Originally Posted By: dakkon
Originally Posted By: Andrew

In the A1500 we are running +/-85Vdc rails

Does the rail voltage remain constant regardless of load impedance?

I am under the impression, that amps which have power ratings that do not double as load impedance halves varies their rail voltage...If the rail voltage is held constant, then as the impedance halves the power output should double, infinitely in a theoretical situation.

Going off of Ians' chart the rail voltage that Andrew provided, the rail voltage remains constant until there are 3 channels driven at 100%, at which time the rail voltage reduces when a 4ohm load is present. At 3 channels driven @100%, the rail voltage should reduce to approximately 46Vrms or 77% of 60.095 Vrms. the 77% reduction in voltage is representative of the difference between 650W and 500W.

Do i have a correct conceptual understanding of how this works?

The rail voltage remains constant until we reach the maximum continuous current capability of the power supply, at which time the rail voltage will reduce or "sag". This is why the power output drops at a certain point when more channels are added. At that point the maximum rail voltage is no longer the limiting factor in output power, it's now the supply current and the subsequent drop in rail voltage. If we had an unlimited supply current available, the power output would keep doubling at each halving of the load impedance until we reach the current limits of the amplifier output stage, which has current limiting protection. On the A1500 this will not take place until you're down into sub-2ohm territory.