Amps that switch on when receiving an audio signal


I see that there are power amps from Cambridge Audio and Parasound that switch out of standby and into operating mode when they receive an audio signal. This seems to me a pretty cool feature -- cool in more ways than one, of course. (Energy saving, etc.) Are there other amps that do this? Are there many? Is this becoming something of a commonplace and I'm just now noticing it?

Thanks.

-- Howard
hodu
I have an old Harman Kardon amp from the mid 90s that has that option.
As for subs, most powered subs offer this option.

A while back I bought an amp on ebay (can't remember the brand) that was listed as "dead" for parts only. When it arrived I noticed it had an auto on switch. I turned the switch off and the amp worked great. After some research I adjusted the auto on trigger and that worked great also.
My Sunfire 300 only uses 20...25w stand-by so no need to switch on-off. It stays on 24/7 and always ready to blast music.
My Sony does, and also turns itself off with no signal after 15 minutes. Utterly love both features. I hit pause on the Sony server when music is playing, leave the house, and both units auto shut off.