Amps vs. Watts - What is more important

Discussion in 'AV Receivers' started by Paul D. K., Dec 19, 2003.

  1. Paul D. K.

    Paul D. K. Stunt Coordinator

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    I've compared two different amps and don't understand the trade-offs. I've decided on Amp 2 but want to make sure I haven't missed something. The first amp "doubles down" the other doesn't - at least mathematically - based on published specs. Which one is better for low level listening and better clarity? Driving B&W 802's or 803's.

    Amp 1: 200 W/channel @ 8 ohms; 400 W/channel @ 4 ohms; Peak to peak power - 55 amps. Dampening factor - 800 (static).

    Amp 2: 250 W/channel @ 8 ohms; 400 W/channel @ 4 ohms; Peak to peak power - 150 amps. Dampening factor - 750 @ 50 hz.
     
  2. Chu Gai

    Chu Gai Lead Actor

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    Most likely irrelevent. I'm assuming that distortion for both is inaudible and that the lower ratings also 20-20 and all that. If your speakers are say 4 ohm nominal, then you want to get a handle on what the amp's short term capability is into 2 ohms but this looks like quite a bit of power. The DF is irrelevant. With regards to the amps # that was given, you'll need to get further clarification from the manufacturer as some lump the total amps for all channel into that #. Basically, as a speaker's impedance drops, it'll require more amp to drive the same voltage into the speaker.
     
  3. Paul D. K.

    Paul D. K. Stunt Coordinator

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    Chu -

    Amp 1 is a five channel amp. Not sure of the 2 ohm rating. The 55 amps peak to peak is with all channels running.

    Amp 2 is a mono-block and has 650 watts @ 2 ohms.
     
  4. Dan Driscoll

    Dan Driscoll Supporting Actor

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    Power, measured as Watts, is Current multiplied by Voltage (P=IE). So wattage changes proportionatly with a change in either voltage or current. This means that a circuit outputting 50 amps at 5 volts equals 250 watts. But a circuit outputting 5 amps at 50 volts also equals 250 watts. So while the power is equivalent, it is not equal.

    WRT to speakers, high current watts are better than high voltage watts. This is because speaker motors (voice coils) are basically inductors. Inductors are current storage devices, in the same sense that capacitors are voltage storage devices. Inductors are much more efficient when driven by high current than when driven by high voltage. So high current amplifiers exert better control over the speaker motor than a high voltage amplifier does.

    Why the difference? It is easier and cheaper to increase voltage in an amplifier than to increase current. This is why some less expensive high power amps (i.e. receivers) struggle to drive some speakers, especially low impedance speakers (2 or 4 ohms), while amps with a lower power rating but higher current drive the same speakers with ease.
     
  5. Chu Gai

    Chu Gai Lead Actor

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    Well yes...sort of. If you've got a musical selection with significant energy in an area of the musical spectrum where the impedance is at some minimum, then you'll need sufficient current to drive whatever voltage is called for. However, if your amp can't provide the voltage needed, it's irrelevant how much current you've got...things aren't going to sound good.

    Volts are cheaper than amps. Sure. But it's not about volts, nor is it about amps. It's about how much work is required to give a certain SPL. So, then what's the unit term for work? Volts...amps..or...?
     
  6. Doug Brewster

    Doug Brewster Second Unit

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    [​IMG]

    I didn't sign up for this class...didn't take the pre-requisites...[​IMG]

    So, riddle me this, isn't the performance also dependent on available power ("reserve")? Isn't that what makes A and A/B amps superior - they have their current constantly available?

    Please professor. I need these credits to graduate!!

    Slow and easy, please. I'm following the best I can :b and am interested in the course material.
     
  7. Paul D. K.

    Paul D. K. Stunt Coordinator

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    So - is there a bottom line? Which of the two amps?

    I find the techinical discussion educational and interesting (especially since the EEs that I work with didn't have time to talk about this before going on vacation), but I'm trying to make sure that buying #2 is the better of the two options.

    Thanks,
     
  8. Paul D. K.

    Paul D. K. Stunt Coordinator

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    Chu -

    Do I take your original response to mean either amp will do just fine and that you don't think that one has an advantage over the other?
     
  9. Kevin. W

    Kevin. W Screenwriter

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    You must not forget the efficiency of the speakers. There is a big difference from a speaker 88db vs 93db sensitive. Remember it takes doubling of the power to get a 3db increase.

    eg: 88db

    128w/1m = 109db

    eg: 93db

    16w/1m = 108db

    With a higher sensitive speaker either amp would do fine.

    Kevin
     
  10. Paul D. K.

    Paul D. K. Stunt Coordinator

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    Kevin -

    The speakers I have are B&W 803's (although I may upgrade to 802's). The sensitivity is 90 db. I'm assuming that this meets the definition of a high sensitivity speaker. Am I correct?

    Thanks,

    Paul
     
  11. Lewis Besze

    Lewis Besze Producer

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    High current amps [55amps are easily qualify as such]needed for a so called "tough to drive" speakers,and even then when you crank things up. So for low level listening, you would be fine with any of the 2.
     
  12. Chu Gai

    Chu Gai Lead Actor

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    Lewis is probably right. Would I have a preference is another matter but my preferences might not be yours. I would tend towards the monoblocks because IMO they offer greater flexibility. One amp dies you're not out of sound. I also happen to like power and the knowledge that amps can deliver power to 2 ohms. It's one of those manly things. I leave the finesse to the Men are from Mars Women are from Venus (so what's your head doing stuck in Uranus) crowd. I make no apologies for it nor do I make any sonic claims of superiority. This is just me.
     
  13. Shiu

    Shiu Second Unit

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    Everything being equal, take the high current one if you have 4 ohm speakers. For 8 ohm speakers, even 55 amps should be plenty.
     

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