I bought bad Mission 753's, T's and x-overs fried, worth fixing?

[timbert]

Still having tweeter or xo problem

The previously posted schematic matches my xo. Where justblair has a 5.5ohm resistor, I have two identical-looking ones glued together in series, and the one I can read says 2.2 ohm. In-circuit it measures 5.7 ohm.

I have soldered in the new xo resistors mentioned in a previous post and replaced the voice coils with ones from another set of tweeters. I have fabric ones on standby. I am now engaged in isolating a tweeter/xo problem. I hooked up my amp outputs only to the tweeter terminals on each speaker. Now, one tweeter is about ten times louder than the other, and when I bridged the high and low freq speaker terminals, the woofers/mids are even but one tweeter puts out almost nothing, even at 1/2 volume or more on the amp. I put the meter on both tweeters, with music playing, and one was 6 mV when at the same volume setting the other 80 to 150 mV, so I guess there's a crossover problem. I swapped the tweeter magnet with another, and it was still very low output. I measured the capacitance of the tweeter cap in the xo and it's about 6.4uf when the schematic calls for 6.8, which I assume is within range, and since I don't have an inductance meter I can't test the coils. I tried bypassing the resistor and cap and using only the inductor in parallel with the tweeter, and it appears the inductor is what is causing the decreased volume. When the amp is connected directly to the tweeter, the volume is where it should be. What do I do next?

Meanwhile, I noticed the 4.7 ohm resistor on the woofer section is bad on this xo, but not on the other. Could this affect the tweeter section of the xo, even though they're not on the same circuit and when the amp is only driving the tweeter?

 

[justblair]

Re: Still having tweeter or xo problem

The previously posted schematic matches my xo. Where justblair has a 5.5ohm resistor, I have two identical-looking ones glued together in series, and the one I can read says 2.2 ohm. In-circuit it measures 5.7 ohm.

From memory mine has two resistors in series to make up the 5.5

I have soldered in the new xo resistors mentioned in a previous post and replaced the voice coils with ones from another set of tweeters. I have fabric ones on standby. I am now engaged in isolating a tweeter/xo problem. I hooked up my amp outputs only to the tweeter terminals on each speaker. Now, one tweeter is about ten times louder than the other, and when I bridged the high and low freq speaker terminals, the woofers/mids are even but one tweeter puts out almost nothing, even at 1/2 volume or more on the amp. I put the meter on both tweeters, with music playing, and one was 6 mV when at the same volume setting the other 80 to 150 mV, so I guess there's a crossover problem. I swapped the tweeter magnet with another, and it was still very low output. I measured the capacitance of the tweeter cap in the xo and it's about 6.4uf when the schematic calls for 6.8, which I assume is within range, and since I don't have an inductance meter I can't test the coils. I tried bypassing the resistor and cap and using only the inductor in parallel with the tweeter, and it appears the inductor is what is causing the decreased volume. When the amp is connected directly to the tweeter, the volume is where it should be. What do I do next? [/B]

If you are sure that the inductor is the issue, you can order up a new one, though I would look at buying a matched pair. It is possible that the inductor is shorted out. You could check this by measuring the DC resistance of both inductors. If one is a lesser value of the other, then that is probably what it is. Madisound do inductors. Keep to an air cored one.

Meanwhile, I noticed the 4.7 ohm resistor on the woofer section is bad on this xo, but not on the other. Could this affect the tweeter section of the xo, even though they're not on the same circuit and when the amp is only driving the tweeter? [/B]

I would not think so. Each section works as an independant filter in this design.

And to prove it, you have tried attaching the tweeters with the woofer section disconnected and still have the issue.

 

[timbert]

Looks like the "bad" inductor is not actually shorted but while the resistance on the good one is .2 ohm and the other is 1.5 or so. I removed both and sure enough, the bad inductor will attenuate either tweeter by about 10x volume, to my ears. There is enough melted plastic in both to make an ordinary person think they should both be replaced.

