Let's talk about pedals and power supplies for a moment. This is going to be a long rambling brain dump so get comfortable and bear with me ;)

Almost all the pedals that we make have special circuits inside that take the voltage that you put into the pedal and boost it to either 30V or they convert it to a bipolar power supply of ±15V (the equivalent of a 30V input). The catch is that the charge pumps or boost converters that are used to do this have a maximum input voltage that they can take before they release the magic blue smoke. These circuits, especially the boost converters, suck up a lot of current at 9V to generate the voltages that the circuits require.

On those pedals we use an overvoltage protection circuit to limit the maximum voltage that is allowed into the pedal to keep the magic blue smoke inside the chips where they belong.  We also have use a reverse polarity protection circuit to help prevent damage if a power supply that is center positive is accidentally used (99% of guitar pedals use center negative power). Anecdotally, I have had once instance in the field where someone accidentally plugged a 9V AC supply into a pedal. The reverse polarity circuit DID kick in and save the pedal, but i don't guarantee that it will save it every time!

All of our pedals also use soft-touch momentary switches that don't make any clicking sound. These switches trigger a relay inside the pedal to switch from true bypass to the effect. Unfortunately, these relays are current hungry as well and can take as much as 40mA to energize the coil.

That being said, lets talk about power supplies. The majority of our pedals like the PMEQ and all of the preamp pedals require a regulated 9VDC supply with a minimum of 100mA of current. Using a supply that has more current available won't harm anything as the pedal will only take what it needs but using more than 9V risks damaging it. Other pedals like the EQFH and EQFH Pro need a bit more current (200mA minimum) while the EQ4H pro needs a minimum of 250mA and the Thespian needs a minimum of 500mA.

Are all 9V/100mA power supplies equal? Unfortunately they are not.

DC power supplies can be dumped into two different categories:  regulated and unregulated.  What’s the difference?

The classic examples of this are the old Boss ACA adapters vs the Boss PSA adapters. The ACA is an unregulated power supply while the PSA is a regulated supply. An unregulated power supply might say that it can output 9V/100mA but this is when there is no load connected to the supply output. When you do connect a load (in this case a guitar pedal) to the power supply, the output voltage will often drop. How much it drops depends on a number of factors, but the main take-away is that the output voltage is unreliable and if it sags enough it might be too low for the pedal to power on properly. Sometimes the manufacturer will advertise the pedal as 9V, but the unloaded voltage output is actually higher, like 12V, so that when a load is connected the voltage will drop to 9V.  The problem now is that the overvoltage protection kicks in and disconnects the voltage input from the rest of the pedal before it drops from 12V down to 9V.

A regulated power supply will output a constant voltage regardless of the load.

How can you tell the difference? The bad news is that there is nothing on the power supply label that will indicate that it is regulated vs unregulated. The only way to really tell is in the marketing description and price. Usually when a pedal is regulated the company will say so as it's deemed a selling feature. If they say "Boss PSA compatible" then it's probably regulated. The other way to tell is by price. Regulated supplies are usually more expensive than unregulated ones. Also, generic no-name brand supplies that you can find on amazon, ali express, temu, and other online marketplaces are usually unregulated (and also have very little, if any, filtering in them so they will hum and buzz quite a bit).

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While we’re on the subject of power supply labels, there are a few things to look at on the label that will help you understand what the power supply does and doesn’t do.

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If you look at the picture there’s a bunch of important information in there along with all of the regulatory symbols.  These are the important things and how to interpret them:

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In the top right underneath the P4522 text there’s a symbol that tells you the polarity of the power supply. There are two concentric circles.  The + symbol points to the outer circle and the – points to the inner circle. This shows that it is a center negative supply.  The symbol is a universal standard so it’s easy to tell if the power supply is suitable for guitar pedals.

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The input specification is listed underneath the Dunlop logo.  100-240V~50/60Hz 0.4A.  what does this mean?   There are 4 bits of information here.  This supply can be used in any country where 1) the mains power is between 100V and 240V, 2) it can be used in any country where AC power is either 50Hz or 60Hz, 3) the ~ symbol denotes that it takes AC voltage , and 4) that it will consume 0.4A (400mA) of current when plugged in.   For 99% of us this just means that the pedal will work in whatever country you are in.

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The output specification is the most relevant part for us.   There are 3 key pieces of information here. First, 18.0V. Next, the solid line over the --- line and finally, 0.5A.  What does this mean?  The output of this pedal is 18V.  The solid line over the dashed line means DC. The 0.5A (500mA) means the maximum output current is 500mA.  While the 500mA rating is suitable for any of our pedals, the 18V output is not and may damage them.   This label would need to be 9.0V --- 0.5A in order to be safe to use with our pedals. 

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On a side note, if the output specification was 9.0V~0.5A DO NOT USE IT.  The subtle difference is the ~ instead of the solid and dashed lines would indicate that this is a 9.0V AC output, not DC, and is not suitable for guitar pedals.  Some Line6 pedals like the DL4 DO require an AC power supply, so keep an eye out.

Isolated power supplies vs daisy chained.

Some people use the terms "isolated power supply" interchangeably with "regulated power supply". This is not the case. While most quality power supplies from Cioks, Voodoo Labs, and others are both, one doesn't imply the other. If you are daisychaining several pedals together using a single regulated power supply, you don't have an isolated power supply set up. What does this mean? An isolated supply means that each output tap is electrically isolated from the other and is independent. This means that the current draw from one output doesn't affect the other. For example, if you have a voodoo labs supply with five 9V/100mA outputs driving 5 pedals that each need 100mA, you are good. However If you are daisy chaining these pedals together and your wall wart can only output a maximum of 400mA and those 5 pedals collectively need 500mA you're going to run into a situation where something isn't going to work at all, or behave unpredictably. Regarding the electrical isolation,  if you have a pedal in your signal chain that has issues – maybe there’s a bad ground in it or it’s old and it’s developed some problems that make it buzz or hum, if you are not using an isolated power supply that noise can work its way into the electrical ground propagate noise into other pedals that are in your signal chain.

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I hope this helps clear up a bit of confusion pertaining to power supplies and what the cryptic messaging is that is written on the wall warts. If you have any questions (or if I’ve made things worse) please drop me a DM or a comment below.

 

Cheers!