The Retro DoubleWide 500 series compressor sounds fantastic! This all tube design is built from the ground up taking its cue from the famous 1960's STA Compressor. The Doublewide features four NOS 6BJ6 small variable-mu tubes that function as the actual compression circuit and is configured in a fully complementary push-pull design. The sound is big and ballsy, fat and rounded. Exceptional on vocals and guitars and in the convenience of the 500 series format!