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It's getting hot

Discussion in 'Tools Of The Trade' started by djtunes, Feb 20, 2012.

  1. djtunes

    djtunes Checking Reality

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    My RMX1450 is getting hot.

    For a while now I have been using my QSC RMX1450 in bridge mono to run my subs daisey chained one to the next. My theory is that the subs recieve 700w each in this config. The specs say bridge mono 4ohms = 1400w. My subs are 800w max so I figure its a good match.

    I have been running my tops ZX1 passives with the QSC GX5 (500w x 2). Seems like the tops are getting more than enough power because I usually keep the GX5 amp gain around 12oclock and the RMX amp gain around 3oclock (this is the piont where it will clip at about the same time as my mixer clips).

    My RMX has been getting REALLY hot sometimes. At a school dance last weekend, and at a wedding this past Sat. (This wedding was a bunch of young ones wanting new stuff played loudly) is when I started noticing it more because I have been touching the amps instead of just watching the clip lights.

    I don't want my amp getting this hot. The GX is humming along a little warm but the RMX is HOT!!!
    At first I was thinking I'll keep a fan blowing into the back of the rack all night to keep it cool. Then I thought... yeah till the amp just goes bye bye. Not the option I want to use.

    I figure I'll stop running mono with the RMX. I'm gonna start using my GX5 to power the subs running stereo 8ohms, and the RMX for the tops running stereo 8ohms.

    I'm hoping the jump down from 700w to 500w on the subs won't be missed too much by me, and that the tops will still be loud enough to keep up.

    I feel like I'll run safer like this. What do y'all think?

    Eventually I want a louder system altogether but I can't afford it. So, other than that advice, what do y'all think?
  2. djtunes

    djtunes Checking Reality

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    I'm also kicking around the idea of picking up the GX7 to power the subs. It is 750w stereo 8ohms.
    I wish I could sell my RMX + my GX5 + whatever else random unused equipment I have sitting around and get 2 GX7s to run the show. It has a built in crossover that will eliminate some weight in the rack and leave more room for air flow. If one amp died in the middle of a show the other one would get me through the night in 4ohms.

    It would be nice to just hang onto all of my amps and add to what I have.
  3. Scottie B

    Scottie B Member

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    I had a rack of plx3102's running subs at 4 ohms bridged in a nightclub. They ran balls out for 4 Hours a night 3 nights a week. They pushed heat out the front of them as intense as a space heater, never a problem. You're producing alot of current at that configuration. Alot of heat is pretty normal when you're near clipping.
    Last edited: Feb 20, 2012
  4. djtunes

    djtunes Checking Reality

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    I wish I knew a place where I could run mine balls out for 4 hrs when it's that hot and see if it will shut down. I did it for 2.5 the other night with no prob. I'm afraid to lose the amp in the middle of an event.
  5. NickyB

    NickyB Gear and Equipment Moderator

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    When building your new system down the road, think HEADROOM, HEADROOM, HEADROOM..... Always get moe power than you'll ever need and let the amps run at idle...... It'll cost you more up front BUT it'll also last a whole lot longer. When I buy a sub, if it's rated for 500w RMS, I'll drive it with an amp that has 1000w RMS but run the volume at 50%.

    Afraid of losing an amp halfway through a gig? Does this mean you're doing paying gigs without a backup?
  6. Ken Heath

    Ken Heath Super Moderator...da-ta-daaa!!! Staff Member

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  7. hippydog

    hippydog wuz here when it was Red.

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    some thoughts
    Just because an amp is rated for 4 ohms doesnt mean it likes it :)
    Also, not all speakers are created equal, just because its rated at 8 ohms doesnt mean in reality it cant be a little higher or lower..
    When running at four ohms, your speaker cords can become pretty darn important, Your wires should be oversized..
    Bridging an amp is not meant to try and pull extra wattage out of your amp.. Bridging is meant to give you more configuration options.. If your system is undersized.. then your system is undersized.
  8. Conanski

