Mission 753 speaker modding

[BOONDI]

Hi Ian, Peter, all.....

I was reading a back issue of the suplement the other day and the article in question was about mission 752 series of speaker. It stated that Mission were using Audax drivers in this series. Will have a dig around to see if I can find it, but, it def said Audax......

[Ianm2]

yes the 752s def used an audax bass, and the 754s in the mid. aerogel with the pointy phase plug, good speakers, 752s, 5% worse than proac response 3s at £3,000 then....long time ago

had em both at the same time

[BOONDI]

Yes Ian, I kinda had a hankering for the 752's, but couldn't afford them at the time. Ended up building my own using Audax drivers loosely based on the 752's and WAD KLS 3 series. Gold tweeter was a right pain, changing with the weather.....

Eventually settled on TWO25A tweeter as a replacement. Much cheaper for about 90% of the sound.....

[Roppu]

Sorry for writing here in such an old thread but just hoping Justblair or someone else into this can help.
I'm not happy at all with my Mission 753 Freedom's sound and would like to replace electrolytics and cables. Drawing my crossover schematics I realize it is quite different from Justblair's one and, more than everything, the two lowest woofers are connected in parallel. Since I bought these speakers used, is it normal or did someone do some "magic" into them? Attached is my schematic.
Any suggestion for the caps brand I might use?
Thank you very much

[bob orbell]

This is very simple, if you don't like the Missions, sell and buy something you do like, but listen first before buying. Bob

[Richard]

Hi Roppu and welcome,

Bob has good advice as usual although you already have the speakers and probably can’t return them easily so you may want to experiment or repair/restore them.

Have you checked the tweeters are working? If they are ferrofluid it can dry up resulting in lesser treble or they may be blown.

The only review I found which discussed any technical detail did say, “This paralleling of drive units” ( https://www.hifi-review.com/153625-mission-753.html para 3) but that may be correct or just the reviewers assumption.

Difficult to say how accurate either of the circuit drawings are; yours may be modded and the one in the first one may have an error. You could try checking the DCR of the drivers to see if it gives a clue.

There are quite a few 753 sites which may be worth a read, just google “mission 753 schematic”

https://willys-hifi.com/blogs/news/m...sover-rebuilds

https://www.usaudiomart.com/details/...mages/2042878/

https://www.stereonet.com/forums/top...pgrade-thread/

https://www.diyaudio.com/community/t...fixing.107658/

etc etc, looks like problems and mods were common so try to get the original correct circuit, then test your drive units and xover components, then rebuild them as standard.

[Roppu]

Hi Richard. First of all thank you very much.

It seems like I did some error drawing the schematics. I'm uploading it again

Originally Posted by Richard

Hi Roppu and welcome,
Bob has good advice as usual although you already have the speakers and probably can’t return them easily so you may want to experiment or repair/restore them.

Actually Bob doesn't know many things about these speakers and me but honestly I don't mind.
Yes I would like to dig in before giving up, Richard[/quote]

Originally Posted by Richard

Have you checked the tweeters are working? If they are ferrofluid it can dry up resulting in lesser treble or they may be blown.

Tweeters are fine. I only miss basses and stage

Originally Posted by Richard

The only review I found which discussed any technical detail did say, “This paralleling of drive units” ( https://www.hifi-review.com/153625-mission-753.html para 3) but that may be correct or just the reviewers assumption.

Great finding, though it seems the paralleling is referred to having more drives with the same function

Originally Posted by Richard

Difficult to say how accurate either of the circuit drawings are; yours may be modded and the one in the first one may have an error. You could try checking the DCR of the drivers to see if it gives a clue.

Indeed. I did an error too and just uploaded the right one for Freedom ones (mine). What figures should I expect measuring the DCR?

Originally Posted by Richard

There are quite a few 753 sites which may be worth a read, just google “mission 753 schematic”

https://willys-hifi.com/blogs/news/m...sover-rebuilds

https://www.usaudiomart.com/details/...mages/2042878/

https://www.stereonet.com/forums/top...pgrade-thread/

https://www.diyaudio.com/community/t...fixing.107658/

I will dig into someone that I hadn't seen yet

Originally Posted by Richard

etc etc, looks like problems and mods were common so try to get the original correct circuit, then test your drive units and xover components, then rebuild them as standard.

Yes, I would like to replace at least the capacitors, wiring and binding posts. Wiring is soldered on washers. Washers are blocked to the binding posts with steel nuts. Then the signal is transferred from the binding posts to the washers through a piece of steel! It's crazy

Thank you again!

