The PC-2A side-chain allows some additional control of the photocell to slow it’s attack time and extend it’s release time by a set amount. The attack time can be slowed using the internal ‘Attack’ trimpot to further reduce ‘pumping’ artifacts until they are inaudible. Rotate the ‘Attack’ trimpot anti-clockwise for ‘fast’ attack and clockwise for ‘slow’ attack. This is very useful with acoustic guitars fitted with piezo pickups, giving them a fuller more rounded tone.
There’s also an internal ‘Knee’ trimpot which smooths the PC-2A’s transition into compression to further improve transparency. Rotating the ‘Knee’ trimpot anti-clockwise gives a ‘hard’ knee transition into compression like a limiter and clockwise for a ‘soft’ knee and more gradual transition into compression. With the ‘Knee’ trimpot fully clockwise and a slow attack the PC-2A is incredibly transparent, in fact you won’t be able to hear it compressing at all, but you will hear it working as a tone enhancer. It works fabulously on ‘difficult’ instruments such as 5-string active bass, that is, instruments with wide dynamic range, fast transients and wide frequency response – situations where a transistorised or opamp based compressor would not be able handle the signal without loss of clarity, definition and coherence.