The A-131 is an exponential voltage controlled amplifier designed mainly for controlling audio signals. The VCA has two audio inputs, each with an attenuator. They are amplified by the combination of the gain control and the two CV inputs. The VCA output is then passed through a further attenuator to control the overall output level from the A-131
A-131 History: Since the A-131 has been released, there have been three different versions: Version 1: (manufactured up until 2001) The first versions of A-131 were designed using CEM3382 Curtis chip. This version of the A-131 was unable to process slowly varying control voltages as it had AC coupled signal in/outputs. Version 2: (manufactured between 2001 and 2013) The second version of the A-131 was designed with the CA3080 OTA chip, which was able to process slowly varying control voltages as it had DC coupled signal in/outputs. This chip is no longer manufactured. Version 3: (manufactured from 2013) The current version of the A-131 is designed with the high-end VCA V2159 chip. It is able to process slowly varying control voltages as it has DC coupled signal in/outputs. The exponential response is also improved.
Unfortunately it's not possible to upgrade older modules because the new circuitry is totally different.
