Positive Grid Booster is a boost pedal available under the Drive effect group and is inspired by the MXR Micro Amp pedal.

MXR Micro Amp

The Micro Amp allows you to boost your signal with a preset amount of gain up to +26dB for lead work or adjust between two different guitars with unmatched output (i.e. humbuckers to single-coils). It can also provide a permanent boost in a long effects chain where signal drop off is a problem.

Company typePrivate
IndustryConsumer electronics
Founded1972; 52 years ago (1972)
HeadquartersRochester, New York
Productseffects pedals
ParentDunlop Manufacturing

MXR is a New York–based manufacturer of effects pedals from Rochester. The company was co-founded in 1972 by Keith Barr and Terry Sherwood[1] [2] and incorporated as MXR Innovations, Inc. in 1974. The MXR trademark is now owned by Jim Dunlop.

image of early MXR sales and engineering staff at NAMM Show
NAMM Show in LA
450px MXR effect pedals 1
MXR dyna comp, phase 45, phase 90, distortion +, carbon copy


MXR co-founders Terry Sherwood and Keith Barr met as high school students at Rush-Henrietta Senior High School in Henrietta, New York, a suburb of Rochester, New York. Together they started Audio Services, an audio repair business, where they repaired stereos and other music equipment in their rented basement apartment. This experience led them to form MXR and they began producing their first original effect pedal design: the Phase 90. This was quickly followed by the Distortion +, Dyna Comp, and the Blue Box. Michael Laiacona joined this early MXR team in a sales position. Barr later left MXR and went on to found Alesis while Sherwood and four managers/engineers of MXR, John Langlouise, Phil Betette, Tony Gambacurta and Richard Neutrour, co-founded Applied Research & Technology. Mike Laiacona and his wife went on to found Whirlwind USA.[3]

Jim Dunlop acquired the MXR brand in 1987 and continues the pedal line of original MXR classics, such as the Phase 90 and Dyna Comp, as well as modern pedals like the Carbon Copy and Fullbore Metal. Dunlop has also added a line dedicated to bass effects boxes, MXR Bass Innovations, which has released the Bass Octave Deluxe and Bass Envelope Filter. Both pedals won Editor Awards in Bass Player Magazine and Platinum Awards from Guitar World Magazine. The MXR Custom Shop is responsible for recreations of vintage models such as the hand-wired Phase 45, as well as doing limited runs of pedals such as the Custom Comp.

Reference Series (1973–1984)

85px MXR M
MXR M-101 Phase 90
78px 1979 MXR Distortion %2B
MXR M-104 Distortion + (1979)
75px MXR M 105 Phase 45
MXR M-105 Phase 45

The first MXR effects pedal was the M-101 MXR Phase 90 phaser. The Phase 90 was used on the first two Van Halen albums.[4] The MXR Phase 45, followed, as well as a programmable version, the Phase 100. Like other pedals of the time, MXR pedals prior to 1981 did not have LEDs, A/C adaptor jacks, or true-bypass switching.

The first period is known as the "Script period," in reference to the cursive logo on the case. The earliest script logo pedals were made in the basement shop of the MXR founders[5] and the logos were silk screened. These very first pedals can be identified by a slightly larger font "MXR" on the case.

The "Box Logo Period 1" began around 1975-6 and lasted until 1981, and is named for the writing on the front of the box. The "Box logo period 2" started in early 1981 and went until 1984, when the company stopped making pedals. The main change in this era was the addition of LEDs and A/C adaptor jacks. These pedals used 1/8" power jacks and had exactly the same circuit board as their pre-1981 box logo brothers.

Model Effect Name Year Intro
MX-101 Phase 90 1974
MX-102 Dyna Comp 1974
MX-103 Blue Box 1974
MX-104 Distortion+ 1974
MX-105 Phase 45 1974
MX-106 Noise Gate Line Driver 1975
MX-107 Phase 100 1975
MX-108 10 Band Graphic Equalizer 1976
MX-109 6 Band Graphic Equalizer 1976
MX-117 Flanger 1976
MX-118 Analog Delay 1976
MX-120 Envelope Filter 1976
MX-133 Micro Amp
MX-134 Stereo Chorus
MX-137 Power Converter
MX-138 Power Plate
MX-142 Distortion II
MX-143 Limiter
MX-144 Loop Selector
MX-148 Micro Chorus 1982
MX-152 Micro Flanger 1982
MX-157 Headphone Amp 1982
MX-180 Omni Multi Effects 1983
MX-181 Omni Footswitch 1983

Commande Series (1981–1984)

In 1981, MXR introduced the Commande Series, a line of plastic (Lexan polycarbonate) pedals. Their design departed from the Reference Series in several respects. The input, output and power jacks were all moved to the top of the case to allow a tighter grouping on the floor, or pedal board.

2000 Series (1982–1984)

The Series 2000 was a complete rework of the Reference and Commande lines of pedals. They were higher quality pedals, with electronic FET switching and dual LED indicators. They had a contoured, all-metal chassis and an easily removable battery. They had a fully rubberized bottom and were remote-controllable. Most of the pedals had dual outputs with distinctly different sounds.