Madisound has two different .3 mH inductors, one 19 gauge wire and the other 20. I am taking JB's word that the originals are .3 mH. I have an old oscilloscope that I don't really know how to use other than doing signal traces to diagnose bad amps, but if I really knew how to use it maybe I could measure inductance on the "good" inductor I have.

I am inclined to buy the physically smaller .3 mH inductor so it will fit, plus replace all 6 caps in each crossover for peace of mind's sake. Is that a problem?

TIP:I bought a $10 USD Radio Shack rubber-bulb desoldering iron which has made my life much easier.

 

[timbert]

The tweeter and crossover repairs are complete. I did not use the new fabric voice coils, but the aluminum ones swapped out from another pair of Peerless tweeters. I replace all the resistors on the xo, plus the inductor (which justblair measured to be .3 mH) that was severely attenuating one of the tweeters. I replaced the inductors on both xo's with ones from Madisound.

The result is too much tweeter, to my ears.

How do I tweak this? Add resistance to the tweeter? The xo has two 1 ohm resistors in parallel, which yields 1/2 ohm, I believe. Without taking apart the crossover, can I just add diferent resistors to the tweeter and experiment?

 

[justblair]

When I replaced the cap in my tweeter crossover I got too much tweet in my tweeter. Start by trying just one resistor instead of the two in parrallel, this will give you 1ohm. It should ease things for you. I am running mine with 1.1 ohms resistance just now and it is just about right.

I would try the fabric cone in there just for the hell of it. It may not be any better, but it gives you options.

The freedoms used fabric. I personally didn't like them as much as the non-freedoms. I think that the metals have more detail. With the metal "guards" in place they are a bit tizzy, but removing the guards tames this. I have some fine lambswool and some moleskin adhesive pads that I will experiment with to see if I can smooth them out further. Just finding a few hours spare to play with them is proving difficult right now. I have an amp project that is refusing to work for me!

 

[sreten]

The result is too much tweeter, to my ears.

How do I tweak this? Add resistance to the tweeter? The xo has two 1 ohm resistors in parallel, which yields 1/2 ohm, I believe. Without taking apart the crossover, can I just add diferent resistors to the tweeter and experiment?

Hi,

unless you have 4 ohm replacement diaphragms (DCR ~2.7R) you
need to add 6R in parallel with the new tweeters (DCR~5.4R).

This will correct the croosover operation and increase the effect
of the series resistors - which you can adjust up to say 2.2R.

/sreten.

 

[timbert]

Forgive my ignorance, I have confused myself. Sreten, the two 1 ohm resistors that are parallel to each other, aren't they also said to be in series on the + input to the tweeter? When you say to add a 6R resistor in parallel, exactly where do I do that? Would it connect to both sides of the tweeter? Before or after the inductor?

The new coils in the tweeter are 5.4R, so where exactly do I add a resistor, and what rating and power value, going by the above schematic? I am trying to get as close to the factory sound before continuing.

To repeat, I have rebuilt the factory XO to original, but have replaced the blown stock 4ohm tweeter coil with an 8ohm one because that's all I could find.

Many thanks and sorry for my dumb questions.

 

[sreten]

Hi,

The 6R (standard value 5.6R or 6.2R) is wired across the tweeter.
The 1 ohm resistors can be used for a 0.5R, 1R (omit 1) or 2R
series resistor.

Ideally after finding the right balance the capacitor and inductor
woulds be reworked for an 8 ohm tweeter, but above will work.

/sreten.

 

[timbert]

Well I listened on and off to the bright tweeters for a few weeks, and even tried a few episodes of rock-concert level music. I used my 100 watt NAD 2200 and drove it into clipping. I have a couple spare amps so I wasn't very careful. Everything was fine except for the neighbors. Today I finally soldered the 5.6 ohm 10W resistors as suggested to the tweeters, and they cut back the highs severely. Also, at the external speaker terminals I get 10.4 R on my digital multimeter. I think, to start, they need to be cut to a level about half of what the 5.6R cut them. Should I be experimenting with the resistors at the crossover, or with the resistors I just installed right at the tweeter?

