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Which is worse for the amp?

Discussion in 'Amps and Cabs [BG]' started by adamaarts, Jun 7, 2003.


  1. adamaarts

    adamaarts Supporting Member

    Apr 19, 2001
    Corona, CA
    Beta tester Source Audio, demos/reviews of many others
    I have a Carvin R1000 which at practice and gigs i run through the drummers Ampeg 8x10. Today at practice i started in bridged mode (1000 watts 4 ohm) with the volume at 5 exactly, and played maybe an hour or so. I checked the amp, and it felt hot just standing there so i touched the back next to the fan and around the sides and it was almost burning to the touch. it also smelled kind of warm. so i switched back to stereo (350 watts 4 ohm) but had to crank up the power amp level to keep the original volume (i have to compete with 2 mesa half stacks), which made the peak light dim a little, but i turnned down just a tad until it came off, and added some compression to limit my peaks.

    i was really wondering, which is worse for the amp, to run very hot, or to push it too hard? i also feel that pushing it would cause unwanted distortion and/or noise which could possibly damage the speakers.

    thanks for all who reply
     
  2. Well to me if its running damn hot then you are pushing it too hard. Because by pushing the amp hard you are causing it to dissipate more heat through the transistors being turned on harder etc.

    Why do you need thunderous amounts of volume at a rehearsal anyway? and even so.. at a gig? I use a 100Watt power amp with a preamp rack in a death metal band. I run it on about 5 on the master and thats enough to ceretainly be heard. At gigs i'm told to turn down as its too damn loud.....

    :D:D

    Merls
     
  3. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    My opinion, if you're that loud at a rehearsal, then you aren't rehearsing, you're jsut covering up the little things that you should be working on . . .

    Nevertheless, the answer to your question is that yes, you are running it too hard in bridge mode, and still running it too hard in stereo. You'll eventually have problems with it either way.
     
  4. adamaarts

    adamaarts Supporting Member

    Apr 19, 2001
    Corona, CA
    Beta tester Source Audio, demos/reviews of many others
    we practice loud at rehersal sometimes, like last night when we just went through our set list, and jammed a little, we didnt really write new material.

    also, the floors are bare concrete so the bass doesnt move the ground like it should on a regular house floor so i just turn up a little just to get a decent volume rather than feeling it.

    i guess in the furture i will try not to puch to hard.

    what specific problems would this cause? a blown amp?
     
  5. My death metal band used to have this problem. You all need to turn down. You see what happens is this. "the guitarist is too loud, so you turn up, then he hears this and turns his amp up" etc etc It goes up and up until you are pushing your amps.

    My band still rehearses way too loud. We needs ear plugs and drown everyother rehearsal room out. I run my rig at 5 the guitarist at 3 on his carvin 100 watt tube head. Earplugs are a must.

    The room we rehearse in has concrete walls and concrete floors. Put some old carpet down. That helps. We used to play has a band facing forward, but only to get used to that. Now we are a gigging band we rehearse in a circle. The sound clashed and forced us to turn down.

    When we had a lead singer i showed him how to "set the levels" for the band. So we would jam on a song and he would go around and turn us up/down in accordance. Once we understood the level and our sound then seeing as the singer has gone, we know what to set.

    This is rehearsal, you could in effect just play through tiny combo amps. You're practising timing and trading off on each other. This isnt a competition.

    I agree with what was said up above. The louder you are, the more mistakes you are covering because it just becomes a wall of noise. As a band you will improve. I am speaking from experience because everything u have mentioned is exactly what my band did.

    On pushing your amp. Yes it can result in a blown up amp. At best it may burn out some components that will need to be replaced. So too, drive your amp too hard, you create distortion, which if becomes excessive becomes clipping which becomes pure DC and good buy speakers too. TURN DOWN.

