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Equal Power Ratings Don't Mean Equal Power?

by August 30, 2004
Q: I would like to know the answer, because I owned a sony 545 that was rated at 100wts, then I upgraded to a sony 845 that is also rated at 100wts. The 845 sounded much stronger,cleaner just plan better also w/ less effort far as the volume was concerned. Now can someone please tell me why do they sound so different?

Audioholics: When comparing power specs between different Receivers, you must pay careful attention to the test conditions that apply to the specifications.

For example:

  • Many lower end models and brands tend to rate the power of their amplifiers at 1 kHz, as opposed to full bandwidth. The difference between a full bandwidth (20 Hz to 20 kHz) and 1 kHz can be as much as 20 % of total power.
  • When comparing RMS power, make sure the rated distortion for the given power is comparable between the two models. It is easy for an amp to look like it delivers more power than another one whose power is rated at a lower distortion level.
  • When comparing multi channel power ratings, be certain that the ratings of each amp are under the same loading constraints:
    • Check the load impedance rating (IE. 8 ohms).
    • Verify how many amps are being driven simultaneously. (Note: Many Receivers only rate power for two channels driven).
    • Check the bandwidth of the rating as mentioned in the 1st bullet.

It is quite easy to estimate the power capability of a receiver just by inspection. Listed below are seven items to look for in a Receiver to determine its power capabilities:

  1. Size of power transformer.
  2. Amount of Filter Supply Capacitance.
  3. # of discrete output transistors per channel.
  4. Surface area of heatsinks for power amplifiers.
  5. Fuse rating of power supply.
  6. Fuse rating of power rails.
  7. Weight of Receiver.

The Bottom Line

Don't be mislead by rated power to determine just how capable a Receiver will be a producing enough sound for your speakers and loudness preferences. Be extra careful when comparing specs between models and brands to make sure you are comparing apples to apples.

In terms of the Sony 845 model sounding "much stronger,cleaner just plan better also w/ less effort far as the volume was concerned" , I can attribute that to the reasoning above.

The model 845 probably has a bigger power supply, and more capable power amplifier, which is more able to drive your speakers with clarity and authority. Don't be concerned about the volume knob not having to be turned up as loud as the older model. This has little or no relevance to the power capabilities of the two models. It is quite possible that the 845 model has a volume knob that peeks out much sooner than the 545 model.

Note: Never use the position of the volume knob to determine the power capabilities of two Receivers. This is a very inaccurate method of determining power.


About the author:
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Clint Deboer was terminated from Audioholics for misconduct on April 4th, 2014. He no longer represents Audioholics in any fashion.

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