Sunday, February 14, 2016

Mission 782 repair

--- EDIT  - please scroll to the bottom of this article for the edit ---

Hi everyone.
It seems that I'm having as much bad luck in transportation services, as I'm having good luck in auction items.

I've been looking for a pair of floor standing mission "old school" speakers.
There is a reason for that: old school mission speakers where made-in the UK (not China like later ones), with excellent craftsmanship and even better engineering. 
As newer models have been labeled dull and flat, old models, particularly the ones using fixed vented pole designs for the midrange drivers, where something to look for and then keep with.
The mission engineers managed to match the crossovers to the perfect driver for that type of frequency response. This brilliantly mated combination, produces results comparable to speakers costing 5 to 10 times as much. This, to me, was Mission's trademark... archiving results through efficient engineering, beating "costly materials and drivers" with brain. It has everything to do with me...engineering instead blindly mixing expensive components and then making the client pay for it, claiming the old "exclusivity" excuse. 
Don't get me wrong; good materials produce better results, it's just that whenever not so good materials with good engineering produce the same results, then the obvious conclusion is that applying the same engineering effort to better materials would give your client a better "ride for the money"... mission did that for some time and I absolutely respect that.

The 782 are a perfect example of what mission used to be:

Back to my history: after a lot of searching and some frustration trying to convince some ebay traders that there was no difference on shipping a pair of speakers 10 miles of 10.000 miles, one very nice lady accepted my challenge and allowed me to bid on a pair of 782.

The 782 are a brilliant designed true 3way speaker. It features a 13cm midrange fixed vented pole ceramic design speaker on top, together with a 2,5cm silk dome tweeter, both enclosed in the top end of the speaker  on a pyramidal shaped box. Then at the bottom, there is a side-firing 16,5cm woofer made from nomex, that enjoys practically 2/3 of the speaker body box for volume and reflecting.

So summing up, after a LONG search, I managed to source a set of some of the best cost/quality speakers known to man.
There was some degree of risk! The reason that make the 782 so exquisite, is that they where produced for a little time... and that was due to a mid-driver production problem! The original drives that came with the 782 where the Keraform 82-LF130/QS. Excellent design, reasonable build quality but a terrible detail. The coil protective plastic sheet, had a glue whose chemical composition reacted with the soldering on the metal, generating extreme corrosion. This would lead to increase in electrical resistance, reducing sound power and quality, with time the oxidation would inflate the once flat soldering and make the coil rub against the magnet walls and producing heat and drag, and ultimately the degradation would just insulate the parts and the driver is dead.

Most people facing this, just decided to trash or sell the speakers. for some time it was possible to buy replacement parts from Keraform, but, in time those would have the same fate.


Obviously, Mission was aware of this and discontinued the series, then instructed the technicians to accept warranty repair claims, and substitute the driver with the Audax HM130Z0 Aerogel units. These where better, more expensive drivers that would perfectly replace the Keraforms without impact in sound quality/image.




So there are some 782 out there that whee trashed, others where sold as repair item, others for parts, others perfectly repaired and updated... and of course, the original ones... few in working order.

I knew this; I accepted that ... and even managed to find a set that was original and in perfect working order. Sure i was expecting some soldering degradation, but I would be able to peel off the plastic, clean the chemicals and re-do the soldering and wrap the coil back with a non acid glue. This, unfortunately never came to be. My couriers, managed to kill the midrange drivers on both speakers. I'm working out the insurance claims at the moment, and apart from some very unpleasant dealing with customer care, the escalation seems to work... so I'll wait until I add to this article the details... either for the best or the worse of it.

While grabbing the speakers I immediately felt a heavy item loose inside one of the speakers. Bad news for sure, confirmed when opening the speaker:
The front protective cover has the pins broken and clearly had suffer a large squashing impact.
A hole was easy to spot where the cone pole would be, and the inner speaker baffle filling was observable.
In panic, I immediately rushed to the next speaker... no good news there either:
The center pole was loose, running around the speaker driver, however no heavy loose part was felt and the mounting point of the cone pole was still in place. but the pole was broken and heavily marked. 


Ok... time to access the total damage on the first speaker:

First I toolk a clamp to remote the broken plastic pins that used to hold the protective front cover. then, using a screwdriver, I gently removed the rubber housings, exposing the Philips screws.


Then I removed the front assembly, which holds the tweeter.

I finally removed the driver assembly and got hold of the destruction:

Whatever hit the driver, pushed the cone pole in, with enough force to rip the magnet from the driver structure, then the weight if the magnet ripped the wire plug wide open. 


This is the dismantled driver.... and, of course before any attempt to fix, a conductivity test was taken...

At least the tweeter was in perfect order


So conclusions: the main drive was dead...by many different forms of assassination attempt all at once. Independently, I would not foresee a bright future ahead of this speaker, it is an original Keraform, and the oxidation is way into the soldering.
on the inner side, the bump is the result of extreme oxidation process.


Conclusion: I've made an insurance claim for the transportation, ordered a couple of AUDAX aerogel, and I'm now waiting delivery. Will update this post soon.

UPDATE:
So the AUDAX drivers arrived. They are a thing of beauty, but their cast ring is bigger than the Keraforms... a lot bigger. They are also made from aluminum instead of plastic as you would find in the Keraform. In essence, they are a lot better built.


