Hi guys,
I have an old set of B&W DM6's that I'm refurbishing. The one tweeter was blown, so I've bought a set of TW26's for cheap that I'm going to put in which are on the way to me now from Holland.
Next thing, when I tested these loudspeakers out a while ago on my Sansui AU 4900, something was pushing the amp into protect mode when I turned the volume up around 10 o'clock. Is it likely that the capacitors in the DM6's have deteriorated causing their reactances to drop slightly, thus decreasing the total impedance which results in drawing too much current from the amp, pushing it into protect mode?
Anyway, I was planning on recapping the crossovers as a matter of course, and maybe this will solve the aforementioned problem. Here is a schematic:
So, for the pair of speakers I need:
C1 50uF x 2
C2 30uF x 2
C3 35uF x 2
C4 3uF x 2
C5/6 2.2uF x 4
C7/8 3.3uF x 4
Is there any specific voltage rating or type of capacitor that I should get? It doesn't specify in the service manual. I would guess that they are all bipolar electrolytic, in my limited experience of electronics I haven't seen nonpolar above 1uF, but I'm likely wrong.
Also, some of the values are proving difficult to find such as the 35uF. I have seen other people doing recaps on speakers, and they use a number of smaller capacitors in parallel to get close to the equivalent value. Is this accepted practice?
Thanks
Jono
I have an old set of B&W DM6's that I'm refurbishing. The one tweeter was blown, so I've bought a set of TW26's for cheap that I'm going to put in which are on the way to me now from Holland.
Next thing, when I tested these loudspeakers out a while ago on my Sansui AU 4900, something was pushing the amp into protect mode when I turned the volume up around 10 o'clock. Is it likely that the capacitors in the DM6's have deteriorated causing their reactances to drop slightly, thus decreasing the total impedance which results in drawing too much current from the amp, pushing it into protect mode?
Anyway, I was planning on recapping the crossovers as a matter of course, and maybe this will solve the aforementioned problem. Here is a schematic:
So, for the pair of speakers I need:
C1 50uF x 2
C2 30uF x 2
C3 35uF x 2
C4 3uF x 2
C5/6 2.2uF x 4
C7/8 3.3uF x 4
Is there any specific voltage rating or type of capacitor that I should get? It doesn't specify in the service manual. I would guess that they are all bipolar electrolytic, in my limited experience of electronics I haven't seen nonpolar above 1uF, but I'm likely wrong.
Also, some of the values are proving difficult to find such as the 35uF. I have seen other people doing recaps on speakers, and they use a number of smaller capacitors in parallel to get close to the equivalent value. Is this accepted practice?
Thanks
Jono
Thanks for the replies. Have checked out some prices on the Mundorf caps, and they are definitely out of the price bracket, even the lowest range (MKP's it is? Andy, I searched MKSP4's and didn't come up with anything..)
I don't mind having to build up caps, if that is the way to go. I could use those Solens which would cost me 75$CA incl shipping. I could also use Mallory 150s for the smaller sizes and F&Ts for the larger.
Is there any objection to using a single 80uF in place of the 50uF and 30uF (C1 and C2), or are they paralleled for a reason?
Are there any voltage ratings I should adhere to for crossover caps?
Thanks
I don't mind having to build up caps, if that is the way to go. I could use those Solens which would cost me 75$CA incl shipping. I could also use Mallory 150s for the smaller sizes and F&Ts for the larger.
Is there any objection to using a single 80uF in place of the 50uF and 30uF (C1 and C2), or are they paralleled for a reason?
Are there any voltage ratings I should adhere to for crossover caps?
Thanks
Sorry I was typing too quickly.
Have look at http:\\www.rs-online.com and search for MKPS capacitors.
Have look at http:\\www.rs-online.com and search for MKPS capacitors.
If the amp is shutting down, I'd tend to suspect the amp, not the speakers. What are the basic stats of the Sansui? Is it an integrated amp, AV receiver, or what? Rated power output? And saying it shuts down with the volume at 10:00 o'clock isn't very useful unless we know how hot the signal source is?
I've noticed at friends' houses that some AV receivers, particularly Denons, develop a tendency with age to "shut down" at lower and lower volume levels. Also, "10:00 o'clock" could be close to full power with a CD source if the amp has a lot of gain. The DM6s are not very efficient, and are happiest when driven by a very stout amplifier. In the '70s I had a friend who owned a hifi store that sold B&Ws, my recollection is that, for example, the GAS Son Of Ampzilla would run out of steam on the DM6s, but the Ampzilla would drive them happily.
