"High Current" amplification??

Discussion in 'Archived Threads 2001-2004' started by David Taylor, Oct 23, 2002.

  1. David Taylor

    David Taylor Agent

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    Here's a question from a novice:

    What advantage do you get from a receiver that claims to have a "high current" amplifier like Denon or Onkyo as opposed to the regular receivers from Pioneer or Sony. Most of the "high current" receivers are lower wattage (i.e. 60 watts or so) as opposed to most of the others which are around 100 watts. Any insite would be appreciated.

    Thanks!
     
  2. Tom Grooms

    Tom Grooms Second Unit

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    Marketing B*S*, just like the wise man wrote, dont believe everything you read.
     
  3. Yogi

    Yogi Screenwriter

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    Some of it is marketing BS and some of it is true. The thing is you need current to move the woofers and not watts, esp. at low impedances. If your speakers were 8 ohm constant impedance then a receiver thats rated at 100 W would be more powerful than a receiver rated at 60 watts, but the thing is that speakers are far from constant loads. Most dip down to 6 ohms and lower and some 4 ohm speakers dip down to as low as below 2 ohms. Now when a speaker dips below 8 ohms it puts more demand on the amp power suppply for higher current. So if a speaker is drawing 1 amp at 8 ohms it will demand 2 amps at 4 ohms and thats what distinguishes a high current amp from a low current amp. A low current amp will lose control and sound smeared while a high current amp will still sound in control and defined as the speaker dips in and out of those low impedance points. An ideal high-current amp will be able to double its output with each halving of impedance (in theory).

    Hope that helps.
     
  4. Rob Rodier

    Rob Rodier Supporting Actor

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    I don't think it is marketing at all.

    -rob
     
  5. KyleGS

    KyleGS Second Unit

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    I agree with Rob- I would stick with the "higher end" brand such as H/K, Denon, Onkyo, etc. You get what you pay for. My H/K 125 (45x5 watts "high current") seems at least TWICE was powerful as my Sony DE-835 (100x5 watts).
     
  6. Harold A

    Harold A Stunt Coordinator

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    If you go over to www.audioholics.com they have a lot of good technical information on that sort of stuff. This is the page I am specifically talking about : http://www.audioholics.com/techtips/...nceptions1.php
    They say that while certain manufactures claim high current +/- 50,60,70 amps what ever it is It doesn;t not say how long they can deliver it. So a bass note requires more then a millisecond or two of those amps but probably will not get it.
     
  7. Chu Gai

    Chu Gai Lead Actor

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    With regards to high current amplification, unfortunately, IMHO, there's no easy answer. To some extent it is a load of BS, especially the way some manufacturers play the game.
    As Yogi pointed out, some speakers have impedances that drop to low values at certain frequencies. Also they may have high phase angles between voltage and current. It maybe is more accurate to say that any frequency there is a phase angle associated with the impedence. Faced with this type of situation, the amp will have to deliver more current than if the speaker behaved like an 8 ohm resistor.
    We can calculate the peak current by knowing what the peak voltage is and dividing it by the impedence. Let's say your speakers bottom out at a little over 2 ohms. If you've got electrostatics its lower. Now take your run of the mill 100 watt receiver. At clipping the receiver will put out about 28 volts (rms) with 40 volts peak. So, 40/2=20 amps is the amount of current that receiver will be putting out at clipping. Now if your receiver can put out more than 20 amps it just won't clip. Some manufacturers quote values much higher for peak current. However given a particular setup, its a moot point since if your unit can deliver 25 amps and another can put out 100 amps neither one is going to be clipping.
    Now if your speaker were strictly a resistive load, and using the same 100 watt receiver, we'd find that at that power, the peak current would be 5 amps at 8 ohms and 7 amps at 4 ohms. The people who market amps with high current want big numbers. Its a sales tool. So what they do is to treat the speaker as resistive and then they determine the peak current by defining it at the peak output voltage using a small-value resistor with tone bursts. Now speakers though aren't purely resistive loads, they're reactive. However if they determined the peak current using a reactive load the numbers would be smaller and not have that 'je ne sais quoi'. So here you and I sit where we're trying to figure out which is the better performing receiver or amp based on peak currents but we're faced with the fact that the values were determined resistively and our speakers behave reactively.

    One other point to keep in mind is that can clip two different ways.

    It has run out of voltage. Since the amp has two output stages, one of the stages will remain conductive and tries to keep the load under control. I'll grant you its still not a pleasant thing to hear.

    It has run out of current. In this situation, the entire output stage becomes nonconducting and the load goes nuts resulting in massive oscillations with voltage swinging all over the place. This oscillation is even worse sounding than running out of voltage.

