Mooer Pedal Yellow Comp Optical Compressor 2013/8/14

Mooer Pedal Yellow Comp Optical Compressor

Mooer Pedal Yellow Comp Optical Compressor

By Chris Loeffler


Players looking to add compression to their arsenal are generally looking for one of two things… the snappy, highly effected compression that is a tone all in itself and enjoyed by many Country and Funk players or a way to slightly enhance the tone they already love with a smooth evening out of their playing and a slight increase in sustain. Although every component in the compressor circuit plays a role in how the effect sounds, the way compression happens starts with a voltage controlled amplifier.

Many classic compressors used ICs or FET transistors, which offer distinct attack, sustain, release, and decay characteristics many find pleasant, but these designs rely on complex circuits and have issues handling large signals. Optical compressors, on the other hand, rely on light dependent resistors to adjust their value based on the brightness of a light source (which is controlled by input signal). The result is smoother and less distorted compression with a simpler design. The Mooer Yellow Compressor falls in this category.

The Mooer Yellow Compressor takes a finally tuned optical compression circuit and crams it into an incredibly small casing, allowing it to fit on even the most crowded pedal board. Controls include Volume, Comp, and Tone, and the pedal features true bypass switching and is powered by most 9v adaptors.

What You Need to Know

  • The Mooer Yellow Compressor is highly transparent and is more felt than heard through most of the sweep of the compression range. In more subtle settings, it slightly thickens and focuses the signal, evening out arpeggios and chords by smoothing out the volume differences of the various frequencies abd creating a rounder tone. It maintains the subtle nuances of the input signal and increases sustain without noticeably altering the tone. The attack and release of the compression is tame and natural at most settings and doesn’t have the pump or quack associated with extreme compression effects.
  • In front of an overdriven amp or overdrive effect, the Yellow Compressor delivers a detailed and slightly more rounded signal with plenty of signal transients for the gain to latch onto, generating pleasant and rich harmonic distortion. When placed after a gain effect, the Mooer reigns in the less tame harmonics to create a liquid, present tone without the darkness or muddying effect many non-optical pedal compressors impart.
  • At the lowest settings of the Comp control the compression is so subtle that anyone outside of the person playing it (who would “feel” the slight tightening of the tone) wouldn’t know the Mooer Yellow Compressor was on. From 10:00 to 2:00 the squash becomes more noticeable as lower volume signals get boosted and higher volume frequencies are pulled back. The last quarter of the control squeezes the signal to a uniform volume for all frequencies without significantly altering the input tone.
  • Even with the Comp control turned all the way down (which does lower the output volume), there is a significant amount of output boost over unity gain available via the Volume control. Higher compression settings with the Volume control maxed easily push a clean amp into overdrive.
  • The EQ control is very similar to EQ most overdrive and distortion effects employ, with the lowest settings accenting the bass and reducing the treble, and the opposite true of the highest settings. Unlike the traditional EQ control of gain effects, however, the mids tend to stay faithful to the pre-EQ signal and to never get too boomy in the low end or too shrill at the high end in extreme settings.


  • Due to the nature of compression and the amplification of a signal in general, extreme settings do introduce an escalated noise floor. The noise is less than most gain/compressor devices at extreme settings and wouldn’t be distracting outside of the Volume and Comp controls being cranked into a clean amp in a quiet room.
  • Players seeking the up-front squash and pump of a classic FET or IC architected compressor (like a vintage Ross or Orange Squeezer) may find the Yellow Compressor too transparent and not as tone effecting as they would like. While it can get close, the Mooer is smoother, less clipped and more suited to tone enhancement and limiting than as an obvious effect.


The Mooer Yellow Compressor packs a lot of tone into a very small package. From squashed funk chords to subtle tone enhancement, it does an admirable job bringing out the best qualities of the tone it’s being fed without drastically altering it. Witty wordplay not intended, the Mooer gives players “more”… more volume, more tone shaping, and more sustain.

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