Amp Specifications

Discussion in 'Archived Threads 2001-2004' started by Samuel Des, May 31, 2002.

  1. Samuel Des

    Samuel Des Supporting Actor

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    In general, are amplifier power specifications more reliable? (as compared to receiver specifications.)
     
  2. chung_sotheby

    chung_sotheby Supporting Actor

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    I would have to say yes. Receiver sometimes only state what the power is for one channel driven. Good Amps tend to over build the guts, like the toroidal transformers and capacitors, as to protect the amp from overloading. Receivers, on the other hand, tend to spend the least amount of money on their amps. Sometimes, with good stand alone amps, the specified wattage is actually lower than what the amp can do.
     
  3. Samuel Des

    Samuel Des Supporting Actor

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    Thanks Chung. I have two rules of thumb taken from the I-net, and it really confuses the comparisons.

    1. Take the max power consumption. Divide by number of channels. Divide by two. This is supposed to approximate the "true" power, or:

    2. Take the 4 ohm rating and divide by two to get the true 8 ohm rating.

    Using these rules of thumb, I have found very unusual discrepancies among amps and among receivers. I think my HK-7000 "passed" these "truth" tests, but I didn't check the numbers yet.

    My concern is that, with a new amp, I want to make sure I'm getting what, well, they say I would be getting.

    Is either rule okay?
     
  4. chung_sotheby

    chung_sotheby Supporting Actor

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    Both rules are rather general observations. If there was any rule that I would trust, though, I would go with the first one, that seems to make a little more sense. The second rule is correct in a purely theoretical sense, but not in the real world. Ideally, an amp would double in power with the halving of impedence. So a 100w amp into 8 ohms would be a 200 watt amp into 4 ohms. Most amps show a 1.25-1.5x multiplication factor in the halving of impedance, but this is mostly because of the internal components not being able to handle the heat that a 4 ohm output will produce. So while an amp may be able to safely do 150 watts at 4 ohms, it may also be able to do 100 watts into 8 ohms, not 75 watts into 8 ohms as your second equation calculates. As for receivers, I generally use a very broad rule of thumb that a receiver will only output about 60-80% of its rated power, all channels driven. But at the same time, your ears will probably bleed if you have 5 channels (or more) driven at 100 watts into any somewhat sensitive speaker setup.
     

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