Approx price of 200W...?

Discussion in 'AV Receivers & Amplifiers' started by russyj, Jul 31, 2012.

  1. russyj

    russyj
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    Hi All,

    Recently upgraded from a Denon 1907 to a Onkyo 875 running KEF IQ5's (and a BK XXLS400). I mostly listen to music, and initially wasn't impressed with the 875 musically (normal mode runs ~120W), then switched it to bridged mode (200w) and was blown away. For the record I listen to my music rather loud (-10db on the 1907, -15db on the 875 in bridged), and the source is an Arcam CD72.

    To allow me to use the 875 in bridged mode without having to unplug/replug cables every time I want surround (you need to physically rewire the connectors to go bridged to normal surround) I put in a Beresford speaker switch.

    I'm now thinking what I'm doing is stupid, as I don't really use the HDMI functionality of the 875 over my 1907, and that I'd be better off selling the 875, using the 1907 for movies and a separate amp for music.

    Because I like my music loud, I need the wattage. The 875 cost me just under £300 2nd hand, but I can't seem to find any 2 channel amps that will give me 200W for anywhere near that money.

    My question is this - does the 875 in bridged mode represent exceptional value for money (W/£), or am I missing the point somewhere here?

    Kind regards and thanks in advance,

    Russ
     
  2. dante01

    dante01
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    Why do you need 200 watts per channel?

    I can get a 50 watt amp to output audio that is beyond advised safety limits and cause permanent hearing damage. Maybe look up what watts are?

    200 watts equates to what you'd expect of a small mobile disco PA system.

    You get the same SPL levels regardless of the wattage. -15db is the same whether you are powering the speakers with 20, 200 or 2000 watts. Watts are not a unit of loudness or sound pressure.
     
    Last edited: Jul 31, 2012
  3. Nevaborn

    Nevaborn
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    Just to back Dante up 200 W is overkill and will not improve volume or quality of sound.
     
  4. russyj

    russyj
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    I was under the impression that generally higher wattage led to less distortion at higher volumes?

    Also surely the db scales on the receivers are purely indicative, as your actual SPL levels depend on a speakers signal/noise ratio or "sensitivity", which the amp can't know?
     
  5. dante01

    dante01
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    No, you have to look at how much THD and signal to noise distortion an amp produces in relation to the wattage. High wattage itself is no indication of these figures being any lower than a less powerful amp. What does tend to happen is that amps from the same manufacturer use better components in their higher end amps that are more powerful than the cheaper amps. The better components yoeld better THD figures in relation to the signal passing through them at higher volumes. It isn't the higher wattage responsible for the better audio, it is the higher grade components being utilised within the amp.

    Look at some of the rather expensive high end stereo amps and their power ratings. Their power is much lower than many entry level AV amps. Such amps surpass AV amps when it comes to their audio abilities, especially in relation to music.Much more time and effort is spent on reducing THD with these amps and wattage is of lesser importance. Wattage is more important if you've difficult or low impedance speakers to drive and has nothing to do with the clarity of the signal. A high wattage signal can be as distorted as a low wattage signal, in fact you may even get more distortion as the signal is amplified than you'd notice at lower volumes with a high powered amps. Distortion apparent within a signal is just as suceptable to amplification as the audio within a signal.
     
    Last edited: Jul 31, 2012
  6. russyj

    russyj
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    Ok fair point on sound quality, I was incorrect there.

    With regards to straight up SPL though, sensitivity of speakers is defined in db/w/m, therefore at a given distance the higher the wattage the louder the sound produced by the speakers no? For example if I had a 50W amp I'd have to crank it right to maximum to get the same sound level as a 100W amp, which can introduce clipping and distortion. Hence "headroom", running amps at less than full whack.

    Basically, for a given speaker, you need higher wattage if you like music loud and undistorted, no?
     
  7. dante01

    dante01
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    And you are having to crank your amp all the way up to get the -15db you like? Your point is hypothetical. Why does it matter that you have to put the volume slightly higher than if you'd a more powerful amp to get the exact same end result? Can your speakers actually handle a constant 200 watts and exactly how loud do you think it would sound if you pushed an amp to output 200 watts via your speakers? I'd be hiding behind the sofa waiting for the drive units to fly across the room. Do you have a cat? Buy it a suit of armour while you're at it :D Pushing 200 watts into your speakers will damage them!

    Another point, a 100 watt amp isn't twice as loud as a 50 watt amp. It just doesn't work like that. A watt is a unit of energy, like horsepower or joules. In audio, a watt is used to describe the energy output of a receiver or amplifier used to power a loudspeaker. The relationship between power output and speaker loudness or volume is not linear or straight (+10 watts does not equal +10 dB). For example, if you compare the maximum volume of a 50 watt amplifier with a 100 watt amplifier the difference is only 3 dB, barely greater than the ability of the human ear to hear the difference. It would take an amplifier with 10 times more power (500 watts!) to be perceived as being twice as loud (a +10 dB increase). Keep this in mind when purchasing an amplifier or receiver. 2X the power output = +3 dB increase, 10X the power output = +10 dB increase, or twice as loud. Your speakers do not even have the capabilities needed to allow you to perceve a difference. Your speakers are only rated to be able to handle 15 - 130w, why any need for an additional 70 watts and especially seeing as you're probably not even using anywhere near 100 watts with your current set up.

