I have a pair of old 1972 B&W DM4 speakers. They are in fairly good condition, but I would like to rebuild the xover. The inscriptions on the caps and coils in the original filter are gone over time...
Does anyone have a schematic of this three way filter? Or a clue where I could find it?
Marc
Does anyone have a schematic of this three way filter? Or a clue where I could find it?
Marc
Member
Joined 2002
Maybe you can email them and ask. Let them know what model and that you either want to buy the parts from them to repair them your self..
Member
Joined 2002
Right on Thumb's up for that one : O) This is the only forum that i hang out on all day sometimes..
But back to your speakers..
How do they sound. i almost bought a pair but i was told that i could build better pair for less money : O)
J'
But back to your speakers..
How do they sound. i almost bought a pair but i was told that i could build better pair for less money : O)
J'
Hi Marc
Havent got the schematic but x-over frequency from the 8" to the celestion hf1300 is 4000 Hz and to the Coles 401 supertweeter i think around 8000, mind You this was the mid seventies and my memory fades as the beard goes whiter. Realy nice speakers thou, need a bit of wall support not to become to lean in the bass.
Havent got the schematic but x-over frequency from the 8" to the celestion hf1300 is 4000 Hz and to the Coles 401 supertweeter i think around 8000, mind You this was the mid seventies and my memory fades as the beard goes whiter. Realy nice speakers thou, need a bit of wall support not to become to lean in the bass.
JasonL said:
They have been 'neglected' way too long, these B&W's!
So they tend to sound a bit harsh, no sweet top end. I do not remember how much my father paid for them in '74 but I do remember going to the shop with him and buy these speakers together with a Marantz receiver and a Revox open reel deck. Very 70s!
I still have the Revox (in mint conition) and the speakers. The Marantz went to a brother of mine.
If I remember well, these were very engaging speakers, even though their set up in my parents house wasn't perfect at all.
Wether or not you could build a better pair for less money than the price for a good pair of second hand B&W's depends of course on the money you want to spent on vintage items.
However I do think that speakers are very different nowadays from what was being engineered 30 years back. Most speakers are much more transparent e.g. an they can handle more power.
When I compare the DM's with the pair of AlonIV in y living room, there indeed is a world of difference.
I admit it, my question in the first post is just the first step back in time to my childhood.
Once I almost bought these speakers, but I choose a pair of IMF super compact instead.
I guess you already found the user manual?
I guess you already found the user manual?
Hi Zeno
This is a photo of my dm4 xover.
Pls pardon photo quality
Caps vaues left to right are as follows
Between yellow and green coil- 2.2uF on left 1.5uF on right
Row of 3 caps 1uF on left 0.68uF in middle and 3.3uf to right
Between black and white coils- 4.7uf on left 3.3uF on right
Caps have values molded onto them and appear to be 100volt
All coils appear to have no values marked –sorry
As to sound- very musical indeed- not bad for their vintage-probably still better than most consumer cr*p around these days- purchased at 2nd hand store- had to replace surrounds to woofers.
Hope this helps – pls let me know if I can add any further info.
This is a photo of my dm4 xover.
Pls pardon photo quality
Caps vaues left to right are as follows
Between yellow and green coil- 2.2uF on left 1.5uF on right
Row of 3 caps 1uF on left 0.68uF in middle and 3.3uf to right
Between black and white coils- 4.7uf on left 3.3uF on right
Caps have values molded onto them and appear to be 100volt
All coils appear to have no values marked –sorry
As to sound- very musical indeed- not bad for their vintage-probably still better than most consumer cr*p around these days- purchased at 2nd hand store- had to replace surrounds to woofers.
Hope this helps – pls let me know if I can add any further info.
Attachments
Hi Georg a,
I checked the filter in my DM4's. They are screwed on the back of the speaker, identical to the xover on your picture. Is the xover in your DM4's sitting on the back of the baffle?
