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Amp went poof!

post #1 of 20
3/18/13 at 4:51pm
Thread Starter 
I am wondering if any tech types can weigh in on a situation that recently occurred.
While sitting around the other day an obnoxious noise emanated from one of my theater speakers like a death throe.
It was then silent.

I checked the Cine Nova multi channel amp and the light corresponding to the dead speaker was lit.
I took the dead Klipsch RC-7 speaker to my local repair shop and explained what had transpired.
The cones are fused and no longer move.
The tech there said it sounded as though a burst was sent from the amp and fried the speaker.They put the blame directly on the amp.

I am now wondering if this might occur with the other channels of this amp and remaining functioning speakers.
I have never heard of this and wonder if this type of occurrence does happen on occasion, if so it makes home theater a very costly hobby.

The amp module has finally been repaired and is en route back to my location. I have also had the speaker repaired, luckily parts were still available. I am hopeful that Earth Quake will eventually spring for the repairs to the speaker.

Earth Quake stated maybe a source component caused the failure. I have now had the pre amp tested for anything unusual and have spoken at length with Marantz's tech department about this issue. It is their conclusion that the failure resides solely within the amplifier which in turn caused the speaker to blow. I have also had conversation with the repair depot that fixed the speaker; they have the same opinion as well.

I then contacted the two other source component companies in my system, Blu ray player and my digital HD cable service both state their products could have in no way caused the issue that occurred to the amp and speaker unless they were connected directly to the amp, which they were not.

My dilemma is do I trust this amplifier enough to put it back in to service? I have not used the amp since the failure took place. I am very hesitant to re instate it after I re install the module. Earthquake has been unable to provide any assurances that this fault will not occur again to the amp or speakers connected to it or how to prevent such a failure, or what they are prepared to do in regards to compensation should this occur again.

The service depot made up some inline fuses for me to add to the positive side of each speaker terminal at the power amp outputs. I am bi wiring but they state only the woofers require this type of fused protection.
Will this fuse system stop another occurrence should it occur?

Should the amp factory not be able to have diagnosed the failure and know what the issue was and how to avoid another occurrence going forward?

Would or will another amp manufacturer fare any better?

I was at my local hi fi dealer recently and was explaining to him the issues as I see them.
He states that by inline fusing I will be altering the sound output.
He also had $90.00 fuses that are claimed to not alter the sound.
But using the lower grade wiring and inline fuses will degrade the sound to some degree he states.

There is also no guarantee that fusing would prevent another of these issues should it ever arise, at least not to the amp.

I will probably get the module back next week and have no idea what the next step will be other than putting the amp back together.
It seems there is no way to pin point what caused the issue whether it was a freak occurrence within the amp or something else.

The amp is still on warranty and there is a possibility of a return if it was their product that caused this issue.
Would another amp fail as well
In decades of listening and multiple audio products this has never happened but I do not ever want this type of failure to ever occur again.
Ideas?
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post #2 of 20
3/18/13 at 6:59pm
Hi Kiwi,
Quote:
Originally Posted by kiwi2000 View Post

. . . I am hopeful that Earth Quake will eventually spring for the repairs to the speaker.
Who is Earth Quake? Are they the dealer that sold you the amp? Or the manufacturer?
Quote:
Earth Quake stated maybe a source component caused the failure.
No, it was clearly the amp at fault. A source component could not have put out a signal that would cause the amp to "pop" a speaker.
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My dilemma is do I trust this amplifier enough to put it back in to service? I have not used the amp since the failure took place. I am very hesitant to re instate it after I re install the module.
Did they say what was found wrong with the module? That would go a long way in assessing whether it might happen again.
Quote:
The service depot made up some inline fuses for me to add to the positive side of each speaker terminal at the power amp outputs. I am bi wiring but they state only the woofers require this type of fused protection.
No, the tweeters are susceptible also, depending on the failure mode. If a transistor shorted and sent DC to the speakers, then yes, the crossover would likely protect the tweeters. But if the amp sent a transient, that would go through the crossover and could damage the tweeters. Again, it would help to know what went wrong the first time.
Quote:
Will this fuse system stop another occurrence should it occur?
More than likely, if they are fast-acting fuses.
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Should the amp factory not be able to have diagnosed the failure and know what the issue was and how to avoid another occurrence going forward?
They should know exactly what happened. The fixed it, didn't they? they must know what they replaced.

