As the saying goes, and as Charles alluded to, there is an exception to every rule. And from a technical standpoint I don’t find it surprising that the Aries Cerat Concero 65 SET amp can provide excellent results with the CS 3.7.
First, while the speaker’s impedance is of course very low, as well as challenging in terms of phase angles at certain deep bass frequencies, it is relatively flat throughout most of the frequency range. Which will minimize the tonal consequences of impedance interactions with the amp, that would be problematical pairing many SETs with many other speakers. Second, both the amp (apparently weighing 220 pounds per monoblock) and its power tubes (each of the paralleled 813s has a plate dissipation rating of 125 watts) are monsters. And given the 65 watt rating of the amp the tubes are probably being run conservatively, in a region that provides better linearity than if they were being pushed closer to their limits.
It would be interesting to know the output impedance of the amp, or equivalently its damping factor. (The output impedance of the 4 ohm tap would be approximately 4 ohms divided by the damping factor). If that is relatively low (for a SET), say in the vicinity of 1 ohm (equivalent to a damping factor of 4 or more), it would further account for the amp pairing well with the CS 3.7.
In any event, if you purchase that amp keep away from the wire that runs up to the plate cap on top of the power tubes, as can be seen in this photo. It probably has around 2,000 volts on it. Probably only around 1,000 volts or so on the plate cap of the driver tube, though. 😉
Good luck, however you decide to proceed. Regards,
-- Al
First, while the speaker’s impedance is of course very low, as well as challenging in terms of phase angles at certain deep bass frequencies, it is relatively flat throughout most of the frequency range. Which will minimize the tonal consequences of impedance interactions with the amp, that would be problematical pairing many SETs with many other speakers. Second, both the amp (apparently weighing 220 pounds per monoblock) and its power tubes (each of the paralleled 813s has a plate dissipation rating of 125 watts) are monsters. And given the 65 watt rating of the amp the tubes are probably being run conservatively, in a region that provides better linearity than if they were being pushed closer to their limits.
It would be interesting to know the output impedance of the amp, or equivalently its damping factor. (The output impedance of the 4 ohm tap would be approximately 4 ohms divided by the damping factor). If that is relatively low (for a SET), say in the vicinity of 1 ohm (equivalent to a damping factor of 4 or more), it would further account for the amp pairing well with the CS 3.7.
In any event, if you purchase that amp keep away from the wire that runs up to the plate cap on top of the power tubes, as can be seen in this photo. It probably has around 2,000 volts on it. Probably only around 1,000 volts or so on the plate cap of the driver tube, though. 😉
Good luck, however you decide to proceed. Regards,
-- Al