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setting up an amp

Discussion in 'Sound, Music, and Intercom' started by zac850, Dec 9, 2004.

  1. zac850

    zac850 Well-Known Member

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    So, my school is getting an amp that should be showing up tomorrow.
    We are getting a BEHRINGER EP2500. I know Behringer isn't the best equptment, but it was cheep enough, so, oh well.

    Anyway, this amp is 500 watts at 8 ohms and the speakers we're going to be using are 400 watts at 8 ohms. So, would I need to turn the gain down on the amp or will it only put out 400 watts for the speakers.

    I assume that it is the second, but I'm not sure. I've never set-up an amp, so I am just unsure of what to do with the gain settings.

    I hope this makes sense. I'm coming off 3 weeks of back to back shows, and its 11:30, so my brain isn't really working right now.

    I just don't know what to do with the left and right gain settings on the amp, everything else I can do. I hope that makes sense.

    Good night all, thanks very much.
     
  2. RelativeMischief

    RelativeMischief Member

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    Oi, thats a toughie. I would've recommended checking your speaker specs before buying an amp :p You could've gotten a better quality amp matched to your speakers for the same amount. However, for what you've got, the amp is gonna put out 500W at 8ohms no matter whats hooked up at the other end. Best thing to do would be turn your amps down by 6dB or so. That should give you some breathing room. You have to bear in mind however, that your amp is gonna be running a little cool now, so don't judge anything by the LED's on the amp. Don't attempt to get it running at nominal, you'll just fry your inputs.

    Hope I helped!
     
  3. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    For what it is worth Zac, I always run my amps at full gain and control my overall volume from the board.

    The reason that I do this is because I find the lower frequencses sometimes get lost or are lacking if the amp is turned down.

    Just keep an ear out for any distortion and keep your eye on the clip meter and you should be fine.

    With your speakers being suited to your amp (ie the amp output is greater than your speakers) you will (should) hear any distortion, in which case you drop the gain a little. On the other hand, were your amp underpowered, you are more likely to damage the speakers by clipping the amp in order to drive them.

    If you are unsure. Wind the amp back to begin with. I know some people who just cannot stand having the master out on their board sitting at 30%. Even though the sound is good and at the right level.
     
  4. zac850

    zac850 Well-Known Member

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    I k now that the speakers are 400 watts at 8ohms and for the price, that was the closest we could do. It is better then our old amp, that only put out 250 watts at 8 ohms.

    So, if I keep the gain on the amp turned way down, that will help save the speakers? I assumed this, but I just want to make sure.

    Thanks guys,
    -Zac
     
  5. ccfan213

    ccfan213 Active Member

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    my only problem with turning my master up to 30 is that if someone else uses my board they may do something dumb, or if someone sees that i have that much power @ a concert they may try to make me turn it up.
     
  6. ccfan213

    ccfan213 Active Member

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    my only problem with turning my master up to 30 is that if someone else uses my board they may do something dumb, or if someone sees that i have that much power @ a concert they may try to make me turn it up.
     
  7. zac850

    zac850 Well-Known Member

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    OK, so...
    1) I assume that the extra 100 watts is harmful for the speaker and will cut down on speaker life, correct? Also, I assume that the excess power will cause clipping and other nastyness in the speaker... Also, is this correct?

    2) Now that we're going to have an amp, I was wondering about power in the booth. The amp will be sitting under the table in the booth, pluged into the same circuct as a projector, a computer, the sound board, a mini disk player, a CD changer, and 2 desk lights. I can (if needed) change most of this stuff over to the lighting side of the desk, with its own seperate circuct without overloading anything (we have 2 20 amp circuts to the booth, one for lights and one for sound).

    How much of this stuff should I move to keep speaker hiss to a minimum. I assume that it would be OK to keep the sound board on the same circuct, but what about the mini disk player and the CD changer. Also, is it even worth it, will there be enough hiss heard at the speakers to warrent this extra work?

    Thanks a lot guys!
    --Zac
     
  8. disc2slick

    disc2slick Active Member

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    zac,

    as far as I know, having the Amp on the same circuit won't create lots of hiss. so long as you don't have lots of power cables running along side your sound cables you should be fine
     
  9. Peter

    Peter Well-Known Member

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    The only time I have have to worry about where things are pluged in at my auditorum is the fact that we have two different sets of plugs, (one white and one orange). The orange ones are dedicated computer plugs, and have a seperate (longer) ground rod then the other circut does. The only problem is, two ground rods usualy means that there is a small bit of current wanting to get from one rod to the other, and that can make a bit of hiss, so i just make sure all my sound equipment is pluged into one or the other. (there are horror stories floating arround the internet about guitar players who's amp is pluged into one circut and the mic system is on a differnt ground, and them getting zapped through the mouth singing into the mic. I kinda doubt that the difference in voltage/amperage is that much... but.... i dont really see how it can hurt to be safe.

