Pedal boards transformers and power units 3


This blog Nr 3 will give some simple advice on transformer and power units. These are the boxes or plugs that take down the 230VAC power so it can be distributed to the pedals or any other electrical appliance at the correct running voltage and ampere, well near enough ! Below I will show you my power rig is simple and best to keep it that way, remember that every added pedal unit is a possible added noise source. I will just go through the spec so that we can match this up to the pedals in the next blog post. In general be very aware of cheap units, they are cheap because the materials are not top rate and the circuitry not the best. Look for power banks with isolated channels and a variation in output. For transformer check that these have circuit protection and low noise technology built-in.

Power units


This is my Voodoo labs pedal power ISO 5. The ratings are: 60/50 Hz, with 3X9VAC-100mA outputs, a dual 9 & 12VAC-400mA output and one 18V-100mA output. All these channels are isolated, this is a must. So why is the (mA) milliampere important here …well the definition of one ampere is a measure of the rate of electron flow in an electrical conductor or circuit. One ampere of current represents one coulomb of electrical charge (6.24 x 1018 charge carriers) moving past a specific point in one second. In other words at any point in the circuit and during one second  6.24 quintillion electrons (6.24 x 1018 charge carriers) are moving, this causes the electrical current. As we measure in milliampere (a factor of 1000 less) this means that 100mA corresponds to 100 x 6.24 x 1015

So the higher the ampere rating, the more flow and the higher the current. by-the-way, voltage is the difference in charge or energy between two points in the circuit and the current is the rate at which the charge is flowing between those two points. So this obviously will affect things

If your pedal is rated for 400mA that means it needs that current to work properly but your power source only gives 100mA then it’s not getting the power to run properly and it will not.

The outputs


Here is the output

  1. 3x9VAC at 100mA for all pedals operating from a 9V battery or require less than 100mA.
  2. one 9V high current output for devices requiring 400mA but can power low current pedals.
  3. 12V high -current output for devices needing 12v and 400mA or less.
  4. 18V output but at 100mA. This will power pedals requiring 29V batteries or less then 100mA. Should not be used to power 9V pedals 


This is my Carl Martin(Big John) power supply with 7X9VAC outputs at 600mA so no variation in output here. Although this unit also has 7 individual isolated outputs the earthing is not good on individual channels which means it gives a good amount of noise in the pedal board and it is leaving my rig. I actually think they have stop making this model. The new one is the Pro Power version 2 offers a number of features. It is switchable (110-230 V) AC input, and split that into 8 individual isolated and regulated 9v (150mA) – 12v (150mA) outputs, with extended power at output 7-8 9v (350mA) 12v (300mA), you have a power supply you can use virtually anywhere US or EU. There is a simple DIP switch on the back of the ProPower version 2, which allows you to switch the voltage of each output between 9-12v. I do not have this but its worth checking out.

Below is a generic power bank you can get online from china and it’s very common that people setting up there first pedal board will buy one of these.

It looks similar to the Carl Martin (Big John) power bank with several channels but at 9VAC-100mA. The difference is that the channels or not isolated in any way and will contribut to an increase in noise in your pedal board system. There is a reason why Voodoo labs ISO 5 cost ~£120 and this generic on costs ~£20 ! The Carl Martin V2 power supply costs ~£110. It is worth investing a Voodoo or Carl Martin power banks !


Transformers are common and the quality varies widely in quality some are utter rubbish and please be wary of cheap chinese ones, good chinese units are fine though !!

The first photo below shows generic transformer I used on my BOSS RC30 this resulted in a mass of noise and general disturbance in the whole rig .

Then I changed it to this one which is from BOSS and specially made for there pedals.  It is fine to use one which is not BOSS but again check the power rateing on the pedal.


Note the difference between the generic and the specific BOSS transformer. The generic has an input at 100-240 V and 50-60HZ at 0.8A and delivers 9V-2000mA output. The BOSS one is also 100-240 V and 50-60HZ but at 250mA and delivers 9V-0.5A output, so very different outputs and the BOSS PSA-230 ES power supply has a built-in output current protection circuit which ensures you don’t damage your device. If the protection circuit triggers it will cut out, sparing your pedal. Keeping in mind that the BOSS gives 250mA output current which is close to my BOSS RC30 looper, or any other BOSS pedal, which needs a 195mA or lower current. If the current increase to 250mA the circuit is protected not the case for the cheaper transformer with 2000mA current.  Although both of these work, cheap adaptors do not have circuit protection and the BOSS has low noise technology built-in. 

So the choice is yours but if you consider these numbers at least you know what your dealing with and can design your power source specifically for the pedals you will be using and reduce noise and limit the build up of Electro Magnetic Fields (EMF) which you will hear through your amplifier. Many do not take this in to consideration when setting up there first pedal board.

Published by Filip Solberg

Bespoke built custom guitars in the East Neuk of fife Scotland. We build high quality guitars to exact details of the customer. Pick ups, woods and all hardware are specifically chosen based on tone and play-ability required. We do not have any stock guitars these are built for order only.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.