In a British speaker like the B&Ws, the ESR of the capacitors was likely taken into consideration when the crossovers were designed and measured, and changing to different capacitor types could well change the frequency response of the system. If you feel the need to replace the caps, I'd try to get as close as possible to "like for like" with your component selection, particularly if there are any electrolytics in there.
I've noticed at friends' houses that some AV receivers, particularly Denons, develop a tendency with age to "shut down" at lower and lower volume levels. Also, "10:00 o'clock" could be close to full power with a CD source if the amp has a lot of gain. The DM6s are not very efficient, and are happiest when driven by a very stout amplifier. In the '70s I had a friend who owned a hifi store that sold B&Ws, my recollection is that, for example, the GAS Son Of Ampzilla would run out of steam on the DM6s, but the Ampzilla would drive them happily.
In a British speaker like the B&Ws, the ESR of the capacitors was likely taken into consideration when the crossovers were designed and measured, and changing to different capacitor types could well change the frequency response of the system. If you feel the need to replace the caps, I'd try to get as close as possible to "like for like" with your component selection, particularly if there are any electrolytics in there.
Thanks for the comprehensive reply.
The Sansui is a 35W RMS into 8ohm integrated stereo amplifier. It is being driven by a line level signal at its aux input (like it should be). I've heard that the DM6's are best driven by 2x 100W power amps? Unfortunately I don't have that at my disposal, however, I see no reason that by supplying a low output ie 35W to the speakers which are rated at much higher power that the amp would go into protection.
So you think I should leave the crossovers as is and go over my amp?
The Sansui is a 35W RMS into 8ohm integrated stereo amplifier. It is being driven by a line level signal at its aux input (like it should be). I've heard that the DM6's are best driven by 2x 100W power amps? Unfortunately I don't have that at my disposal, however, I see no reason that by supplying a low output ie 35W to the speakers which are rated at much higher power that the amp would go into protection.
So you think I should leave the crossovers as is and go over my amp?
I repaired a pair of DM6's for the friend I sold them to 10 years ago. They were shutting down his amp repeatedly, but did not blow the speaker fuses, so I knew the problem was before the drivers. All xover components checked out okay. Finally, the cause: corrosion around the connectors on the inside back panel was forming a very weak short circuit.
Take out the woofers and all the stuffing. Keep the stuffing from each speaker in a separate paper bag. Remove the xovers, noting which wire goes to which terminal. Look at the back panel and you'll probably see some discoloration, perhaps blue, around the terminals. Scrape it out. Put the speakers back together. They'll work.
Don't bother rebuilding the xovers if you're not going to upgrade components. I can't imagine why you wouldn't want to spend a few bucks to get better parts. Those are excellent speakers. I bought mine in 1976, one of the first 50 pairs B&W imported to the US. I still like their sound when I visit my friend.
How did you select the tweeter to use as a replacement?
Peace,
Tom E
Take out the woofers and all the stuffing. Keep the stuffing from each speaker in a separate paper bag. Remove the xovers, noting which wire goes to which terminal. Look at the back panel and you'll probably see some discoloration, perhaps blue, around the terminals. Scrape it out. Put the speakers back together. They'll work.
Don't bother rebuilding the xovers if you're not going to upgrade components. I can't imagine why you wouldn't want to spend a few bucks to get better parts. Those are excellent speakers. I bought mine in 1976, one of the first 50 pairs B&W imported to the US. I still like their sound when I visit my friend.
How did you select the tweeter to use as a replacement?
Peace,
Tom E
Thanks mad, will check that out and hopefully its the problem! I think these are also one of THE pairs in South Africa.
The tweeter: basically one of my TW20's conked in. I've done some reading on the net, and apparently they are renowned to blow the HF fuses. Anyway, also I read on the net that a more than adequate replacement is the TW26.
The tweeter: basically one of my TW20's conked in. I've done some reading on the net, and apparently they are renowned to blow the HF fuses. Anyway, also I read on the net that a more than adequate replacement is the TW26.
Hi Andy5112405,
if you worked for B&W you are probably the best person to respond to this enquiry. I haven't got the article and "adverts" in front of me but as I recall it the DM6 was a unit with a three tiered baffle on two built-in legs and was occasionally known as "The Pregnant Penguin". (Which I always found appealing.)* Is that correct?
If not ignore the next comment! But if it is can you comment on the cross over and the claims by B&W that this unit had essentially First order cross overs and was pretty heavily promoted as being phase linear or "minimum phase". The cross over looks to be a mixture of 1st, 2nd and 3rd orders......