I noticed that the plastic domes of the so called 'super tweeter' are both damaged. They have a crack running almost entirely through the dome. I guess they have become brittle over the years and did not survive uninteded touching ...
A shame.
They do play very well though, even the high notes. I hooked them up tonight, put them close to the wall and started playing music.
Like them a lot!
I checked the filter in my DM4's. They are screwed on the back of the speaker, identical to the xover on your picture. Is the xover in your DM4's sitting on the back of the baffle?
I noticed that the plastic domes of the so called 'super tweeter' are both damaged. They have a crack running almost entirely through the dome. I guess they have become brittle over the years and did not survive uninteded touching ...
A shame.
They do play very well though, even the high notes. I hooked them up tonight, put them close to the wall and started playing music.
Like them a lot!
Hi Zeno
Yes PCB on back of front baffle, super tweeter under pcb in photo.
SAd to hear your tweetes damaged.
I know how good this unit can sound, dont know if you can still get replacement units - pehaps try wilmslow audio in UK ..?
I currently use them in rear channels of HT setup.
Cheers
Yes PCB on back of front baffle, super tweeter under pcb in photo.
SAd to hear your tweetes damaged.
I know how good this unit can sound, dont know if you can still get replacement units - pehaps try wilmslow audio in UK ..?
I currently use them in rear channels of HT setup.
Cheers
I believe the supertweeters are Coles (STC) 4001, still available
from Falcon Acoustics at reasonable prices, unlike Wilmslow.
http://www.falcon-acoustics.co.uk/pl28p10.htm
Personally in terms of rebuilding the crosover I'd just bypass
the Polyester film capacitors and solder all connections, but
you could repace the capacitors.
Replacing the coils is pointless.
🙂 sreten.
from Falcon Acoustics at reasonable prices, unlike Wilmslow.
http://www.falcon-acoustics.co.uk/pl28p10.htm
Personally in terms of rebuilding the crosover I'd just bypass
the Polyester film capacitors and solder all connections, but
you could repace the capacitors.
Replacing the coils is pointless.
🙂 sreten.
So they had different production types. I was wondering if we were talking about different B&W type.george a said:
The PCB is screwed from the outside of the back of my speakers and the four holes are covered with plastic plugs.
My set still have a sign with the serial numbers on them. 67399 and 67400.
Production date must be after 1973 or 1973.
B&W was (and still is???) "selling speakers to the British Queen" the sign says.. .
Well, it doesn't say it in so many words, they have a logo with a crown, tellin the customers they are trustworthy
sreten said:
Thats is what I thought last nigt, playing Leonard Cohen's ten new songs. These speakers ar incredible good in repoducing the human voice, btw.
Coils don't really age, I guess. Maybe Intertechnik or som other specialists do build better ones nowadays.
The caps are another story, so is the inner cabling. Very thin strands of wir in these speakers. I will start with that and look for replacement tweeters.
B&W finished with the 'DM/4' in 1981.The later model was not as good as the early. early had a very heavy Plywood baffle board with plastic stand-offs for the grill mounts, the later models had a chipboard baffle board with triangular chipboard off cuts for grill fixings.
Mid/bass unit:Early ones were black coated baskets with name plaque on magnet, the later were just plain alloy & no plaque.These are the two obvious differences i noticed, i did notice my very early ones had a foam stocking around the unit baskets, the later a cloth stocking..
All my Bass units are knackered now, i've tried stripping & cleaning but no good.Theclear suspension rings between the Cone & baskets are shot.
If anyone knows of a replacement i'd love to hear.I did contemplate replacing the Bass units with a new more modern alternative unit, i contacted Wilmslow audio & they recommended one even after claiming they knew nothing about the original unit, that alone put me off.
Mid/bass unit:Early ones were black coated baskets with name plaque on magnet, the later were just plain alloy & no plaque.These are the two obvious differences i noticed, i did notice my very early ones had a foam stocking around the unit baskets, the later a cloth stocking..
All my Bass units are knackered now, i've tried stripping & cleaning but no good.Theclear suspension rings between the Cone & baskets are shot.
