Can I operate the 60W amplifier (or any of the others) into a 4 ohm or 2 ohm load for more power?
Four ohm loads will often be acceptable, but I strongly recommend using paralleled (or more powerful) output transistors. It may also be necessary to use a small heatsink on the drivers, as their dissipation is usually more than doubled. Two ohm loads are very difficult for any amp not designed specifically for this impedance. I do not recommend using any of the published circuits for 2 ohm loads.
