Powertrain1250, Pedal Power in a Class all its Own...

OR... what makes this pedalboard power supply sound so good?

My last article "Batteries, Wall Warts and the Future of Pedal Power Supplies" gets pretty deep into the technical nitty-gritty of pedal power. This time I want to focus on a more thorough product review of the powertrain1250 (PT1250). Also, I want to discuss what makes this power supply sound so good, as well as what features make the PT1250 stand out from the crowd.

The powertrain1250 has eight DC power outlets divided into five separately isolated zones. If you have more than 8 pedals you can daisy-chain several pedals on each outlet. You just need to make sure the combination of pedals daisy-chained together draw as much as or less current than the outlet can handle. For example, if the outlet is marked 210mA, and each of your pedals draw 50mA of current, then you can daisy-chain four pedals on that outlet (4 pedals x 50mA per pedal = 200mA... AOK).

The three "LDV" zones are what makes the powertrain1250 special. Not because they are 9V and can handle 210mA each. Not, because they are each independently isolated from all the other zones, but because of the trim pot next to each outlet. This is not your typical adjustable outlet, in fact the trim pot doesn't adjust the voltage, rather it adjusts the reaction time of the outlet. It is called "Load dependent voltage" or "LDV" for short. What does that even mean? Well, it goes back to a lot of hoopla about certain batteries making pedals sound better than other batteries.

Let me explain. When I first heard claims that different batteries make the pedals sound different, my gut reaction was to think "this is a load of snake oil". Then our friend Tommy Hatcher brought over a box of batteries and his vintage Fuzz-Face pedals and we started listening. The brand of battery really did seem to make a difference. I thought probably the batteries are not all exactly 9V and that we were hearing a difference in the headroom of the pedal.

So I set up a bench power supply with an adjustable voltage output. We adjusted the power from 9.6V down to 4.5V, but the pedals sounded exactly the same all the way down. Then what was making the pedals sound differently, if not the voltage?

To see what was going on, I hooked up an oscilloscope to monitor the batteries and began switching out different batteries. What I saw on the scope was totally unexpected. The battery's voltage was dipping and diving ever so slightly with each note that was being played. The batteries that sounded the best were the ones doing the most exaggerated dipping and diving. What I learned was this, as notes were passing through the pedal the pedal was drawing more or less current from the battery; and, as the current fluctuated, so did the voltage on the battery. Check out this graph (NOTE: for this picture, I set up the scope to give exaggerated readings in order to highlight what was happening on a much more subtle scale) you can see how the battery voltage dips when the signal through the pedal peaks and the battery voltage recovers when the signal dips. The effect of this is to give the pedal sound a softer edge.

Batteries do this because they generate voltage by means of chemical reactions, and those chemical reactions don't happen instantly, they have a bit of a time lag. So when the pedal demands more current, the voltage dips for a fraction of a second, then recovers. However, regular power supplies don't do this. They deliver current instantly and don't dip. Some power supplies have a way to adjust the voltage. Voodoo labs calls it a SAG control, but all it does is lower the voltage, which does cut headroom and that can change the sound of some pedals, but it's not the same as how a battery reacts. We found that even when a battery starts to get weak, it can still put out 9V if there is not much demand for current, but the weaker the battery gets, the more it starts to dip and dive with a demanding signal.

So for the powertrain1250, we designed a way to adjust the reaction time of the outlet, rather than adjust the voltage. Using the LDV control you can go from a stiff power supply with no dipping and diving, to what can be consider a nearly dead battery that dips and dives like crazy. No other pedal power supply has this, we invented it!

It needs to be said that results will depend on the pedal in use. Some pedals don't really care what you use for power, and other pedals don't sound good at all if the power dips too low. The pedals that seem to sound best when you play with the LDV setting are discrete analog pedals. I suggest that you experiment with playing through your pedal while slowly adjusting the LDV up and down, when you find a sweet spot, then leave it set there. Unlike a battery, once you set the LDV trim pot on the PT1250, it will stay that way, whereas a battery eventually is going to get weaker and drift away from the sweet spot.

I feel that the rest of this review is going to be anti-climatic after discussing the LDV. So what is left to say? A word about isolation. Each isolated zone is electrically separated from the other zones. This can help a lot with noise problems. For example, some digital pedals can pollute a power supply with clocking or sampling noises, and an analog pedal on the same power, especially one that has a high gain setting, will pick up that noise and amplify it. Keeping digital pedals on their own separately isolated zone solves this issue.

Another thing about isolation is that each zone acts like a separate battery, you can daisy-chain two 9V zones in series to make 18V, just like you can with two batteries. You can also, hook up two zones in parallel to get more current. For example, connecting two 9V 210mA zones in parallel will give you a single 9V 420mA zone.

The right-most zone is made up of four outlets that share 500mA of 9V power. This is where you want to connect any high power pedals. Since these four outlets share 500mA, you need to make sure the combination of all pedals daisy-chained on these adds up to 500mA or less. However, although the outlets are marked 500mA, this is a conservative number. In fact, this is the minimum guaranteed output under the worst possible conditions, minus 20%. In other words, if you were playing in the desert sun with 130V AC coming from the power company, it could still really handle 600mA; and in more realistic conditions, 700mA would be more like the actua