The MXR Distortion+ is a distortion pedal originally released in 1979 by MXR, a two-knob design built around a 741 operational amplifier chip and a pair of clipping diodes. General Guitar Gadgets, which documents the circuit for builders, calls it "very popular and good sounding distortion."12
How the circuit works
The Distortion+ is an op-amp distortion. The gain stage uses a JRC741 operational amplifier as IC1, and the clipping is produced by D1 and D2, listed as 1N914 diodes or another clipping device. The build documentation also lists an optional 100µF aluminum electrolytic capacitor at position C8.1
The circuit is, in General Guitar Gadgets' words, "strikingly similar to the DOD Overdrive 250 distortion pedal," and the site's project for it uses the same ready-for-transfer PCB layout file as its DOD 250 Overdrive project.1
Controls
| Control | Pot | What it does |
|---|---|---|
| Gain | 500k reverse log taper | Sets the amount of distortion1 |
| Volume | 10k log or 50k log on some versions; 100k log on the reissue | Sets output level1 |
The Volume pot value is worth knowing if you are servicing or building one, because it has varied across versions: 10k log or 50k log on some, with the reissue using a 100k log potentiometer.1
Connections and power
- Input: stereo quarter-inch jack, J11
- Output: mono quarter-inch jack, J21
- Footswitch: heavy duty 3PDT, Sw11
- Power: 9V battery (B1, not included in the kit version) and a DC jack, J31
- Power requirement: 9V2
History and players
Guitar World dates the original release to 1979 and notes the pedal was "arguably most associated with Ozzy axe man Randy Rhoads and was used to push his Marshall stack into pure distorted bliss."2
The pedal has been discontinued and reissued: General Guitar Gadgets notes that it was "discontinued at one point and reissued after several years of absence on the new pedal market."1
The Distortion+ also has a long history on players' boards. A Vintage Guitar magazine writer recalled of the early seventies: "my primary effects were a CryBaby Wah, a MXR Distortion Plus, and a MXR Phase 90."3
MXR has since built on the Distortion+ name with a signature version for Randy Rhoads, the MXR Randy Rhoads Distortion+2, and other distortion pedals in the line, including the MXR Distortion III and the MXR M104 Distortion+.
Videos
Reverb
Elmo Karjalainen
Grant Kelsay
Questions
What chip is inside the MXR Distortion+?
The circuit is built around a JRC741 operational amplifier IC, listed as IC1 on the General Guitar Gadgets project documentation. The clipping is done by a pair of 1N914 diodes, D1 and D2, or another clipping device in that position. That simple op-amp plus diode arrangement is what gives the Distortion+ its character.
Was the MXR Distortion+ ever discontinued?
Yes. According to General Guitar Gadgets, the Distortion+ was discontinued at one point and later reissued after several years of absence from the new pedal market. Guitar World dates the original release to 1979.
What power does the MXR Distortion+ need?
The pedal runs on 9 volts. It takes a 9 volt battery, which is not included in the General Guitar Gadgets kit version, and a DC jack, listed as J3, for an external power supply.
What did Randy Rhoads use the Distortion+ for?
Guitar World's Daryl Robertson writes that the Distortion+ is arguably most associated with Ozzy Osbourne guitarist Randy Rhoads, who used it to push his Marshall stack into what the magazine calls pure distorted bliss.
What volume pot value does the reissue Distortion+ use?
The Volume Control potentiometer has been traced as 10k log or 50k log on some versions, and the reissue uses a 100k log potentiometer for the Volume pot, according to General Guitar Gadgets.
Sources (3)
- MXR™ Distortion+™ Clone: DIY Kit, PCB & Schematic, General Guitar Gadgets, 2014-05-12
- Best pedals for classic rock: recreate the tone of legends, Guitar World, 2022-07-18
- Wah-Wah Pedals, Vintage Guitar magazine, 2001-06-05
