MXR Dyna Comp

The MXR Dyna Comp is a two-knob compressor pedal that evens out the volume differences between your notes, giving weak notes more body and level so the sound stays consistent no matter how hard or softly you play. Dunlop calls it one of the most popular compressors of all time, and describes it as able to tighten up your signal, add rich sustain, or create the percussive, clicky sound heard on numerous hit records¹. It was released in 1972 by the original MXR company and is still available from Jim Dunlop's revived MXR line today²³.

What makes the Dyna Comp sound the way it does is its circuit: it popularized the OTA (Operational Transconductance Amplifier) style of compressor, in which a single chip handles the gain reduction⁴. There is no separate dry path, so you hear only the compressed signal, which is a big part of its character.

What it does to your sound

A compressor reduces the dynamic range of your signal: loud notes get pulled down, quiet notes get pushed up, and the result is a more even, sustained sound. The Dyna Comp does this with a fixed release time of 1 second and an attack time of 5 ms, with up to 36 dB of maximum compression². In practice that means long, singing sustain when you turn the Sensitivity up, and a tighter, more consistent picking response at lower settings.

The circuit divides into five blocks: an input buffer, an OTA amplifier, an envelope detector, an output stage, and the power supply³. A 2K trimmer inside adjusts the bias currents of the OTA's differential inputs to balance the chip³. The circuit was widely copied: it was used as a reference design for the Ross Compressor, the T-Rex CompNova, the Ibanez/Maxon CP5, CP9 and CP10, and many boutique pedals³.

The controls: Output and Sensitivity

The M102 has just two knobs, which Dunlop describes as straightforward and easy to use¹⁰¹. Guitar.com's take: with just two knobs, it's easy to dial in and hard to make sound bad¹⁰.

The manual includes sample settings for different styles, with names like Nashville, New Wave, Squash, Nasty and Bottleneck². Guitar World publishes two well-known starting points¹¹:

• Country chicken pickin': Output 8, Sensitivity 3, the classic "snake eyes" setting, with a Telecaster at the bridge pickup¹¹.
• Andy Summers-style rhythm: Output 6, Sensitivity 6, with single-coil pickups¹¹.

Power and connections

The Dyna Comp runs on one 9-volt battery (installed by removing the bottom plate) or a 9-volt AC adapter such as the Dunlop ECB003/ECB003E, or a DC Brick power supply². It draws only 3.3 mA, so a battery lasts a long time. Input impedance is 1 MΩ and output impedance is 10 kΩ, with a nominal input level of -5 dBV². You run a cable from your guitar to the INPUT jack and another from the OUTPUT jack to your amplifier².

History and versions

The Dyna Comp was released in 1972 by MXR, made in Rochester, New York³. Early units carried the script logo and used a distinctive one-layer white/yellow PCB with all components on one side; the original script model is no longer available in that form³. A non-LED block logo version followed around 1980⁹. When Dunlop acquired MXR in 1987, the PCB was progressively redesigned with modern components and a double-sided board with red solder mask³.

Dunlop's current lineup includes several versions:

The MXR Super Comp followed in the footsteps of the classic Dyna Comp, adding an Attack Level knob and a status LED to the simple Sensitivity and Output controls²⁰.

What reviewers said

MusicRadar calls the Dyna Comp a classic for good reason, noting it has been featured on pro boards for decades and cloned many times, though its review of the Mini found the two controls make finding a subtle tone somewhat laborious¹⁴. Guitar.com calls it the original red box that helped define the sound of modern country, funk, and 80s pop¹⁰. Premier Guitar's review of the Custom Shop '76 Vintage Dyna Comp found it addictive to use:

Premier Guitar, on the Custom Shop '76 Vintage Dyna Comp¹³

On That Pedal Show, Dan and Mick compared a JAM Dyna-ssor with Dan's original '70s script logo DynaComp, noting it uses an OTA chip and that Mick loves its grab-and-squish character as an overt effect²¹.

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On JHS Pedals' channel, Josh Scott showed an original block logo unit and noted vintage examples in good condition land around the $300 mark on the used market²².

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Who uses it

The Dyna Comp quickly became a favorite among Nashville session players, where it is still rooted in their traditions²³. Guitar World documents several famous users¹¹:

• David Gilmour used it on numerous Pink Floyd tracks recorded during the late '70s, where it was a key element of his Strat's sustain into a Big Muff or other overdrive¹¹.
• Pete Townshend has often used a Dyna Comp on stage since the late '70s as a clean boost for solos¹¹.
• David Byrne often used one at extremely compressed settings for his rhythmic and melodic lines with Talking Heads, notably on the outro of "Drugs"¹¹.

The Dyna Comp and the Ross Compressor

The Ross Compressor is a mildly modded Dyna Comp circuit²⁴. According to Aion FX, the Ross has better power supply filtering and thus lower noise, but is otherwise very similar to the Dyna Comp²³. JHS Pedals offers a mod service that turns a Dyna Comp into the coveted Ross Compressor for less than buying an original²⁴, and Griffin Effects sells a Ross conversion it describes as the holy grail of compressor mods, converting the Dyna Comp to the same circuit as the Ross²⁵.

Mods

The Dyna Comp is one of the most modded compressor circuits around. Documented circuit mods include³:

• Lowering or removing the 0.001uF C5 capacitor (to between 100pF and 470pF, or removing it entirely) for a fuller or emphasized top end.
• Enlarging the output series 0.05uF capacitor C9 to 1uF for a fuller bottom end.
• Disconnecting C7 to remove the bottom envelope detector, at the cost of some envelope ripple on lower notes during decays.

Shops also offer tone control mods for the Dyna Comp²⁶, and Molten Voltage has built Dyna Comps with its own enhancements, switched in and out with a MIDI switcher²⁷.

Videos

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Questions