Fiio E12 DIY Limited Edition Portable AMP HeadPhone Slim Amplifier 24V High voltage,high current power supply 2 simple screws for quick and reliable internal access Comes with op-amps for 12 sonic combinations Please double-check for correct orientation of op-amps and adapter PCBs before installing the op-amps and the PCBs onto the main board and re-check after installation. Installation with reversed orientation may destroy op-amps and the E12DIY. 4 architectural variants;The buffers come in through-hole and surface-mount variants (the latter of which need to be soldered onto the adapter PCBs for use). The op-amps also come in single-channel and double-channel variants. Thus there are four arc