Vintage Late 70's/Early 80's Limiter
 
Model 143
 
This larger red box from the late 1970s/early '80s is one of the smoothest and cleanest-sounding pedals from that era. Many of the "vintage" comp pedals you'll come across are much too noisy, dull sounding, and squashy; but this MXR is very transparent, smooth, and especially low-noise. It imparts a bit of softness to the sound, taking the edge off the highs and the boom out of the lows; so while it's a natural and even sound, it will not suit users who want brightness or fat low end. Otherwise the signal is remarkably uncolored.
 
In spite of the "Limiter" label it seems to work best as a gentle compressor for general signal smoothing; it doesn't actually do a very good job of limiting sharp spikes. If you need to use it for that purpose though, I got decent results by setting the attack and release to their fastest settings. Note that the attack knob turns clockwise from fastest setting to slowest, but the release knob goes "backwards" from slowest to fastest. The envelope is very smooth, and it is easy to forget that this unit is switched on.