If they can' tell you what went wrong, it means that they either don't care to, or they don't want you to know.
Quote:
Would or will another amp manufacturer fare any better?
I would hope so.
Quote:
I was at my local hi fi dealer recently and was explaining to him the issues as I see them.
He states that by inline fusing I will be altering the sound output.
He also had $90.00 fuses that are claimed to not alter the sound.
But using the lower grade wiring and inline fuses will degrade the sound to some degree he states.
Uh, no. He is trying to scam you. A fuse will not alter the sound.
Quote:
There is also no guarantee that fusing would prevent another of these issues should it ever arise, at least not to the amp.
Again, the fuses will go a long way toward protecting the speakers. All of my amps have built-in fuses at the speaker terminals, and most of them have protection relays as well. I'm surprised the your amp doesn't have them built-in.

Now, the fuses probably won't prevent the amp from failing, but if it does, it means they didn't fix it the first time and need to fix it again. But at least you will have spared your speakers.
Quote:
I will probably get the module back next week and have no idea what the next step will be other than putting the amp back together.
It seems there is no way to pin point what caused the issue whether it was a freak occurrence within the amp or something else.
Again, try to get an itemization from the repair as to what was replaced. Even if you didn't pay for the repair, you deserve to know what was done. If you find out anything, post it here.

Quote:
The amp is still on warranty and there is a possibility of a return if it was their product that caused this issue.
Would another amp fail as well
It is the amp that caused the issue. If it was a design flaw, it could certainly happen again. How long has this amp been on the market? How many have they sold? Any other reports like yours?
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post #3 of 20
3/18/13 at 8:36pm
Sounds like DC to the speaker. Have seen it before with older amps failing. It will probably never happen again in your lifetime. A newer ampliifer would be much less likely to fail, but other than that...parts will eventually fail with anything, but may not result in the same occurence.

B.
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post #4 of 20
3/18/13 at 10:36pm
Hi Brian,
Quote:
Originally Posted by Brian B View Post

Sounds like DC to the speaker. Have seen it before with older amps failing. It will probably never happen again in your lifetime. A newer amplifier would be much less likely to fail, but other than that...parts will eventually fail with anything, but may not result in the same occurrence.
I completely agree with what you say with regards to an older amplifier, but Kiwi's amp is still under warranty. True, it could simply be infant mortality, but that usually occurs in the first 100 hours. I would worry that it's a design problem that causes output transistors to short. I am also suspect of any amp that doesn't provide some form of protection to the speakers.
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post #5 of 20
3/19/13 at 5:48am
Quote:
Originally Posted by kiwi2000 View Post

I am wondering if any tech types can weigh in on a situation that recently occurred.
While sitting around the other day an obnoxious noise emanated from one of my theater speakers like a death throe.
It was then silent.

I checked the Cine Nova multi channel amp and the light corresponding to the dead speaker was lit.
I took the dead Klipsch RC-7 speaker to my local repair shop and explained what had transpired.
The cones are fused and no longer move.
The tech there said it sounded as though a burst was sent from the amp and fried the speaker.They put the blame directly on the amp.

I've seen this happen many times. One of the more common failures of power amplifiers results in power transistor(s) shorting and basically connecting the amp's high current power supply to the speaker. Usually the output of the amplifier averages to be zero volts with momentary excursions plus and minus of that. When this failure happens, the output of the amplifier becomes a steady 40 to 80 volts plus or minus with a lot of current behind the voltage.
Quote:
I am now wondering if this might occur with the other channels of this amp and remaining functioning speakers.

It can happen with any power amplifier that lacks a good speaker protection mechanism which covers a fairly high percentage of them. The bullet-proof solution is a relay that disconnects the speaker from the amplifier if the amplifier starts acting strange. Problem is, relays cost money. In terms of production costs, this sort of protection has a parts cost of less than $3 per channel in AVR production quantities. There are other means including a solid state crowbar transistor or other device that shorts out the output of the amplifier and forces fuses and things to blow elsewhere in the circuit, sacrificing them to protect your speakers.
Quote:
I have never heard of this and wonder if this type of occurrence does happen on occasion, if so it makes home theater a very costly hobby.

