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

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

    Lots of what I read today indicates many speakers do better with high current. Is this true or just audio mag ballyhoo?

  • #2
    Some speakers present a complex impedance load to the amp. Some amps go nuts trying to drive such a load while others handle it with aplomb. From what I read in the past, the Apogee Scintilla was very hard to drive. I vaguely recall that its impedance may have dropped to one ohm at some point.

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    • #3
      If a speaker presents a low impedance - Ohms Law mandates an increase in Current.
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      • #4
        A speaker rated at 4 Ohm nominal can typically drop to below 3 Ohm, usually just above the woofer impedance peak which typically occurs around 150Hz or so. Most decent amps these days can handle that, but receivers dedicated to home theater may have some problems due to their power supply having to cope with 7 or more channels.
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        • #5
          B&W for one tends to have impedance minimums way below the normal Re x 0.7, so even though rated at 8 ohms they don't play nice with typical AVRs rated for 6 ohm operation.
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          • #6
            Most all amps are rated in Watts (watts rms from reputable mfgs.) An additional amp rating is the minimum impedance speaker the amp will reliably drive (e.g. 8 ohm, 4 ohm, etc.). The lower the speaker impedance rating, the higher the current capability. So the minimum speaker impedance is a way to ascertain higher current amps (all else being equal).

            This does not account for electrical phase a particular speaker may present to an amp and whether the amp will have problems that. That's significantly more complicated to ascertain and mostly not available in mfg.'s spec.s.

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            • #7
              As a starting point I would look for a doubling of power with every halving of impedance. 100w @8ohms, 200w @4ohms, 400 @2ohms

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              • #8
                Originally posted by ugly woofer View Post
                As a starting point I would look for a doubling of power with every halving of impedance.
                That has nothing to do with the amp's ability to drive low impedance loads. It's also not indicative of the quality of the amp, even the $11k Bryston 28B3 monoblock lacks that capability. Most SS amps double their power output at small signal levels when the load impedance is halved. It's only maximum power that generally increases by a factor of roughly 1.7 with halving of impedance. In practice that's of no consequence, since you shouldn't be running anywhere near maximum power to begin with.
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                • #9
                  Originally posted by ugly woofer View Post
                  As a starting point I would look for a doubling of power with every halving of impedance. 100w @8ohms, 200w @4ohms, 400 @2ohms
                  That's been my understanding also.
                  I remember reading a review of a Luxman amp in Stereophile a number of years ago.
                  It had something like 150W/ch at 8 ohms, 300w/ch at 4 ohms, 600w/ch at 2 ohms, and 1200w/ch at 1 ohm! (if I remember correctly)
                  That to me is textbook "stiff" power supply and high current.

                  Here's a 2008 Luxman review that shows similar measurements.

                  https://www.stereophile.com/solidpow...lux/index.html



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                  • #10
                    Originally posted by Dwight View Post
                    Lots of what I read today indicates many speakers do better with high current. Is this true or just audio mag ballyhoo?
                    Look at the amp spec sheet for the output current. Much more realistic spec than looking at 8 - 4 - 2 ohm loads.
                    craigk

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                    • #11
                      Check out an amp like the Aragon 4004 MK II. I have one and you can practically weld with it.

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                      • #12
                        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.
                        Great amp that is really stable to one ohm, and sounds great too.
                        craigk

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

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                        • #13
                          Originally posted by ugly woofer View Post
                          As a starting point I would look for a doubling of power with every halving of impedance. 100w @8ohms, 200w @4ohms, 400 @2ohms
                          That's more of an indication of the quality of the power supply.

                          Originally posted by Dwight View Post
                          Lots of what I read today indicates many speakers do better with high current. Is this true or just audio mag ballyhoo?
                          An amplifier that current limits, due to either activation of protection circuitry, or limitations of the output stage will not sound as good as an amp that doesn't current limit. Another factor is that with most newer class AB amplifiers, you're getting a fairly skimpy class A operating region. This region gets smaller with lower impedance speakers. You can either spec or build 8-ohm speakers, or look for amplifiers that claim high current capability. One indicator of the current capability is to count the number of output transistors (more is better; an amp with 10 large output transistors per channel will generally have more current sourcing capability than an amp with 4 such devices), but you will need to see inside the chassis or find photos online to see.

                          Regards,

                          Rob

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                          • #14
                            Although a little bit easier to drive than the Scintillas (amplifier punisher), when looking for an amp to drive the Apogee Caliper sigs I wanted to see a healthy 8 ohm rating and a doubling of power as ohms halved. Generally, an amp that did that had no, or very little issued, driving the Apogees, or the Carver Amazings. Funny thing, while listening to music at moderate volume (loud) with the Amazings the crossovers get so hot you can smell the dust? burning off them. Smells like when you fire up the central heat for the first time in the winter. Driving them with Acurus (poor man's Aragon).
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                            • #15
                              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.
                              Brian Steele
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