Erm...what the heck IS the 4 ohm switch?
Don't Push It!
ahem.
It is
not uncommon to find those switches on... shall we say... lesser A/V (and some hifi audio) receivers. They either limit the current capability of the power amp section, or perhaps just add some series resistance, so that the amp won't be overtaxed by a low impedance load. Yamaha fan that I am, I'll note that Yamaha is
notorious for employing this kludge. I guess the switch, even if it also has some ancillary circuitry besides some power resistors
, is cheaper than building a power amp/power supply with sufficient grunt to handle 4 or 8 ohm loads equally well.
Rando internet photo -- although, with some chagrin, I must admit that I have one of these. I picked it up from the freebie pile at a regional antique electronics swapmeet a few years back, OK?