I copied this from a post from Kent of ESS. He's the expert on F81s. Has them. Sells them. Rebuilds them.
The Stax ELS F-81 is one of the most difficult loads one can find. From 40Hz-800Hz the impedance is well above 100 ohms. Around 180Hz the impedance peaks around 512 ohms! Amazing.
Solid state does not like this sort of load. A Zoebel network is highly recommended if using solid state. OTL tube amps are ideal but can be pricey. Transformer coupled tube amps will handle this kind of load.
Power output will depend on required SPL in the listening room. A smallish room with a nearfield set-up will yield SPL in the 90-92 range with a mere 60 watts. I use an ARC D-70, 65 watts, with good results except for clipping if I want to drive things. Or I have an ARC Ref300, 280 watts, that will drive them louder than I like without clipping issues. Well I can clip the Ref300 but then I am pushing the speaker close to failure, probably the transformer.
Any power amp will need to have a large, robust and stable power supply. An ARC VT130, 110 watts, would be ideal with these speakers and is within your budget. The AtmaSphere M-60 would be a great match if maybe just a little under powered.
The Stax ELS F-81 is one of the most difficult loads one can find. From 40Hz-800Hz the impedance is well above 100 ohms. Around 180Hz the impedance peaks around 512 ohms! Amazing.
Solid state does not like this sort of load. A Zoebel network is highly recommended if using solid state. OTL tube amps are ideal but can be pricey. Transformer coupled tube amps will handle this kind of load.
Power output will depend on required SPL in the listening room. A smallish room with a nearfield set-up will yield SPL in the 90-92 range with a mere 60 watts. I use an ARC D-70, 65 watts, with good results except for clipping if I want to drive things. Or I have an ARC Ref300, 280 watts, that will drive them louder than I like without clipping issues. Well I can clip the Ref300 but then I am pushing the speaker close to failure, probably the transformer.
Any power amp will need to have a large, robust and stable power supply. An ARC VT130, 110 watts, would be ideal with these speakers and is within your budget. The AtmaSphere M-60 would be a great match if maybe just a little under powered.