Your amp requirements will depend on your room, desired listening levels, system, prefered music and individual taste. With that in mind, I suggest you find something that can deliver at least 200 Watts into 4 Ohms. The 3.5's are not forgiving of abberations in the upper frequency range and benefit from an amp that can deal with the demands the equalizer presents in the lower frequenicies. With all due respect to Rcprince the best amps I've heard on the 3.5's were Krell KMA 160's in an all Krell system. I have not heard them with the Thresholds that were rumoured to be used in their development. I did hear them sound nice but underpowered with Forte, so I think it's fair to presume that the higher powered (quality?) Thresholds might work well. I have heard them sound nice with big solid state c-j's (A's) and would imagine that the right Pass equipment would work well. I did not care for the sound with Adcom, Rotel, Mark Levinson, Spectral, McCormack or c-j tubes, and all for different reasons. I can't speak from experience but Audio Research tubes are rumoured to work well. Pertinent 3.5' specs: Bandwidth (-3dB) 20Hz-22KHz, Amplitude response 23HZ-20KHz +/-2 dB, Sensitivity 88/89dB (depending on vintage) @ 1 watt-meter, Impedance 4 Ohms (both nominal and minimum), Recommended Power 40/50 (depending on vintage) - 250 watts. When I questioned Jim Thiel about the power recommendations he said that they were used with the standard 8 Ohm ratings of quality solid state amps that were able to "double down" in mind, and suggested doubling those figures if using tubes. IMHO the 3.5's (and most Thiels) cry out for high quality amplification to make them sing. Good luck!
