Power ratings in HCC confusion

Discussion in 'AV Receivers & Amplifiers' started by russraff, Mar 12, 2003.

  1. russraff

    russraff
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    Being in the market for a new AV amp, I was drawn towards the March edition of Home Cinema Choice which reviewed some models I was interested in. Reading the amps' test bench results, I was confused by the Yamaha AZ1 and more so the Denon A1SR. These models seemed to loose power when driving 4 ohm loads, while all the other models increased their power as I'd expect. I know some cheaper models don't have the guts to drive difficult loads, but the A1SR? Am I missing something, here?

    For those with out the mag, the results for both the AZ1 and A1SR were “120W @ 8ohm, 110W @ 4 ohm”, with the Yamaha having slightly less distortion.

    Russell
     
  2. nathan_silly

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    If a amp outputs less power into 4 ohms (compared to 8 ohm) it means the amp hasn't got enough current for 4 ohm speakers. 4 Ohm speakers are harder to drive, therefore the amp requires more current from the power supply. If the power supply isn't sufficient, the output decreases (and THD increases)

    If you're not getting 4Ohm speakers, don't worry about it.

    Krells double the output at every halving of impdeance, for example- 200W into 8 Ohm, 400W into 4 Ohm, 800W into 2 Ohm, and 1600W into 1 Ohm. That shows the amp has pretty much unlimited current reserve (whopping great torodial power supply)
     
  3. General Skanky

    General Skanky
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    The Yamahas normally have a current impeding switch on the back of their amps. My A2 did. Basically to curb their output as I understand it to prevent the amp being overdriven.

    I 'hate' the way HCC does amp output measurements anyway.

    I've talked about it a few times before. As far as I'm concerned in an AV amp, we need to know the output with 'all' channels driven, not just the main pair! It's ridiculous.
     
  4. EvilMudge

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    Yeah, HiFi News test in a much better way. If you read the recent shootout where the Rotel and Pio2011 came out on top, they were the only amps (apart from the THX Ultra rated JVC) that didn't drop power dramatically with all channels driven. I think one was specced at 100W Stereo and dropped to 30Wx5.
     
  5. alexs2

    alexs2
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    Thanks for the comments re:Krells there nathan,something I've been saying for a while.....it's not just the transformers though(certainly having 2kW rated transformers ensures there's no limiting there)but also the immense power supply capacitance these things have(usually in excess of 200,000uF in the higher power models).This ensures very little power supply voltage drop even at increasing current demands,and being able to deliver 50A into 1ohm loads is very rare indeed....a few people may remember the Apogee Scintilla with its 1ohm load....only a few amps were ever capable of running this.

    4ohm speakers are only harder to drive in terms of greater current demands,often where lower specc'd amps are unable to cope,and especially at low frequencies.

    I'm surprised at the Denon giving poor results in this test,as it's performed well elsewhere.
     
  6. sounddog

    sounddog
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    EvilMudge ... from memory HiFi News tested 5 amps. So from what you've said ... They all droped power dramatically with all 5 channels driven, except for 2 + 1 of them that didn't. So to be fair to AV Reciever manufacturers ... 2 out of 5 dropped power dramatically with 5 channels driven while the majority didn't.

    Vikki
     
  7. alexs2

    alexs2
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    All comes back to the power supply.....many manufacturers take the view that compromises and cost savings can be made by cutting back on power supply components(often very costly)on the assumption that most people won't be using all 5,6 or 7 channels to the max simultaneously.
    Thus,when you do,with one of these compromised amps,the supply voltage and current delivery drop dramatically.

    The Rotels and Pioneers usually have adequate power supplies,at least for 4ohm loads.
     
  8. russraff

    russraff
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    HCC do test amplifiers with all channels driven, but rather list each channels output seperately. The ratings that I listed were with all channels driven, but with the front channels measured only. The power supply in the A1SR is an enormous toroidal design, complimented by 2 large capacitors. Thisshould be okay for 4 ohm loads, but going off the findings of HCC, it isn't. This is what confused me. Perhaps the A1SR's technical stats aren't the same as those encountered in real life?

