Buying a power amp for PA, what is going to work?

Discussion in 'Other Amps' started by American Viking, Mar 18, 2011.

  1. American Viking

    American Viking Well-Known Member

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    We've acquired a decent PA but it is missing the power amp.

    I'm thinking we may need something along the lines of 2000+ watts. I'm planning on running kick drum, maybe all drums and vocals. This power amp has to be able to over power two or more Marshall full stacks.

    I'm seeing some decent priced stuff like Gemini DJ power amps for a couple hundred bucks. Are these going to work for what I need as a live PA or do I need to go with something else like Crown which would be triple the price? Is there a difference between a DJ power amp and a regular one...?

    I know a little about everything but running live sound other than guitar or bass is where I'm the least experienced.
     
  2. johnfv

    johnfv Well-Known Member

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    Having worked live sound for decades, I suggest one of the major amp brands for quality and reliability: QSC, Crown (also Peavey and Yamaha). I've also had good luck with a couple Behringer amps and they are quite affordable. One important consideration is weight of the amp; if you are building a power rack that can make a huge difference. Some of the high end amps are very powerful AND lightweight (using more sophisticated technology). For example QSC PLX series amps are top quality and and lightweight.
     
  3. rustyrat

    rustyrat New Member

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    what do you have for pa cabs? Subs and hi packs? You will most likely need 2 power amps minimum, I run 3 2500 watters for my system. 1 for the subs, 1 for the hi packs and 1 for the monitors. i dont think 1 will cut it if you run 1 side for the subs and 1 side for the hi packs. Might end up clipping the amp to get the volume you need.
    RR
     
  4. jcmjmp

    jcmjmp Well-Known Member

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    AV - Stick with good quality power amps. QSCs are great, as are Crown and others as johnfv has stated.

    The first thing you need to estbalish is the "program power" or "average power" power rating of your speakers, not the RMS rating. Your power amp should be approx 1.25 to 1.5 that rating in continuous power power delivery.

    If you plan on having drums and bass goind through the PA, I strongly suggest at least 1 powered sub (800w min.) or a passive sub pair + crossover and a good EQ depending on what your setup is as not to overwhelm the main speakers.
     
  5. tonefreak

    tonefreak New Member

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    not to hijack the thread or anything, but what IS a crossover?

    i assume it splits the bass frequency's and sends them to the subs, and the mids and trebs and sends them to the hi packs. but where do you run it? like an EQ, between the mixer and the amps?

    and powered sub's don't need a crossover?
     
  6. madmmx

    madmmx New Member

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    You should really match the power of your amp to the power handling of the cabs you are going to power with it.

    If you have two 500watt cabs, you dont need a 2000watt power amp. You could blow your speakers with it. Dont under power your speakers either. That could blow speakers easier than over powering them.

    You could use a 2000 watt amp to power 2 500watt mains in mono on one side of the amp and use the other side for monitors though. We would really have to know what you have and how far you want to go with the sound on what to recommend. If you want to really get into it, you could get a crossover and an amp for subs, mids and tweeters. You will get the best sound that way but it is alot of gear to haul.

    We just switched over from a biamp setup to all powered speakers and it makes life much easier on your back
     
  7. jcmjmp

    jcmjmp Well-Known Member

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    A crossover divides up the frequencies into lows & mids/highs or lows/mids/highs.

    Some powered subs have a built-in X-Over where the power amp feeds the sub and you wire the main speakers from the sub. Simple. Some non-powered subs also have this option.

    Some powered subs (and non-powered subs) have an internal X-Over but no output. In this case, you'd use 1 mono out for the sub feed from the board into the sub's power amp and the mixer's main out to the amps for the tops would be eq'd taking into account the subs.

    Hopefully I explained it clearly enough. :hmm:
     
  8. madmmx

    madmmx New Member

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    You could run the EQ before the crossover then the crossover goes to each amp for subs ,mids and tweeters.

    Powered subs should have crossovers built into them. Powered mains should have them too and they are usually bi-amped from the main speaker and tweeter
     
  9. American Viking

    American Viking Well-Known Member

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    Thanks for all the help so far.

    ...and FWIW this will be mainly for a rehearsal PA. It probably won't be moved around much at all, if at all.

    I'm actually not sure on the speaker rating as they were given to us and it looks pretty shitty actually. They are just some home-built cabinets, not done particularly well I might add but they should do the job.

    If I get a chance I will list all of the stuff we have and maybe that will give you guys more of an idea of what I might need and the best way to set it up. I haven't really even looked at it much because it doesn't look like the racks were put together very well. Like I said it was just given to us by a guy who just had too much stuff lying around, just without power amps.
     
  10. jcmjmp

    jcmjmp Well-Known Member

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    100% BAD ADVICE.

    For program power 500w cabs, I'd use a minimum of 750w program power amp while being careful that the mixer is set properly in the single channel bus and the different group busses.


    Why? Because with live music, the dynamics make it so that the amp needs the extra headroom so it doesn't clip into hard DC. Using a 500w amp into 500w speakers will garantee a meltdown down the line if you use the speakers to their full power rating.

    This is not like a home setero where everything is compressed. Live music is very demanding on a system

    The kick drum and bass are the worst. They always ending pushing the system to its limits and good clean power is essential for making sure the front of house mix is clear, distortion free and the speakers are not handling clipped peak power from the amp because its under powered.

    Burnt out speakers is a reality, not myth or fiction.
     
  11. johnfv

    johnfv Well-Known Member

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    Yes. General rule is to have more power available than what speakers are rated for. Speakers get blown by clipping, have plenty of headroom to ensure your amps don't clip. Of course if you were to send all 750 watts to your 500w cab you still could blow them, that's where "careful that mixer is set properly" comes in :) Also, clip limiters on the amp can help if any short "accidents" occur.

    AV, if you are not moving the amps around that does change things. Weight doesn't matter and the reliability is less of a concern. QSC RMX series are quality (and heavy) amps at a lower price - I have several of those. I've never tried Gemini and am a little skeptical, I'd go with Behringer if you really need to keep it low cost. I've been happy with the 2 amps I have, this is hell of a lot of amp for the price:
    Buy Behringer EP4000 EUROPOWER Power Amp | Live Power Amplifiers | Musician's Friend
     
  12. Moose Lewis

    Moose Lewis Well-Known Member

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    During my traveling years, the groups I worked with put most of our money into systems - and had some nice ones. I second most of what is being said here. More power than your speakers are rated for - just don't dime the amp.

    Unless you find one soooo dirt cheap that you don't care about it dying in a week, stay away from Gemini. Crown rocks, but their lower line does not. IMHO, QSC gives you the best bang for the buck... and they are a quality amp, generally. About Behringer - other than EQs and similar rack gear - see Gemini. I've gotten joy out of Crown, QSC and Altec... although I am currently using a 1000 watt Samson amp; but it is not old enough to know if it's reliable.
    :cheers: Cheers
     

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