Power supply with old Boss pedals

Boss ACA adapter The older Compact series Boss pedals, say from before 1997, are designed for the ACA adapters. In Europe these are the ACA-220 adapters, in the US the ACA-120. These old ACA adapters supply 9 volts DC (direct voltage) according to the label. However, that is an unregulated voltage of 9 volts.

What does unregulated mean?

Unregulated adapters give a higher voltage at low currents. That is, even though there is 9VDC on these ACA adapters, you measure about 12 volts at a very small current (such as the Boss CE-2 with 8 mA). To compensate for this, the old Boss pedals are equipped with a zener diode and a resistor: 12 volts are converted into 9 volts. Today, the PSA adapters are on the market. These are regulated adapters: the output voltage is always 9V regardless of the amperage. The newer pedals have the sticker "Use Boss PSA Adapter only"; the diode and the resistor are no longer present in the circuits of these pedals.

How do I power my Boss pedals?

Simple: If there is PSA on the sticker, then simply use a Boss PSA-230 / PSA-220 or a "standard" 9V adapter (polarity: outside plus pole, inside minus pole). It's a different story for the ACA pedals. The aforementioned zener diode and resistor work fine at 12V unregulated, but 9V regulated input does not provide enough voltage to go through the zener diode. You will see that the red LED is not or hardly lit. Number of solutions. Either you power your "old ACA pedals" via 12 volts, or you put a 9V battery in it, or you modify your pedal to bridge the zener diode and the resistance by internally moving a wire (contact us if necessary. do this for you), or you power the pedal through a daisy chain!

How does a daisy chain help me?

A daisy chain is a cable with which you can loop different pedals together and thus power multiple pedals from 1 power point (such as a normal 9v adapter or power plant). This divides the ground between several pedals; the zener diode and resistance is bypassed. You will notice that your LED simply lights up. No need to solder!