Electro-Harmonix Op-amp Big Muff Pi

The Op-Amp Big Muff Pi is a fuzz, distortion and sustainer pedal made by Electro-Harmonix, sold as a reissue of the company's late-1970s op-amp Big Muff¹. Where every other Big Muff variant generates its sustaining distortion with four transistors, this circuit relies on op-amps, the small integrated-circuit amplifier chips, and three gain stages rather than four¹². The original run lasted only about two years and produced a few thousand units, and those vintage pedals now command high prices, which is what brought the circuit back as a current production pedal³⁴.

Electro-Harmonix describes the reissue as a faithful re-creation of the original late-70s Op-Amp Big Muff Pi, sometimes also called the IC or V4 Big Muff, in a compact die-cast nano enclosure with true bypass switching¹⁵. Big Muff collector and historian Kit Rae, quoted on the maker's own page, characterizes the sound as:

What the Op-Amp Big Muff is

The pedal sits in the wider Big Muff Pi family as its odd one out. Premier Guitar calls it "a true black sheep" of the family: where other Big Muffs share a common four-stage silicon transistor architecture, the 1978 Op-Amp Muff substituted op-amps for the four transistors, a short-lived experiment that produced a tone signature different enough that, in that reviewer's words, "some Muff purists don't consider it a real Muff at all"⁷.

MusicRadar's Trevor Curwen notes it still delivers the typical Big Muff Pi combination of fuzz and distortion, "but the devil is in the detail here"⁶. Guitar World's reviewers describe the Op-Amp as more saturated than its other Muff siblings, and as a completely different circuit from the original quad-transistor Big Muff, a shift driven by part availability⁸. Delicious Audio's history of the 1977-78 pedals records that the move to op-amps was made to reduce manufacturing costs⁴.

The V4 op-amp circuit

In 1978, EHX briefly switched the Big Muff Pi from its traditional four-transistor circuitry to a design based around the more cost-effective op-amp integrated circuits, with one less gain stage⁶. This Version 4, the rarest of the two op-amp Big Muff versions, used two op-amp chips: one RC4558NB and one of several versions of the 741 chip, such as the UA741CP, UC741TC, LM741CN, and LM741CM⁹¹⁰. The circuit designers were Howard Davis, E-H's Manager of Analog Circuit Design from 1976 to 1981, and former EHX designer Michael Abrams¹⁰.

A few practical points distinguish the V4 for players comparing versions:

• The tone is very consistent from unit to unit, unlike the transistor versions⁹
• Kit Rae describes a very deep crunch, flat mids, and superb deep bass control, though they are not as good for palm muting as some earlier Big Muffs⁹
• The Stompbox Book's history notes these are more consistent from example to example, with a bit less gain and low end¹¹
• Supposedly only a few thousand were made before production returned to transistor circuitry¹⁰⁶
• The original had no LED, no true bypass, and a 1/8" (3.5mm) tip-positive power jack, the reverse polarity of typical pedals¹⁰

Two of the three circuit boards used in the V4 were also used in the Little Big Muff enclosure with the same circuits, and the late-1970s Deluxe Big Muffs used a nearly identical circuit to the V4¹⁰.

The V5 Op-Amp Tone Bypass Big Muff π

The Version 5, circa 1978 to 1981, continued the op-amp design and added a tone bypass switch, making for a brighter tone thought to have more overall presence in its ability to cut through a mix¹¹. It is the most common of the two op-amp Big Muff versions⁹. The V5 used the same two op-amp chips as the V4, one RC4558NB and one of several 741 variants¹⁰.

The tone bypass switch completely bypasses the tone circuit. Kit Rae describes the result as a huge, brighter distortion tone with flatter EQ and slightly more mids, a heavy classic rock sound, with a slight 6-7 decibel volume boost in bypass mode; the non-bypass mode is very close to the traditional Big Muff sound⁹¹⁰. The V5's low end frequencies sound slightly less tight than the V4's¹⁰. On the original V5 there was no on/off switch, and the tone knob had no effect in bypass mode¹⁰. These were the last op-amp Big Muffs made before the design was phased out around 1980 or '81 and the transistor version continued¹⁰.

Billy Corgan and Siamese Dream

The op-amp Big Muff's fame rests largely on one player. Billy Corgan used the original Version 4 briefly on the Smashing Pumpkins' Gish album, to very good effect on Siamese Dream, and on several tracks that later appeared on Pisces Iscariot, all recorded 1991 to 1993¹⁰¹. Electro-Harmonix's own page says the pedal "was popularized by the brilliant Billy Corgan who first used it on the Smashing Pumpkins' epic 1993 album Siamese Dream"¹. Kit Rae's history records that in the Siamese Dream sessions he used a vintage USA Big Muff through a Marshall JCM 800 100 watt head¹⁰.

Once word spread of the Siamese Dream sound, resale prices of V4 and V5 Big Muffs skyrocketed and they became expensive and rare collectibles¹⁰. Guitar.com's Michael Watts notes that Corgan "played a huge role in the resurgence in popularity of the Big Muff in the 1990s"¹². On the JHS Pedals YouTube channel, Josh Scott put it more bluntly: "They kind of quit selling it and then Billy Corgan uses it" and the op-amp reissue followed¹³.

The 2017 Op-Amp Big Muff π reissue

Electro-Harmonix announced the reissue in December 2017, after founder Mike Matthews reached out to Corgan about bringing the original op-amp series back¹⁴¹⁵. The reissue was engineered by Gino Maisano, based on the original Michael Abrams and Howard Davis op-amp circuit design, and was built from an original schematic rather than traced or measured from an actual vintage V4 or V5¹⁰. It shipped in the standard EHX nano-sized cast metal enclosure, assembled and tested in Long Island City, New York¹⁰.

The reissue carries the standard Volume, Tone and Sustain controls plus a Tone Bypass switch, just like the V5¹⁶¹⁰. Kit Rae notes the bypassed tone is brighter and harsher but missing the trademark mid scoop Big Muffs were known for¹⁰. Guitar.com's buyer's guide describes the switch as making the circuit skip the dual-filter tone control, resulting in a more full-frequency, less scooped sound¹⁷. The circuit uses through-hole capacitors and diodes with small surface-mount resistors, and "ICBM" is printed on the circuit board, a reference to the Euthymia ICBM, one of the first clones of the op-amp Big Muff¹⁰.

After Corgan was videotaped playing and talking about the reissue, he stated:

Guitar.com's review concluded simply: "It's that Siamese Dream sound, or near as damn it"¹². MusicRadar's round-up praised it as a very different circuit to the standard Big Muff, easy to fit into a band mix, with "almost nothing sounds as huge"¹⁸.

Power and connections

The reissue ships with a 9V battery and can be powered by an optional 9-volt AC adapter, the EHX 9.6VDC-200 type¹¹⁶⁴. Sockets are input, output and power, and the pedal is true bypass¹⁹. Current draw is 5mA¹.

MusicRadar's review found the Tone knob "gets a little too thin and nasty at the clockwise extreme while being a little woolly at the other," with sweet spots in between⁶.

Price

The maker's current list price is $96.20¹. At launch in December 2017 the U.S. street price was $80.90¹⁶. MusicRadar's verdict on value: "Those after that particular Smashing Pumpkins experience will find it here, in a reasonably priced compact pedal from the original manufacturer"⁶.

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