Hello,
I have heard the Parasound Halo A21 on numerous speakers at numerous dealers and it is an amazing amplifier, let alone for the cost even at full retail of about $2,300. it does offer a true class A up to about 7.5wpc (straight out Richard Schram's Email to me about this amp) and is beautiful sounding. I could recommend it for many systems or applications so easily and with no reservations at all. In fairness, I have not the NAD model, but for what I have heard in the A21, I thoroughly enjoyed it every single time. What Rlwainright said about the damping factor getting above 100 or so is true. All the damping factor is is the ratio of the power amp's. output imedance to the input imedance of the speaker at a given frequency. That then has a strong impact on how well the amplifier functions as a constant voltage source despite varying current loads and that in turn impacts the amplifier's ability to control the load (cones / diaphragm, etc.). Higher is always better in general though, especially at a very low frequency, such as 20Hz, since bass draws more current than treble, etc. Hope that helps. Parasound A21.
I have heard the Parasound Halo A21 on numerous speakers at numerous dealers and it is an amazing amplifier, let alone for the cost even at full retail of about $2,300. it does offer a true class A up to about 7.5wpc (straight out Richard Schram's Email to me about this amp) and is beautiful sounding. I could recommend it for many systems or applications so easily and with no reservations at all. In fairness, I have not the NAD model, but for what I have heard in the A21, I thoroughly enjoyed it every single time. What Rlwainright said about the damping factor getting above 100 or so is true. All the damping factor is is the ratio of the power amp's. output imedance to the input imedance of the speaker at a given frequency. That then has a strong impact on how well the amplifier functions as a constant voltage source despite varying current loads and that in turn impacts the amplifier's ability to control the load (cones / diaphragm, etc.). Higher is always better in general though, especially at a very low frequency, such as 20Hz, since bass draws more current than treble, etc. Hope that helps. Parasound A21.