Burnt 4000 watt amp.

[dudermn]

Ive got smoke comming out of some speakers at a club i work at.
and.... i hope its not a problem due to impedance issues....
The pa is this Crest Audio
The subs are twin JBL :: Product
One has a EAW: LA212 as its top and the right a Peavey PV115 2-Way 15" Speaker Cabinet | GuitarCenter as its top.
Sooo if the right and left channel subs run 1600 watts at 4 ohms separately and the tops run 1000?? and 800? watts at 4 ohms on top of (connected in parallel). i get a total of 2-00 and 1800 watts per channel, which is pretty much the rated usage out of the p.a. for 4 ohms stereo
The peavey though doesnt list a rating of 4 ohms so i just figured its double the wattage of its 8 ohm rating.
Now if the subs are JBL :: Product which run at 2000 watts that gives me 2200 watts of power at 4 ohms.

From watt i know about speakers....as long as the wattage from the speakers isnt smaller than the wattage of the amp you wont burn your speakers. if the wattage of the speakers is higher than your amp theres nothing to worry about.

So far i cant say anything is wrong.
The amp can handle 8 ohms 4 ohms and 2 ohms and the speakers dont ask for more than what the amp handles.
Though.... on power up power down there is a click sound from the left channel the one that runs an extra 200 watts....So that eastern acoustics speaker probably $ucced us over. Damn do i hate black market equipment.

Now... i run a compressor with a ratio of 7 to 1 and a threshold of -15 which brings all the input to a reasonable level before it starts pushing the amp to keep dum deejays from peaking the amp.

We run the amp at 0 dbs some times and it peaks at -6 dbs because of the compressor.

The whole set-up was run in a pretty dangerous fashion before.
There are 2 amps. One for the right side and one for the left. Basically both amps were bridged and the left speakers for example ran through both left outputs of the amp (the bare wires for the top and the speaktec connector for the sub). There was also a +20 db gain and no compressor.

Upon my arrival i herd that one amp had a very ugly whinning sound to it and decommissioned it (it was probably the capacitor for the output stage) .
Hooked all the cables up right and let the system run at full for a good 8 hours at max to make sure nothing overheated.

1 month later (and about 4-5 gigs later). As im in nyc. The owner of the club calls me....the amp started to smoke.
The next day i come in and everything is the way i left it. i turn the amp on and indeed... it started smoking. i brought the old amp in to see if we can use it as a backup and that burnt out before i even got to attach a set of speakers to it.

i have a theory though that the amps burnt out only because they were old and that i didnt do anything wrong.
What do you guys think?

[garageband]

.as long as the wattage from the speakers isnt smaller than the wattage of the amp you wont burn your speakers. if the wattage of the speakers is higher than your amp theres nothing to worry about.

i have a theory though that the amps burnt out only because they were old and that i didnt do anything wrong.
What do you guys think?

What do I think? I think you burnt it up. The "they were old, anyway" explanation holds zero water and if I were your boss I'd consider taking it out of your paycheck.

Your assumptions about power rating and distribution and peak handling are incomplete, at best.

The amp can handle 8 ohms 4 ohms and 2 ohms

While that's strictly true, you sure can't run anywhere near full power into a complex 2 Ohm load? Why? Because speaker impedance is not resistance and changes with input power and frequency. It's dynamic. If you hook up a DVm and one side shows 2 Ohms and you proceed to run that amp at 60%+ for any length of time with a full-range program, you will smoke that amp. That's the long story short - you did it.

Best thing to do is pop it open, find the big cap in the amp's PS that got smoked and swap it for a new one. Electronic Components Distributor | DigiKey Corp. | US Home Page

[the evil]

While the power rating of a speaker is just that, that doesnt mean an amplifier with max output of less than the speaker handling cant blow it, in fact its usually the opposite. Its way better to have a high power amplifier at lower gain than a smaller amp at higher gain. The smaller amp causes distortion and the distortion can cause a speaker to fail prematurely regardless of the speakers rating.

Most newer amplifiers have fuses or other overload protection against the amplifier blowing up due to impedance problems and or voltage irregularities. This of course depends on the amp.

You should look to see if fuses were replaced with an inappropriate size, but i would definitely open it up and see what happened in there.

As far as the speakers smoking, thats a sign of the voice coil heating up and burning, which was most likely caused by insufficient power/ distortion. You should check the ohm of each speaker to see if they are damaged beyond use.

