A friend with a new house has an integrated amp with one set of speaker outputs. He was hoping to be able to hook up a second set of speakers to it, so he could play Pair A or Pair B, or both simultaneously.

I can rig up a simple switch box that will allow him to play Pair A or Pair B, but rigging it so that both pairs play at the same time gets more complicated (presumably they'd have to be wired in series).

I see that Parts Express has "speaker selection systems" that claim "Amplifier is fully protected against low impedance and overload by a protection On/Off switch. Switch is located on the bottom so protection can't accidentally be switched off and damage the amplifier."

Does anyone know how these things work or have a schematic? Even though these things are inexpensive, I hate the spring clip terminals they come with so I'm thinking of making a diy version as a housewarming present.

Thanks in advance.

• PE "Speaker Selection System"