There are few guitar effects that have developed a cult of personality around them like the one that has arisen around the InterFax HP-1 Harmonic Percolator fuzz. Perhaps it's because there were so few of the original pedals made, and so few people have actually played one, that the legend has bulged beyond the boundaries of reality. Perhaps it's because the Percolator's most vocal and well known user—Steve Albini, iconoclastic recording engineer and guitarist for raucous rock progenitors Big Black, Rapeman, and Shellac—enjoys something of a cult of personality as well. Perhaps it's because the Percolator is such a unique design, and makes such an incredible, abrasive racket. I would confidently surmise that all of these factors play a roughly equal role in the rise of the curious cult of the Harmonic Percolator.
The origins of the HP-1 lie in early 1970s Milwaukee, Wisconsin, in a small electronics repair business established by a man named Ed Giese. The business was called InterFax Electronics, and specialized in the repair of amplifiers and keyboards. In addition to his repair skills, however, Mr. Geise was also a creator of electronic devices. He reportedly designed and built quite a few utilitarian audio tools, such as cable testers, but he also created a small line of instrument effect pedals, including an equalizer and the HP-1 Harmonic Percolator. These products were sold direct from the InterFax place of business, as well as through some local Milwaukee music shops. The Percolator, despite its almost comically boring beige box and spartan controls, sold well enough that Geise kept producing it in small batches for some time, and both it and its creator seem to have developed something of an eccentric reputation among local musicians.
The Harmonic Percolator is interesting not just because of how few were made or who uses it, but also because it's a genuinely unusual design with a very identifiable sound. In the world of guitar effect pedals, where nearly every circuit is a copy or variation of some previous design, something truly, strikingly original is a rarity. The HP-1 circuit (which was likely made in four slightly different variations) veers into weird territory by pairing a germanium PNP transistor and a silicon NPN transistor together in a way that, according to the lore, generates only even-order harmonics. As those of us who've dabbled in audio know, even-order harmonics are supposed to make our ears happy and content, while their odd-order counterparts are supposed to make our ears want to run for their lives in the opposite direction. Of course, this is a vast oversimplification of the subject, and the relative goodness or badness of a sound is entirely subjective, but this is a short article and these are necessarily broad rules of thumb.
The HP-1 is quite simple to operate, with a single footswitch to turn it on or off, and two little sliders to control it, one of which is labeled "Harmonics," while the other is labeled "Balance." As you might be able to deduce, Harmonics equates to the amount of fuzz, while Balance pertains to the output level. Despite these simple controls, and its reputation as a sonic doomsday device, the Percolator is capable of a fairly diverse range of tones. A lot of people, Albini included, push the gain and output and only kick it on when they need an over-the-top fuzzpocalypse sort of sound, but it's actually capable of some very interesting low-gain tones as well. Keeping the Harmonics slider below the halfway point, with output around unity, doesn't really alter the basic character of the tone much. It just adds a bit of musical compression and a rich, slightly edgy, harmonic sheen. Nudge the gain on up past halfway, though, and the filth begins to congeal into a chewy, fuzzed-out ball of hair and gristle unlike any other dirt pedal you've ever heard. The compression and sustain this pedal imparts is incredible, and its flat, full-range frequency response equates to a thick, meaty low-end and plenty of clarity up top. The overall sonic profile is very unique and instantly recognizable if you've had your earholes assaulted by one before. The beauty of this pedal's sound is in the ear of the beholder, though, and while some proponents of the Percolator have equated its tone to the warm grunge of a saturated tube amp, others have described it as sounding like nasty solid-state grind.
The best place to hear the Harmonic Percolator in action is in the context of a Shellac album or live performance, being used by Steve Albini, its most vocal champion and most widely known user. A good example is "Shoe Song" from the excellent 1000 Hurts album, where the pedal basically gets its own solo section at roughly the 3:20 mark. Contrary to popular belief, however, the Percolator is far from being the "secret" to Albini's singular guitar tone, which is based around a Travis Bean aluminum-neck guitar, a Fender Bassman head, an Intersound IVP preamp running into a solid-state Carver power amp, and a homemade, full-range cabinet setup that is more akin to a small PA system than a traditional guitar stack. In Albini's rig the Percolator only gets used occasionally, during the "crazy" parts. As he says in one of several YouTube videos where the pedal is discussed, he uses the Harmonic Percolator mostly when he's feeling "too lazy to play the guitar for the next couple of seconds."
The InterFax HP-1 Harmonic Percolator is a curious case in effect pedal history, and as Geise reportedly passed away at some point in the '90s, we may never unravel all of the mysteries of the original fuzz box. There are, however, a handful of copies and variations on the circuit being made, including the Fredric Effects Harmonic Percolator, the Inductor Guitars Mellifluous Pussy MP-1, and Catalinbread's Karma Suture. The most accurate recreation, though, is undoubtedly from Chuck Collins at Theremaniacs in Wisconsin, who not only owns the rights to the InterFax name now, but has actually dissected a number of vintage Percolators to recreate the original circuit with great precision. His devotion to Geise's original design is such that he even houses his HP-1's in the same plain, boring, unspeakably beige enclosure, for a pedal that only a true cult member could love.