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What spec would I look for to indicate an amp or receiver is high current?

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  • #16
    Originally posted by Brian Steele View Post
    I'll give a slightly different perspective.

    ​1. Any amplifier with a high damping factor will essentially double the current it delivers to a speaker if the impedance is halved - up to the power output limits of the amplifier.
    ​2. For the most part, I'll bet that few of us run our amplifiers up to their peak output level, except perhaps if we're talking about a cheap pro audio environment.
    ​3. From (1) and (2), IMO a high damping factor is much more important for current delivery than the ability of the amp to double its peak output power when impedance is halved.
    Except that damping of an amp depends on the speaker it is connected to. You can use a generic load and get a number, but it doesnt mean much. Also, cheap amps that use lots of negative feed back have high damping ratings and do not control ringing . many engineers prefer low damping amps, Nelson Pass being one, claiming that to high of damping kills the sound qualify of a speaker, especially in the bass.
    craigk

    " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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    • #17
      Originally posted by craigk View Post

      Except that damping of an amp depends on the speaker it is connected to. You can use a generic load and get a number, but it doesnt mean much. Also, cheap amps that use lots of negative feed back have high damping ratings and do not control ringing . many engineers prefer low damping amps, Nelson Pass being one, claiming that to high of damping kills the sound qualify of a speaker, especially in the bass.
      ​Not quite - OVERALL damping is dependent on the speaker impedance (and the impedance of the cable as well, which tends to be small in comparison). An amplifier's damping is basically a measure of its output impedance, which is not dependent on any speaker.. But I agree that you will see it mostly quoted in terms of a specific impedance connected to it, i.e. "500 at 4 ohms", likely because that sounds more impressive than a spec that reads something like "Output impedance: 0.008 Ohms". Marketing at work

      FWIW I don't agree with Nelson Pass concerning high damping. Exactly the opposite in fact.
      Brian Steele
      www.diysubwoofers.org

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      • #18
        I'd look for a heavy amp, indicative of a larger transformer, which is necessary for the greater current required to drive lower impedance loads.

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        • #19
          Originally posted by Brian Steele View Post
          FWIW I don't agree with Nelson Pass concerning high damping. Exactly the opposite in fact.
          ​Hopefully, you do realize that Nelson Pass does know his stuff regardless of opinion.

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          • #20
            Originally posted by View Post
            ​Hopefully, you do realize that Nelson Pass does know his stuff regardless of opinion.
            ​Sure. How something sounds though is a matter of opinion, which tends to be personal in nature. Some people prefer Bose, so...
            Brian Steele
            www.diysubwoofers.org

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            • #21
              A lot of good stuff in this thread. I think everyone's hit on something that is important for high current output, but they're all related as well.

              Power doubling as load impedance halves
              That's a measurement of both the power supply stiffness, and the effective resistance of the output devices themselves, but mostly the power supply. The main thing that indicates is that the supply is either regulated or way over sized. The output devices, if inadequate, will start dropping voltage as well but only perhaps a few volts causing clipping slightly earlier. Either way I do feel that's a pretty good indicator of a high current amp but I don't think that's the only consideration.

              Damping Factor
              That's the load / output impedance and as stated above more of a measurement of output impedance. As Craig pointed out, this can be tricked by negative feedback. An amp with inadequate output devices or power supply but a heavy negative feedback loop will look like it has a very high damping factor, but will still clip early under high current loads and not necessarily handle low impedance. I don't think that's a reliable indicator at all.

              Heavy
              For a linear supply, that's a good indicator of the power capacity of the supply. High power transformers have equally high weight, though a EI core transformer will weigh more than a toroidal for the same VA rating. However, there are some really good switching supplies these days that can eliminate that weight and still be capable of really high current. Pro amps in particular are moving in that direction to save weight since they have to be transported all the time.

              More output devices
              The more paralleled output devices you have, the lower their effective resistance and the higher power the safe operating area. Generally a good indicator, but there's also the specific devices used to consider. A large set of crappy transistors can be beaten by fewer high quality devices. If they're the same package type, i.e. TO-220, TO-3P, TO-3 etc, the thermal properties should be sort of similar so that's not a bad consideration.

              So generally, in my opinion it's a combo. I'd look at the power rating at the minimum rated nominal impedance. If they specify maximum output current, that's a really good direct indicator, but not many regular amps provide that. How the amp reacts to highly reactive (capacitive or inductive) low impedance loads is a whole other discussion, I can't think of anything on a spec sheet that will tell you that definitively.
              Electronics engineer, woofer enthusiast, and musician.
              Wogg Music

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              • #22
                IMHO, when you're looking at amplifiers, looking at power supply is probably the best indication of whether or not it's a turd. But this is tricky, and it depends on the end goal. For example, just because the amp has a huge power supply doesn't necessarily mean it's going to be the best sounding amp. For example, I had a Carver TFM-55 and a Carver TFM-35; the 55 sounded terrible (IMO) and I love the mids and highs from the 35... but neither of those Carvers were very stout in the bass department.

