A noise source is an essential component of random bit generator, and is either an application or a device to provide entropy from analog noise. In 2008, Colesa et al. first proposed two software strategies for constructing noise source based on race conditions. However, Colesa et al.'s designs require a lot of threads and even suffer from a low bit rate. Moreover, setting a parameter for each system is complicated since the parameter is related to the entropy and the bit rate at the same time. In this paper, we propose new constructions of noise source based on race conditions. We call them NSRC-1 and NSRC-2. The bit rate of our designs is improved by up to 819 times higher on multi-core systems with high entropy. The parameter adjustment becomes straightforward by removing the relation between the parameter and the entropy. Additionally, since NSRC-1 and 2 require only two threads at once, they are more available software-based methods for harvesting entropy not only on general devices but also on mobile devices.