I do not know why I did this, and I definitely did not need another rabbit hole to go down, but in the early 2000s I started revisiting and researching what I consider the Big Muff of distortion: the Distortion+.

Once I began looking into the circuit, I found a surprising number of copies and variations, especially from Japan.

For this article, I wanted to keep the list focused on pedals whose schematics I have personally examined and confirmed as using the same basic Distortion+ design.

Some pedals are often described as relatives of the Distortion+, but they use different clipping methods, additional gain stages, or more complicated tone circuits. I have left those out.

The production dates of some Japanese models are difficult to establish, so the order below is based on the best information I could find.

1974 MXR Distortion+

Using a simple design with a single op-amp followed by two germanium diodes, it has only two controls, Output and Distortion, with no tone control.

The Distortion control does more than increase gain. As it is turned up, the frequency response changes and some low end is removed from the gain stage. This helps prevent the distortion from becoming too loose or muddy, but it also contributes to the sharp, biting character of the pedal.

The germanium diodes begin clipping at a relatively low level. This creates strong compression and saturation while limiting the maximum output. The result is the gritty, compressed sound that made the Distortion+ famous.

The pedal became closely associated with Randy Rhoads and Bob Mould. Rhoads used it to push his Marshall amplifiers, while Mould made its raw, heavily saturated character an important part of his guitar sound. They were two very different guitar players who used the same pedal in very different ways.

1974 DOD Overdrive Preamp

The question of which pedal came first has been debated for years because both the Distortion+ and the original DOD Overdrive Preamp are generally dated to 1974.

The earliest DOD version was housed in a large enclosure and did not carry the 250 model number. Although some of its components date to 1972, they were salvaged from older electronic equipment, including IBM computer cards, and do not represent the date the pedal was built.

DOD founder David Oreste DiFrancesco later described the original Overdrive Preamp as a part for part copy of the Distortion+. This strongly supports the MXR as the earlier design, with the DOD following shortly afterward in 1974.

The earliest version used the same basic single op-amp design and germanium clipping diodes as the Distortion+. Other early examples used silicon diodes, which produced less compression and more available output. DOD also changed some of the filtering and component values as the circuit developed.

Compared with the Distortion+, the later DOD versions generally have less saturation, more output, and a clearer, more open sound. At lower gain settings, the pedal works well as a boost. As the gain is increased, it produces a harder and more aggressive overdrive.

The 250 designation was added later, and the pedal eventually moved into the smaller gray enclosure most players recognize today.

1975 Coron Distortion

Before the Distortion 10 and Distortion 15, there was the original unnumbered Coron Distortion. Made in Japan during the late 1970s, it was closely based on the MXR Distortion+.

The circuit follows the same basic design, with a single op-amp gain stage followed by two opposing diodes that clip the signal to ground. However, the Coron reportedly uses silicon clipping diodes instead of the germanium diodes found in the MXR.

Like many Japanese pedals from this period, versions of the same basic pedal appeared under several names. These included the Asama Engineering AC703 Distortion, Bias Distortion, J&J Distbox, KMD Distortion, Labo Distortion, Memphis ME-20 Distortion, MX four Distortion, and Nashville Distortion.

The exact relationship between every branded version is difficult to establish without examining each schematic. However, they all appear to belong to the same Japanese manufacturing family that eventually produced the Coron Distortion 10 and the higher output Distortion 15.

1976 Coron Distortion 10

The Coron Distortion 10 is a Japanese variation of the Distortion+ design. It uses the same basic single op-amp gain stage followed by two germanium diodes that clip the signal to ground. Coron changed the filtering and several component values, giving the Distortion 10 a smoother and darker sound than the original MXR.

At lower Distortion settings, it works as a warm, slightly dirty boost or overdrive. As the control is increased, the sound becomes thicker and more compressed before moving toward fuzz. Coron described this same progression in its 1981 brochure, from soft distortion at lower settings to a harder fuzz tone at higher settings.

The Distortion 10 originally appeared in yellow and was also offered in red and orange.

The same pedal was sold under several different brand names as the Grant Distortion 10, HMI Distortion 10, Musikbörsen Distortion 10, and Storm Distortion 10.

1977 DeArmond Square Wave Distortion Generator

The DeArmond uses the same overall structure as the Distortion+. It has a single op-amp gain stage, opposing clipping diodes to ground, and controls for gain and output. Changes to the filtering and component values give it a different voice.