                ​Edit: Just looked at pics of the Aragon and the Carver power supplies and yup, that explains it. Carver's looks like a toy compared to the Aragon's.

                I think Adcom is the biggest bang for buck amplifier out there, not saying the best amp, but best bang for buck.

                Originally posted by johngalt47 View Post
                Check out an amp like the Aragon 4004 MK II. I have one and you can practically weld with it.
                ​Yes, 100% agree. I have a 4004 MK II as well, and while I haven't heard the non-MK II version, I think they're very similar so that's a good option as well. The only "problem" with those Aragons is that they're so good, when you're designing a speaker you could have a nasty impedance problem and not think it's a big deal. Not a big deal unless someone else wanted to build those speakers too, then they're doomed to finding a high current amp as well.

                ​Stated watts/ch don't mean a whole lot to me in amplifiers unless I'm very familiar with the manufacturer. That Carver TFM-55 was rated at 500w/ch @ 4 ohms, while my Aragon is rated at 400w/ch at 4 ohms. And the Aragon will absolutely CRUSH that Carver TFM-55 everywhere.​
                "The ability of any system to produce exceptional sound will be limited mainly by the capability of the speakers" Jim Salk
                "Audio is surely a journey full of revelations as you go" JasonP

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                • #23
                  Originally posted by mattsk8 View Post
                  ... just because the amp has a huge power supply doesn't necessarily mean it's going to be the best sounding amp....
                  Certainly demonstrable in the Pro Amp market.
                  The better amplifiers will publish performance under a variety of load conditions.

                  "Not a Speaker Designer - Not even on the Internet"
                  "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                  • #24
                    Originally posted by Sydney View Post
                    The better amplifiers will publish performance under a variety of load conditions.
                    Yes I think that is the best first indication you may encounter that an amp is more capable, if it has a full spectrum(20hz-20khz) output spec with no time limitation then it should be capable of comfortably driving a speaker with that rated impedance indefinitely. If there is only a peak or burst rating at 1khz for a 20 miliseconds for example then you know the amp really isn't capable of running at that load.
                    Paul O

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                    • #25
                      Originally posted by wogg View Post
                      A lot of good stuff in this thread. I think everyone's hit on something that is important for high current output, but they're all related as well.

                      Power doubling as load impedance halves
                      That's a measurement of both the power supply stiffness, and the effective resistance of the output devices themselves, but mostly the power supply. The main thing that indicates is that the supply is either regulated or way over sized. The output devices, if inadequate, will start dropping voltage as well but only perhaps a few volts causing clipping slightly earlier. Either way I do feel that's a pretty good indicator of a high current amp but I don't think that's the only consideration.

                      Damping Factor
                      That's the load / output impedance and as stated above more of a measurement of output impedance. As Craig pointed out, this can be tricked by negative feedback. An amp with inadequate output devices or power supply but a heavy negative feedback loop will look like it has a very high damping factor, but will still clip early under high current loads and not necessarily handle low impedance. I don't think that's a reliable indicator at all.

                      Heavy
                      For a linear supply, that's a good indicator of the power capacity of the supply. High power transformers have equally high weight, though a EI core transformer will weigh more than a toroidal for the same VA rating. However, there are some really good switching supplies these days that can eliminate that weight and still be capable of really high current. Pro amps in particular are moving in that direction to save weight since they have to be transported all the time.

                      More output devices
                      The more paralleled output devices you have, the lower their effective resistance and the higher power the safe operating area. Generally a good indicator, but there's also the specific devices used to consider. A large set of crappy transistors can be beaten by fewer high quality devices. If they're the same package type, i.e. TO-220, TO-3P, TO-3 etc, the thermal properties should be sort of similar so that's not a bad consideration.

                      So generally, in my opinion it's a combo. I'd look at the power rating at the minimum rated nominal impedance. If they specify maximum output current, that's a really good direct indicator, but not many regular amps provide that. How the amp reacts to highly reactive (capacitive or inductive) low impedance loads is a whole other discussion, I can't think of anything on a spec sheet that will tell you that definitively.
                      Good post.
                      craigk

                      " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

                      Comment


                      • #26
                        I think the Aragon weighs something like 47 lbs. I had to open mine up once and I think it has 12 output transistors per channel. Also, I think it is a dual-mono design with two big toroids.

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