This is a vintage 1979 Ross Compressor electric guitar effects pedal. This particular example, serial number 57531, is in very excellent all original condition and includes the original box with the original Ross pedal line advertisement! Quite interestingly, this particular example displays an anomalous and rare mis-printed graphic, as both control knobs are missing their respective designations for “sustain” and “level.” VCA (voltage controlled amplifier) compressors are perhaps the best for guitar applications, and of a small group of great vintage guitar VCA compressors, the early gray Ross is considered the absolute best. Many boutique brands simply copy the Ross Compressor’s exact schematic, and it has since become the most replicated compressor pedal ever made. The Ross compressor uses an integrated circuit (IC) to give precise control over gain reduction. This results in a less colored signal with minimal distortion. This early production example was produced by KEAS Electronics. Inc. for Ross. It is in very excellent all original cosmetic condition, it works perfectly, and sounds fantastic. Admired amongst players, collectors, and pedal builders alike, this example is one of the finest available!