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Question Help! One of my speakers is causing my amp to switch off

meanmrcustard

Active member
Mar 6, 2021
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Hello everyone! I was hoping someone could help me with an issue I'm having issues with my speakers


I have a pair of floor standing Monitor Audio speakers, not sure of the model but attached a photo. When I connect them to my Amp (Marantz PM6005) they will cause the amp to shut down after some time (usually about 30 mins to 1 hr). The amp seems to just switch off (no red light which I understand is protection mode), it won't switch back on straight away but I can switch it on again after a few minutes. I'm not sure whether it's overheating or something else.

It seems to only be one speaker that causes the problem as I can replicate the issue when one speaker is plugged in on it’s own but not when the other is. I’ve tried multiple cables and amps and am seeing the same problem. They used to work fine and this issue came about suddenly.

For what it's worth is worth (i don't know if this is relevant) both speakers are bi-wired, but I've tried the same wires and wiring on each speaker and the 'good' speaker still doesn't cause any issues.

I was hoping someone could provide some pointers for:

a) how i could diagnose the problem
b) what i might be able to do to fix it
c) whether it would be worth paying someone to look at the speakers (they were a gift so i don't really know what they are worth and whether just buying new ones would be better)

Thanks in advance!

IMG_7753.JPG
 

Gray

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Nov 27, 2015
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I'm not sure of the model number either but I've got no excuse.
It's certainly one of the models I made / tested when I worked for MA.....hopefully not your actual pair :)

You say they've caused different amps to shut down.
Do they sound clean and undistorted when they are working?

With them disconnected, a first check you can do from the outside:
With a finger either side of the dustcap, (important for even travel) gently push the cone to feel for any scraping between voicecoil and magnet (which can be a result of overheating).
Compare the feel all 4 main drivers.

If all feels smooth, second check from the outside (if you've got a meter) would be the DC resistance.
Your links are removed so you can compare the resistance across the HF terminals, then the LF terminals to see if there's any significant difference between the 2 speakers.

If all is well there (if readings are close) there's really no more diagnosis you can do.

If, on the other hand, you found the readings to be totally different, then it depends how involved you want to get with the dismantling, isolating, measuring, swapping elimination process to narrow things down further.....or whether you like them enough to pay for some attention, ideally with a free estimate first.
 
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abacus

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Sep 24, 2008
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First of all forget bi-wiring as the difference will be minimal at best, put the links back in on the speakers (You can make up some cable links if you don’t have the original links) and run them single wired to see if this solves the problem, if not then swap the speakers over and see if the fault transfers to the other channel, if not then there is a problem with the amp, if it does then there is a problem with the speaker, in both instances you will need to take the faulty component to a professional repairer. (Don’t use fancy cables (2.5mm sq. OFC is all you need) as some have high capacitance which can cause problems for some amps)

Bill
 

meanmrcustard

Active member
Mar 6, 2021
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Hi All,

Thanks for all of your replies!

You say they've caused different amps to shut down.
Do they sound clean and undistorted when they are working?
Yep they seem to be fine, also tried them with a NAD amp (again not sure of the model) with the same results

With them disconnected, a first check you can do from the outside:
With a finger either side of the dustcap, (important for even travel) gently push the cone to feel for any scraping between voicecoil and magnet (which can be a result of overheating).
Interestingly, 3 of the 4 have no scraping, the only one that does is the top one of the 'good speaker' not sure what to make of that!


Will try to get hold of a multimeter to test resistance and will try single wiring the speakers to see if either of those provide me with more information. Will report back when I know more
 

TrevC

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Jun 12, 2013
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As this speaker has two bass drivers I would listen to them individually close up and make sure normal quality sound is coming from each one. It could be that one of them has shorting turns after overheating.
 

Al ears

Moderator
You have tried different amps, can you borrow another pair of speakers to try? This would pinpoint the problem to the speakers which would then need a professional check up.
however with the costs in evolved it might be cheaper to buy a new pair of speakers....
 

meanmrcustard

Active member
Mar 6, 2021
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Hi Everyone, some updates. Caveat before all of this is that I pretty much have no idea what i'm doing, but I'm leaning towards 'this is probably not going to be worth the money for me to get a professional to repair' so here we are. Provided i don't kill my amp/self I'm comfortable messing around.

I got hold a multimeter to check the impedance. On both speakers (the good one that doesn't seem to short the amp and the bad one that does) i got a reading of about 12 on the low frequency terminals on both and a reading of 1 on the high frequency terminals. That feels.. Not Good, would that be an accurate assessment?

I've also tried not bi-wiring (by using some wire to link the terminals) and that doesn't seem to work either. In fact, when testing the 'bad' speaker on it's own using this set up it seemed to throw the amp much more quickly (ie in seconds rather than after about 20 minutes).

Through my limited understanding of resistance (ie google) I understand that wiring in serial increases the resistance. Is this something that could work with my speakers? ie Wire the left side speakers to the right side speakers and wire those to the amp? Would that cause any sound/explosion issues?

