I own a fairly new DT50 and HD500 that have worked fine up until about three weeks ago. During church the volume on the DT50 dropped to about half the normal level on the I, II, and III- topology-based tones. The tone based on the IV topo stayed at full volume (needless to say the congregation got a little confused when the Mesa sound was all I could really play through and be heard.) I tested the pedal and amp separately, and each works on its own- the pedal plugged into my Micro Cube produces full volume tones, and all four topologies on the DT50 work fine when it is used without the HD500. I've tried a different XLR cable, though I have yet to try the AES/EBU cable I've been hearing about. I don't think it is a blown tube, since the amp works fine at both regular and half volume settings without the HD500. I also have not tried updating firmware, etc, which I will attempt this weekend. Thanks in advance for any tips you might have!