    Conanski Active Member

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    QSC amps are very well built, the RMX series in particular is very robust and will stand up to they type of use you are exposing it to indefinitely, I don't kow for a fact but I'd speculate that the majority of RMX amps in use see nothing but bridged mono applications and you rarely hear about any failures.
    As for the difference between SPLs generated by a GX5 in stereo and your RMX1450 in bridged mono, you will most likely find.. should you evenetually get the oportunity.. is that not only do you not lose any output but you may even gain a little. The reason for this is two fold, first is that a 4ohms bridged load is the most difficult for an amplifier to drive so it's operating at minimum efficiency and wastes roughly have of the energy it consumes in generating heat. Second is that the numbers on the spec sheet for this load are a little misleading since they only reference 1khz.. which isn't within the normal operatiing range of a subwoofer. If you look at the 20hz-20khz spec for the other loads you will see that it is a little lower than the 1khz spec, so you can also expect the 4ohm bridged(=2 ohms/ch) output at subwoofer frequencies to also be a little lower.
    What all this boils down to is that your subs are probably only seeing about 500w each now and the amp is dumping another 800w or so into heating the room which equates to about a steady 10A draw from the wall, and a GX5 will produce the same audio power while only consuming about 3.3A, so you get the same result, lighten the amp rack and also easy your electrical burden. I pulled these current draw specs from the QSC manuals so they are accurate and represent 1/8 power or typical music content with light clipping, but I suggest you not try and do the math because the numbers won't add up.. AC wall power does not directly translate into audio watts. Anyway.. enough said, I'll just add that I generally don't like running an amp at anything less than 4ohm stereo or 8ohms bridged because they just become to inefficient.. you'll make better use of the available AC power with a larger amp running stereo.
    Last edited: Feb 20, 2012
  9. Hutt

    Hutt Pro Dj groupie since 1996

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    has the amp been cleaned??
  10. djtunes

    djtunes Checking Reality

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    Nicky, I have a back up Peavey amp.

    Hutt, the amp has not been cleaned inside. Only the fan cage area. Is there any instruction on doing this myself?

    Paul O, thank you, thank you for that input. I'll be running both amps in stereo from here out. When I use just one sub the amp does stay cooler, and I'm usually impressed with the output I get when using one sub running bridged.

    Thanks a lot for all of the replies.
  11. digitalphantoms

    digitalphantoms New Member

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    I concur with Paul, run stereo, keep the RMX on the sub as it uses the older, heavier power supply type transformers that tend to do better IMO with subs, especially if you clip them. You will not have as much output, BUT you will run cooler and will not be drawing as much current from the wall. I had an RMX 2350 or what ever the model number is around there. It was a beast... heavy, ran hot when pushed down to 4ohms on a sub, but like Paul mentioned, they just don't die...

    take the top off that amp and use an air compressor to clean it out... IMO this should be done at least twice a year depending on use... My PLX's got regular use 1-2 times a week and they built up enough dust just doing school dances that the air flow was restricted. I even used rack fans to help and I could tell when they needed to be cleaned.

    There are a couple of people selling PLX3402's on here on the used gear board... you should pick one of those up for your subs... You will wonder why you didn't do it sooner... best bang for your buck... plus they have twice the output at half the weight... In addition, they are much smaller than the deeper RMX
  12. dboomer

    dboomer Member

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    Hey Roger

    I see you are running different lines of amps. My question is ... do they both have airflow in the same direction? If not any they are close together you could be sucking the hot exhaust of one amp into the intake of the other.

    Once you determine the airflow direction there's nothing wrong with adding additional fan cooling to your rack. More pro systems run like that.
  13. djtunes

    djtunes Checking Reality

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    If I remember right both amps are blowing out of the front. I'm gonna check on that tonight.
    Thanks guys.
    Last edited: Feb 21, 2012
  14. djtunes

    djtunes Checking Reality

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    Returnig to this thread I have a thought. With the output of the RMX in bridge at 1400w I thnk I should be using 12GA speaker wires. I went over some older threads by me about my system and someone said this:

    "Think of a shower for a minute.

    You need adequete pressure (watts)
    You need a large enough supply line (12 guage speaker wire)
    You need lots of jets for the water to flow thru(speakers)


    You can buy a bigger more expensive shower head but if you don't have enough pressure or supply line size it is useless."

    Maybe my cables are too small. Not saying that is the main reason for the heat just another thing I'd like some input on.

    I'm sure the wires inside the speaker aren't 12GA. The subs have 1/4" inputs. Someone said the connection point on a 1/4" plug is about the size of the end of my finger nail. So are 12GA cables even gonna matter?