Step 1 -  place the old Keraforms on top of the new AUDAX and use a light colored pencil to template the cutting line on the aluminium .

2- use a dremel tool to cut the excessive aluminium. MAKE SURE you protect the new cone from debris... I just covered it with gum-tape.


3 - Start cutting,

4 - After cutting the metal from the driver, put it next to the wood and template the extra cut... the better you cut the metal, the less you need to adjust the wooden part.

5 - Place the driver and use the drill tool to have new holes for the drivers screws.

6 - Place everything back together and enjoy your brand new UPGRADED Mission 782. These will not go bad of fail...and they sound a lot better than they cost.






----- Edit -----

Hi everyone again.
I decided to update this article as several of you commented on the original and some new ideas came into play.
First of all, thanks for commenting. It's a joy to know that this article has been helpful to others and that they also share their knowledge.This is what the web is all about.

Now starting with what got me into this edit: I recently upgraded my cinema & games room (yes I'll be updating those too), but by removing 2 slave amplifiers and buying a clone for my Marantz CD5000, left me with a surplus of 2 Marantz amplifiers (a PM 4400 and a 55 Special Edition) and a NAD C520 cd player.
Since I spend more time at the office than at home, I decided to move the PM4400 and the NAD to the office. All I now needed to do was to source a set of speakers.

More or less at the same time, my cousin decided to build his cinema and audio listening room. I managed to go to my first choice in audio - my good friend Bob  . While searching for the items my cousin would buy, I managed to find 2 pairs of 782s... and then later that day, while explaining him how much better these are when upgrade-repaired, I instantly started finding myself going upstair and listening more and more on my 2 782's.
Weeeeellllll my cousin only neede 1 set, so i brought the other set for my office.

The set I brought has 1 driver faulty and the other driver already replaced by mission like Chris Galloway stated on his comment. I thought this would be an excellent time to look at what misison built audax drivers would look like and perform.
I also thought, this is a good time to put in practice Adrian Vos method of fitting the driver in one of them, vs my old method on the other.

ALSO, AUDAX continued to evolve the good old HM130Z0... not in it's last iteration as HM130Z12, it has a better plastic seal of the foam dumper, better coil and magnet so, by reason, should sound even better.
So yeah i brought 2. This time i chased AUDAX website, only to get to AAC's website and finally there, source the distributors. I chose the first entry - AARV and got an excellent deal and very decent shipping.


So now for some conclusions: 
The Mission AUDAX made replacement driver vs the AUDAX HM130Z12.
The difference is clear. The AUDAX HM130Z is a loaded, heavy magnet, very robust beast. The mission driver is not only smaller but also plastic structured and clearly not as robust.
In the end, the Mission driver is very good, no doubt and the sound it outputs has an excellent image and is quite refined, however, unless I'm loosing it, I believe that I got slightly more detail on the HM130Zs, particularly at louder volumes.  It doesn't come across as a surprise as, this being a device that produces precision mechanical waves, the more robust it is framed, the better it insulates the thrust into actually producing what it's being asked for.




The repairs:
As expected, the un-repaired KERAFORM unit was long gone and looked even worse than my previous ones.



So deciding to go for both drivers, I then went for on driver on my method, grinding the outer frame out and fitting it in:


And for the other, I decided to give it a go on the Adrian Vos method. in essence I decided to dremel the driver contour out:


 and then groove in steps of 2mm up to 4mm





And then, peel GENTLY each 2mm thick slice and go on to the next until I had a 4mm socket to place the driver in

]


This is the end result.


Comparing the methods, 
on the left Adrians method, on the right my old method
























Final marks:

Andrians method is MUCH FASTER AND EASIER. It also requires you to know how to manage a power tool and have firm hands, or you will end up defacing the speaker's outer wood shell. I still prefer my method as the final package looks tighter, but I find no difference in sound.

HM130Z's vs Mission own driver - IF you have the keraforms, you should opt for the HM130Z, else if you already serviced your speakers and have the mission aerogel AUDAX replacements, I don't believe the effort is worth it except if you are really trying to get the absolute best possible sound out of it. If, like me, you really want these babies to eclipse much higher line speakers, then the 110 euro it's gonna cost you, plus the afternoon grinding metal and wood is worth it.
But the mission aerogel is a very good option and certainly costs half the money and 1/10th the effort.

HM130Z0 vs HM130Z12 - If buying for the first time, go for the 12's, if you already have the 0's the juice is not worth the squeeze... but you can always try to use Adrian's method and simplify the "squeeze".

It ends up being a "do you pursue audio nirvana or not?" question.

I'm now the happy owner of 2 pairs of repaired/upgraded 782's and the guys at the office went crazy when they started singing. They've just finished the run-in... boy do I love these speakers.

--- re-edit for location tips and sound test with spectrometer ---


Positioning of the speakers in the Room:






The speaker on the rigth should be another 20 cm away from the wall, but this IS a meeting room and function takes precedence! That board has given birth to some preety spectacular ideas that help paying for all this stuff so... 


As you can see, sound is coherent both next to the speakers and on the far side of the room. 
This room has carpet and sound/heat insulation on both ceiling and walls, so not the best for sound propagation (thought rather good avoiding weird echos).

The spectral analisys shows very pleasent sound pressures across the frequencies, without excessive high frequencies and excessive low frequencies.

:)


ohhh and the treble, bass balance are all neutral, and loudness is off








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