Can a faulty amplifier blow a tweeter or a woofer just by being turned on?

[Bob from Florida]

Now that I saw the other pics you're probably right,if it was like I thought it was it would also destroy part of the cone where they attach to it.
It's ironic that I searched before posting to see if there is some insulation and I saw none on the new ones.

The hazards of long distance troubleshooting....

 

[Ken Tajalli]

I am not so sure the speaker is burned. The lack of any "burned" oder is the red flag. Take a look at a zoomed shot of the OP's original picture. The black stuff on the voice coil coupling leads is an insulating/damping material - I've seen this before - not burned wiring. Another red flag is - the black wires crimp connector has been solder by someone - maybe previous owner. If they did this with the connector plugged into the speaker, that would explain why the voice coil wire is partially or completely unsoldered from its terminal. Look carefully at the zoomed photo and you will notice many strands of that wire have pulled out of the terminal hole. Unplug one of the wires going to the driver and check the resistance of the driver with your multimeter.View attachment 365970

Well spotted, I was just about to point that out.
However, why did previous owner solder that wire?? Hmm
Did he have any issues? was he trouble shooting the same issue? I wonder!
I would check continuity with the same meter. From input port of the speaker to bass driver wires, there should be minimal resistances. Just to make sure Xover is OK.
Next thing, gently check movement of the cone, it should go in and out freely. Last thing, check the speaker using the meter, it should read around 4 ohms.

 

[Veganfloyd]

I am not so sure the speaker is burned. The lack of any "burned" oder is the red flag. Take a look at a zoomed shot of the OP's original picture. The black stuff on the voice coil coupling leads is an insulating/damping material - I've seen this before - not burned wiring. Another red flag is - the black wires crimp connector has been solder by someone - maybe previous owner. If they did this with the connector plugged into the speaker, that would explain why the voice coil wire is partially or completely unsoldered from its terminal. Look carefully at the zoomed photo and you will notice many strands of that wire have pulled out of the terminal hole. Unplug one of the wires going to the driver and check the resistance of the driver with your multimeter.View attachment 365970

Thank you, Bob. I understand that the task was to measure at the golden bit revealed by unplugging the wire. The reads were 0.1 ohm after falling down from initial larger values. What would the interpretation be?

 

[Sokel]

Thank you, Bob. I understand that the task was to measure at the golden bit revealed by unplugging the wire. The reads were 0.1 ohm after falling down from initial larger values. What would the interpretation be?

Also measure resistance with each probe to each of the golden bits as you have it disconnected.

 

[Bob from Florida]

Thank you, Bob. I understand that the task was to measure at the golden bit revealed by unplugging the wire. The reads were 0.1 ohm after falling down from initial larger values. What would the interpretation be?

From your latest pics, it looks like both wires are unplugged from the speaker. You have 2 terminals, put one probe on one terminal and the other probe on the remaining terminal. What do you measure in ohms across those 2 points?

 

[Veganfloyd]

From your latest pics, it looks like both wires are unplugged from the speaker. You have 2 terminals, put one probe on one terminal and the other probe on the remaining terminal. What do you measure in ohms across those 2 points?

Thank you, it's 3.1 ohms.

 

[Bob from Florida]

Thank you, it's 3.1 ohms.

That is a good reading for a 4 ohm speaker. There is still a question about how good a connection we have because of the strands pulled out of the terminal hole.
Next, verify - as Sokel asked - the connections through the crossover. Measure from each disconnected wire to the terminals on the back of the speaker cabinet. Woofer circuits should not have any series capacitors, so you should get a reading from each wire to at least one terminal on the back of the cabinet.

 

[Veganfloyd]

Thank you guys. I am getting again 0.1 ohm readings after falling down from initial larger values when touching a speaker binding post and a wire previously connected to the woofer. This works only when going for the same colored post and wire. Otherwise, there is no reading available. So presumably, this is as it should be judging from Ken's post #42. The woofer is moving freely to touch.