    Maybe I'll get more gain before clipping on the amp with 12GA cables.?
  15. digitalphantoms

    digitalphantoms New Member

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    You are correct. 1/4" inputs do not have much surface area actually conducting the electricity in most cases. There are some higher end 1/4" connectors I have seen out there that are better than others, but IMO, 1/4" connectors are better left for low voltage situations. Keep in mind that 1/4 plugs do not lock (in most cases, now there are locking 1/4 plugs on the market, but not that popular) and you can easily pull the cord out of the speaker and if this happens at high volumes all kinds of bad stuff can happen... arcing, shorting, etc... CONVERT YOUR 1/4 INPUTS TO SPEAKON! in almost every situation it can be done without opening the cabinet up, cutting, soldering, etc... And it can be done cheap. A 1/4 connection can definitely be viewed as a "choke point" as far as current goes.

    For high current applications 12 gauge is definitely a requirement. You can easily convert all of your cables over to speakon just by ordering connectors and replacing them also... Go to partsexpress.com to get all the connectors you need. Is 1400 high current? not really, but 12 gauge cable is of course desirable. Minimum 14 gauge. Are you daising chaining the cabinets, or are you running two cables out of the amp? Daising chaining puts the entire load on the first cable also. Just food for thought.

    To your question: are you going to gain more headroom before clipping? absolutely NOT. If you are truly trying to get more out of your current rig, more can be done by balancing your input gains, EQing the system, crossing cabinets over at points that they perform well in, cleaning your amps, making sure you have adequate voltage coming into your system, coupling the subs, optimizing your setup location to use corners and walls to add extra DB on the dance floor etc... there are all kinds of things you can do.

    I would recommend switching over to speakon for safety and quality. If your not running 12 gauge cables, and can afford them buy them. If you are expecting more output from a 12 gauge cable over a 14 gauge cable, you are probably not gonna get it... Currently, do your cables or connectors get warm?
  16. djtunes

    djtunes Checking Reality

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    Thanks for the feedback.

    My cables don't get warm.

    BTW I'm from Elkhart, IN... not far from Buchanan.

    Not missing lake effect snow. ;)
    Last edited: Feb 28, 2012
  17. hippydog

    hippydog wuz here when it was Red.

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    What guage speaker wire do you have now? How long are the cords?

    they are not.. and it doesnt matter.. resistance increases over distance..
    A high resistance would affect your output power and the damping affect of the amp.. but dont think? it would make it run hotter then normal?
  18. djtunes

    djtunes Checking Reality

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    My cables are all 16g. I didn't think I was using enough power to make a diff. Maybe to the subs I'm wrong.

    Randy you asked: Are you daising chaining the cabinets, or are you running two cables out of the amp?

    I'm daisy chaining the subs. I have a 6' coming from the banana plugs on the amp plugged into the outputs designated in the manual. Then daisy to the next sub it is a 6' if they're coupled, or a 20' most other times when they are set apart.

    #1 What kind of difference/advantage is there in running 2 cables out of the amp?
    #2 How exactly do I do this? Would I attach the ends of 2 cables to the same connect points on the banana plug? 2 pos. ends to the pos. terminal on the plug etc. Hard wire the correct + & - ends of 2 cables to the binding posts?
  19. DropZoneDJs

    DropZoneDJs New Member

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    I used to be in car audio. Same rules apply. Your amp is running at 2ohm. Some amps run hot at this if it is really not designed to do it. Some amps won't even function if you try it. Basically you have two 8ohm speakers, connecting them make them the way you did your amp sees it as 4ohm, then you bridged the amp now it sees it as a 2ohm load. Car audio guys would always get in trouble doing this because most car audio speakers are 4ohm, and their amps were seeing much lower ohms than 2....Toast in no time. I had a Crown XS1200 that could do it and did for about 4 years, tried it with the Behringer EP4000, would not function at all. Specs are only good at 4ohm.
  20. djtunes

    djtunes Checking Reality

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    Then why are the specs for bridge mode listed as 8ohm - 800w, 4ohm 1400w? I'm sure there is something I'm mostly clueless about. Thing is I've been using the amp like this for like a year and done school dances and stuff for hours on end running the subs like that. The amp is not even rated for 2ohm in bridge and the manal indicates not to use a 2 ohm load in bridge.

    ??

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