Isolated Power Supplies: What’s the Point?

Why are isolated pedalboard power supplies used?
The lowest cost genuinely isolated pedalboard power supplies start at around $100, and can reach in excess of $300. Simple daisy chain style adapters are available for less than $5, yet these larger isolated supplies remain hugely popular. What possible reasons could there be to pay forty times the price for something larger, heavier, and more difficult to install? Are isolated power supplies just a marketing trick to relieve gullible guitar players of their cash, and redistribute it to greedy electronics companies?

This is one of my most often re-watched YouTube videos. It’s a full Buckethead solo set from the Ardmore Music Hall in Philadelphia in 2016.

You can see from the video he is using just cheap wall power supplies with cables running everywhere. He still sounds awesome, and if it’s good enough for Buckethead, then it ought to be good enough for me. Case closed, right?

Well, as with many things in engineering, it depends. If we look a little closer at that video, we can see a mixture of analog and digital pedals. It looks like most of the analog pedals don’t have power cables, so we can assume these are running on batteries, and that the digital pedals each have their own individual wall wart. So, it turns out that these are isolated by default, as they each have their own power supply.

Batteries need replacing which is costly and environmentally unfriendly over time. Multiple wall outlets are required, and there are multiple points of failure. Also, using different wall sockets can sometimes cause hum from ground loops. It also doesn’t look super pretty, if you care about that sort of thing. Dealing with those issues is why many people opt to use a pedalboard power supply.

So why not use a single wall power supply and just daisy chain them together? You can certainly do that, and in many cases it works fine, but there are some problems. When you daisy chain devices together, the DC + and – lines are common. If a fault such as a short circuit develops on one of the devices, it can short everything in the chain, potentially damaging multiple pedals at once. In many cases, particularly when using digital pedals, noise can be injected in to the audio at a level that makes the system unusable. This is one of the reasons why digital pedal manufacturers often specify that isolated power supplies should be used, and daisy chain power supply providers sometimes include a disclaimer about using them with digital pedals. So why is this, and how does isolated power fix it?

Digital devices include microelectronic packages that are switching on and off at high speed; thousands or millions of times per second. This switching generates radiated and conducted emissions that can pass through the circuit or the air, and in turn can be picked up as noise in the audio. The level and frequency of the emissions will depend on the specific device. In digital effects pedals, this noise will be identified during the design and testing of the device, and the engineers will filter it out of the audio path so that it does not get passed through the patch cables to the next pedal. However, this is not always the case on the power side. The unfiltered noise can be picked up in the power circuit and pass out along the power cable. With a daisy chain, or non-isolated power supply, the noise can then pass along the common return and into an adjacent pedal. Since the adjacent pedal has no way of knowing what it will be connected to or what noise might be passed to it, it has no mechanism to filter it out. It can then pass the noise in to the audio. If the second pedal is a gain pedal, it may even boost the noise.

Isolated power supplies resolve these issues by ensuring that there is no physical connection between each power channel for any noise to pass between pedals. It’s like running each pedal from its own power supply, as in our Buckethead example, but with the convenience of a single power input, easier cable management, neater appearance etc.

So why are isolated power supplies so much more expensive? As we discussed above, an isolated supply is much like having individual supplies on each output. A ten-output supply with all outputs isolated is essentially ten separate little power supplies in one unit. Of course, there are still some components that can be shared, but the component count, and hence cost, is much higher. To provide the physical isolation, an isolation transformer is normally used. There needs to be one for each output, and these are expensive components; again increasing the cost of an isolated supply. Isolated supplies often come from better known brands, and the manufacturers will usually add other features such as high current outputs, regulated outputs, and short circuit protection. You can be sure that these designers specified reliable, low noise components, and did proper regulatory and safety testing. These all cost money and make an isolated power supply more expensive to buy initially, but as well as avoiding digital noise and protecting against damage, your isolated power supply from a respected brand is more likely to be reliable and last a long time.

One thing worth bearing in mind when considering an isolated power supply, there are a numerous off-brand power supplies from sources such as Amazon and eBay that are described as isolated but are not. Be careful with these. If it’s a very low cost power supply, it may not be fully isolated. These can still be useful as cheap power distribution for your pedalboard, but they won’t protect against the digital noise issue.

For further information, here is a video here where I connect some different pedal boards to daisy chain supplies and you can hear the noise and how the use of an isolated supply fixes it. Stay isolated, my friends.

You can also check out Mission power supplies by clicking here.

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