@Ken Tajalli , I bought these off a charity auction, so I know nothing about the previous history, and the charity wouldn't know either.

 

[Bob from Florida]

Thank you guys. I am getting again 0.1 ohm readings after falling down from initial larger values when touching a speaker binding post and a wire previously connected to the woofer. This works only when going for the same colored post and wire. Otherwise, there is no reading available. So presumably, this is as it should be judging from Ken's post #42. The woofer is moving freely to touch.

@Ken Tajalli , I bought these off a charity auction, so I know nothing about the previous history, and the charity wouldn't know either.

Possibly all is well except for the voice coil wire going to the terminal hole for the black wire. Do you have soldering skills?

 

[Veganfloyd]

None at all. My local audio dealer works with a reasonably priced repair centre, so I will pass this on to them. They already started sourcing a replacement woofer, so I will update them on the diagnostics and they will take it from there.

Going back to my Loxije A40, should I still get it checked for ultrasonic oscillation? My understanding would be that there are now no indications to do so (beyond baseline risk of random malfunction with any electronic equipment) given that the recent Menuets must have arrived to me with the woofer issue, and the woofer is not blown. The first Menuets clearly had the tweeter dead since playing the first note, so it seems extremely unlikely that the amplifier could have anything to do with it.

 

[Bob from Florida]

None at all. My local audio dealer works with a reasonably priced repair centre, so I will pass this on to them. They already started sourcing a replacement woofer, so I will update them on the diagnostics and they will take it from there.

Going back to my Loxije A40, should I still get it checked for ultrasonic oscillation? My understanding would be that there are now no indications to do so (beyond baseline risk of random malfunction with any electronic equipment) given that the recent Menuets must have arrived to me with the woofer issue, and the woofer is not blown. The first Menuets clearly had the tweeter dead since playing the first note, so it seems extremely unlikely that the amplifier could have anything to do with it.

It may be as simple as cleaning up the soldered end, twisting it tightly, and re-soldering. An alligator clip on the voice coil wire should be sufficient to prevent overheating of the cone. New woofer works too.

Sounds like you had 2 instances of “bad” luck there. Since streaks come in “3’s”, I would be careful of when the third one strikes…..

 

[egellings]

If the output of a faulty S.S. amplifier is stuck on a rail other than ground level, then the woofer takes the hit. If the amplifier is oscilatting, ususally at a high frequency, then it's bye-bye tweeter. Motorboating could take out a woofer as well. The midrange driver, if there is one, would be shaking in its bandpass filter as it watched its world collapse around it.

 

[EdW]

In #11 @Veganfloyd reports settled dc of just a few mV although settling process is longer than I might have guessed. So likely that the amplifier is not shorted to one of its power supplies. I did see in the data sheet for the Loxjie a40 amp that it uses an Infineon amplifier module MERUSTM MA5332MS which should make the design fairly foolproof. This particular module may be powered with +/- supplies but also with a single power rail. A single power rail might give rise to a noisier startup?
@Veganfloyd - checking the amp for ultrasonic instability should be straightforward and quick - I no longer have test equipment but your dealer would need an oscilloscope, a high power 4 ohm dummy load, and a signal generator (the generator to see whether an input signal can provoke instability) - should literally just take a few minutes, This is not exhaustive but should prove the point.
The provenance of the speakers does not seem great though!

 

[Ken Tajalli]

In #11 @Veganfloyd reports settled dc of just a few mV although settling process is longer than I might have guessed. So likely that the amplifier is not shorted to one of its power supplies. I did see in the data sheet for the Loxjie a40 amp that it uses an Infineon amplifier module MERUSTM MA5332MS which should make the design fairly foolproof. This particular module may be powered with +/- supplies but also with a single power rail. A single power rail might give rise to a noisier startup?
@Veganfloyd - checking the amp for ultrasonic instability should be straightforward and quick - I no longer have test equipment but your dealer would need an oscilloscope, a high power 4 ohm dummy load, and a signal generator (the generator to see whether an input signal can provoke instability) - should literally just take a few minutes, This is not exhaustive but should prove the point.
The provenance of the speakers does not seem great though!