    PS for more info on this, look up "ground loop" or "ground loop hiss" or something similar on google
     
  10. zac850

    zac850 Well-Known Member

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    Well, we hooked up the amp and it is WONDERFUL!

    We have the gain somewhat lower then normal, to compensate for overpowering the speakers. The nice thing is, the speakers don't hiss anymore! Before we were running the outputs of the main board as 2 mic inputs of a powered board, and from that to our speakers. Now, however, main out is going to the amp, and it is silent now.

    We are using the old soundboard/amp as a monitor for the keyboard, and listening to the difference between the two is amazing.
     
  11. tjbaudio

    tjbaudio Member

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    Some things to keep in mind:
    how Beringer specks there amps compaired to QSC or Croun is not the same. But you have the amp so I wont come down too hard. Just know that the B stuff is just like the real thing with out paying for R&D and with cheeper parts that may not protect the speakers when it failes.

    Now the real problem with the preveous posts in the thread. Gain at the amp is just that, gain. That knob is not a limiter or a power controle. It is there to match the signal leve in the reast of the system to the speakers and needed volume. You can still clip an amp that is only 1/4 of the way up. By lowering the gain at the amp your console has to provide more level to reach the same volume in the room. This is not a bad thing because it also reduces the amount of hiss (as you found) There is a balance between too much gain (lots of hiss) and not enough (clipping and distortion before the volume is loud enough.) Clipping the console is just as bad as clipping the amp.
     
  12. zac850

    zac850 Well-Known Member

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    Yes, I know that Beringer isn't the best company. The problem is, the purchase was donated, and I was told $300, it ended up being $370 for this amp. It was either this or an American DJ, so I decided that Beringer would be the better buy.

    The Beringer manual said that at 8 ohms we shouldn't use a speaker lower then 400 watts, so, yes, I know its bad, but its better then what we had, under-powering the speakers by 150 watts.

    Also, just out of curiosity, what is the negative thing with overpowering an amp? I understand the hiss thing, but as long as i keep levels low enough and don't do that, what is the problem with putting an extra 100 watts into the speakers?
     
  13. mbenonis

    mbenonis Wireless Guy Administrator

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    You should be fine running the speakers with the amp at full gain - I'm not sure how mathematically, but it all works out fine. Search the Theatre-Sound list-serv archives for some interesting reading on this topic.

    http://www.brooklyn.com/theatre-sound/index.html

    As far as the mains distribution, I would make sure that all audio equipment is plugged into one circuit, and preferably the other equipment is on a different circuit - this will reduce noise on the power line. Note that the important thing is that all sound equipment is on the same circuit, not that other stuff is moved to a different circuit.

    Btw, this may sound unimportant, but I'm glad to see that the amp requires a balanced input - don't defeat this with a cheap, unbalanced cable and some funky adaptors (believe me, I've seen some weird wiring at my school).

    Enjoy the new amp!
     
  14. Radman

    Radman Well-Known Member

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    I reccomend the "Sound Reinforcement Handbook" to anybody here who hasn't read it and works with sound. The edition I have is ancient and it is still a treasure trove of info.

    In matching speakers to an amp, there are many ratings that can be given. Contonuous, Program, and Peak are common for speakers. The amp should generally fall around half the peak rating for the speaker.

    Continuous is a worst case scenario rating, peak is what it can handle for periods less than 1/10 a second, and program is average usage.
     
  15. tjbaudio

    tjbaudio Member

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    Somthing to consider is that the rating of an amp is how many watts it is capable of delivering. The rating of a speaker is how many watts it can electricaly disipate or how much abuse it can take. There are many ways to mesure what an amp can produce and what a speaker can take. Speakers are the most trouble some to mesure. There are many ways to mesure the ratings that Radman mentioned. Some manufatuers are conservative some are not. Many dont give the sircomstances of there raitings. Some are mesured with full sprectrum noise (conservative raiting) some are mesured with a 1K tone (easy teast for most speakers.)

    I tend to run an amp with an RMS raiting around 1.5 to 2x the RMS raiting of the speaker. That gives some head room for peaks. Just because an amp is capable of 1000 watts does not meen it is delivering it all the time. I have used a 1000W amp on a 3W speaker as a booth monitore. How hard you are pushing the amp deturmins how much power is deliverd to the speaker. Most of the time you are only pushing a few watts any way.

    I also recomend the yamaha book, probably the best reference there is for PA.
     
