Currently, there are about 4 amps, but 2 of them are low dollar temporary amps while I am experimenting with a Forte' model 3. It won't be even close to the original amp when finished, due to having to replace output transistors, power capacitors, and few other parts. At the moment, a Carver A220 is in the system, and has surprised me quite a bit, sounding way better than I expected. Before that, a flurry of inexpensive amps were tried, and even a digital amp that I built. It has become the sub amp, and does very well.