You both seem to be in Cambridge.
Go do it for him, he'll buy you dinner and booze!

 

[Veganfloyd]

Thank you, all.

Things are getting weirder and weirder. I thought it might be a good idea to swap the woofers to see if the one previously under suspicion of being faulty would play fine in the other speaker, which it did. As I opened the other speaker, I noticed that the insides of the woofer area looked pretty much the same, including the soldering on the black cable. So it must have been by design and the previous owner probably did not tinker with it. The only major difference is a more neatly looking voice coil. This gave me a nagging thought that I should check out the first speaker, as maybe simply unplugging and plugging the woofer back in could have an impact. And the woofer is back in action which I'm more confused than happy about.

So, either he woofer played fine for the first few minutes in my posession, then something caused it to lose the connection, or it arrived in a non-working state which was fixed by unplugging and plugging it back in. Could the amp have anything to do with the former? Does either scenario have a plausible scientific explanation?

Just in case, when I initially identified that the woofer was silent, I confirmed it with a second amplifier, so any issues with bass reproduction on the amplifier side or wrong/loose connections are unlikely.

EDIT: Is the re-soldering job still desirable or should I just start enjoying them?

 

[Bob from Florida]

Thank you, all.

Things are getting weirder and weirder. I thought it might be a good idea to swap the woofers to see if the one previously under suspicion of being faulty would play fine in the other speaker, which it did. As I opened the other speaker, I noticed that the insides of the woofer area looked pretty much the same, including the soldering on the black cable. So it must have been by design and the previous owner probably did not tinker with it. The only major difference is a more neatly looking voice coil. This gave me a nagging thought that I should check out the first speaker, as maybe simply unplugging and plugging the woofer back in could have an impact. And the woofer is back in action which I'm more confused than happy about.

So, either he woofer played fine for the first few minutes in my posession, then something caused it to lose the connection, or it arrived in a non-working state which was fixed by unplugging and plugging it back in. Could the amp have anything to do with the former? Does either scenario have a plausible scientific explanation?

Just in case, when I initially identified that the woofer was silent, I confirmed it with a second amplifier, so any issues with bass reproduction on the amplifier side or wrong/loose connections are unlikely.

EDIT: Is the re-soldering job still desirable or should I just start enjoying them?

You could gently "tug" a bit on the questionable voice coil wire that appears to be somewhat disconnected and see if it is firmly attached. Any give at all then I would re-solder.

 

[Ken Tajalli]

Thank you, all.

Things are getting weirder and weirder. I thought it might be a good idea to swap the woofers to see if the one previously under suspicion of being faulty would play fine in the other speaker, which it did. As I opened the other speaker, I noticed that the insides of the woofer area looked pretty much the same, including the soldering on the black cable. So it must have been by design and the previous owner probably did not tinker with it. The only major difference is a more neatly looking voice coil. This gave me a nagging thought that I should check out the first speaker, as maybe simply unplugging and plugging the woofer back in could have an impact. And the woofer is back in action which I'm more confused than happy about.

So, either he woofer played fine for the first few minutes in my posession, then something caused it to lose the connection, or it arrived in a non-working state which was fixed by unplugging and plugging it back in. Could the amp have anything to do with the former? Does either scenario have a plausible scientific explanation?

Just in case, when I initially identified that the woofer was silent, I confirmed it with a second amplifier, so any issues with bass reproduction on the amplifier side or wrong/loose connections are unlikely.

EDIT: Is the re-soldering job still desirable or should I just start enjoying them?

I very much doubt that soldering was done at factory.
If the diaphragms can freely move in and out, without scraping noises, and the voice coils resistances are both about 3-4 ohms, then the drivers are fine.
Your issue could be bad wiring from Xovers to the drivers, bad connectors etc.
Follow the wires back to the Xovers.