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Mission M70Mk.II crossover

Sam Cogley

Sam Cogley

Last of the Time Lords
Subscriber
Apparently the crossover for these little buggers was continuously refined over the several years that they were in production, and as such I have not been able to locate any information regarding the specific crossover design in my pair. These have two chokes, a 1 ohm wirewound resistor, and two capacitors which appear to be non-polar electrolytics. One of the caps is a 3.3uF, the other, larger capacitor's label is obscured by glue in each cabinet. Anyone know what it should be? I'd like to rebuild the crossovers with some better parts.
 
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Bump for the afternoon crowd.

I'd probably have to dissect one of the crossovers to figure out what the other cap is, which I'd prefer to avoid until I'm actually ready to rebuild them.
 
I tried to get the white glue to let go so I could read the side of the cap, but no go. Unsoldered the ends of the caps and tested them - the obscured cap read 3uF (larger in size but smaller in capacitance than the other one), together they read right at 6.3uF. Ordered some nice Daytons from Parts Express, along with a replacement Dayton resistor. When they get here I think I'll rebuild the crossovers on terminal strips screwed to the inside of the cabinet rather than having them hang on the terminal cups.
 
I might have tried to answer your question as I am in the process of re-furbing a set myself. I did one foam tonight but got into it too late to do both. I will try to have a look before work in the morning. I hadn't planned to do the caps yet as I couldn't even listen to these yet as there was a lot of rubbing.

Question: did you do the foam on yours and was the paper cone all tacky? Mine sure was.
 
I just opened up one of my 70 mkii's to take a look. The tweeter(Vifa d 19 td-08) only has a 4.7 cap and a coil inductor, no resister. The woofer has no caps or coils! Mine might be a later run and maybe they were cutting costs.

The woofer feels sticky but hairs and stuff don't stick to it. My Polk woofers are stickier.
 
They apparently kept simplifying the crossover as time went on.

So far, there are no signs of degradation on my surrounds. Time will tell, I guess.
 
Well, crap. Obviously both caps had drifted out of their values. The new parts came in today, and I tore the original crossovers apart to get the chokes out for reuse. After I manged to rip the hidden cap free, it was marked 2.2uF instead of 3uF like they had measured (the 3.3uF also measured high, somewhere around 3.6uF). So, with a 3uF and a 3.3uF, I have them at the crossover point I've always heard, but not the one the designers intended. I'll order the 2.2uF parts and swap them out at some point.
 
Oops. Too bad about that.

I literally just hooked mine up 5 minutes ago and am hearing them for the first time as they rattled really badly when I got them sans foam. They sound pretty fair for the $10 I paid for the speakers and $8 for the foam. :)

I hope you get yours sorted out.
 
I'll take my M70 mkII's apart tomorrow and see what I can for values. I refoamed mine a year ago and the woofers don't look anything like the others posted. Mine are poly. The foam didn't fail, it shifted on the frame. Coil drag. The Brits do say to rotate them from time to time.
 
They sound quite good, but it's not that big of a deal to swap out the 3uF for 2.2uF. I forgot to order rebuild parts for a few other speakers the first time around, so it wasn't a big deal to order the right parts.
 
2.2uF caps were in today's mail. I'll bring the M70Mk.IIs home from the office tonight to swap them out. I'm doubting that I'll really notice the relatively small change in crossover point, but I'll feel better knowing that they're operating as the designer intended (and probably better, since they'll have nice film caps instead of those bipolar electrolytics installed).
 
I need to refoam mine. They're great sounding speakers. Cracking them open and seeing how cheaply they're built only adds to the magic they put out.

Sent from my ZTE Olympia
 
RamblinE said:
I need to refoam mine. They're great sounding speakers. Cracking them open and seeing how cheaply they're built only adds to the magic they put out.

Sent from my ZTE Olympia
Click to expand...

I'm pretty sure nearly every penny went into the drivers.
 
RamblinE said:
I am so very much okay with that.

Sent from my ZTE Olympia
Click to expand...

Me too, but a bit better cabinets or crossover parts would have been nice. At least the inductors were decent quality, and the crap capacitors were the only thing that would really detract from sound quality.

2.2uF caps installed in place of the incorrect 3.0uFs. I'll take them back to the office tomorrow for testing.

It's a crossover night...replaced the parallel pair in some battered Genesis G1s with a single 10uF and built 60uF bundles out of two 25uFs and a 10uF for my BA A150 IIs. Might go pull out the Infinity Reference R-Ls and rebuild those while I'm at it.
 
OK, I was surprised at how noticeable the difference between the 3.0uF and the 2.2uF cap really is. They're sharper all around now than they've ever been.
 
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