Peavey Amp Failure

[nickb12345]

Hi All

 

Having a bit of problem with a couple of Peavey PV2600 Amps and would like to pick your brains.

 

We used to have a Peavey HiSys4 PA system which was replaced with an RCF Art 300 system at the start of the year. At the time we didn’t have enough money to replace all the amps. So we kept the old peavey 2600s. Infect as the amps are rated at 900w in 4ohm stereo we used one to run all our tops (2x 300w 8ohm per side).

 

Now yesterday the 2600 caught fire... I didn’t see it but apparently there were flames, but by the time I got there it was just arcing and smoking lots! Now this was at the end of the night so it had been running with constant music for about 6 hours and did tend to get rather warm, but not so hot I would expect it to go like that. Upon inspection one of the high voltage tracks between the transistors? And a large resistor seems to have taken the brunt of the problem, burnt right through the pcb. Yesterday we had quite a bad electrical storm and a few power surges, I am kind of putting the failure down to this and the age of the amp (over 4 years apparently).

 

However tonight we have replaced it with the other 2600, identical amp from the old pa. Now this one is cutting out when run to the normal level, I think its thermal cut-out. It’s shutting down completely (no power lights etc) for about 15-20 seconds then coming back on. The problem is reduced at lower sound levels.

 

Now.... Have we gone wrong with the calculations somewhere and are actually running these amps too hard or could I just have two faulty amps with unrelated problems?

 

Either way we have asked for emergency budget to purchase a new amp, this time we will get the one recommended by the original supplier of the cabs so we won’t have any worries about ratings of amps etc.

 

So I guess the million dollar question is.... will the other 2600 catch fire? Is this an accident waiting to happen? Or am I worrying about something as simple as equipment getting old?

 

 

Thanks

 

Nick

[Brian]

... will the other 2600 catch fire? Is this an accident waiting to happen? Or am I worrying about something as simple as equipment getting old?

TBH, 4 years, or even 8 years, is not old. I know of amps still running which are much older than that. Somewhere in the store I have some amps which must be 15-20 years old and they still work just fine.

 

The issue will be either one of maintenance, or rather lack of it, or bad luck.

 

On the maintenance side of things - are the amps a permanent install? When were they last cleaned? Is there a chance that someone spilled some drink into it recently? Without seeing the faulty unit it's difficult to give an accurate diagnosis but I'd go with 'external factors'. I don't think a power surge/brownout is the likely cause. One other possibility is that one of the output devices failed, maybe just a bad device, which might explain the resistor burnout. In general amps don't die when over-driven, I couldn't find a schematic online to check but I'd be surprised if there wasn't some form of SOA protection to look after the output stage.

 

The fact that the second amp keeps going into thermal shutdown really does suggest an installation issue.

[bobd]

I have heard of PV2600s doing this when run into clipping and without proper ventilation. I have used them extensively ensuring that the air flow is adequate and never with the clip light on into 4 ohms and never had a problem with PV2600s that are way over 4 years old.

 

I was once told by someone who thinks he knows what he's talking about that if you turn the attenuators up full, push the desk up full and run them in a rack with the doors closed they get very hot and start cutting out. No surprises there then.

 

Bob.

[adamburgess]

We once had a PV1500 catch fire powering the HF on some HiSys4s. Took one side of the amp completely out - the whole board.

Tried turning it on a few days later and the other side worked fine, although the fan was on full!! The amp was only 18 months old and saw very little abuse - nowhere near clipping on the HF.

 

Coincidence??

[nickb12345]

Hi All

 

Thanks for the replies.

 

Installation shouldnt be a problem, its in prompt corner of our stage which is very cool and rather clean. Installed in a rack with three other amps with 1u between each amp. All amps blow front to back (I think, maybe the other way round) and have plenty of space both infront and behind the rack. There is 2u between the bottom amp and the floor and about 8u between the top amp and the next piece of equipment in the rack. Cables are all neatly tied out of the way not blocking any vents or fans.

