I just have to take a minute and throw this company's customer service some love. I have an MXR M87. Although I do have some background in sound reinforcement, I'm not that experienced with bass compression. I been trying to use compression on my bass at gigs and have been disappointed that it didn't seem to have any effect and I thought maybe it was broken. He didn't make any effort to deny that it might be broken. He very painstakingly explained how to use the tool and the way that guitar and bass players typically use them. He suggested that first I try again to test out the unit with the insight he shared, then as a second stage test, to go to a guitar shop and try one of theirs the same way, then as a third option, I could send it in to him. I'm fairly convinced now that I just wasn't using it right. The knobs, switch, and jacks are all in good shape. Pro-tip - don't use the volume on the instrument as much to limit the volume. Crank it and let the compressor and amp do that work. Apparently, lots of guitar players will literally dime the volume and do all signal strength tenuating through the effects and amp. Also, MXR has fantastic customer service.