The official site of Ay_Emul is located at http://bulba.untergrund.net.
On the official site, you can find the latest versions of Ay_Emul (including beta versions, which eventually become much more functional than the previous official release), skins, music archives, links to thematic resources, utilities, documentation on file formats, AY and YM programming, packages for embedding emulation in their programs, source texts, as well as technical information on chips AY-3-8910/12 and YM2149.
If you want to write music for these chips, you can download the Vortex Tracker II editor for Windows from the official site. This is another major project of mine, which is based on the Ay_Emul engine and the knowledge accumulated during its writing about various formats of ZX Spectrum music.