Thanks again for all your help!
 

meanmrcustard

Active member
Mar 6, 2021
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You have tried different amps, can you borrow another pair of speakers to try? This would pinpoint the problem to the speakers which would then need a professional check up.
however with the costs in evolved it might be cheaper to buy a new pair of speakers....
I have another pair of speakers that work fine with this amp (PSB imagine minis) so i'm 99% certain it's the speakers that are causing the issue, and 90% certain it's one of them in particular
 

muljao

Well-known member
Jul 18, 2016
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I'd still run one set of cables from each speaker and join the posts with jumpers so you're not bi wiring them. I'd setup on speakers "A" and see how it goes. If is good forget about it. If not I'd try speakers "B"

Obviously if it still happens there's an issue, but if you then swapped cable runs so speakers were opposite and see if the same speaker still causes the issue. It could be time consuming, but it could isolate something else
 

Gray

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Nov 27, 2015
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I have another pair of speakers that work fine with this amp (PSB imagine minis) so i'm 99% certain it's the speakers that are causing the issue, and 90% certain it's one of them in particular
Yes, you said you'd tried other amps - I don't doubt there's a problem with a speaker.
Don't connect L & R speakers together in any way.

Assume you're UK based. What part?
 

meanmrcustard

Active member
Mar 6, 2021
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I've got the current wiring set up which seems to be not breaking anything, in spite of running for a good hour now , including at volumes much higher than would normally throw the amp:

Right hand speaker (the 'good' one) single connection to amp with jumpers between high and low terminals
Left hand speaker (the 'bad' one) just the lows connected to the amp, the highs not connected at all

This would lead me to think the left hand tweeter is the issue?

Another interesting thing i found is that when the terminals are connected with jumpers, the resistance on the good speakers is 12ohm regardless of which terminals you test on (as opposed to 1 and 12 when not connected), for the bad speakers, when jumper'd, both terminals read as 1 (as opposed to 1 and 12)


Assume you're UK based. What part?
East London, which is probably why it looks prohibitively expensive to get someone to fix it! Only place i could find near me would charge £45 just to look at it plus anywhere between £55 and 90 an hour to fix it
 

Gray

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Nov 27, 2015
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This would lead me to think the left hand tweeter is the issue?
It would lead anyone to think the same.
Remove the tweeter, disconnect one* of its terminal wires, then measure the resistance across the terminals of the tweeter.
Do the same on the other cabinet and compare your readings.

(*Disconnecting one, rather than both, is enough to electrically isolate the tweeter - and leave you no chance of reversing the pair on reconnection).
 

meanmrcustard

Active member
Mar 6, 2021
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Remove the tweeter, disconnect one* of its terminal wires, then measure the resistance across the terminals of the tweeter.
Do the same on the other cabinet and compare your readings.
Just tried this, reading of about 6 on both cabinets
 

Gray

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Just tried this, reading of about 6 on both cabinets
OK, so nothing proved there.
Your readings would suggest that your suspected 'bad' tweeter isn't bad.
However, the obvious thing to do now is swap the tweeters over.
Ensure you refit the wires to the correct terminals (+ and - are marked on the tweeters)

Once swapped......if your amp cuts out, you were right about the left tweeter being faulty.
If you continue to play on for another hour without problem.......it wasn't the fault.
 

meanmrcustard

Active member
Mar 6, 2021
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Tried the tweeter swap and you were right, doesn't seem like the issue is with the tweeter; the 'bad' tweeter works fine in the right speaker and the 'good' tweeter in the left speaker still trips the amp.

Am i right in saying that if the tweeter isn't at fault, the only other option is the crossover or the cable that connects the 2? or is there something else that could be at fault?

I've contacted Monitor Audio who will sell me a replacement crossover for £60 I'm tempted to just suck it up and pay the money but will be annoyed if i spend the money without solving the issue!

Thanks,
Simon.
 
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Gray

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Am i right in saying that if the tweeter isn't at fault, the only other option is the crossover
I reckon you are.
Fortunately your amp's protection circuitry is allowing you to do successful diagnosis.
Guess what I'm going to suggest now.....
Swap the crossovers. I will be (more than) surprised if you don't now prove that to be the cause.
Although £60 is far from cheap, it's less than they could have charged.
And, don't forget, that £60 (or likely more) would have been on top of those labour charges you quoted from a repairer.

Remember to note all connections to ensure identical reconnection. Because just one reversed connection will undo all your good work.
 
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Gray

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Remember to note all connections to ensure identical reconnection. Because just one reversed connection will undo all your good work.
....and, coincidentally, the following thread is the perfect example of how:
 

meanmrcustard

Active member
Mar 6, 2021
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update on this, i swapped the crossover and the crossover from the 'good' speaker works fine on the 'bad' speaker.

I've managed to figure out the model of the speakers (Silver 5i) and have also managed to acquire a cheap second hand pair that isn't in full working order but my hope is that between the 2 pairs I'll manage to cobble together a working set!
 
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Gray

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update on this, i swapped the crossover and the crossover from the 'good' speaker works fine on the 'bad' speaker.

I've managed to figure out the model of the speakers (Silver 5i) and have also managed to acquire a cheap second hand pair that isn't in full working order but my hope is that between the 2 pairs I'll manage to cobble together a working set!
Hopefully the secondhand pair were less than the £60 cost of a new crossover.
You must end up with a working pair now.
(+ a few spare parts) (y)
 

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