Power Output Varying With Ohms

[ChGr]

What's the science/engineering behind the fact that some amps have a constant power output regardless of the ohm rating of the speakers (McIntosh seem to do this) whereas in most amps the power output varies with the ohm rating? I understand the concept of the resistance, but what's with the McIntosh specs in this regard?

 

[TLS Guy]

What's the science/engineering behind the fact that some amps have a constant power output regardless of the ohm rating of the speakers (McIntosh seem to do this) whereas in most amps the power output varies with the ohm rating? I understand the concept of the resistance, but what's with the McIntosh specs in this regard?

McIntosh amps generally have auto transformers at the output. I actually do not like the system and Mac would not be my choice of amp.

It is done to absolutely avoid the possibility of DC off set from amp failure damaging expensive speakers which they would be on the hook for. Of course Mac have a lot of flowery language about balancing loads, but I'm sure my explanation of why they do it is correct.

 

[slipperybidness]

What's the science/engineering behind the fact that some amps have a constant power output regardless of the ohm rating of the speakers (McIntosh seem to do this) whereas in most amps the power output varies with the ohm rating? I understand the concept of the resistance, but what's with the McIntosh specs in this regard?

A true load invariant amplifier would be the IDEAL amplifier. Of course, in the real world it simply is not possible to design a completely load invariant amplifier.

And, I agree with TLS completely on his comments.

 

[ski2xblack]

What's the science/engineering behind the fact that some amps have a constant power output regardless of the ohm rating of the speakers (McIntosh seem to do this) whereas in most amps the power output varies with the ohm rating? I understand the concept of the resistance, but what's with the McIntosh specs in this regard?

I think the specific answers you seek lie in properly defining "power" while considering the amp's output impedance and speaker load. Some hints: the industry long ago adopted the voltage source paradigm for amplification; even the output-tranny coupled McIntosh amps have fairly low output impedance, and so power (current) will vary with the load; excepting some exceedingly rare fringe odd-balls, speakers are designed assuming low output impedance amplification is being used.

 

[Ampdog]

What's the science/engineering behind the fact that some amps have a constant power output regardless of the ohm rating of the speakers ......

There is something wrong with such a statement. Assuming that the rail voltage(s) are constant (ideally so), Mr. Ohm says that power equals sq.(voltage) divided by resistance. Thus unless the voltage supply does some funny things, the output can never be independant of the ohm rating of the load ....

 

[TLS Guy]

There is something wrong with such a statement. Assuming that the rail voltage(s) are constant (ideally so), Mr. Ohm says that power equals sq.(voltage) divided by resistance. Thus unless the voltage supply does some funny things, the output can never be independant of the ohm rating of the load ....

With the Mac auto transformers you have to use the right transformer tap to get the best power output. It is similar to the old days of tube amps with taps on the output transformer.