[dudermn]

As far as the speakers smoking, thats a sign of the voice coil heating up and burning, which was most likely caused by insufficient power/ distortion. You should check the ohm of each speaker to see if they are damaged beyond use.

the amp burnt not the speakers...

GB....check the equipment. And youll see that it was a 4 ohm load not a 2.
unless of course those 8 ohm tops cut the 4 ohm bottoms to a 2 ohm load :/

as for the other thing...
"The amp can handle 8 ohms 4 ohms and 2 ohms."
and you said "you sure can't run anywhere near full power"
but that was out of context dude

i said "The amp can handle 8 ohms 4 ohms and 2 ohms and the speakers dont ask for more than what the amp handles"...well the right side at least.... As in that the speakers arent asking for more juice than the amp has at any impedance....

As for the full power thing... does that hold even if the input doesnt breach -6 dbs ?

Thanks for the quick reply.

[garageband]

As in that the speakers arent asking for more juice than the amp has at any impedance....

I'm saying this not a useful conceptualization.

Lower impedance loads suck more power. Reduce the impedance to zero (short circuit) and it will max out. That's how the amp sees it. The fact you have anything in parallel in this circuit is recipe for trouble and calls for special attention. Resistance for parallel circuits is: 1/r=1/r+1/r+.... You can see things get small fast which makes for an unhappy amplifier. In series, you have r=r+r+...

[dudermn]

ahm... 4 ohms plus 8 ohms is equal to 4 than

I can accept the fact that i couldve burnt the amp....
but what about the other amp that wasnt even connect to anything ? How do you explain zat !

[dudermn]

"i brought the old amp in to see if we can use it as a backup and that burnt out before i even got to attach a set of speakers to it"

[garageband]

4 ohms plus 8 ohms is equal to 4

No. It's equal to 2.6666 Ohms. Like I said, it gets small fast.

"i brought the old amp in to see if we can use it as a backup and that burnt out before i even got to attach a set of speakers to it"

Didn't you say it was already fried previously? Presumably it was from running through the same PA rig.

[dudermn]

oh come on !!! i got things backwards ?!
its 4 plus 4 equal 8, and 8 and 4 equals 2 ?

Ya.... i did decommission it, maybe deep down inside i felt left out from the fun of seeing the pa fry and i wanted to see for myself what it looks like .

Before the amps where bridged (mono). With one speaker at 8 ohms and one at 4 running off the same output (not parallel)... That i dont think is good either.
Having only one amp left... i had to make things work.

The other thing i want to ask ls that fixing the amp is just gonna take a new capacitor or two. Right?

[venuestudio]

Ive got smoke comming out of some speakers at a club i work at.
and.... i hope its not a problem due to impedance issues....
The pa is this Crest Audio
The subs are twin JBL :: Product
One has a EAW: LA212 as its top and the right a Peavey PV115 2-Way 15" Speaker Cabinet | GuitarCenter as its top.
Sooo if the right and left channel subs run 1600 watts at 4 ohms separately and the tops run 1000?? and 800? watts at 4 ohms on top of (connected in parallel). i get a total of 2-00 and 1800 watts per channel, which is pretty much the rated usage out of the p.a. for 4 ohms stereo
The peavey though doesnt list a rating of 4 ohms so i just figured its double the wattage of its 8 ohm rating.
Now if the subs are JBL :: Product which run at 2000 watts that gives me 2200 watts of power at 4 ohms.

From watt i know about speakers....as long as the wattage from the speakers isnt smaller than the wattage of the amp you wont burn your speakers. if the wattage of the speakers is higher than your amp theres nothing to worry about.

So far i cant say anything is wrong.
The amp can handle 8 ohms 4 ohms and 2 ohms and the speakers dont ask for more than what the amp handles.
Though.... on power up power down there is a click sound from the left channel the one that runs an extra 200 watts....So that eastern acoustics speaker probably $ucced us over. Damn do i hate black market equipment.

Now... i run a compressor with a ratio of 7 to 1 and a threshold of -15 which brings all the input to a reasonable level before it starts pushing the amp to keep dum deejays from peaking the amp.

We run the amp at 0 dbs some times and it peaks at -6 dbs because of the compressor.

