- HL2+ AK4951 Companion Board With HL2 IO Board The IO board is a general purpose control board and depends on the programming of its RPi Pico processor. The AK4951 Companion Board Kit implements a dedicated Hardrock-50 amplifier control interface and is also capable of controlling the Icom AH4 ATU (and compatible, there are many). This is not to mention the Mic and Phones jacks, Speaker connector, CW sidetone, and FPGA gateware built-in keyer. The IO board (with the appropriate code) can control the HR-50 as well and if you use it, you would simply not use the CB Kit DB9 cable/connector, power switch/harness/header (unless you are using the HL2+ 55mm Front End Plate which has a power switch opening provided), and rear end plate. The IO board end plate has no accommodations for these (and has its own DB9). Using the IO board requires using its rear end plate. Other than this, the two (CB and IO) can coexist and be used at the same time. All functions of the HL2+ AK4951 Companion Board remain intact and functional in the presence of the IO Board.