'For these Sonus Faber’s you need an amp that can almost double it’s wattage from 8ohm to 4ohm to 2ohm (eg: 100w 200w 400w) And that means amps that deliver hefty current. No tube/ Mosfet/Class D amp for these. You need big amp/s that have "bi-polar (bjt)" output stages this type of amp will do these speaker justice. As right through the bass and upper bass they are 2.5ohm, and at the low bass with 4ohms and -50degrees phase angle load (EPG), this can look like 1.5ohms to the amp.
Just a snippet from the Stereophile test results on these speakers.
"With an impedance magnitude that drops to 2.5 ohms throughout the upper bass (fig.1). There is also a punishing combination of 4 ohms magnitude and –50 ° electrical phase angle at 70Hz that will suck gobs of current from the amplifier."
Stereophile in the review above used Mark Levinson No.33, Boulder 860 and the Parasound JC1’s these are all bi-polar (bjt) output amps.'
Post written by Georgehifi few years back