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Prism (Legacy)

Based On
BOSS® FA-1 FET Amplifier
Effect Type
Boost / Preamplifier
Build Difficulty
Project Summary
An extremely loud and tonally-flexible boost/preamp with a two-band EQ, most notably used by The Edge of U2.

Legacy PCB

Designed for the 1590B enclosure with side-mounted jacks, which some builders prefer. Bypass PCB (optional) sold separately.


In stock

Updated Version

The same circuit, but updated for the 125B enclosure format for a more streamlined build. The bypass switch PCB is integrated.


In stock

Project overview

These things have recently gotten a lot of attention since someone found out that The Edge from U2 uses one as part of his sound. Originals routinely sell for over $500 on eBay.

The Boss FA-1 FET Amplifier was released in the early 80’s and discontinued in 1985. The original was not a traditional pedal, but instead an always-on effect with a clip on the back, with the idea that you actually wore it and your guitar plugged straight into it before going to the rest of your chain.

My version adds a footswitch and LED to turn it into an actual effect that’s more at home on the floor than clipped to your belt. Otherwise, it is completely faithful to the original circuit. If you’d like to experiment, it also has additional pads allowing you to use a DIP8 dual opamp instead of two stock SIL HA1457Ws as in the original. (I recommend the LM1458 as a great alternative to two HA1457s. I couldn’t hear the difference in an A/B test.)

If you want to read more about this pedal, Music Gear Reviews has a fantastic article.


Project Documents