Of all the early versions I tested, I found the Square Wave to have the best overall sound. It retains the basic texture of the Distortion+ but sounds fuller, smoother, and better balanced. It has warmth without becoming muddy and enough bite to remain clear.

1977 Guyatone PS-102 Zoom Box Distortion

The Zoom Box was manufactured in Japan by Tokyo Sound, the company behind the Guyatone brand.

The Zoom Box uses the familiar single op-amp and diode clipping design, but its filtering and silicon clipping diodes give it a tighter and clearer response. It is less compressed than the germanium Distortion+ and has a somewhat more aggressive character.

The same circuit later appeared as the Vox 1901 Distortion.

1977 Ross Distortion

Another favorite of mine is the Ross Distortion. The earliest version was housed in a small Bud Industries enclosure that closely resembled the enclosures used by MXR. Bud Industries was the enclosure manufacturer and had no connection to Ross founder Bud Ross.

After MXR objected to the similarity between the pedals, Ross moved to the larger custom enclosure with angled sides and recessed controls that became associated with the company.

The circuit was also extremely close to the Distortion+. It used a single 741 style op-amp followed by germanium clipping diodes. The basic design remained the same, although the op-amp and some component values changed between production versions.

The germanium diodes give it the same thick, compressed, and saturated character as the Distortion+, while the circuit changes give the Ross its own balance and feel.

Late 1970's Memphis ME-20 Distortion

The Memphis ME-20 is a Japanese variation of the Coron Distortion 10. The Memphis line is often attributed to Maxon and is believed to have been manufactured for distribution in the United States, although surviving documentation is limited.

The schematic I examined uses the same basic single op-amp gain stage and two 1N270 germanium diodes found in the Coron 10, placing it firmly within the Distortion+ family.

Most of the circuit is nearly identical to the Coron 10. The main difference is lighter filtering at the output, which allows more high end to pass. This gives the Memphis a somewhat brighter and more open sound while retaining the compression, grit, and saturation produced by the germanium diodes.

It is a surprisingly versatile pedal. At lower Distortion settings, it can produce a slightly distorted jangle or crunchy overdrive. As the control is increased, the sound becomes more compressed and aggressive, eventually moving into full psychedelic fuzz. Like the Distortion+ and Coron 10, it has only Volume and Distortion controls, with no separate tone control.

Steve Turner of Mudhoney was also known to use one. In a 1992 issue of Guitar Player, he said, “We use a lot of different fuzz boxes. On the road I use a Big Muff, a wah-wah pedal, and a Memphis Distortion box, which looks like an MXR.”

The ME-20 is not simply a pedal that resembles the Coron. It is a closely related version of the same basic circuit, with a small filtering change that gives it a slightly brighter voice and a wide range extending from dirty boost to fuzz.

Circa 1980 Coron Distortion 15

The Coron Distortion 15 uses the same basic single op-amp and hard clipping arrangement as the Distortion+, but it is not simply a renamed Distortion 10. It uses silicon clipping diodes instead of the germanium diodes found in the Distortion 10, along with changes to the gain and filtering.

The silicon diodes clip at a higher level, giving the Distortion 15 considerably more available output. This allows it to work as a boost at lower settings and push an amplifier harder than the Distortion 10. As the Distortion control is increased, it moves from a lighter overdrive into a more forceful and compressed distortion with a fuzz-like character.

Coron’s 1981 brochure claimed that the Distortion 15 produced approximately three times the output of an ordinary distortion pedal. The brochure described its sound as soft distortion at lower settings, tube amplifier style distortion in the middle, and hard fuzz tone at higher settings.

The only rebranded Coron Distortion 15 I could confirm is the Grant Distortion 15.

1981 Vox 1901 Distortion

The Vox 1901 Distortion was made in Japan by Guyatone. The schematic I examined is identical to the Guyatone PS-102 Zoom Box Distortion.

That makes the Vox 1901 the same circuit under different branding rather than a new variation. It has the same tighter response, silicon clipping, and more aggressive character as the Guyatone.

The Road to the Dire Wolf

Researching and comparing these circuits was only the beginning. Each pedal showed me a different way the basic Distortion+ design could be changed while still retaining its character. In the next part, I will explain how everything I learned from these pedals led to my own changes and how those ideas eventually evolved into the Dire Wolf.