    Russell
     
  9. Daneel

    Daneel
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    They tested 6 receivers. 3 performed badly:

    Onkyo TX-SR700 - 2 x 135W, 5 x 35W
    Sony STR-VA333ES - 2 x 115W, 5 x 45W
    Yamaha RXV-1300 - 2 x 150W, 5 x 65W

    3 did well:

    JVC RX-DP10 - 2 x 190W, 5 x 140W
    Pioneer VSX-D2011 - 2 x 143W, 5 x 135W
    Rotel RSX-1055 - 2 x 120W, 5 x 95W

    All at 8 Ohms.

    Of all the Hi-Fi magazines I've looked at Hi-fi News is the best for reviews. They do blind testing on group reviews and the technical information appears to be of a high standard. I just wish the Denon 3803 had been in that round-up.
     
  10. alexs2

    alexs2
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    Daneel.....I'd like to second your comments re:HiFI News...of all the magazines out there,it does seem to post the most objective reviews on a consistent basis,and also publishes decent slabs of work by respected audio researchers and engineers.

    If there's a drawback it's that HFN is mainly a HIFI magazine,with occasional though increasing looks at AV.

    As to the results....pretty much as expected from prior experience!
     
  11. sounddog

    sounddog
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    Okay was 6 ... but three good is 50% so not ALL manufacturers are culprits.

    But lets look at percentages ...

    Onkyo TX-SR700 - 2 x 135W, 5 x 35W == 26%
    Sony STR-VA333ES - 2 x 115W, 5 x 45W == 39%
    Yamaha RXV-1300 - 2 x 150W, 5 x 65W == 43%
    JVC RX-DP10 - 2 x 190W, 5 x 140W == 73%
    Rotel RSX-1055 - 2 x 120W, 5 x 95W == 79%
    Pioneer VSX-D2011 - 2 x 143W, 5 x 135W == 94%

    Looks to me like all except the Pioneer are very lacking in terms of the power supply to power 5 speakers ... especially when you consider most of them actually have 7 channels ... how bad would the figures be then.

    Would be interesting to get similar figures for 5 channel power amps.

    Vikki
     
  12. Electric Mayhem

    Electric Mayhem
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    Russell

    Those figures don´t match up with the Online Reviews though which has the Yamaha producing 226 watts into 4 ohms and the Denon producing 308 watts into 4 ohms.

    Here is the A1SR

    and here´s the YAMAHA AZ1

    Unless theres something missing from the Online Review or they´ve buggered up the Mag Reviews.:confused:
     
  13. Daneel

    Daneel
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    Not at all.

    If you look at the power ratings these receivers have it's clear there is a distiction between those that live up to expectations and those that don't.

    The Rotel for example is rated at 5 x 90W and the Pioneer, while never mentioning power with more than 1 channel driven, I would expect to be around 100W x 5. I don't have the spec handy but I doubt that JVC claims more than 5 x 140W.

    The rest however are disapointing. Given the price I would not be pleased to find that a receiver in this group did 5 x 65W or less.

    One thing I do find interesting and so take these figures with a pinch of salt, is that the power consumption rating for the 2011 is 660W, 5 x 135W is 675W and that line shows no sign of dropping anytime soon, so with 7 channels powered it would far exceed its consumption rating.

    I find this very suspicious and mentioned it in another thread but no one seemed interested.
     
  14. russraff

    russraff
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    Those ratings that HIFI News give out are very revealing. Those Onkyo and Sony ratings are very bad!

    I may be wrong, but I seem to remember HIFI Choice (who I think are better than most at giving out technical details) did a comparison between amps in 5 and 7 channel modes. Most amps ran out of steam in 7 channel mode. I have thrown all my older mags out, so I can't check, but I think that was the general consensus.

    Jase:
    Yes, I know. Thats one of the reasons that I was confused. Here is a more detailed copy of the Denon's rating:

     
  15. EvilMudge

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    WRT to the HFN review, if anyone has the opportunity to read it, the Sony performed appallingly in the lab test, I beleive they decided that the surround and rears were run in bridged mode, with appalling channel seperation.
     

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