Hi all
I have been looking this weekend at my trusty Mission 753 non freedoms. So far with this speaker I have carried out 2 successfull mods.
1. I removed the metal grill that "protects" the metal dome tweeter. A very good result on this one. I always found the freedoms to be too soft for my tastes. The non freedoms a bit harsh. The non freedoms with the tweeter mod gets close to my tastes.
2. I applied "no more nails" between the basket and the magnet. This has made a subtle but worthwhile improvement to the clarity of the speaker.
Next up I plan a rewire and some improvements to the crossover. I took some time to map the crossover.
My schmatic
My plans are as follows
The last one I have some questions over. Excuse my ignorance when it comes down to impedence. The reason for wanting to do it is that I recently moved to bi amp (using gainclones) and the difference in clarity was dramatic. Separating the filters looks easy in terms of wiring, I just add a couple of binding posts and wire to them. Impedence though I dont understand fully.
What will be the effect in separating them? Will the volume go out of balance? What would be the impedence be at the inputs to each crossover, or what do I need to know to measure it?
Within my plans have I made any stupid errors?
I don't plan to make any changes that are irreversible, but I would appreciate any guidance that will increase my chances of success.
Thanks in advance
Blair
I have been looking this weekend at my trusty Mission 753 non freedoms. So far with this speaker I have carried out 2 successfull mods.
1. I removed the metal grill that "protects" the metal dome tweeter. A very good result on this one. I always found the freedoms to be too soft for my tastes. The non freedoms a bit harsh. The non freedoms with the tweeter mod gets close to my tastes.
2. I applied "no more nails" between the basket and the magnet. This has made a subtle but worthwhile improvement to the clarity of the speaker.
Next up I plan a rewire and some improvements to the crossover. I took some time to map the crossover.
My schmatic
My plans are as follows
- Replace the coffin style resistors with decent quality wirewounds
- Replace the 6.8uf cap on the tweeter's filter with something nice. suggestions please?
- Replace the back to back 470uf caps on the mid's filter with a decent bipolar cap, suggestions please?
- Replace the back to back 1000uf caps on the lower end filter with a pair of good quality 'lytics, probably nichicon fine gold or similar. Open to suggestions though?
- leave the existing inductors for the moment. I don't have the facility or know how to measure their values, let alone pick replacements.
- Replace the 10mf bipolar cap on the mid range filter with higher quality, again suggestions?
- Split the mid and low end filters and go tri wire!?
The last one I have some questions over. Excuse my ignorance when it comes down to impedence. The reason for wanting to do it is that I recently moved to bi amp (using gainclones) and the difference in clarity was dramatic. Separating the filters looks easy in terms of wiring, I just add a couple of binding posts and wire to them. Impedence though I dont understand fully.
What will be the effect in separating them? Will the volume go out of balance? What would be the impedence be at the inputs to each crossover, or what do I need to know to measure it?
Within my plans have I made any stupid errors?
I don't plan to make any changes that are irreversible, but I would appreciate any guidance that will increase my chances of success.
Thanks in advance
Blair
Hi,
Some notes :
Tri-wiring and tri-amping is a simple as you describe.
You can make the amplifiers gains adjustable slightly for tweaking.
Each amplifier in the bass section will see an easier load.
You should "bypass" the midrange 235uF capacitor with a film type.
Try Falcon components : http://www.falcon-acoustics.co.uk/
🙂/sreten.
Some notes :
Tri-wiring and tri-amping is a simple as you describe.
You can make the amplifiers gains adjustable slightly for tweaking.
Each amplifier in the bass section will see an easier load.
You should "bypass" the midrange 235uF capacitor with a film type.
Try Falcon components : http://www.falcon-acoustics.co.uk/
🙂/sreten.
sreten said:
Thanks for the suggestions Sreten. Couple of more questions
You mention that the amps will see an easier load on the bass sections. The LM3875 I believe aint so hot driving lower impedences. Is there anything that I can do to increase the effective impedance if the amps struggle?
You mention "bypassing" the 235uF capacitor I always took this to mean connecting another cap in parrallel with it. Is this what you mean? I would have thought I would be better replacing it altogether with a better cap? Apologies my terminology is confused.
And thanks for the link, I shall peruse that one later!
Hey Justblair,
Sounds like a fun project, I have always wanted a pair of 753s!