 

[sreten]

Today I finally soldered the 5.6 ohm 10W resistors as suggested
to the tweeters, and they cut back the highs severely. Also, at the
external speaker terminals I get 10.4 R on my digital multimeter.
I think, to start, they need to be cut to a level about half of what the
5.6R cut them. Should I be experimenting with the resistors at the
crossover, or with the resistors I just installed right at the tweeter?

Hi,

it sounds like you have wired them in series with the tweeter rather than in parallel
which will be too dull and impedance wise completely wrong for the crossover.

/sreten.

 

[timbert]

Here's where I put the new resistor on the tweeter. Is this not said to be in parallel with the tweeter?

 

[sreten]

Hi,

That is in the right place but then i do not know where the
10.4 R measurement comes from, something is confusing.

Change it to 8R if it has too much effect.

/sreten.

 

[laser21]

Hi,

my tweeter just died

http://i65.photobucket.com/albums/h219/justblair/TweeterBAck.jpg
its exactly as in the picture. From mission 753.

Any place, where I could buy it from? You guys are clearly experts here...you could save me a lot of time looking for it! Thanks

 

[timbert]

I was able to order replacement voice coils from Madisound here in the US, but they are 8 ohm coils, not 4. They fit fine and work okay, but the tweeter was very loud, and as recommended I've added a resistor and now it's too soft, so I continue to experiment. Please let me know if you find 4 ohm coils or entire replacement tweeters. Also, I did other work on the crossovers so that may be the problem I am having, but I'm not sure.

 

[Blue_Max]

Recently I found that tweeters of my pre-Freedom 753s are gone too.
Don't know if it matters, but they were bi-wired too.
The amp is an Arcam A85

Label at the back of the Mission 753 HF unit state:
Mission
Part No. 53-HFLM21
Made in Denmark
Qc 941215
Cat No. 811877
4 Ohms

Madisound are out of stock.
Does anyone where to get a replacement?!
Both aluminium diaphrams are fine. Can they be re-wound?

Thanks

Job CF
Goring-by-Sea

 

[mowog44]

How bizarre.
Just found this thread by googling the same problem also with my Mission 753's.
I (well it was the wife actually) blew the tweeters and both x-overs.

I have already replaced the crossovers (supplied by Mission) but the tweeters are a different matter.
Mission are out of stack and won't be getting any more.

I'm currently sending mine down to a company in London called "Wembley Loudspeakers" who are going to try and fix or replace them.

I'll let you all know how it goes.

 

[Blue_Max]

Mision tell me that tweeters for 753s are no longer available.

Someone suggested rewinding. Is this feasible?

 

[ShinOBIWAN]

Mision tell me that tweeters for 753s are no longer available.

Someone suggested rewinding. Is this feasible?

Get in touch with Wembley Speakers as mowog suggested. They're well known for drivers repairs and its likely they'll be able to assist you in some way or another.

 

[timbert]

As the person who originally posted I thought it was only right to close things out on my issue. I parted out the woofers on ebay to some very happy Mission owners, and the tweeters with the wrong coils to a guy in Germany. One pair of the drivers sold for $15, another for $115, so if you use ebay keep that in mind. No one on ebay was interested in the repaired crossovers, and I tossed the cabinets in the trash. I could not bring myself to do it and had my little son drag them out there. I have the original tweeter diaphrams with the torn windings if anyone wants them. Maybe a cottage industry could crop up in rewinding these things if there was enough demand.

I rarely give up on projects, stubborn as I am, but this one nearly overwhelmed me. I learned a lot along the way, thanks to everyone here. I still use daily the speakers I've had for 15 years, Paradigm 11se Mk II towers.

Cheers,

Timbert

 

[sreten]

http://www.madisound.com/catalog/product_info.php?manufacturers_id=143&products_id=8443

Hi, out of stock, but may still be ordereable, /sreten.