BOSS ACA to PSA power supply mod

The older BOSS pedals may not work correctly with a modern AC power adapter (like a 1-Spot or Boss PSA). These older pedals required the Boss ACA adapter and they have a sticker on the housing right next to the power supply jack. The ACA supplied a higher voltage than the PSA. The ACA voltage is unregulated and the PSA supplies a regulated voltage. The ACA-style pedals have a series resistor (and diode) that drops some voltage from the power supply. The pedal might not get enough voltage if you use a PSA power supply on a ACA pedal.

In my case I had a CE-3 chorus that worked fine with a battery. But when I used a PSA supply the LED wouldn't light up when I engaged the pedal. I also had a HM-2 that sounded really terrible and ratty with the PSA supply.

There are two workarounds:

1. Daisy-chain the power supply (in parallel) to some non-ACA pedals. These will drop the supply voltage.

2. Modify the ACA pedals to accept the PSA supply.

The mod is simple: jumper the series resistor. The newer Boss pedals do not have this series resistor. This mod has no effect if you are using the battery - the resistor is cut out of the circuit if nothing is plugged in to the power supply jack. The jumper can be placed at the numbered wire connections at the end of the board near the control knobs.

Here is the ACA sticker on a DS-1 Distortion pedal.



For all the pedals in my stash, the mod is to jumper the blue wire that goes to the power supply to the yellow wire that goes to the input jack. On the CE-3, that's holes 2 and 3.



Here's the jumper for holes 2 and 3 on the CE-3 chorus. I just used part of component lead for the jumper wire.



For the HM-2 Heavy Metal the holes are 4 and 5.



Ah, the DS-1 has two sets of blue and yellow wires! Joy! But by looking at the connections to the power supply jack and input jack you can see that holes 10 and 11 should be jumpered.



Here's the jumper between holes 10 and 11 on the DS-1.



The pedals can now be used with a single modern AC adapter power supply. They also sill work fine when daisy-chained to other pedals. And they still work fine when power by an internal battery. Joy!

This article by stinkfoot provided some very useful background information on the ACA/PSA issue.