Anyway ignore this if I have misunderstood any (or ALL ) of the relevant data!
* The appearance of the speaker that is.....not the concept of a pregnant penguin! Don't want to be confused at this crucial point!
Thanks, Jonathan
if you worked for B&W you are probably the best person to respond to this enquiry. I haven't got the article and "adverts" in front of me but as I recall it the DM6 was a unit with a three tiered baffle on two built-in legs and was occasionally known as "The Pregnant Penguin". (Which I always found appealing.)* Is that correct?
If not ignore the next comment! But if it is can you comment on the cross over and the claims by B&W that this unit had essentially First order cross overs and was pretty heavily promoted as being phase linear or "minimum phase". The cross over looks to be a mixture of 1st, 2nd and 3rd orders......
Anyway ignore this if I have misunderstood any (or ALL ) of the relevant data!
* The appearance of the speaker that is.....not the concept of a pregnant penguin! Don't want to be confused at this crucial point!
Thanks, Jonathan
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Hi Makepeace,
I purchased a pair of DM6 as well (in Jan 2011) from a guy of who owned 2 pairs.
unfortunately mine pair suffers as well from damaged tweeters (1 speaker in particular (=right one), the other one is OK). I replaced a tweeter with an original TW20, but it also started to make some unpleasent noises (cracking).
After opening the DM6's I saw that they have been tempered with during the years, not good I suppose...
I found a pair of DM12's with TW26 tweeters and took those to fit in my DM6's but after a while the TW26 tweeter of the right speaker made a cracking sound as well.
I was also thinking of replacing the X-over with a DIY model.
After reading this thread, maybe it's indeed better to change the wiring and all the connectors due to corrosion.
What about your status? Did you change the crossovers & the wiring eventually?
I purchased a pair of DM6 as well (in Jan 2011) from a guy of who owned 2 pairs.
unfortunately mine pair suffers as well from damaged tweeters (1 speaker in particular (=right one), the other one is OK). I replaced a tweeter with an original TW20, but it also started to make some unpleasent noises (cracking).
After opening the DM6's I saw that they have been tempered with during the years, not good I suppose...
I found a pair of DM12's with TW26 tweeters and took those to fit in my DM6's but after a while the TW26 tweeter of the right speaker made a cracking sound as well.
I was also thinking of replacing the X-over with a DIY model.
After reading this thread, maybe it's indeed better to change the wiring and all the connectors due to corrosion.
What about your status? Did you change the crossovers & the wiring eventually?
Hi jorisc,
Sorry its taken me sooo long to reply. I ended up fixing my dad's old Yamaha A-760, 2 x 80W, which is much happier with the DM6s so my conclusion is that the Sansui was struggling a bit..
Re the DM6's, I bought a pair of TW26's on Marktplaats a while back.. The problem was, in my excitement I didn't read the ad properly, and it turns out one is slightly broken. It has a far lower output than the other so I'm sure somethings wrong
.
I have just got hold of a Lenco L70 TT so have resumed the search to either find someone who can fix this TW26 or replace it (and hopefully not have to replace both.. I decided not to touch the crossovers, as my conclusion is that they are in good working order and don't need looking at just yet.
What are the developments on your side?
If anyone knows of a single TW26 or a pair of TW20's that are going, PLEASE let me know, I would be eternally indebted.
Sorry its taken me sooo long to reply. I ended up fixing my dad's old Yamaha A-760, 2 x 80W, which is much happier with the DM6s so my conclusion is that the Sansui was struggling a bit..
Re the DM6's, I bought a pair of TW26's on Marktplaats a while back.. The problem was, in my excitement I didn't read the ad properly, and it turns out one is slightly broken. It has a far lower output than the other so I'm sure somethings wrong
. I have just got hold of a Lenco L70 TT so have resumed the search to either find someone who can fix this TW26 or replace it (and hopefully not have to replace both.. I decided not to touch the crossovers, as my conclusion is that they are in good working order and don't need looking at just yet.
What are the developments on your side?
If anyone knows of a single TW26 or a pair of TW20's that are going, PLEASE let me know, I would be eternally indebted.
Don't know if this applies but are you sure the caps are electrolytics anyway? I've got two pairs of DM2's and one of DM4's and they all use metallised polypropylene, B&W made quite a thing of it at the time due to the fact they don't age. Would they have used inferior caps in their new flagship models?
All the best
Graham
All the best
Graham
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