At present in the Institude for Nuclear Research of RAS has been working on the creation of a large-volume scintillation detector at the Baksan Neutrino Observatory (BNO) to register natural low-energy neutrino fluxes, including from astrophysical sources. One of the prototypes of such a detector being developed at the BNO is an acrylic sphere with the diameter of 500~mm filled with a liquid scintillator. Matrices of silicon photomultipliers (SiPM) as photosensors are used to measure the total light output from the interaction of particles in a scintillator and to obtain images of such events. This approach makes it possible to separate useful events from background ones and thereby to lower the background when monitoring Supernova explosions in our Galaxy. The paper describes the prototype of a large-volume detector and presents the measurement results.