  16. mixsa

    mixsa Member

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    how close is your amp to your speakers. i dont know where youve got your speakers placed, but if they are down by the stage its best to have the amps as close to the speakers as possible - as the voltage loss over speaker cables is a lot more than over a balanced xlr.
    so if your speakers are by the stage it would be best to have the amp under the stage or somewhere close.
    and its best if you can keep all the sound stuff off one circuit, even if this means running an extension lead back to the booth to run the amp
     
  17. zac850

    zac850 Well-Known Member

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    Yea, it requires a TRS or XLR input, which was good. I was kind of surprised, because I thought it had a TRS output, but ended up having only Speakon output (which was almost bad, considering that the snake we just installed 3 days ago has only TRS returns). Of corse, then I realized that I had 2 speakon to 1/4 inch adaptors, so its all good now.

    Anyway, thats very reassuring to here. As I'm sure you all can tell, I'm not to much of a sound guy, so I'm just sort of probing in the dark to make this work. I'm not going to be pushing the speakers or the amp very hard, so we should be safe for all of that.

    Thanks a lot guys!
     
  18. sound_nerd

    sound_nerd Active Member

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    ITs kind of vaigue, but PLEASE tell me that you are not running the output signal from the amp into an audio snake back to the stage. The wire used in the snake is not meant to carry such a signal. The length of leads that you need, and the output of your amp require at least 14awg speaker cable, if not 12awg. There is no way you should ever run an amps output through the returns on a snake, and then to the speakers. Thats a major problem just waiting to happen. The returns on the snake are meant to be used for fx racks /monitors and such. I hope I just read what you said wrong, and you are actually running seperate speaker cables from the amps output to the speakers input. 8O
     
  19. zac850

    zac850 Well-Known Member

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    Erm, well....

    Yes, that is what we're doing.

    OK, well, here is a question. Is this a very very big bad thing that will break things now, or is this a "well, in theory this is bad, but ya know, in practice it isn't that bad." I know that it is best to keep the amp close to the speakers, but we are in a gym, with the booth in the back, and no safe place to put an amp near where the stage is set up.

    I don't know where else we could put the amp besides the booth. The only other thing that I could think of would be to buy 100 feet of 1/4 inch speaker cable or XLR cable and run it through the conduit and snake it up and around the way we did with the snake. The problem is, this is a BIG hassle, and I would like to avoid this if it can be avoided.

    So.... is this a big concern or is this one of those "well, in theory this is bad, but in practice you will still be OKay"


    I'm a bad sound guy ::hangs head in shame::

    EDITS::

    MISTXA, well, as I said above, we're in a gym, so there is really no other place to put the amp besides in the booth, because, well, its a gym and bad things would happen otherwise.

    I was also reminded by the sound guy to ask about running 4 JBL speakers (250 watts at 8 ohms) as opposed to the 2 Peavey Cabinets (400 watts at 8 ohms). We would run 2 JBL's on each circuit of the amp, in parallel I think the term is. We would be taking the output from the amp into one JBL, and then output from that JBL into the second. I thought I remembered hearing at some point that the load on the amp would still be 250 watts. Is this true? Any opinions on this or that?
     
  20. mbenonis

    mbenonis Wireless Guy Administrator

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    This is a bad thing now, and it's akin to running a high current appliance off a puny little extension cord. It could be dangerous. Not only that, but it may cause interference on the mic inputs.

    However, there is a simple solution: don't put the amp in the booth as you originally planned, but rather at the other end of the snake, and send the signal to the amps over the returns. This will avoid the problem and actually give you slightly better performance from the speakers. As far as power, if possible, run a heavy duty extension cord from the amp back to the booth. In a pinch, if you don't get any hum, you're OK, but it's always better to get the amp on the sound circuit.

    Edit:

    Well, if you can't put the amp by the stage, you need to buy appropriate gauge speaker cable and run that to the stage along with the snake for safety.

    As far as the wiring of the speakers: no matter which way you wire the speakers, you always add up the wattage for the total power output of the amp. However, you do need to worry about the resistance, which is measured in ohms (forgive me if you already know this stuff - I'll say it anyway for the benefit of those who don't know). When speakers are wired in series, you simply add the resistances for the total. For example, two 8-ohm speakers in series total 16 ohms. However, if they are run in parallel, you have to use a nasty equation or memorize some values. The equation is as follows:

    [​IMG]

    There are some values you can simply memorize:

    Two 8-ohm speakers in parallel total to 4 ohms, and two 4 ohm speakers (or 4 8-ohm speakers) in parallel total 2 ohms.

    Absolutely make sure that the total resistance on the amp is not lower than the rating of the amp, which is likely 2 ohms (but check this!). From your description, it sounds like you will be fine with the JBL's.
     

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