This is not really a horror story to me because I bought these on Craigslist for $60, but I hooked them up and got no tweeter sound, and they just sounded bizarre and about 1/3 as loud as they should be. I unscrewed the tweeter but before I unsoldered it, I removed both crossovers and saw they were melted to the interior foam. Here's a photo of one of them. That's the horror story, and I'm not sure how an amp could do this, maybe they plugged the speaker into an ac outlet? It got so hot in there some of the solder on one corner melted and dripped down to the end of the PCB, as did much of the glue. I attached one of the tweeters to a regular amp and slowly increased the volume. I had it turned up about halfway before I heard faint music, so does that mean the tweeters are fried as well? The tweeters are the square type; other version came with round ones. I am sure the previous owner had them bi-wired or bi-amped, because the jumper bars on the banana plugs were missing.
These are Mission 753 units, serial number 530007238. The crossovers say "53-xover/B05". Are worth fixing? I have a DMM and have done limited PCB work, and I have an oscilloscope I barely know how to turn on. My other speakers are all rear-ported: Paradigm 11se Mk 3, 5se, Titan (version 1) and some little Sound Dynamics 2 ways, and I thought these front-ported Missions might be nice to compare with what I already have. There was a guy selling these woofers on ebay for $40 each, so I thought what the heck. I read on this forum that the crossovers are not "conventional" 2 way design, so I need some advice from a fellow DIY addict. Thanks in advance.
Tim
These are Mission 753 units, serial number 530007238. The crossovers say "53-xover/B05". Are worth fixing? I have a DMM and have done limited PCB work, and I have an oscilloscope I barely know how to turn on. My other speakers are all rear-ported: Paradigm 11se Mk 3, 5se, Titan (version 1) and some little Sound Dynamics 2 ways, and I thought these front-ported Missions might be nice to compare with what I already have. There was a guy selling these woofers on ebay for $40 each, so I thought what the heck. I read on this forum that the crossovers are not "conventional" 2 way design, so I need some advice from a fellow DIY addict. Thanks in advance.
Tim
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Very insensitive drivers mean they are fried. Did you check what Foxx510 asked ? All drivers showing nominal dc resistance values ?
If the woofer is OK ( normal volume ) the it could have been a badly clipped signal ( massive overdive ) or RF ( oscillations).
DC offset would burn the woofer and keep the tweeter safe if the standard series capacitor was in place.
Here the resistor appears to belong to the tweeter and that end is burnt !
However the coil at the other end also got hot ! DC after breakdown due to oscillations ? Burnt components is something but a burnt pcb like this 'really' something else !
If the drivers are gone then replacing them with the original might be expensive. I'm surprised that you say both units were similarly damaged.
If the woofer is OK ( normal volume ) the it could have been a badly clipped signal ( massive overdive ) or RF ( oscillations).
DC offset would burn the woofer and keep the tweeter safe if the standard series capacitor was in place.
Here the resistor appears to belong to the tweeter and that end is burnt !
However the coil at the other end also got hot ! DC after breakdown due to oscillations ? Burnt components is something but a burnt pcb like this 'really' something else !
If the drivers are gone then replacing them with the original might be expensive. I'm surprised that you say both units were similarly damaged.
timbert said:
Big amp, under-powered resistor.
We started the damping foam on a set of Tangent RS4s on fire once. Driven by a Bryston 4B, John Greenbank (magaging director of Tangent) asked us to keep turning it up. Acrid smoke started billowing out of the square ports & very shortly after the woofer went quiet. Boy did it stink. Fresh woofer and we were enjoying music again in 15 minutes.
dave
My son is removing the drivers on one speaker so I can test them. Here's the other crossover, showing burnt foam and the solder that ran down to the bottom of the board in two places. Remind me again how I'm measuring te drivers with my Fluke DMM? I assume I have to clip the two leads off.
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I popped off two drivers and they measure 3.9 ohms between the two leads, out of circuit. Ran speaker leads to them and fired up the amp and they sound like drivers would sound without a box. Yes, both crossovers were similarly burnt, here's a photo showing one of the coils that melted the plastic it was coiled around.
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An externally hosted image should be here but it was not working when we last tested it.
Hi,
you may be able to persuade another tweeter into the faceplate
depending on how the tweeter is made. Photos of a disassembled
tweeter would help. You never know - a diaphragm from another
tweeter may fit also - depends on missions source. e.g. :
An externally hosted image should be here but it was not working when we last tested it.
/sreten.
Looking at it the crossover look as as if it may be saved. The resistors are fried sure, but other than that the rest looks OK.
I love the Mission 753's. I have a pair that I have tried a few mods on. Funny enough I was thinking along the lines of replacing the tweeters at some point.
Are your tweeters the metal dome or the silk (ie freedom model)
I have a schematic for the crossover from my non freedoms if that helps any. My crossover board is of a different layout. I understand that there were a few revisions.
Here are a few piccies of the tweeter assembly.
I dont have one with the dome disassembled. However to describe briefly
The dome is not attached to the magnet assembly with screws or anything. The rectangular faceplate has a set of four clips. You just prise them apart and the assembly disassembles in your hand. The clips of the faceplate match the lugs that you can see in my last picture.
