This is a power amplifier module I purchased from AliExpress. It's a full discrete amplifier, meaning it doesn't use an amplifier IC, which is quite romantic, isn't it (?) I built it, but I couldn't get a power transformer, so I never used it. (Therefore, I cannot answer any questions about its operation, please understand.) The operating power supply is AC ±18V. Please be aware that this is a product of amateur soldering when purchasing.