    So is having adequate current capability important? Sure but you probably need far less than you think.
     
  8. Yogi

    Yogi Screenwriter

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    Speaking in RMS terms I would think that if a receiver can deliver 10 amps RMS into the worst load of say 2-4 ohms you can say that the amp is adequately powerful. Peak current numbers are, I think, BS as we dont know how long the receiver can provide that peak current.
     
  9. Richard Harvey

    Richard Harvey Stunt Coordinator

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    Fairly easy: most, if not all, "non" high-current amps only advertise their wattage at a particular frequency. For example, the receivers you see at your typical Best Buy or Circuit City will say stuff like "100w x 5 @ 1Khz" meaning that it can provide up to 100w per channel, for 5 channels, but only when the output frequency is 1Khz. What good is that? Well, really pretty worthless. Since the human ear can hear from 20Hz-20Khz or better, you want something that can provide adequate power along the ENTIRE hearing frequency range.

    This is typically what high-current amps are touting; independent of frequency, then can provide maximum power. When needed, they can exceed their "average" power rating for short duration when clipping would normally occur. That said, I would take a 60w "high current" amp over a 100w @ 1Khz any day of the week. The 60w would consistently outperform the 100w with HT material. Read your specs carefully. Most low $$$ hardware at your typical retailer can't deliver near what they claim on the "big" numbers outside the box. Read the fine print.

    Rich
     
  10. Chu Gai

    Chu Gai Lead Actor

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    Well that all depends upon your speakers and the levels that you're playing them at Richard. If both amps, given a particular set of speakers in a particular environment aren't being driven into clipping, its a moot point. Sure you can choose the higher current one, but if the price disparity is substantial, it's good for the person on a more restrictive budget to know he/she can safely get by. Again, as I pointed out, the marketing guys are quoting you high current levels into resistive loads. Try sending them an email asking them to restate their current ratings into reactive loads and see if they get back to you.
     
  11. Richard Harvey

    Richard Harvey Stunt Coordinator

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    Technically that may be true, but after replacing my old receiver with a new "high current", I could swear that in general I get much cleaner output at ALL levels. My old receiver (a Sony) would also tend to hiss more at higher levels (even before clipping), whereas my new receiver has no hiss regardless of level or material. This may have nothing to do with specs/wattage, but I can clearly hear the difference, and my new 70w receiver clearly blows away the older 110w receiver.

    Rich
     
  12. Justin Lane

    Justin Lane Cinematographer

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    The problem with calling a receiver "high current" is what actually is defined as "high". One manufacturers version of "high" will differ from another manufacturers. Really it is just another marketing feature now of days.

    The only rule of thumb I would go by, is that a so called high current receiver usually has a BJT amplifier stage (generally capable of larger current drives) , while cheaper non high current jobs use FET amplification stages. Still this does not really mean anything, because it is up to the manufacturers implementation.

    J
     
  13. Chu Gai

    Chu Gai Lead Actor

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    well the Spectral is FET based....it ain't cheap and its got a fair amount of current [​IMG]
     
  14. Yogi

    Yogi Screenwriter

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    PASS, B&K, LLANO are all FET based and are truly high current and can compete with the best BJT based amps in their respective price ranges.

    Usually BJTs have lower impedance and higher output per device so a FET amp will have more output devices per channel to achieve the same output compared to a BJT but that by no means implies that the FET amp is weaker. Its harder to design FET amp and they work best when biased into Class A. When designed right and when biased into Class A (like PASS and LLANO) FET amps can achieve phenomenal sound.

    Also most good receivers use opamps in their driver stages and BJTs in their output stages while the cheaper ones use opamps (ICs) throughout.
     
  15. Rutledge

    Rutledge Stunt Coordinator

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    This was my experience in 1980 with a NAD 3020 20wpc int. amp and a Pioneer SX780 receiver with 45 wpc.

    I had 4 Advent/1 speakers rated at 8 ohms(found out later 6 ohms was more accurate)with 4 speakers running there was audible distortion with no volume. With some volume there was much distortion.
    The ouput IC blew out after a couple of months. 4 months later it blew another. I sold it to a guy who hooked up 4 speakers and he blew another one.
    The Pioneer could not deal with what amounted to a 3 ohm load.

    My next purchase was the NAD. rated at 20 watts but probably close to 35-40 watts. I hooked up the 4 advents and it didn't even blink. It got hot, but that was all.

    22 years later I still own it and listen to it. By the way it sounded better than the Pioneer too.

    I am now running a Sony DA333Es receiver built in 1999.
    This is before they moved production to Malaysia and cheapened the product. I am running 4 ohm Mirage speakers and it sounds good. No problems at all.

    I will never buy a Pioneer audio product.
     

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