It would be worth looking at madisound for your parts, you'll need to pay overseas shipping, but when I compared the prices between uk parts suppliers and US the difference was more than worth the shipping costs. Plus there was a greater range. They have Eagle Metal Film resistors which are non inductive and may prove superiour to the wire wound versions and at $1.20 each they aren't going to break the bank.
http://www.madisound.com
You could also look at internal damping sheets, upgrade the terminal post (which you'll have to do to tri-wire) and upgrade the sound absorbant material.
Hope this helps.
Ian
Sounds like a fun project, I have always wanted a pair of 753s!
It would be worth looking at madisound for your parts, you'll need to pay overseas shipping, but when I compared the prices between uk parts suppliers and US the difference was more than worth the shipping costs. Plus there was a greater range. They have Eagle Metal Film resistors which are non inductive and may prove superiour to the wire wound versions and at $1.20 each they aren't going to break the bank.
http://www.madisound.com
You could also look at internal damping sheets, upgrade the terminal post (which you'll have to do to tri-wire) and upgrade the sound absorbant material.
Hope this helps.
Ian
justblair said:
Not really, unless you go for a parallel amplifier topology.
If the bass ampliier is not struggling much now, two of
them will not with only one bass section each to drive.
justblair said:
Ok. Something like 220uF bipolar with 10uF film bypass will be fine.
🙂/sreten.
Its just one of the fun projects that I have been inspired to by sites like this and the helpfulness of the site dwellersianpengelly said:
Great tip on the site. The metal films are defo on the shopping list.ianpengelly said:
They also seem to have a nice selection on the parts. I am looking at the mundorf supreme caps. I can get a 6.8uf for the tweeter no probs. Though it costs a bit... Not sure wether its good value for money?
Still lost a bit on the choice for the caps to replace the mid range pair of lytics. The value is much higher than I can find in the good caps.
The pair of 1000uf I will probably replace with Nichicon fine golds. The choice of these is simple. I use this cap on the 4 power amps that I have built already. If I am making more amps I will have to buy another 4. Might as well buy 8. Is this a good choice?
The missions are already fitted with internal damping sheets on the side walls (not full sized) I don't know if that will make a difference in this case. The MDF is also pretty thick and heavy... Maybe I will look at it when I get to fine tuningianpengelly said:
The sound absorbing material looks pretty basic. Its just foam cut to cover the back wall of the speaker case. I will certainly be looking at this in the future
sreten said:
Thanks for clarifying. I think I will "suck it and see" on this. My belief was that the lm3875 struggles into low impedances, looking at the schematic, the bass drivers are paired up in series. That (excuse my newbness) will produce a high impedance. I am still confused, but I am sure that all will reveal itself in the testing. I will start by disconnecting the low pass filter and listening. If it works I will go ahead and order parts for a third pair of amps.
sreten said:
Again thanks for clarifying... I feel a bit dumb now for not getting that straight away.
Can you point me at good quality 220uf caps?
Right I have been doing some searching on the internet. And I have a parts list sorta sorted out. I would appreciate some constructive criticism
Per speaker
Tweeter
Sonic Craft Sonicap MKP 6.8uf 220VDC – 5% tolerance
Vishay Roederstein MKP1837 0,01mF MKP 100VDC – 1% tolerance
Eagle metal oxide resitors
Mid
2x Black Gate standard 470uf polar cap 50v
Vishay Roederstein MKP1837 0,01mF MKP 100VDC – 1% tolerance
Eagle metal oxide resitors
Bass
2x Black Gate standard 1000uf polar cap 50v
Vishay Roederstein MKP1837 0,01mF MKP 100VDC – 1% tolerance
Eagle metal oxide resitors
My maths tells me this will cost about £80 for all the parts.
I would welcome suggestions for bringing down the costs or getting better results for the same sort of budget?
Per speaker
Tweeter
Sonic Craft Sonicap MKP 6.8uf 220VDC – 5% tolerance
Vishay Roederstein MKP1837 0,01mF MKP 100VDC – 1% tolerance
Eagle metal oxide resitors
Mid
2x Black Gate standard 470uf polar cap 50v
Vishay Roederstein MKP1837 0,01mF MKP 100VDC – 1% tolerance
Eagle metal oxide resitors
Bass
2x Black Gate standard 1000uf polar cap 50v
Vishay Roederstein MKP1837 0,01mF MKP 100VDC – 1% tolerance
Eagle metal oxide resitors
My maths tells me this will cost about £80 for all the parts.
I would welcome suggestions for bringing down the costs or getting better results for the same sort of budget?
justblair said:
You don't need MKP's on the bass section.
