A-Designs EM-Gold is a pre-amp for the 500 series, manufactured by A-Designs.
Official description[]
EM-Gold - The EM-Gold’s combination of EM-Silver and EM-Red transformers make for the perfect sounding floor tom. It is also the preamp you should reach for when you want that speaker moving, low/mid thump from heavy guitars. The EM-Gold is ideal for fattening up thin-sounding sources; on mics lacking low mids or upper bass warmth; and mid transients, such as percussion and drums. It also shines on vocals, bass, and even drum machines. If you’re going to move air (the secret of a big sound), go for the Gold.