Passive Current Attenuator

A crucial part in the development process of a compressor is to design its control element which reduces the audio signal controlled by voltage. This is also where the main technological concepts show the most obvious differences.

The alpha compressor uses elysia’s fully discrete and temperature compensated Passive Current Attenuator (PCA). This circuit transforms the incoming signal into a current which is then reduced controlled by voltage. The triggering can be compared to that of a VCA with a predictable characteristic curve. The core consists of sixteen discrete transistors which are kept at a defined temperature by an exclusive heating system, avoiding unwanted fluctuations.

Unlike industrial ICs, the PCA works purely passive – it has no internal amplifiers and only reduces incoming signals. Not until the signal leaves the PCA, a downstream amplifier stage converts the current into voltage again, and the make up gain is added by a separate stage. The characteristic curve of the control voltage has been optimized for mastering applications, resulting in precise but gentle gain reduction performance. If stronger and more audible results are on the agenda, the switchable feed forward mode is a perfect alternative.

Further advantages of the PCA are its enormous bandwidth and its extremely fast control speed. Even huge level changes are done in just a few microseconds – an important premise for a fast and flexible compressor. The PCA plays an important role in the overall sonic character of the alpha compressor. It enriches the music with natural overtones by producing a healthy amount of K2 and K3. The sound becomes richer in character and inspires especially digitally mixed productions with that certain something.