http://www.customaudioelectronics.com/amp_selectors.htm
Features:
• Safely and silently switch up to 4 amplifiers into the same cabinet or load device!
• Unique priority circuit only allows 1 amp on at a time!
• Protection circuitry safely guards unselected amps.
• Provides multiple line level outputs with a level control for each amp to drive effects and power amps.
• Front panel LED's indicate status of each amp.
• Super low noise buffer circuit provides impedance matching and eliminates passive instrument input.
• Remote controlled from simple latching footswitches or controlled by a wide variety of MIDI system controllers utilizing latching footswitch type functions.
• Remote power supply for lowest noise.
• 2 auxiliary line outputs. Useful for mixing external preamps with the selected amp.
• Line level volume loop can be used to remote control line level volume or for patching in noise reduction units, effects, etc.
Benefits:
• Sonically transparent passive switching elements provide unsurpassed clarity while uniquely switching up to four amplifiers (one at a time) into a common speaker system or load device.
• Easily allows for the popular system configuration of a center dry cabinet with stereo effects cabinets (a stereo power amp and effects would be required). See diagram.
• Provides a line out for each amp regardless type. No need to modify amps for line outs and effects loops. Even non-master volume amps work fine!!
• Eliminates the need for multiple speaker cabinets and/or load devices when using multiple amps.
• No elaborate switching system required. Simple latching footswitches are all that are needed to control status of amps.
There is also Skrydstrup R&D:
http://www.skrydstrup.com/as44.htm
Our new AS44 Amp Switcher is truly a unique product.
4 amplifier heads can be used with only ONE cabinet.
In addition you have 4 control switch functions for remote switching i.e. channels on your amplifiers.
All outputs on the AS44 Amp Switcher are floating stereo TRS jacks, ensuring that no ground loops and/or hum/noise will occur when using this unit. Even the Line Outs on the rear are floating stereo TRS jacks.
The AS44 is fully Midi controllable, and recognizes both Midi Program Change and Midi Control Change commands.
EDIT: Oops, I just realized the 1 space requirement, but figured I'd leave the info here-- in case others may find it useful.
Brad, I know others are talking about how the unused amps don't need load protection, but there is NO WAY that I would risk my valuable amps with something other than the CAE, Skrydstrup, or the now discontinued Egnater Amp Selector. While technically the guys who are saying that the unused amp doesn't need a load are correct, one spike may be all it takes to be facing a rather inconvenient situation at a gig, and/or a potentially disastrous repair bill.