Prism FET Amplifier - Boss FA-1

Prism (125B) - BOSS® FA-1 FET Amplifier Guitar Pedal PCB



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Project overview

The Prism FET Amplifier is a pedal conversion of the obscure but highly sought-after BOSS® FA-1 FET Amplifier. The original, which was manufactured from 1980 to 1984, was an always-on effect that clipped to your belt and ran on a 9-volt battery.

It’s a solid circuit, but the non-standard implementation prevented it from getting much attention—although it was famously used by The Edge which caused vintage prices to skyrocket.

The Prism is the same circuit in an alternate format, converting it to a standard pedal with a footswitch, LED and 9V adapter jack.

The original FA-1 used the long-obsolete HA1457W chip, which is a single version of the LM1458 (as evidenced by the similarity of “1457” and “1458”, and similar datasheet specifications). For the updated version of the Prism, extensive A/B testing was done to verify that the LM1458 performs exactly the same as two HA1457Ws and is sonically indistinguishable.

As a result, this new version eliminates the option to use the HA1457W and only supports dual op-amps. However, the previous version of the Prism is still available if you really do want to use the HA1457W.