Those IC-based Muffs had a unique growl and bite that distinguished them from their transistorized cousins, and made them highly desirable among select fuzztone cognoscenti. Erik Miller of Euthymia Electronics satisfied his personal op-amp jones by creating the ICBM Fuzz ($165 retail), which retains a vintage vibe while upgrading the components and providing true-bypass switching.
The Volume, Tone, and Sustain controls mirror those of the Muff. However, the ICBM’s Tone is voiced to craft huge sounds (ranging from thunderous, yet focused, bass to agreeably bright highs), and its Sustain delivers that paranormal singing quality characteristic of the most magical elder Muffs. Other than a minor quibble over the lack of an AC adapter socket (offered as an option), suffice it to say that the ICBM blew away the three vintage Muffs I had available for comparison, and I ordered one on the spot.