Gretsch Expandafuzz

Rare use of the µA748 op amp. The 25pF caps on each op amp are external compensation caps. These limit the working bandwidth of the amps so they don't squeal away with ultrasonic oscillations. The odd pin numbering is due to giant 14 pin packages (6 pins are NC). Note the +/-9V supply provided by dual 9V batteries, each is switched by a jack.

Excellent gut shots found here: http://tonemachines.blogspot.com/2012/06/gretsch-expandafuzz-1973.html

Components are all 1973, latest date seen is on one of the pots for 47th week (late '73).

The bottom portion (U5/U6) is the Controfuzz.

The Controfuzz portion appears to be a fairly standard op amp distortion, until you consider the non-inverting input of U6. Hey, that's our same input signal that U5 is getting! U6 is configured as a difference amplifier, amplifying the difference between the inverting and non-inverting inputs. Interesting variation, couldn't tell you yet how it sounds. Let's let Mark Hammer describe it:

"Well, the Controfuzz is a quirky, but interesting, beast. While it provides sizzling fuzz, and a fuzz/dry blend, it does so in a manner that creates the illusion of a sustained note getting fuzzier towards the end. Too often overlooked, well worth building, and a fairly simple circuit on its own."

http://www.diystompboxes.com/smfforum/index.php?topic=63718.0