[Brian]

I’m no expert but I’m still not certain the updated circuit drawing is correct for the HF unit. I expect a capacitor of some value in series and I usually see one on the positive side, I’ve never seen a crossover drawing without one for a multi-way speaker. Just looking around the web now and I can’t see any examples of a crossover without one. See http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm for many examples. The 3rd link from Richard shows a schematic that looks far more likely to work properly, imo. ( Note: I viewed the page at the 3rd link once and it won’t allow me to view it again without joining....very odd)

I’d like to see a picture of the rear panel of the speakers. If it’s a decent sized plastic tray I would remove the crossover entirely, drill 4 more holes for binding posts in the plastic tray so you can fit 6 binding posts to each and internally connect each pair of posts to the relevant drivers. Remove the crossovers and get a suitable sized plastic box and build an unmodified crossover externally from the speakers. Use whichever components from the current set that are correct and if you need some new components buy cheap to start with. Once done and satisfied all is as it should be, you can tweak things easily given the crossovers would be external. I’d start by building the crossover following the one in the link from Richard.

Apologises if I’m talking nonsense though, I hope others chip in, it’s an interesting situation. I admit I don’t know anything about this particular Mission speaker, only that I found everything much easier with my own speakers once I moved the crossovers to external boxes.

Good luck with it.

Brian

Link to crossover...

https://www.google.com/search?q=miss...5R-Ww7U_qf5uHM

and this one that includes inductor values though obviously no indication of whether or not this is correct and standard.

https://www.google.com/search?q=miss...6sAXFsNM1jfprM

[Richard]

Originally Posted by Roppu

Hi Richard.


Indeed. I did an error too and just uploaded the right one for Freedom ones (mine). What figures should I expect measuring the DCR?

Hi, here's the impedance curve, nominal 6 ohm,

https://www.stereonet.com/forums/upl...0091c12aa8.png

I'd expect approx 4 DCR drivers if they are in series or much higher around, 12 - 16 DCR if in parallel.

[Roppu]

Originally Posted by Brian

I’m no expert but I’m still not certain the updated circuit drawing is correct for the HF unit. I expect a capacitor of some value in series and I usually see one on the positive side, I’ve never seen a crossover drawing without one for a multi-way speaker. Just looking around the web now and I can’t see any examples of a crossover without one. See http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm for many examples. The 3rd link from Richard shows a schematic that looks far more likely to work properly, imo. ( Note: I viewed the page at the 3rd link once and it won’t allow me to view it again without joining....very odd)

Hi Brian.
Thank you very much for finding the time to check. You were right! I rechecked and it is like I'm uploading again. I'm doing this during night hours and it must be not a good idea since I'm doing mistakes!

Originally Posted by Brian

I’d like to see a picture of the rear panel of the speakers. If it’s a decent sized plastic tray I would remove the crossover entirely, drill 4 more holes for binding posts in the plastic tray so you can fit 6 binding posts to each and internally connect each pair of posts to the relevant drivers. Remove the crossovers and get a suitable sized plastic box and build an unmodified crossover externally from the speakers. Use whichever components from the current set that are correct and if you need some new components buy cheap to start with. Once done and satisfied all is as it should be, you can tweak things easily given the crossovers would be external. I’d start by building the crossover following the one in the link from Richard.

Here is the picture (attached). I might try what you say. Peter Comeau once said there are lots of variants of cross-over's for these speakers. I better checked the joints and it doesn't seem they were put in parallel as a tweak. Justblair, who opened this thread, had a different one. Anyway I will keep your hint as a chance. I will give the links a look again now.

Originally Posted by Brian

Apologises if I’m talking nonsense though, I hope others chip in, it’s an interesting situation. I admit I don’t know anything about this particular Mission speaker, only that I found everything much easier with my own speakers once I moved the crossovers to external boxes.

No nonsense at all and don't apologise. It's much appreciated and I found another error after your hint

Originally Posted by Brian

Good luck with it.

Brian

Link to crossover...
[...]

This is exactly my one

Originally Posted by Brian

and this one that includes inductor values though obviously no indication of whether or not this is correct and standard.
[...]

These inductors values were taken by Justblair but as said he has a different cross-over (they were original Mission 753; mine are the Freedom version and that's another reason why they're not the same).
Thank you again. Will read everything and get back