    The others will work it out. If your guitarist says "hey i cant hear you?!" then you have to say "yup you're way too loud"

    :D:D

    Merls
     
  6. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hi Merl,

    Clipping is not DC, nor does it "[become] pure DC."

    Clipping a power amp can cause it to put out far more power than its actual rated power. That can be, and often is, fatal for loudspeaker drivers.
     
  7. Dear Bob,

    Merlin is wrong, I agree. But not completely.

    This is rather off topic.

    A clipping amp *can* become unstable and put a DC voltage on its output. Actually, very low frequency AC in the .1-1 Hz range. I'm convinced it has to do with the offset adjustment of the coupling capacitors most amps have between the drive section and the power section. I've seen it with my own eyes on a scope screen. It can be recognized by "waving" speaker cones. It tears speakers apart mechanically.

    I'll clarify my view.

    A music signal is never purely symmetrical. Especially with bass guitar, the positive signal peaks are higher than the negative signal peaks, where of course the *mean* level equals zero. Now when the amp clips, the positive signal is clipped first. The mean signal is now unequal to zero, iow. out of balance, and the coupling caps introduce an offset voltage into the power section to counteract the unbalance. When the clipping stops, the balance returns, and the offset is shifted back to 0. Hence the "waving speaker cone".

    If the particular amp were *purely* DC coupled (few <1000W amps are) this phenomenon wouldn't occur, as there are no offset adjusting coupling caps

    WOuld you care to comment?
     
  8. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hi Joris,

    The positive peaks are not necessarily always larger than the negatives. Chances are that they'll vary.

    If the waveform is asymmetrical and it clips, yes, you might get a LF AC component in the output. Compared to the overall signal level, though, those AC artifacts will be fairly small and not by themsleves dangerous to the driver.

    Another phenomenon worth considering is that in nearly all amps, the output impedance effectively increases whenever the signal clips, so damping plummets right at the the points where the amp is putting the highest accelerative forces on the driver. Because it is a sprung mass, the speaker cone has resonance, and it will vibrate at that resonant frequency if it is mechanically excited. And hitting it with those large accelerative forces--i.e., voltages--qualifies as mechanical excitation. What you saw could also be sort of a mechanical heterodyning between the cone's resonant frequency and frequencies in the audio program that are close to the resonance.

    I still think it's a myth to equate clipping with DC. :)
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Back to the original problem..... I would have thought that the amp would have run hotter pushing 350 hard watts than 1000w at less effort to get equivalent volume.

    Is it possible the amp is sick?
     
  10. adamaarts

    adamaarts Supporting Member

    Apr 19, 2001
    Corona, CA
    Beta tester Source Audio, demos/reviews of many others
    petebass, thanks for actually paying attention to my problem, unlike some other people...

    when i run at 350 watts, its only running one amp, or one side of the amp. when i bridge it both amps put out 1000 watts which is more power which is maybe why its running hotter.

    i feel that amps are made to run hot, at least tube amps should. i know heat takes out some power (i read your "cooling" thread petebass)

    my guitarist says that it should be fine running hot, but how hot is too hot?

    i am also thinking to buy a rack and buy a fan for it, then i could also get a new rack tuner. and i will add additional cooling for the amp.

    and im sure the amp isnt sick.


    and to merlin who says its too loud, i agree but our band trys a different setup everytime we practice since the drummers garage is always moved around (hes putting in drywall and a new ceiling for his garage) and this particular time my stack was pretty far from the drummer so i had to push it, also one guitarist is always the "loud" one and seldom listens to what anyone has to say, but what are you gonna do? i could easily put him in his place with my amp, i just choose not to.

    but your point was taken and i do realize that that would help the situation. thanks to those who helped.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    aww go easy on em.... they're good guys just TOO smart sometimes :)

    Here's the thing - it's only putting out 350 watts what the clip light is flickering. Most of the time you're actually pushing less than that.