If anyone knows of a replacement i'd love to hear.I did contemplate replacing the Bass units with a new more modern alternative unit, i contacted Wilmslow audio & they recommended one even after claiming they knew nothing about the original unit, that alone put me off.
Up!
Did anyone change some caps or bypass with teflon or such?
It seems it's already a perfect box, maybe it will brake the magic spell...
Did anyone change some caps or bypass with teflon or such?
It seems it's already a perfect box, maybe it will brake the magic spell...
DM4
No, in the end I bought new tweeters, replaced the cracked ones.
I built a gaincard ampli with some left overs to go with the speakers. My twin daughters are now enjoying this set, simply connecting their I-pods or mac's to the system.
Works like magic.
Z
No, in the end I bought new tweeters, replaced the cracked ones.
I built a gaincard ampli with some left overs to go with the speakers. My twin daughters are now enjoying this set, simply connecting their I-pods or mac's to the system.
Works like magic.
Z
So that's it, nobody touched their DM4 as it's as good as it can be already.
Thanks, I'm also asking myself about an Aiport to stream my iMac music with airtunes.
Thanks, I'm also asking myself about an Aiport to stream my iMac music with airtunes.
Bass SPL
Finally I've messed with my speakers, wondering if some ways may be found to push a bit the spl on the bass unit.
I've taken the XO out and tried to bypass the film caps with 1nF Téflon, highs sparkle like never, so clean! But as they are more readable the bass is lacking even more...
Here are some pics, XO included. The bass unit sounds more mid-high bass than bass. (seems to cut around 3kHz, by ear).
Can a better coil (less resistive?) on the bass help a bit? Bypass of caps wouldn't harm, no spl issue here, isn't it?
All ideas are weclome, like split XO, solder parts in air and avoid any PCB? Stiffen the enclosure with second plywood layer on back/bottom, built an internal brace or such? Damping the steel frame of the bass? If it's free it's welcome 😉
Finally I've messed with my speakers, wondering if some ways may be found to push a bit the spl on the bass unit.
I've taken the XO out and tried to bypass the film caps with 1nF Téflon, highs sparkle like never, so clean! But as they are more readable the bass is lacking even more...
Here are some pics, XO included. The bass unit sounds more mid-high bass than bass. (seems to cut around 3kHz, by ear).
Can a better coil (less resistive?) on the bass help a bit? Bypass of caps wouldn't harm, no spl issue here, isn't it?
All ideas are weclome, like split XO, solder parts in air and avoid any PCB? Stiffen the enclosure with second plywood layer on back/bottom, built an internal brace or such? Damping the steel frame of the bass? If it's free it's welcome 😉
Attachments
Hi Malefoda!
So,is it necessary or not if i 'm mod the Xover of DM4.It can make the sound better? Many thanks
Regard.
I picked up a pair of these at a car boot sale for €15, when I picked them up they sounded quite good after about 20 minutes use, in the beginning they were a bit wooly. Then suddenly three weeks later, they sound all scratchy and odd. Am I right in assuming the capacitors are probably completely shot? There's no damage to any of the drivers, and all I did was let them sit for a few weeks. What is the best way to get at the cross-over, remove the bass woofer?
Woolly and scratch sounds like my old tweed jacket! A good crossover like the DM4 uses MKT capacitors which are going to be very stable. The whole build quality is superb in fact. I'd be looking for a loose wire or shot tweeters myself. You need to use a multimeter to check them.
Just disconnecting and reconnecting connectors will get some fresh metal on them. Crimp connectors do oxidise as well. And yes, you go through the bass to get access. This thread is good:
Le forum de Vintage Audio Laser • Afficher le sujet - B&W pro40 / DM4
Just disconnecting and reconnecting connectors will get some fresh metal on them. Crimp connectors do oxidise as well. And yes, you go through the bass to get access. This thread is good:
Le forum de Vintage Audio Laser • Afficher le sujet - B&W pro40 / DM4
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