12413 compressor is inspired by a famous British unit that was used on The Beatles recordings. Gain control circuit of this compressor is based on zeners. The resistance of the zener changes depending on the current flowing through it. This in turn changes the gain of the amplifier stage. Zener selection is of utmost importance for this compressor.
We tested hundreds of zeners in search of a replacement for the original ones used in the circuit (these original parts are not in production any more). Besides, we added an adjustable high-pass filter for a sidechain and additional Attack and Release settings.
In 12413 module the amount of compression is adjusted with a Hold control. This is not something that you see in other compressors. However, this control is very easy to set up. The more you turn the knob clockwise, the more the unit compresses. We'd also like to mention, that in a modern 12413 recreation (made by a very respectable company) this Hold control is absent. We don't think that removing the Hold control was a step in the right direction.