The whole set-up was run in a pretty dangerous fashion before.
There are 2 amps. One for the right side and one for the left. Basically both amps were bridged and the left speakers for example ran through both left outputs of the amp (the bare wires for the top and the speaktec connector for the sub). There was also a +20 db gain and no compressor.

Upon my arrival i herd that one amp had a very ugly whinning sound to it and decommissioned it (it was probably the capacitor for the output stage) .
Hooked all the cables up right and let the system run at full for a good 8 hours at max to make sure nothing overheated.

1 month later (and about 4-5 gigs later). As im in nyc. The owner of the club calls me....the amp started to smoke.
The next day i come in and everything is the way i left it. i turn the amp on and indeed... it started smoking. i brought the old amp in to see if we can use it as a backup and that burnt out before i even got to attach a set of speakers to it.

i have a theory though that the amps burnt out only because they were old and that i didnt do anything wrong.
What do you guys think?

Amps don't just burn out because they are old. There are plenty of old Peavey CS800 amps out there still kicking ass.

Lets look at the gear involved. The JBL subs are, well, sub par. They have an RMS rating of only 800 watts at 4 ohms (parallel). The EAW equipment is top of the line gear and handles 500 watts all day long (I have used them many times). The Peavey is rated at 8 ohms, not 4 and has a rating (RMS) of around 280 watts based on the 400 watt program rating (the companies way of saying peak power). The Crest amp is rated to 5500 watts at 4 ohms bridged.

In designing systems you generally want the amp to have MORE power than the speakers can handle. This is so that the amp doesn't come near clipping. That will kill speakers faster than over powering. The amp distorts and fries the speakers.

Both top speakers are the limiting factor in this design, The Peavey more than the EAW. Now as to the hook up, if you are bridging the amps then the outputs (where you hook up) are the two positive outputs of the amp, not the left or right output. If you hooked up any other way, you risk burning up the amp.... ouch!! Additionally as GB pointed out, you are running at 2.66 ohms. If this amp was rated to 2 ohms bridge then you would be fine, but it is not, it is rated to 4 ohms bridged. Another way to burn up the amp! I have run Crown Macrotech 5000s at 2 ohms/channel stereo for hours on end in the sun without so much as a hiccup. Thats 2500 watts/channel. But the system was configured at 2 ohms/channel. The frequency response of the signal doesn't make any difference. If it is a good amp (Crest/Crown/Lab Gruppen/etc.) then it will run at 2 ohms if that is what it is rated to. This is evident from the fact that most of the high powered amps like these are used for sub amps, the most brutal of all loads to run.

Do you have any kind of crossover in the system? If you are not then the tops are getting the sub frequencies too.

I would say that it is HIGHLY LIKELY you killed the amps. In fact there is a chance you killed a few speakers at the same time. Most likely you fused the speakers into a short and that killed to amp. Let us know.

[garageband]

Nicely laid out Kent.

The other thing i want to ask ls that fixing the amp is just gonna take a new capacitor or two. Right?

Odds are good. But yeah, if you replace the burnt component(s) and reconfigure the system, you'll probably be fine. Heck, play your cards right, you might come off as some sort of hero.

Most likely you fused the speakers into a short and that killed to amp.

Don't forget to whip out your DVM to see what the amps are seeing.

[dudermn]

I find it strange that they handled 2 ohms for so long....
i ran the crest in stereo. Because the other amp was dead. Not parallel.

There is also the way the amps were stored that is a problem to me. A hot and humid room....To put the humidity in perspective. its hard to understand why there arent any salt crystals forming off the ceiling.

As for the cross over thing.. im pretty sure these speakers have built in filters to keep them sounding good, its not as we used the tops as "tweeters". The jbls help add bass to the place and the other speakers add the missing middle and hi-end. Besides the 2 tops dont really do anything with lows other than help the kick out :/

so if everything was runing at 2 ohms that leaves the amp at 2750 watts per channel....

Either way we had to make compromises as the clubs not doing well. There were 2 problems i had to fix.
1. The volume would fade on the left side now and than.
2. An eastern acoustic speaker burnt out. (i almost fixed it but when i saw how much stuff came off the circuit board and that it was filled with insulation)
3. Configure the cross over because it wasnt working.
4. hook up a snake.
5. keep people from raise the volume to ridiculously dangerous levels.

