ACA pedals produced prior to 1997 require 12 volts DC on the adapter input. The 12 volts are then reduced to about 9 volts inside the pedal, via a resistor and a silicon diode on the negative side of the power supply input.

ACA pedals produced after 1997 require 9 volts DC on the adapter input, and are therefore fully compatible with the PSA supply.

To make your old-style ACA pedal work with a power supply, you can either:

  • run it off a separate 12 volt supply (don’t go out and buy the current Boss ACA adapter, though, as it too was changed to 9 volts in 1997)
  • modify the pedal internally, to defeat the resistor/diode network. This is done either by routing the adapter jack negative wire straight to ground, or (as Boss did it) by taking out the two components and replacing them with jumpers.
  • power the pedal from a daisy-chain style (common ground) power supply, together with at least one PSA or post-1997 ACA pedal. Once you connect the signal cables between them, the old-style ACA pedal will receive full power from the 9 volt source.
ACA pedal with PSA adaptor

To test if your ACA pedal is pre or post 1997, simply power it alone from a PSA or similar supply. If the LED lights up at least as much as with a battery, it is either a post-1997 pedal, or has been modified to those specs. Use it as you would any other pedal.

If it barely lights up at all on adapter power, the pedal is pre 1997. Refer to the above list.