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Power amp specs?

Discussion in 'Amps and Cabs [BG]' started by Mad Subwoofer, Jan 12, 2002.

  1. Can anybody tell me what the minimum acceptable spec would be when looking for rack power? What I am talking about here is Damping factor, slew rate, THD and S/N ratio. Any disadvantages to those weird (to me) switching style amps like the PV DPC and Stewart series? I would love to snag a single rackspace amp but am hesitant to go with anything digital.
    Here is what looks like an awfully good deal but those specs might be questionable?


  2. geshel


    Oct 2, 2001
    Those specs all look fine. THD less than .1% is fine for MI, damping factor doesn't mean much over 100 (wire and crossover resistance brings the number back down again anyway). The thing is, they don't qualify any of the measurements: what THD at full power? What frequency and power that THD spec?

    That amp won't do 2 ohms or 4 bridged, so that might indicate either limitations of its current capabilities or heat dissipation. I'd bet it's probably a pretty good little amp.

    Ah, I see the footnote, 1% THD on the power specs. That's probably reasonable. Still doesn't say what happens above that point - is that 1% just high normal, or is that the very onset of clipping?

    Anyway, there's nothing bad in those specs I can see compared to most other ones. I'd ask around about specific experience with that amp though (I have none :) ).
  3. That amp just sort of caught my eye....I would love to know the minimum acceptable ratings and even a best case scenerio whne looking at specs for any given amp. Specs are subjective I understand, but aren't there some basic set of standards I can compare them to..?? Damping is how fast my speaker cone moves back and forth, like tightness, correct? Slew rate is especially crucial for bass is it not? What would be a decent rate?
    Thanks for your help....
  4. geshel


    Oct 2, 2001
    AFAIK, slew rate and damping factor specs don't really tell you much about the amp. Theoretically, damping factor does indeed have to do with keeping the cone's movement in check. However, a damping factor of 100 would mean that the output impedance of the amp is .08 ohms (damping factor is speaker impedance divided by output impedance, I'll assume 8 ohms here, although they don't specify, now, do they? :)). But the resistance of the speaker cables and crossovers is probably at least this much, and this resistance gets added on the "amp" side of the equation, so IOW a damping factor over 50 even probably is not terribly significant.

    Slew rate is volts per microsecond, which describes how fast the output voltage fo the amp can change. I don't know if the convention is to measure this at the zero point or not - it might not be the same when going from 0 volts to 1 volt as it is from 10 volts to 11 volts. To me, this measurement seems to be useless. At least in an abstract sense. It might be that it indicates enough about the capabilities of the amp that you can use it as a guide, but I don't know - I've never really heard anyone go off about an amp's slew rate. And, it seems to me like this would be most useful for high frequencies. Of course, transients from a bass are high frequency. So. . .if it really means something it seems to me like it would have an effect on slaps and pops and the like.

    It's been a few years since I studied this stuff, and I have only limited experience. So, it could be that I'm misguided a bit. I think the best advice is still to ask around about people's specific experiences. I think for bass power, as long as the power spec is enough, it comes down to weight, heat, and reliability anyway. :)
  5. Doesn't slew rate effect how "slushy" or "blurry" the may sound? I don't know...
    Thanks for your input.

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