Midfi,
Don't return anything just yet. Maybe I'm off base here, but it sounds to me like you are tripping the breaker with inrush current. When you first power on that amp, all the caps inside must charge and do so very quickly. This can cause a perfectly functioning circuit to trip as the initial momentary current exceeds the breaker's rating. However, those same caps discharge slowly unless drained.
I would suggest you try this: Power on the amp (with your pre off). If the breaker trips, turn the amp off then reset the breaker, then turn the amp back on. My guess is that after the breaker trips once (maybe twice), it doesn't trip again...until you turn the amp off for awhile and turn it back on. Instead of turning the amp off, leave it on all the time...it's better for the longevity of your electronics, anyway. Hope that helps and let us all know if that works...
Don't return anything just yet. Maybe I'm off base here, but it sounds to me like you are tripping the breaker with inrush current. When you first power on that amp, all the caps inside must charge and do so very quickly. This can cause a perfectly functioning circuit to trip as the initial momentary current exceeds the breaker's rating. However, those same caps discharge slowly unless drained.
I would suggest you try this: Power on the amp (with your pre off). If the breaker trips, turn the amp off then reset the breaker, then turn the amp back on. My guess is that after the breaker trips once (maybe twice), it doesn't trip again...until you turn the amp off for awhile and turn it back on. Instead of turning the amp off, leave it on all the time...it's better for the longevity of your electronics, anyway. Hope that helps and let us all know if that works...