Nice website about Engineer Malcolm Jones and Falcon Acoustics, UK, sreten.
Inductor said:
Is that because the caps are out of the signal path, or because they are insignificant compared to the 500uf caps that are there?
Other than that. Am I on the right lines?
Regards
Blair
justblair said:
Bypassing is usually done to enhance the mid and treble so is fairly redundant in the bass section. The thinking is that small bypass caps give better response with higher frequencies.
You are on the right path here but I cannot comment on your choice of Black Gates since I have only ever used them in amps and CD players.
P.S. I have used sonicaps and found them to be good value for money and it seems that others agree. Very similar to clarity caps IMO.
Sonusthree said:
Thankyou so much for the reply. That aids my understanding.
I have to admit I chose the Black Gates due to their reputation more than anything else. But I am interested to hear others recommendations on this?
At £80 for an upgrade, part of me is thinking about going down the active crossover route. Linkwitz perhaps. However I have read scary stories about the cabinates needing retuned or the phase going out of whack.
All input gratefully recieved...
I'm in a similar situation. I've just added an extra amp for biamping with a passive crossover. Active crossovers are definitely interesting but it seems like a minefield and I'd still have to keep a cap on the tweeter just for protection. I will try it but I'd like to see how far I can go with the passive route first. Once I have taken the passive crossover to it's limit then I will have a benchmark to compare an active crossover to.
If you are undecided then you could always try changing one thing at a time. Maybe start with the tweeter caps and see if that whets your appetite for further changes?
Don't forget that you don't have to go completely active at first. I.E. Maybe run the tweeters through a simple opamp high pass filter? It would be a good learning experience and would be quite easily reversible and more importantly ..... tweakable!!! The golden rule however is to add some kind of protection for the tweeters since you don't want them to meet any D.C.
My advice: buy the tweeter caps and see if it's for you.
If you have plenty of money: buy the lot and change the parts one at a time to see how each mod changes the sound.
Theoretically at least, this should allow you to hear the speakers at their best before considering an active setup.
Just my two pence ....... and talk is cheap,
Martin.
If you are undecided then you could always try changing one thing at a time. Maybe start with the tweeter caps and see if that whets your appetite for further changes?
Don't forget that you don't have to go completely active at first. I.E. Maybe run the tweeters through a simple opamp high pass filter? It would be a good learning experience and would be quite easily reversible and more importantly ..... tweakable!!! The golden rule however is to add some kind of protection for the tweeters since you don't want them to meet any D.C.
My advice: buy the tweeter caps and see if it's for you.
If you have plenty of money: buy the lot and change the parts one at a time to see how each mod changes the sound.
Theoretically at least, this should allow you to hear the speakers at their best before considering an active setup.
Just my two pence ....... and talk is cheap,
Martin.
Hi,
The active route would obviously mean the speakers cannot be used
with a normal amplifier again, and there are some difficulties working
out what active slopes you need due to interactions between the
drivers and the c/o components.
You can get away with a smaller tweeter amplifier than the other
two by making its input coupling capacitor much smaller than usual.
How bad are the current electrolytic capacitors and the resistors ?
You could reuse some capacitors e.g. the 470uF in the bass section.
You could re-use your smaller caps for bypassing.
Its a lot cheaper to make good quality caps out of say 3 types.
🙂/sreten.
But note :
tri-amping you could remove the treble and bass series resistors.
You could also remove the mid series capacitors, and decrease
the amplifiers input capacitor, but how well this would work
depends on the interaction of sealed resonance and capacitor.
The active route would obviously mean the speakers cannot be used
with a normal amplifier again, and there are some difficulties working
out what active slopes you need due to interactions between the
drivers and the c/o components.
You can get away with a smaller tweeter amplifier than the other
two by making its input coupling capacitor much smaller than usual.
How bad are the current electrolytic capacitors and the resistors ?
You could reuse some capacitors e.g. the 470uF in the bass section.
You could re-use your smaller caps for bypassing.
Its a lot cheaper to make good quality caps out of say 3 types.
🙂/sreten.
But note :
tri-amping you could remove the treble and bass series resistors.
You could also remove the mid series capacitors, and decrease
the amplifiers input capacitor, but how well this would work
depends on the interaction of sealed resonance and capacitor.
Some good suggestions there. Good to hear your opinions on the active thing.
I have decided to stick with the passive route for the moment, for pretty much all of the reasons you have mentioned in the thread. The active frankly scares me.
