Actually, I -am- confused about Phil's post. Phil Leigh;292086 Wrote: > > As an example, if your power amp can swing 40V from its PSU rails, has > an impedance of 2 ohms and is running into an 8 ohm speaker, the max > voltage the amp could deliver to the speaker would be: > 40*(8/8+2) = 32 volts > The power the amp could deliver into the speaker would be (32*32)/8=128 > watts > and > the power lost inside the amp by heating up the heatsinks would be > (32*32)/2= > 512 watts of heat > > That's roughly 25% efficiency. This is for a Class A amp with full > power delivery at all times (not class B!!!) >
In your examples you treated the amp as a voltage source and the output impedance as if it were in -parallel- with the load. But (regardless of the class) I thought output impedance is defined as the part of the internal resistance that's in -series- with the load (again, treating the amp is a voltage source, as you did). If that's right, an amp with an output impedance of 2 ohms driving an 8 ohm speaker will only lose (40-32)*(40-32)/2 = 32 watts of power, not 512, and the efficiency goes to 1 as the output impedance goes to zero. The reason class A amps have low efficiency is because they have an output transistor which dumps current to ground even when the signal is zero. Right? -- opaqueice ------------------------------------------------------------------------ opaqueice's Profile: http://forums.slimdevices.com/member.php?userid=4234 View this thread: http://forums.slimdevices.com/showthread.php?t=46347 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
