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Multi-Way Conventional loudspeakers with crossovers

Mission 751 Crossover Circuit Diagram
Mission 751 Crossover Circuit Diagram
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Old 12th June 2017, 09:18 AM   #31
dewdrop is offline dewdrop  Singapore
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Originally Posted by ThetaII View Post
What capacitor values did you use?
I used 5uF for both.
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Old 12th June 2017, 02:30 PM   #32
ThetaII is offline ThetaII  United Kingdom
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I would guess that 5uF would be fine for the tweeter but not sure that is right for the main driver ....but would need someone with more experience to comment on that. I used 6.8uF for the tweeter as it was suggested in the first page but I believe there is a tad too much lower treble coming through (only just though), so waiting for my 4.3uF's to arrive.
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Old 12th June 2017, 03:05 PM   #33
dewdrop is offline dewdrop  Singapore
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Originally Posted by ThetaII View Post
I would guess that 5uF would be fine for the tweeter but not sure that is right for the main driver ....but would need someone with more experience to comment on that. I used 6.8uF for the tweeter as it was suggested in the first page but I believe there is a tad too much lower treble coming through (only just though), so waiting for my 4.3uF's to arrive.
Thanks for sharing. I guess my problem is it's imbalanced now despite having the same cap values in both speakers. Need to figure how to troubleshoot if the tweeter has gone bad. I know the easiest way is to swap the xo boards and I will know the answer straightaway.
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Old 12th June 2017, 03:09 PM   #34
ThetaII is offline ThetaII  United Kingdom
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That sounds like a good plan to narrow it down. Was there an issue before you changed the caps? ..if not, then that is bad luck.
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Old 12th June 2017, 03:45 PM   #35
dewdrop is offline dewdrop  Singapore
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Originally Posted by ThetaII View Post
That sounds like a good plan to narrow it down. Was there an issue before you changed the caps? ..if not, then that is bad luck.
I don't think the issue was there before the mod. But hey, it could just been that the original caps might have been just right. ;-)
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Old 12th June 2017, 10:45 PM   #36
system7 is offline system7  United Kingdom
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I'd suspect the ferrofluid has gone solid. Reduces level dramatically.

Click the image to open in full size.

Easy enough to replace it:
Sonitus Audio Ferro Fluid (ferrofluid) for Speakers and Compression Drivers 0.5ml from Sonitus Audio 5.00

This is enough for 5 tweeters.

Click the image to open in full size.

You want to do some modelling to guess what modifications might do. Maybe a third order tweeter filter with say a 6.8uF added would lift the 3kHz area, which is mostly what you hear.
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Old 13th June 2017, 01:26 PM   #37
dewdrop is offline dewdrop  Singapore
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Originally Posted by system7 View Post
I'd suspect the ferrofluid has gone solid. Reduces level dramatically.

Click the image to open in full size.

Easy enough to replace it:
Sonitus Audio Ferro Fluid (ferrofluid) for Speakers and Compression Drivers 0.5ml from Sonitus Audio 5.00

This is enough for 5 tweeters.

Click the image to open in full size.

You want to do some modelling to guess what modifications might do. Maybe a third order tweeter filter with say a 6.8uF added would lift the 3kHz area, which is mostly what you hear.
Hey Steve,
This is fantastic suggestions. I will try with the Sonitus Audio Ferro Fluid. Let me try to order it.

Do you have a "How to fix a tweeter for dummies?" guide somewhere?
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Old 13th June 2017, 01:30 PM   #38
dewdrop is offline dewdrop  Singapore
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Originally Posted by dewdrop View Post
Hey Steve,
This is fantastic suggestions. I will try with the Sonitus Audio Ferro Fluid. Let me try to order it.

Do you have a "How to fix a tweeter for dummies?" guide somewhere?
I think I was being a bit lazy not to Google first: found this one which looks very illustrative - Replace ferrofluid in tweeter - a B&W tweeter as an example.
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Old 3rd January 2018, 12:27 PM   #39
Sanj is offline Sanj
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Hi I'm new to diyaudio, but have owned a pair of mission 751 from new. Although they seem to be working fine, I'm a bit concerned about the 'ferrofluid drying out issue', which they may be prone to, due to their age. Which is why this thread is of particular interest to me.
Could you fill me in on whether the fluid replacement was successful, and if so;
how you know how much to put in?
any complications to watch out for?
Any input would be much appreciated.
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Old 3rd January 2018, 07:24 PM   #40
system7 is offline system7  United Kingdom
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Originally Posted by Sanj View Post
Hi I'm new to diyaudio, but have owned a pair of mission 751 from new. Although they seem to be working fine, I'm a bit concerned about the 'ferrofluid drying out issue', which they may be prone to, due to their age. Which is why this thread is of particular interest to me.
Could you fill me in on whether the fluid replacement was successful, and if so;
how you know how much to put in?
any complications to watch out for?
Any input would be much appreciated.
Let me explain it to you. Back in the day about 30 years ago, tweeters could only survive about 10 watts at parties. They tended to blow up.
Click the image to open in full size.
Then somebody discovered a magic mix of aviation fuel Kerosene, magnetic ferric oxide particles and a binding agent which got them working together. This increased momentary power to about a 100W. Because it just wicks away the heat to the magnetic gap.

Nothing is perfect. Hit them hard at parties and the oil tends to evaporate. Leaving solid sludge of magnetic dust. We need to replace the evaporated Kerosene oil.

Parts Express in the US sell you a minescule 0.1mL of new magnetic oil. For $5. Happily, Blue Aran in the UK can do much better, enough for about 5 tweeters: Sonitus Audio Ferro Fluid (ferrofluid) for Speakers and Compression Drivers 0.5ml PS3.60

TBH, the Mission 751 isn't the greatest speaker in the World. But nothing stopping you cleaning out the old solidified gunge and putting some new stuff in there. It's like oiling your bicycle chain. It just works better. Get it wrong by about 50%, it still works.
Attached Images
File Type: jpg Monitor_Audio_Silicone_Grease (2).jpg (88.5 KB, 10 views)
File Type: jpg Ferrofluid.jpg (70.8 KB, 10 views)
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Last edited by system7; 3rd January 2018 at 07:30 PM.
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