Also. I may wish to build a different amp in the future. Triamping gainclones is fine, as each extra stage costs me very little, providing I keep with the one power supply. But I may wish to try something more exotic in the future.
Starting with the tweeters is probably the route I am going to take. I cant find a dealer selling the sonicap as well as the other components I am after, So I am going to have to order seperately anyway. If I am getting a small order of caps (the Vishay and the sonicap) then I dont have to wait till pay day.
That will give me anough for the tweets and also I can try bypassing the mid range caps as well.
Then i can aim for pay day for the next set of mods and see how enthuisiatic I feel then
The orgional lytics look unbulged etc. But they are 10 years old now. i'm expecting that they are a little worn. If i replace them with bog standard lytics I would imagine I will hear some improvement regardless.
I like the idea of using a much smaller imput cap for the tweeters amp. I was thinking of building it with less than the 1000uf power caps as well. Can anyone link me to a site that tells me how to calculate that value?
Thanks again for your intersting suggestions. Its nice to hear some different ideas,
I have decided to stick with the passive route for the moment, for pretty much all of the reasons you have mentioned in the thread. The active frankly scares me.
Also. I may wish to build a different amp in the future. Triamping gainclones is fine, as each extra stage costs me very little, providing I keep with the one power supply. But I may wish to try something more exotic in the future.
Starting with the tweeters is probably the route I am going to take. I cant find a dealer selling the sonicap as well as the other components I am after, So I am going to have to order seperately anyway. If I am getting a small order of caps (the Vishay and the sonicap) then I dont have to wait till pay day.
That will give me anough for the tweets and also I can try bypassing the mid range caps as well.
Then i can aim for pay day for the next set of mods and see how enthuisiatic I feel then
The orgional lytics look unbulged etc. But they are 10 years old now. i'm expecting that they are a little worn. If i replace them with bog standard lytics I would imagine I will hear some improvement regardless.
I like the idea of using a much smaller imput cap for the tweeters amp. I was thinking of building it with less than the 1000uf power caps as well. Can anyone link me to a site that tells me how to calculate that value?
Thanks again for your intersting suggestions. Its nice to hear some different ideas,
I get my sonicaps here ( Ebay): http://cgi.ebay.co.uk/Sonicap-Film-...6213022QQihZ011QQcategoryZ36338QQcmdZViewItem
I've ordered from Italy a few times now and have had no problems and the stuff has arrived quickly.
And he sends you some free and beautifully mis-spelt stickers too.
I made the mistake of trying one out on my Nextel coated amplifier. I now have the choice of removing it and removing a sticker sized patch of paint or putting up with a 'car tuning' style sticker. You know what I mean, the ones that tell all the other boy racers what kind of tyres they have!!
I've ordered from Italy a few times now and have had no problems and the stuff has arrived quickly.
And he sends you some free and beautifully mis-spelt stickers too.
I made the mistake of trying one out on my Nextel coated amplifier. I now have the choice of removing it and removing a sticker sized patch of paint or putting up with a 'car tuning' style sticker. You know what I mean, the ones that tell all the other boy racers what kind of tyres they have!!
Attachments
I was going to use that e-bay shop anyway.... They have both the sonicaps and the vishays, his prices look good
But after seeing the free sticker... I am definately going there. I hope he/she wont be offended if I ask for two. I will (and I am not joking) mount them on the back next to the crossover.
By the way, is that a crystal on top of your amp??
Sreten. I looked at maplin, they have LCR caps they describe for audio. Are they any good? I had sorta made a decision on the sonicap...
Blair
But after seeing the free sticker... I am definately going there. I hope he/she wont be offended if I ask for two. I will (and I am not joking) mount them on the back next to the crossover.
By the way, is that a crystal on top of your amp??
Sreten. I looked at maplin, they have LCR caps they describe for audio. Are they any good? I had sorta made a decision on the sonicap...
Blair
justblair said:
😀 😀 😀 😀 Great minds think alike ... you also get two extra, round, plastic stickers. Mine reside on the rear of my Tannoys above the crossover!! Don't ask me why. It's a childhood habit I never grew out of. Cabinet dampening anyone?
Those 'crystals' are bouncy balls cut in half and supporting another amp. My chakras are already in perfect alignment thanks.🙂
By the way, you should remember that the sonicaps will probably be a little larger than your originals. The 220 volt ones aren't too bad but the higher voltage ones can be h-u-g-e!