 

The amps are serviced every 6 months and tested every 12 months. The failed amp was pretty much clean inside, it was serviced and tested in January. No real build up of dust or rubbish, odd bits around fan grilles and vents but no blockages.

 

All in all I would like to think I look after them pretty well which is why im quite surpised by this failure.

 

Something I noticed today, the new amp thats cutting out only does it when its been under heavy(ish) load for a length of time. In rehearsals etc its fine running at show volumes but in the actual shows its cutting out. But by the time we get to shows in the evening its had 4 hours of constant load, could this be contributing to the problem?

 

Ta

 

Nick

[fogg]

Are you sure that you are not overloading the amp? These will run happily at 4ohms but if your running 2ohm loads etc then they do tend to get a bit hot and thermal out. What speakers are running from the amps, and what part of the pa was this amp running?

[nickb12345]

The amp is running 4x RCF Art 312i Mod-Tops. 2 per a side. They are 300w 8ohm boxes so the amp should be seeing a load of 600w@4ohm per side. As the amp is rated at 900w@4ohm per side I cant see that its overloaded. Unless someone who knows more about sound than me can shed any light on the situation?

 

Ta

 

 

EDIT:

 

Ok guys can I throw another question into the pile. I have a wharfedale MP1800 available to replace the peavey amps with. However this has a lower rating than the peavey amp, but is the correct size for the speakers (600w@4ohm per side). Am I going to have the same problems with this or am I just being paranoid?

 

Thanks

[fogg]

How hard are you driving the amp? Are you clipping the signal before it reaches the amp? ie how hard do your drive the channels are they clipping? is any other outboard such as graphic eqs etc that you are driving into the red? Amps don't like clipped signals

[Shaggy]

How are the speakers after the amp broke? The problems with the new amp could be due to the speakers being damaged and this could create an interesting load that the amp finds hard to drive and thus shuts down.

 

You appear to have a slight misconception as to how amps and speakers interact in normal 2-8 ohm use. Unlike lights a 1000w 8ohm speaker does not draw more current than a 100w 8ohm speaker and cause the amp to blow. It is the impedance that determines whether an amp can handle a load, with some cheaper amps not being able to handle loads lower than 4 ohms. Say you power a big subwoofer (1000w 4ohms) with an amp that only gives 100w into 4ohms. As long as you do not run the amplifier into hard clip it will carry on all night and nothing will be damaged. The reason underpowering speakers is seen as bad is that it increases the temptation to overdrive the amp and clip it. Amps in clip will give far more power out (just nasty sounding power) and even though the peak voltage of the signal has not increased, the rms power of the signal has increased past the power handling of the driver and you blow a speaker.

 

Assuming your speakers are not broken, which I suspect may be the case, then using the wharfedale amp will give you no problems. However given the nature of music signals most people run amps that are 1.5 to 2 times the rms power of the speakers which gives a bit extra volume/headroom with little increased danger of damage.

[nickb12345]

Speakers are fine, not a problem with them.

 

Driving them high but not hard. Signal lights will be on most of the time and clip lights will occasionally light but not running them constantly into the red. Have a Behringer Ultradrive before the amps, but that does not run into clip at all. Got the limiter set on that so it will kick in with loud shouting etc but I cant see how that can effect it?

 

With regards to how how speakers interact with amps, thats why im asking for input from you guys, im a lampie at heart and only know what I have picked up along the way with sound.

 

Also have a MP2800 amp available but that looks a bit too big to my eyes. Apparantly there are two MP1800s available so would you reccomend I run one MP1800 for one side and the other for the other side, splitting the load up more?

 

 

Ta

[jamesperrett]

With regards to how how speakers interact with amps, thats why im asking for input from you guys, im a lampie at heart and only know what I have picked up along the way with sound.

 

The impedance rating on a speaker is usually only a nominal rating. The actual impedance varies with frequency and it is possible that it dips below 4 ohms at certain frequencies. If your audio contains high amounts of energy at these frequencies then it is possible that the speakers are presenting too low an impedance to the amp. It might be worth running just one speaker per side at high levels for a few hours to see if the problem persists.

 

Cheers

 

James.