Main speakers cut out when sub powered on

My suspicion is that when you turn the sub on while a signal is going into it, it briefly draws a huge amount of current from the AC line, until its circuits complete the turn-on process and reach a controlled and stable state. That briefly causes the AC line voltage to drop, in turn causing one of the components in the main signal path to cut out.

The Auto On circuit presumably brings up the other circuits in the sub, including the high power amplifier circuits, in a more controlled manner, because that is what it is designed to do.

Your sub contains a 1,000 watt Class D amplifier. From a technical standpoint my instinct would be to avoid turning a high powered component like that either on or off while a signal is going into it.

Regards,
-- Al

Although I doubt it's the AC line voltage drop because, when I have the sub disconnected from the amp, powering on the sub has no affect on the main speakers/amp, it's only when the sub is connected to the amp the main speakers cut out.

That is not inconsistent with my theory, because there is no signal going into the sub when it is disconnected from the amp. My theory is that the presence of an input signal causes the sub to briefly draw an abnormally large amount of AC current when it is turned on, until all of its circuits reach their normal operating conditions.

The amp is not going into protection mode but the sound cuts out for a brief moment.

It could be any electronic component in the main signal path that is muting or cutting out during that time, not necessarily the amplifier.

Any other ideas?

No, that theory is the only one that occurs to me. Unless, perhaps, your main amp has balanced outputs or is bridged. Let me know if that is the case.

Regards,
-- Al