Modern power amps are pretty reliable. So reliable that it can be argued that the extra expense for an expensive protection circuit is no longer cost-justified. My last AVR failed this way, but it did have protective relays even though it was very inexpensive. You can often tell if an amp or an AVR has protective relays - when there is a click when you turn it on.
Quote:
The amp module has finally been repaired and is en route back to my location. I have also had the speaker repaired, luckily parts were still available. I am hopeful that Earth Quake will eventually spring for the repairs to the speaker.

I'll bet that your warranty has some clever words about "consequential damages" or some such that release the amp manufacturer from responsibility for your speakers.
Edited by arnyk - 3/19/13 at 6:42am
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post #6 of 20
3/19/13 at 6:31am
Thread Starter 
MarkHotchkiss thank you for thoughtful responses.

You can look up Earth Quake sound, they are a manufacturer.

You are in agreement with everyone else it could only have been the amp that caused the failure.

They did tell me what went wrong and also that this type of failure had never happened to them before.
Several things fried in the high frequency area of the amp module. They said the event went through several layers of the module leaving them untouched then fried the high frequency area.

Quote:
All of my amps have built-in fuses at the speaker terminals, and most of them have protection relays as well. I'm surprised the your amp doesn't have them built-in.
The amp has multiple protection circuits but none went off that day. It has a master circuit breaker for all channels and rail fuses for each module. Is that what you are referring to or the set up I have been describing by putting fuses in the speaker wire?
Quote:
I would worry that it's a design problem that causes output transistors to short. I am also suspect of any amp that doesn't provide some form of protection to the speakers.
I am very worried that it might happen again and that the other modules might be susceptible to whatever happened.
the amp does have protection, all sorts they just never tripped.

The speaker crossover was fine as was the tweeter, the woofers not so much.
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post #7 of 20
3/19/13 at 6:48am
Quote:
Originally Posted by kiwi2000 View Post

MarkHotchkiss thank you for thoughtful responses.

You can look up Earth Quake sound, they are a manufacturer.

I found this page particularly amusing:

http://www.earthquakesound.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=351&category_id=87&option=com_virtuemart&Itemid=82

It is written in a style that seems very hyperbolic. I think I know enough about amplifier design to strip away the hype and translate it into good technological writing. The equipment is probably a lot more real world than the publicity they are trying to generate. ;-)

I might add that they seem a lot more interested in protecting the amp than any speakers attached to it...
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post #8 of 20
3/19/13 at 6:50am
Quote:
Originally Posted by kiwi2000 View Post


I would worry that it's a design problem that causes output transistors to short. I am also suspect of any amp that doesn't provide some form of protection to the speakers.
I am very worried that it might happen again and that the other modules might be susceptible to whatever happened.
the amp does have protection, all sorts they just never tripped.

The speaker crossover was fine as was the tweeter, the woofers not so much.

That's the usual situation. The DC that killed your woofer got stopped by the tweeter's crossover capacitor. I' ve seen amps mess up the woofer crosover when they blew, but apparently the woofer itself went first, saving the crossover coil.
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post #9 of 20
3/19/13 at 8:19am
Thread Starter 
Why didn't the protection circuits trip on the amp?
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post #10 of 20
3/19/13 at 9:24am
Quote:
Originally Posted by kiwi2000 View Post

Why didn't the protection circuits trip on the amp?

Reading the doc, it appears that the protection circuits on this product are weighted towards saving the amp from damage.
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post #11 of 20
3/19/13 at 10:16am
Thread Starter 
They did not do a good job of either protecting the amp or speaker.
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post #12 of 20
3/19/13 at 10:18am
Quote:
Originally Posted by kiwi2000 View Post

They did not do a good job of either protecting the amp or speaker.

Makes the point that some valuable properties of an amp can't be found using just a listening test.
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post #13 of 20
3/19/13 at 11:42am
I agree with Mark and Arny's synopsis that the amp latched a rail and applied DC to the woofer coil. What I don't agree with is the idea that a series fuse will add any protection for the speaker in this circumstance - the fuse is designed to prevent the amplifier from failure under short circuit condition, eg user shorts speaker cable. DC fault protection for the speaker requires an active circuit that will either disconnect the speaker via relay or a crowbar that will short the amp but you can guess which an amp manufacturer would choose. Lack of fault protection is poor design.

