I recently purchased the MXR M87 compressor. When it arrived I hooked it up and the LED lights were not responding. In addition the only two knobs that seemed to be working were the input and output. All the other settings seemed to sound the same. I realize that the effect is supposed to be transparent but there was no noticeable difference with different attack, release or ratio settings. Long story short I returned it and was sent another one. I am having the same issues with this one. I thought they may have sent the same unit back by mistake but I checked the serial number and it was a different pedal. Has anyone had this problem or am I doing something wrong? Or is it possible that I got 2 defective pedals with the exact same problem? This is the first compressor I've owned so any help would be appreciated.