarily passed 800mA inrush current at start-up. I was able to power the H9 at 12V from a 9V pedalboard power supply but I had to use a parallel (daisy-chain) cable and a total of four 9V outputs from my power supply totaling 900mA to provide enough headroom for the H9 to start up.

Switching supplies that are not designed for audio use can often be quite noisy, so you would need to check this with your specific rig to make sure noise levels are acceptable. They can also get quite hot. In my test the surface of the converter chip was approaching 50 degrees C in free air just boosting to 12V at 450mA. Higher voltages, and an enclosed unit would get hotter and would likely require a heat sink.

On that subject, if you are using just a PCB, then you would need to install it in a suitable enclosure for pedalboard use and make sure that it was installed safely to avoid any short circuits. Which, in turn, leads to the subject of safety and what protections are designed into the booster. Most pedalboard power supplies from respectable manufacturers will have extensive safety features to reduce the likelihood of damage to the pedals or supply itself in events such as short circuit, over current, over voltage and over temperature. You would want to ask yourself, does the Ali-Baba generic booster PCB have these protections? What happens if something goes wrong and it fries your $700 pedal? I connected my H9 up to one of these for the purposes of testing for this article, but I disconnected it immediately after, and I have no plans on using it for this again. I like my H9 and would prefer to keep it working.

0

Leave a Reply

Your email address will not be published. Required fields are marked *

Cart

loader