It is a relatively common problem; I've had maybe a hundred similar faults across my bench over the years. Fault will be either poor design of simply a part out of spec and SOA being exceeded momentarily in use. Determining MTBF for another amp in the same chassis is going to be difficult. If the other channels also used poor spec components from the same batch they may also fail. Or they may not.

apparently the woofer itself went first, saving the crossover coil

Thanks Arny. That gave me a LOL.
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post #14 of 20
3/19/13 at 12:00pm
Thread Starter 
Quote:
What I don't agree with is the idea that a series fuse will add any protection for the speaker in this circumstance - the fuse is designed to prevent the amplifier from failure under short circuit condition, eg user shorts speaker cable.

So if the amp implodes again your view is that an added inline fuse will not stop the failure?
The service center that repaired the speaker suggested this as a method to control another failure.

What is SOA & MTBF ?

What is a crowbar? Is it what I am thinking big made of steel hook at one end?
Edited by kiwi2000 - 3/19/13 at 1:04pm
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post #15 of 20
3/19/13 at 2:00pm
Quote:
Originally Posted by kiwi2000 View Post

So if the amp implodes again your view is that an added inline fuse will not stop the failure?
The service center that repaired the speaker suggested this as a method to control another failure.
Fuses are relatively slow to operate, even so called 'fast blow'. By the time they have operated a driver could easily have exceeded Xmech and been damaged. Fuses also need to be sized so that they will not blow in service under reasonable expected signals and loads, so are generally too large to protect the drivers. I have seen a lot of amps destroy drivers when under fault, and relatively few damaged amplifiers from faulty loads, eg speaker cable short.
Series amp fuses are to protect the amp by disconnecting it from a faulty load.
Quote:
Originally Posted by kiwi2000 View Post

What is SOA & MTBF ?
Safe Operating Area and Mean Time Between Failure. Think of it this way; a SS device like a power transistor in an amp may be rated for 100V and 10A, but usually not at the same time, so manufacturers supply in their datasheet a drawing showing the area where the device can be operated safely and it is up to the customer (amp manufacturer etc) to design so that the device never goes beyond it's SOA in actual use.

MTBF is simply a statistical measure of the time that can be expected on average between failures of a given product. Your failed amp might be a fluke, or it might be likely to happen again soon due to poor design, I dunno. But failure in fairly modest use does not inspire my confidence.
Quote:
Originally Posted by kiwi2000 View Post

What is a crowbar? Is it what I am thinking big made of steel hook at one end?
Crowbar protection circuits are called that because they act the same as if you threw a metal bar across an electrical circuit. They effectively short it out to save the downstream gear (in this case the speaker) from damage, even if it destroys the upstream gear. Hopefully that has protection to save it though.

[Sidebar] Poof is an old fashioned and I suppose slightly offensive term for a homosexual man down here, so when I read the thread title, I immediately thought it had gone to Mardi Gras and had an absolutely fabulous time.
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post #16 of 20
3/19/13 at 3:15pm
Quote:
Originally Posted by A9X-308 View Post

I agree with Mark and Arny's synopsis that the amp latched a rail and applied DC to the woofer coil. What I don't agree with is the idea that a series fuse will add any protection for the speaker in this circumstance - the fuse is designed to prevent the amplifier from failure under short circuit condition, eg user shorts speaker cable. DC fault protection for the speaker requires an active circuit that will either disconnect the speaker via relay or a crowbar that will short the amp but you can guess which an amp manufacturer would choose. Lack of fault protection is poor design.

IME it is possible to size speaker fuses so that the fuse goes faster than it takes to damage a woofer. Usually start out with a 3 amp fuse and go up if you blow the fuse too often in normal use.
Quote:
It is a relatively common problem; I've had maybe a hundred similar faults across my bench over the years. Fault will be either poor design of simply a part out of spec and SOA being exceeded momentarily in use. Determining MTBF for another amp in the same chassis is going to be difficult. If the other channels also used poor spec components from the same batch they may also fail. Or they may not.

Power transistors are not generic, and finding replacements that work well and last may not be easy if the manufacturer has stopped supplying replacements.
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post #17 of 20
3/19/13 at 3:55pm
We recently had a similar thing happen. The output in a stand-alone DAC (source) blew, it put out static and before the amp shut down the little speakers it was connected to got cooked. The DAC though remained broken with charred output stage so it was easy to troubleshoot.