The whole that is left on the cabinate is a recessed rectangle with a circular hole routed out of it. The circular hole has a flat bottom however, extra space has been routed for the cables to the tweeter.
You might get replacement parts from mission themselves if you e-mail them.
If you have the non freedom version with the metal dome you could enquire about getting the silk dome as an exchange. I would think that you would not require a new magnet assembly, but I am unsure wether the magnet is different between versions. The metal dome version is sharper than the freedom. The freedoms are to my ears a little soft. The metals are quite harsh but can be improved upon for £0 outlay.
If you are using the metal dome version, when you have the tweeter apart, pop out the metal grill "guard" that covers the metal dome. The sound of the tweeter improves quite a bit without it. Replacing the cap that protects and filters the tweeter with a nice one like a sonicap or similar is also recommended in my books. The sound on the standard one can be improved thought you may have to add more resistance to the tweeter to tone it down after (I did)
I do have some kiwame resistors that I intend trying in my mission crossovers. But time is never on my side. I may get them fitted mid september. They might improve the sound further.
Other things you really must try in these once you get them going is to damp/strengthen the big drivers pressed metal baskets. Lovely improvements can be had there for very little money.
My vote would be stick with it. A couple of resistors, and tweeters and you have a pretty good set of speakers for very little money.
Feel free to pm/e-mail me if I can help.
I love the Mission 753's. I have a pair that I have tried a few mods on. Funny enough I was thinking along the lines of replacing the tweeters at some point.
Are your tweeters the metal dome or the silk (ie freedom model)
I have a schematic for the crossover from my non freedoms if that helps any. My crossover board is of a different layout. I understand that there were a few revisions.
Here are a few piccies of the tweeter assembly.
I dont have one with the dome disassembled. However to describe briefly
The dome is not attached to the magnet assembly with screws or anything. The rectangular faceplate has a set of four clips. You just prise them apart and the assembly disassembles in your hand. The clips of the faceplate match the lugs that you can see in my last picture.
The whole that is left on the cabinate is a recessed rectangle with a circular hole routed out of it. The circular hole has a flat bottom however, extra space has been routed for the cables to the tweeter.
You might get replacement parts from mission themselves if you e-mail them.
If you have the non freedom version with the metal dome you could enquire about getting the silk dome as an exchange. I would think that you would not require a new magnet assembly, but I am unsure wether the magnet is different between versions. The metal dome version is sharper than the freedom. The freedoms are to my ears a little soft. The metals are quite harsh but can be improved upon for £0 outlay.
If you are using the metal dome version, when you have the tweeter apart, pop out the metal grill "guard" that covers the metal dome. The sound of the tweeter improves quite a bit without it. Replacing the cap that protects and filters the tweeter with a nice one like a sonicap or similar is also recommended in my books. The sound on the standard one can be improved thought you may have to add more resistance to the tweeter to tone it down after (I did)
I do have some kiwame resistors that I intend trying in my mission crossovers. But time is never on my side. I may get them fitted mid september. They might improve the sound further.
Other things you really must try in these once you get them going is to damp/strengthen the big drivers pressed metal baskets. Lovely improvements can be had there for very little money.
My vote would be stick with it. A couple of resistors, and tweeters and you have a pretty good set of speakers for very little money.
Feel free to pm/e-mail me if I can help.
ashok said:Here the resistor appears to belong to the tweeter and that end is burnt !
FYI The top board does not control the tweeter. Thats the low pass filter for the bass assist woofers.
Timbert. If you have an inductance meter, could you produce a schematic for your version of the crossover... Just out of interest for myself.
justblair, I've looked at your other helpful posts. I do not have an inductance meter, and was thinking of just replacing the resistors and checking the caps and hoping for the best. I saw your schematic in the other post and will look to see if it appears the same, but I'm no expert.
For the tweeters, they are the same as yours and I believe they are Vifa but could not find a current model that looks like this. Here are some pics. Looks like the coil is fused to the magnet because when I pulled it off it started to come unwound. Also, the outer metal shell looks like it was in contact with the outer dome screen, and you can see what appear to be abrasions on the outside surface of it. Is that oil that leaked out of the magnet?
So I guess I need a source for the tweeters, but don't know the original model or its specs so if I have to substitute a more current model and make it fit physically I'd like to not have to mess with the crossover. I guess I'll contact Mission as I doubt I would be able to find tweeters that would just fit right in.
For the tweeters, they are the same as yours and I believe they are Vifa but could not find a current model that looks like this. Here are some pics. Looks like the coil is fused to the magnet because when I pulled it off it started to come unwound. Also, the outer metal shell looks like it was in contact with the outer dome screen, and you can see what appear to be abrasions on the outside surface of it. Is that oil that leaked out of the magnet?
So I guess I need a source for the tweeters, but don't know the original model or its specs so if I have to substitute a more current model and make it fit physically I'd like to not have to mess with the crossover. I guess I'll contact Mission as I doubt I would be able to find tweeters that would just fit right in.
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