There are two ways to check whether the expansion board is suitable for the A-110-4 at hand:

• At the back of the front panel or on the circuit board of each Thru Zero Quadrature VCO is a sticker, informing about the production date. (MMYY – MM = month / YY = year.) If the module was made before October 2015, the upgrade is useful.
• New versions of the A-110-4 come with an IC named TL082, which is situated right behind the Cosinus connector on the circuit board. If such a component is present, the upgrade is unnecessary.

 For upgrading an A-110-4 with the amplifier kit, basic soldering skills are required.