I am not sure anyone knows what went wrong with your setup though. Static through the amp that is no longer there now makes the diagnostic of it being at fault suspect. Your repair shop can put the amp under load and let it cook for a while (with a dummy load). If it survives that, and the opposite, i.e. freezing its components a few times, then I would say the amp is fine. Sources could easily generate static due to software bugs, reception problems (corrupt compressed audio stream), etc. I have heard amps crackle and pop but pure static in a power amp is rare.

At the end of the day, you have a complex situation that is very hard to troubleshoot. And just as hard of a time convincing anyone it is their fault. Once you get the gear back, run it a lot while watching it. The idea is to force the amp to die before the warranty is over.
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post #18 of 20
3/19/13 at 4:14pm
There's a saying in power electronics design..... "The transistors are there to protect the fuses".

It's so true though as fuses, even fast blow, don't act fast enough with transistor circuits. There are "semiconductor fuses" made. They cost about $60 for a 3/4 amp size. One place I have found these is in the gate drive circuits of a 160kw UPS system. Because here the power transistors are directly across the 900 volt 200 amp DC buss. They don't just fail, they explode without these expensive fuses.

Audiophile fuses are snake oil. The gold plating may help an infinitesimal amount for contact resistance but that's it.

FWEIW, I don't have any worries about my main amps killing the speakers. Can't happen! Because I use tube amps with their requisite transformer coupling biggrin.gif

But my subs are off a rebuilt Flame Linear 700. I mean Phase Linear 700 eek.gif
Edited by Glimmie - 3/19/13 at 4:19pm
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post #19 of 20
3/19/13 at 4:31pm
Hi Kiwi,

SOA - Safe Operating Area
For transistors, there is a maximum voltage they can support, and also a maximum current. But they can't support both maximum voltage and maximum current at the same time. So as the current goes up, at some point, the maximum voltage goes down, and visa-versa. If you plot maximum voltage against maximum current on a graph, it typically traces out a five-sided polygon - basically a square with the corner cut off where maximum voltage and maximum current would meet. The area bounded by this pentagon is called the "safe operating area", and if the combination of voltage and current should leave that area, the transistor can be destroyed. The failure-mode of the transistor is most often a dead-short, which would put the full voltage of the power-supply rail to the speaker. If your amp's design exceeded the safe-operating area, the result would be similar to what you saw.

MTBF - Mean Time Between Failures.
This is a statistical measurement of the likelihood of a device failing - be it a simple diode or a nuclear power plant. It is not a trivial thing to calculate (especially for the power-plant). I think what A9X-308 is trying to say is that there is really no way to know the likelihood of your amp blowing again - That it could be an anomaly or it could be a design flaw. I agree.

Thinking about it, fuses in-line with the speaker cables may or may-not protect the speakers. If they are sized such that the power-supply voltage through your speakers would produce a current above the limit of the fuse, then they should always protect your speakers. However, they might also blow in normal use, if you are using the full power of the amp. If you don't ever use the amps full power, then fuses could be useful. As an example, If you never exceed 1/2 power, then selecting fuses for 3/4 power would protect your speakers when a transistor shorts and goes to full power.

As A9X-308 said, relays driven by active circuits are the preferred approach, and thats what most of my amps use. My amps that don't have relays all have speaker fuses. It sounds like your amp does have protection circuitry, but it just doesn't work.

This bothered me:
Quote:
Several things fried in the high frequency area of the amp module.
Maybe I'm not fully aware of different amp topologies, but no amps I know have a "high-frequency area". Maybe I'm just old school. But why would a problem in the "high-frequency area" blow out the woofer?


EDIT:
Wow, in the time it took me to write this, A9X-308, Amir, Arny and Glimmie all posted. I need to learn to type faster . . .
Edited by MarkHotchkiss - 3/19/13 at 4:38pm
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post #20 of 20
3/19/13 at 6:42pm
Thread Starter 
T
Quote:
the idea is to force the amp to die before the warranty is over.

This is a very expensive proposition. The amp manufacturer has in no way stated they will pay for speaker repair/replacement.
This alone is worth many time the cost of the amp.

As stated I was "lucky" it was the center that fried.
Quote:
Maybe I'm not fully aware of different amp topologies, but no amps I know have a "high-frequency area". Maybe I'm just old school. But why would a problem in the "high-frequency area" blow out the woofer?

That is what I was informed.
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