The MXR Series 2000 sported six models. These original pedals in the series included the Dyna Comp, Distortion +, Phaser, Stereo Chorus, Stereo Flanger and Time Delay. In late 1983 MXR announced a digital sound effects pedal generator simply known as the Junior. The Junior was released in early 1984 and was added to the other six pedals in the Series 2000 line. The Junior boasted four sound effects: a laser, a clap, a snare and a high hat. The effects were samples stored on a replaceable 24-pin ROM chip that was produced by MXR. MXR continued to manufacture most of the Reference, Commande and 2000 Series pedals until they closed down in 1984.

Model Number Effect Name Year Intro
M-201 Phaser 1982
M-202 Dyna Comp 1982
M-203 Stereo Flanger 1982
M-204 Distortion+ 1982
M-206 Time Delay 1982
M-250 Stereo Chorus 1982
M-210 Junior 1984

MXR Rackmount Effects

250px MXR racks front %40 Savage Audio
MXR M-124 Dual 15-Band Graphic EQ
MXR M-131 Pitch Transposer Display
MXR M-129 Pitch Transposer
MXR M-126 Flanger/Doubler

MXR also had a line of professional rackmount effects used by the likes of David Gilmour,[6] Stuart Adamson and Mike Rutherford. The first product introduced was the Digital Delay, which had delay times from 0.08ms to 320ms, but users could purchase additional plug-in memory boards that were user-installable and could increase delay times to 1280ms.[7]

Maximum Delay (msec)

bandwidth 1 Memory Board 2 Memory Boards 3 Memory Boards 4 Memory Boards
20KHz 40 80 120 160
10KHz 80 160 240 320
5KHz 160 320 480 640
2.5KHz 320 640 960 1280


Model Number Product Name Year Introduced
MX-113 Digital Delay 1976
MX-122 Case for Delay
MX-124 Dual 15-Band Graphic EQ
MX-125 31-Band Equalizer
MX-126 Flanger/Doubler
MX-129 Pitch Transposer
MX-510 Pitch Transposer with LED Display
MX-136 Dual Limiter
MX-151 Delay System II 1982
MX-175 Digital Time Delay
Pitch-Shift Doubler


In 1983, MXR introduced one of the first multi-effect rack units for guitar and bass, the Omni.[11] The Omni had 6 different effects: sustain, distortion, delay, equalization, flanger and chorus. The main unit was a 2U with separate controls for each effect. There was a footpedal (M-181) that enabled the player to switch the different effects on and off, as well as changing the order of the distortion and equalizer effects, a master bypass as well as an effects loop. Since 2006, the "M-181" product number has been re-appropriated by Jim Dunlop for the MXR Bass Blowtorch Overdrive pedal.

MXR Desktop Effects

In 1980 MXR released the MX-114 Two Channel Graphic Equalizer. From the 1980 Catalog: "The Equalizer's wide dynamic range and interface characteristics allow for a variety of applications. the frequency response of a system can be tailored to compensate for room acoustics, speaker aberrations and program material. Horizontal control placement and the equalizer's compact case permit easy manipulation in studio mix down situation. P.A. applications include: suppression of major feedback frequencies, compensation for high frequency attenuation in miking and rejection of unwanted signals (60Hz hum and noise) Two channels permit separate main and monitor equalization.[12]

Drum Computers

220px MXR 185 Drum Computer
MXR 185 Drum Computer

In late 1981, MXR got the resale rights in the US to sell the KIT (M-178), a digital drum machine. In early 1983, MXR released the M-185 [1] MXR Drum Computer, similar to Roger Linn's Linn LM-1 drum machine with individual pads for the instrument sounds and individual volume controls for each sound.

Jim Dunlop and MXR

220px MXR by Dunlop 1
MXR by Jim Dunlop

Jim Dunlop bought the MXR licensing rights and currently manufactures reissues of some of the classic MXR effects pedals. Dunlop has created new models in addition to the original lineup, including signature pedals such as Eddie Van Halen Phase 90 and Flanger, and Zakk Wylde's Wylde Overdrive and Black Label Chorus.[13]



  1. ^ Art Thompson, Dave Thompson, The Stompbox, Backbeat Books, 1997, p. 106
  2. ^ "In Memoriam: Keith Barr 1949-2010", Mix Magazine Online, Aug 25, 2010
  3. ^ Art Thompson, Dave Thompson, The Stompbox, Backbeat Books, 1997, p. 106-111
  4. ^ "Eddie Van Halen's Rig and Tone Techniques".
  5. ^ Rob Hughes, "Selectron to Distribute Rochester Series Pedals", MI Pro, Oct 2009
  6. ^ Tolinski, Brad (September 1994). "Welcome to the Machines". Guitar World. Archived from the original on 2012-06-17. Retrieved 2011-07-29.
  7. ^ MXR 1980 Catalog
  8. ^ 1980 MXR Catalog
  9. ^ 1980 MXR Catalog
  10. ^ 1982 MXR Catalog & Price List
  11. ^ "MXR". 18 October 2021.
  12. ^ 1980 MXR Catalog
  13. ^ "Current MXR Pedals Catalog".

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