I have a Royce i 620 that im scratching my head on. I have tried 3 or 4 different mics and I cannot turn the volume up hardly at all and it squeals. When I unkey the mic, I get a very loud BOOOOMP sound. Ive tried a turner jm plus 3, a plus 2, a unbranded power mic, 2 d 104s and a stock mic. I own another I 620 that doesn't have this issue, and I can run what I want on it..