The volume swelling was caused by a burnt out channel on one amp.
The eastern acoustic got replaced by a peavy
to use the cross over id need the help of the first burnt out amp... as one amp would handle the bass and the other would handle the top.
snake was done via a 60 dollar mixer.
keeping people from raising the volume was done by the compressor...

And no i didnt burn up any speakers....this is another tale of what happens when you make compromises with audio installations.

i iust wanted to know a few details about what i messed up because i was a douche and what i messed up because i had no choice

wouldve keeping the amps running at -10 helped any ?

[aj113]

I find it strange that they handled 2 ohms for so long....
i ran the crest in stereo. Because the other amp was dead. Not parallel.

Stereo is not the 'opposite' of parallel. Parallel refers to the way the speakers are linked. Correct me if I have misunderstood but your PA is connected thus: Left side of stereo amp to left subs, left subs linked to left tops. Right side of stereo amp to right subs, right subs linked to right tops. Right? (Or possibly you could be going from the amp to the tops first before the subs- either way the result is the same).

A stereo amp is basically just two amps in one case. So for ease of discussion let's look at just one of those amps, i.e. the left. Your sub cab is 4 ohm, and that is linked in parallel to the top. There is no crossover involved other than the passive crossover in the top, which means that ALL frequencies are pumped to ALL cabs. This is not good for sound quality, and in the case of the tops, the passive crossovers will be working under unnecessary strain.

Furthermore, because the subs are half the impedance of the tops, they will be using up twice the power that the tops use, and as we all know, bass frequencies work an amp much harder than other frequencies.

However, the most undesirable element of this setup is the impedance that is created by linking the cabs - as has already been stated, 8 ohms linked in parallel to 4 ohms gives an impedance of 2.66 ohms.

Now, I may be an old git, but in all of my days in PA's, I had a rule which was borne out of some very bad experiences involving burning amps, and which consequently served me very well - don't go below 4 ohms. Manufacturers give amps a 2 ohm rating to make their sales blurb look good. What they are really saying is "The amp will pump out x thousand watts at 2 ohm, but that's just in theory - we don't actually recommend you take it down to 2 ohms."

So what do we get when we put all of this together? We get an amp which is being thrashed to within an inch of its life. Something is going to give within a short space of time, and it sounds to me like it already has. I tell you, if I had linked up a stack in this way, I would have been cacking my pants as my trembling hand hovered over the amp's power switch.

How to proceed in the future:

The subs are 4 ohm, that means the manufactureres didn't really envisage you linking them with anything else, because 4 ohm is about as low as you want to be going. So the subs need an amp each. (Or one stereo amp if you like)

Which means that you need one more mono amp at least for the tops.

If you are really stuck for cash, there is one way you could do it without buying any extra equipment. You could hard wire the subs together in series, making their combined impedence 8 ohms, then you could power them both safely from one "side" of your stereo amp. Then you could link the tops together "normally" in parallel, giving a 4 ohm impedance for the other "side" of your stereo amp.

This would mean your PA would now be mono, but running reasonably safely and effectively.

I would still recommend a small 2-way active crossover though.

[kakeux]

hi there,

The amp is rated 2750W @2Ohms under 1kHz for each channel. So it should be easily capable of driving 2.666 Ohms feeded with music. Am I wrong here?

In my day job, I've seen more amplifier that have burnt because of a too high input level than because using them at their rated power (ok, not the same part will burn but it will definitely smoke also).

I'm no pro in the PA world, but this what I think.

[dudermn]

ya im taking the amps in for a fixing. Afterwards ill rig um up with a crossover as well....though i dont know how we"ll ever pay for the extra cables (somethings tells me im buying um).

[m24p]

oh come on !!! i got things backwards ?!
its 4 plus 4 equal 8, and 8 and 4 equals 2 ?

4 plus 4 equals 2, if you're talking parallel impedance.

[aj113]

hi there,

The amp is rated 2750W @2Ohms under 1kHz for each channel. So it should be easily capable of driving 2.666 Ohms feeded with music. Am I wrong here?

No you're not wrong, but emphasis is on the should. As I said, I personally wouldn't go there, regardless of manufacrurer's specifications.

In my day job, I've seen more amplifier that have burnt because of a too high input level than because using them at their rated power (ok, not the same part will burn but it will definitely smoke also).

I'm no pro in the PA world, but this what I think.

I've never seen an amp blow due to too high an input level. I've seen amps blow as an indirect consequence of a high input level though.