    It requires the exact same amount of power to reach reference levels via your speakers irrespective of the amp or the power at its disposal. Reference level is 85db as measured from your listening position. Most if not all AV amps can exceed this level when used to power speakers within most listening rooms. A dedicate theatre room seating 10 people would probably require more powerful amplification, but even then, not excessively powerful. Prolonged listening to audio in the region of 85db can permanently damage your hearing!

    Go for quality and not quantity, you'll probably get more power anyway, but you definately do not need 200 watts unless going into the mobile DJing business? In which case you'll also need to buy yourself some more capable speakers. ;)
     
    Last edited: Jul 31, 2012
  8. BlueWizard

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    True, but less distortion with a higher powered amp is due to less clipping.

    Each time you double the power, you get a slight increase in volume, barely noticeable. But you do get a higher voltage range, but not as high as you would think.

    Here are the voltages for various power ratings assuming an 8 ohm load -

    _50w = 20 volts
    100w = 28.3v
    200w = 40v
    300w = 48.99v
    400w = 56.6v
    500w = 63.25V

    Notice when you DOUBLE the power, the Voltage only increase by about 41%.

    Then we gave good watts vs bad watts, though this is somewhat metaphorical. It really gets down to the power supply backing up the power amps.

    In most AV Amp, if you have 7 channels of 100w each, for a total of 700w, you probably only have a 500w power supply. The total power of all amps can never exceed the power supply.

    However, it not uncommon for a Stereo amp with two 100w channels to have a 300w power supply. More than enough reserve power to drive the heaviest and most complex loads.

    The next feature is Current (Amperes) Reserve. Many amps have massive short term current reserves to assure that any demand or surge by the amp can be met. So, ultra-heavy power supplies are a plus. Though keep in mind that modern SWITCHING power supplies are ultra-efficient. So they are not physically that heavy.

    In my opinion, if you listen mostly to stereo, then you need a stereo amp. A stereo system can do a very good job for movies, though, of course, you don't get surround sound. But you do get great value for your money.

    If you weigh buying 7 amp channels for £1000 or 2 amp channels for the same £1000, which do you imagine is better, a collection of £143 amps or a smaller collection of £500 amps?

    I would need a PRETTY SUBSTANTIAL amount of money available in my budget to get me to trade my stereo for a Surround Sound system. I'm think something in the range of £5000. Even then, I would weigh the fantastic stereo I could get for that amount of money.

    My philosophy is - Better a good stereo than a so-so surround sound.

    Still, I do understand the appeal of Surround Sound for movies, and for audiophiles, for multi-channel music SACD and BluRays. But, it is still not enough to sway me. Ideally, I would have a spare £20,000, then I would have the best of both Stereo and Surround Sound, but I don't see that day coming anytime soon.

    Check the power supply rating on your amp. From the specs I find, it seems the power supply is 870w, not all of which is available to the amps.

    The amps are rated at 140w to 8 ohms time 7 channels which is a total of 980w. That is very good for a Surround Sound amp. And with 870w available, more than enough to drive the bridge channels to a total of 400w. Though I've not found any place that confirms the power in Bridge Mode. Still, 200w seems pretty reasonable.

    You seem to have gotten an exception deal on the amp, so certainly well worth the price. It is hard to determine what that original model sold for, but the current equivalent model is about £1000 (TX-NR817).

    You can certainly find better stereo amps out there, but not for £300 or anywhere near that. So, I would say you have an exception system for a modest amount of money. If you're satisfied with it, then run with it.

    But, if you come across a spare, £1000 or so, I think we can come up with some suggestions for Stereo amps, the would give the Onkyo a good run.

    Steve/bluewizard
     
    Last edited: Aug 1, 2012
  9. russyj

    russyj
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    Massive thanks to Dante and Steve, that has answered my question in its entirety, and it's not often that happens!
     
  10. russyj

    russyj
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    :D
     
  11. boxrick

    boxrick
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    Out of interest have you tried your 875 in BI-amp mode? I always found that sounded better than bridge mode when I used to own one.
     
  12. russyj

    russyj
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    Hi boxrick, never got to trying it, I was so wowed by bridged I never tried, unless you have a pre-amp crossover I was always under the impression biamping didn't do anything as the speakers internal crossover just bins a load of the power anyway. I will however give it a try next time I start mucking about with the wires, thanks for the suggestion!

    Russ
     

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