The complexity of information processing in the brain requires development of technologies that can provide spatial and temporal resolution by means of dense electrode arrays paired with high-channel-count signal acquisition electronics. In this work, we present an ultra-low noise modular 512-channel neural recording circuit that is scalable to up to 4096 simultaneously recording channels. The neural readout application-specific integrated circuit (ASIC) uses a dense 8.2 mm x 6.8 mm 2D-layout to enable high-channel-count, creating an ultralight 350 mg flexible module. The module can be deployed on headstages for small animals like rodents and songbirds, and can be integrated with a variety of electrode arrays. The chip was fabricated in a 0.18 µm 1.8-V CMOS technology and dissipates a total of 125 mW. Each DC-coupled channel features a gain and bandwidth programmable analog front-end, along with 14b analog-to-digital conversion at speeds up to 30 kS/s. Additionally, each front-end includes programmable electrode plating and electrode impedance measurement capability. We present both standalone and in vivo measurements results, demonstrating readout of spikes and field potentials that are modulated by a sensory input.