[aj113]

ya im taking the amps in for a fixing. Afterwards ill rig um up with a crossover as well....though i dont know how we"ll ever pay for the extra cables (somethings tells me im buying um).

A crossover would be nice, but a crossover is not really going to do anything about your amp blowing. You need to pay careful attention to those 4 ohm subs, that's where your problem is.

[wankerone]

Running anything near two ohms is a problem live. No matter what the amp sellers think the amp might do. The you have pv115, I used a pair of Pv215 which were rated at 4 ohms. Amp one channel used plugged to one plugged to one. I know it was under 2 ohms. I am glad my power amp had a auto cutoff, I was like wtf while the vocals cut out, went through the mic cords etc... after getting down to the fact that is was wired wrong no problem for the last year with similar speakers. I would use two power amps, one for tops and one for subs, you will have power to spare even at a lower rating you can still run stereo or mono. I use a QSC rmx2450, and a behringer ep2500 picked up both used. A regular show is ten bands poppunk and hardcore mostly, no problems with the power amps for the last year and a half. I did have a problem with my powered mixer (used for monitors but that was just my own stupid thing for not storing it right, I am pretty sure it got wet) Watch out for distortion never a friend to PA speakers.

[garww]

"5. keep people from raise the volume to ridiculously dangerous levels".

I used to pop the top and reverse mount the control. You could use the mechanical regulator/govenor trick. a key and lock will work to some degree.

I gotta tell you, though, You were in a bad spot with maginable gear.

[venuestudio]

I would prefer to run subs off one side of the amp and tops off the other side. You are in mono on most rigs anyway. You keep the amp in stereo so it will drive to it's lowest limits. You can run the input of the board into a crossover and out to each channel on the amp to help control what frequencies go to what. The reason it is helpful to run a crossover is to protect the speakers from reproducing frequencies they are not meant to play. That allows them to play louder without distortion. If you help control the speakers you are protecting your amp by extension.

For everyone who is concerned about running an amp at low ohmic values, if your amp is a good amp (as before Crown, Crest, QSC, Lab Gruppen) driving to 2 ohms is not a problem. Good amp is part one. The next problem is how you drive the speakers. The issue that you need to avoid is not having a good gain structure set up, and because of that, drive the amp into clipping or at its limits. I have worked some very large systems over the years with 10s of thousands of watts of amps just to the sub systems. I never had a problem driving 2 ohm loads. The amps where set up to drive to ~ -6dB off of its redline. If you need more output then you increase your equipment rather than risk the damage to your system.

[garww]

hi there,

The amp is rated 2750W @2Ohms under 1kHz for each channel. So it should be easily capable of driving 2.666 Ohms feeded with music. Am I wrong here?

In my day job, I've seen more amplifier that have burnt because of a too high input level than because using them at their rated power (ok, not the same part will burn but it will definitely smoke also).

I'm no pro in the PA world, but this what I think.

The spec only tells you what it will do at 1kHz with a sine wave, or something. You can get a better idea if it says 20Hz to 20kHz RMS, but you still have to account for program material and the loading, etc. in the real world. This is the realm of headroom at certain frequencies, and you're not likely to have a lot of headroom at lower freqs(and at 4-Ohms and less). You ears will, eventually, be able to hear the distortions that you need to avoid.

Good gear should be able to take some very high input levels, but someone have to get a handle on what going on, as there is no real need for excessive input voltage

[garww]

In looking at at spec sheet for the Crest amp, it's looks like a 500watt amp. I would avoid anything with a crappy spec sheet, or at least be cautious as to the ratings.

[venuestudio]

In looking at at spec sheet for the Crest amp, it's looks like a 500watt amp. I would avoid anything with a crappy spec sheet, or at least be cautious as to the ratings.

I think the link in the OP was to a CS5500 amp. That amps specs are HERE. That looks like a 1900W/ch amp at 2 ohms with reasonable distortion.

[garww]

Ya, the Power Bandwidth was close to meaningful - 525 w at 8 Ohm. But there is no minimum RMS continuous over a freq range. It's possible the transformer may supply high current under certain conditions, but they don't have nude pics to examine. Frankly, I've not really followed high current design much. I read all the shit on the Carver amps and noted a swing in a lot of amp designs as time progressed. At lot of amps can spec good if you only send them a pulse tone. In practical terms, it either performs or not