    So when you were running it bridged, it's capable of 1000w but it's probably only pushing 350 or so. I assume 350w because I'm assuming you played at a similar volume both times. Did you notice any change in the operating temperature from one mode to the other?

    IMO, too hot is when you can't touch it without burning yourself. The amp already has a fan so it shouldn't need any more cooling. Are the existing fans working OK? Are the fand getting adequate ventilation? Is the fan's saftety grille covered with dust? I dunno, I'm just guessing......
     
  12. Slater

    Slater Bye Millen! Hello?

    Apr 17, 2000
    The Great Lakes State
    Are you sure you're using a good (proper) speaker cable from the amp to the cab?

    Once, at a gig, someone used a guitar cord (without my knowledge :mad: ) to hook up one of the stage monitors, and the poweramp almost got fried :meh: .
     
  13. adamaarts

    adamaarts Supporting Member

    Apr 19, 2001
    Corona, CA
    Beta tester Source Audio, demos/reviews of many others
    the amp is fairly new, and has no problems with the fan or ventalation. i do use heavy gauge speaker cable, although this time i used a smalled gauge spealer cable from carvin. i am going to upgrade to the twistlok as it handles the wattage better in the high range, but would that help any? seems like it would be insignificant.

    the temperature went down gradually as i swithced to 350 but i cant be too sure since we did take a break shortly after and i left the amp on but turned volume and power knobs down to let it cool, which helped alot also.

    i dont know what else to tell you.
     
  14. I should think that running it at clipping might damage your speakers but the jury is still out on that subject. Running it at 4 ohms bridged shouldn't hurt anything. The amp is rated at 4 ohms bridged, Carvin says it's OK, it isn't clipping ( 4 ohms bridged ) it isn't shutting down, put a small fan blowing on the head. This will keep the case cooler thus keeping some of the internal heat down.

    As a veterian of some 30 odd years of Rock & Roll, I have a lot of buds my age with hearing aids. I've been lucky I guess and still have most of my hearing. Practicing at 1000 watts into 8x10's has got to be doing damage to not just your hearing, but, your band mates too. I tell my kids (i'm a teacher) to invest in hearing aid technology now as most of them will need them when they are my age. (53)
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Like Merlin said earlier, if the amp gets hot, that's a sign that you're pushing the amp hard. If it gets very hot, it's because it's being pushed very hard. Heat is an enemy to electronic devices, which is why amp designers put heat sinks and fans in them, to get the heat out and transfer it to the air.

    If you run the amp in bridged mono driving a 4-ohm load, that is electrically equivalent to driving 2 ohms per channel. That requires more current to pass through the amp's output sections than when you operate at higher impedances.

    When you switch from running in bridged mono to stereo running on just one channel, you have to turn the amp gain up 6 dB to get the same output level you had before. You're more likely to clip the amp in that situation, too. But if you can get the sound level you need without clipping the amp, that's fine. If you can't, go back to bridging the amp.

    I don't know if your amp is running unusually hot or not. But if it is, you should determine whether it's due to a problem in the amp (get it checked out if you suspect this) or just a design shortcoming. A very-low-cost amp just might not have as comprehensive a cooling scheme as your situation demands. Maybe a rack-mount fan panel mounted behind the amp (to help push cooling air flow into it) would help.
     
  16. adamaarts

    adamaarts Supporting Member

    Apr 19, 2001
    Corona, CA
    Beta tester Source Audio, demos/reviews of many others
    i just had another thought. i play an active bass through this rig. i use the active input which cuts the volume by 15 db? 10? im not sure but maybe that cutting sooner is making me have to boost it later, and maybe thats why im pushing the amp harder than i should.

    shoukld i try to run it through the passsive input?
     
  17. rumblethump

    rumblethump Supporting Member

    Mar 25, 2000
    Pioneer CA. 95666
    If you bass doesn't distort when running through the passive input it should help.
     
  18. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It wouldn't matter. It's what you're making the amp do at the end that determines how hard you push it.