THE GREATEST 9V PEDAL POWER SUPPLY EVER? October 30, 2013

mi-audio-power-supply

There’s always tinkering happening at the MI workshop and this is a fine example of the R&D that happens here.

Before our NAMM trip earlier this year, we were putting together our pedal boards and struggled to find an ultra-low noise, super compact  COMPLETELY ISOLATED*** universal 9V power supply. There are some good options out there, but power supplies need not be the size of a lunch box with the right design.

We’ve been throwing around the idea of making a power supply for some time after making a few for the workshop. But it wasn’t until recently that we successfully built a working prototype, shown in all of its naked glory above. With some hand-wound transformers and a very efficient switching transistor, we have come up with a 9V power supply with as many output taps as required, at any current required, and each individual tap is isolated from each other – all able to fit into a standard Crunch Box size pedal.

***ISOLATED GROUND!!! This term gets spouted in the marketing with every power supply on the market and is incorrectly used by a lot. Let’s try and clear this up.***

The aim of your amp/guitar/pedal set-up is to have a single ground path between any two ‘points’ in your signal chain. If you’re using a power supply with a common ground between all the outputs, then you can have multiple paths between any two points. An isolated power supply does this by keeping every the ground of every output tap completely electrically isolated, and relies on the ground connection between your devices to maintain the same reference. This prevents your guitar signal ground from connecting to multiple pedals at the power supply. If there is no isolation, ground loops can occur and that’s when you get that nasty hum and buzzing destroying that tone you’ve worked so hard to get. There’s nothing worse than playing a gig with a noisy, “dirty” setup. This is more common in “daisy-chain setups” and non-isolated power supplies.

Most offenders of the misuse of the term “isolated ground” will say that the ground of the input is isolated from the ground of the OUTPUTS AS A WHOLE. However, the grounds of these multiple outputs are actually all connected together – you might as well use a daisy-chain/wall-wart set-up as the ideal power supply should have isolated grounds for EACH OF THE OUTPUTS.

The amount of current available at this stage is dependant on the current supplied at the input. For our proto, 2A is supplied across all THE SUM of all eight output taps. That means, if you have five drive pedals taking 10mA each, the remaining three output taps have 1.95A available. This allows a whole pedal board (of eight pedals) to be powered comfortably. This 2A can be increased to 20A if we wanted, but 2A is normally sufficient for most board uses.

We hooked up our prototype power supply with our drive pedals, including the PNP germanium Neo Fuzz with great, super-quiet success. No need for reverse polarity leads – the pedal power supply takes care of that for you.

Now, who wants one???