Keeley Super Phat Mod

Op-amp + discrete transistor overdrive

It does NOT use diode clipping in the feedback loop of the op-amp like a Tubescreamer / Blues Breaker / Klon. It uses a JFET input stage > Op-amp gain stage > Two transistor stages that are pushed into soft, amp-like clipping > Active 2-band tone shaping > output buffer.

It's designed to sound like a cranked small Fender/Supro amp on the edge, not a pedal.

Keeley Super Phat Mod (BD-2)
— Compression & Sag: Very low. Open and dynamic. Cleans up like a real amp. Touch sensitive.
— Feel: Loose, spongey, tweedy.
— Character: Transparent low-gain to medium-gain amp-like grit. Fattened Fender