Nope I don't think its needed or does a lot, but I reached out to B&W yesterday who were very helpful and someone is headed into their archives on Thursday so is going to pull out the drawings and e-mail over copies as they think it was on the earlier models but omitted on the later ones, so probably all I have to do is clean out the dust.
If I understand you correctly, the foam was stretched over the rear of the frame or basket of the bass driver.
This is a way of reducing the optimum volume of an enclosure by lowering the Q.
Without this damping effect, the bass may be more dominant - which may, or may not, be to your liking.
Easy ways to test a speaker:
1) Dig up a 1.5V AA Duracell battery and a couple of bits of wire or paperclips. Poke around the drivers and see if you get any crackly noises. 1.5V is well under everything's ratings, so no harm will come.
2) Short out the speaker input with something metal. Tap on the bass cone, with and without the short. It will change tone because the damping is changing. You will likely find you get a crackle from the tweeters when you push the bass in too, especially with a poor short like a screwdriver, because the bass generates a crackly emf. No battery required! 😎
You hope for signs of life if the drivers aren't blown entirely.
1) Dig up a 1.5V AA Duracell battery and a couple of bits of wire or paperclips. Poke around the drivers and see if you get any crackly noises. 1.5V is well under everything's ratings, so no harm will come.
2) Short out the speaker input with something metal. Tap on the bass cone, with and without the short. It will change tone because the damping is changing. You will likely find you get a crackle from the tweeters when you push the bass in too, especially with a poor short like a screwdriver, because the bass generates a crackly emf. No battery required! 😎
You hope for signs of life if the drivers aren't blown entirely.
I'd get back to testing the electrics before worrying about the foam.
A simple way to test each driver is with 1 1.5V battery. Just brush 1.5V across each driver and you should hear a crackle from all of them. The tweeter will be very quiet but you should hear it.
It is very unlikely that you have blown all three drivers.
The Coles mid-range was prone to cracking but that is not your issue here.
If all THREE drivers aren't working you have to look for a common failure point.
The DM2A didn't have electronic protection, that came later with the DM14.
The only common area is the fuse and the crossover.
Have you got continuity between the speaker terminals and the crossover PCB through the fuse ?
A simple way to test each driver is with 1 1.5V battery. Just brush 1.5V across each driver and you should hear a crackle from all of them. The tweeter will be very quiet but you should hear it.
It is very unlikely that you have blown all three drivers.
The Coles mid-range was prone to cracking but that is not your issue here.
If all THREE drivers aren't working you have to look for a common failure point.
The DM2A didn't have electronic protection, that came later with the DM14.
The only common area is the fuse and the crossover.
Have you got continuity between the speaker terminals and the crossover PCB through the fuse ?
Firstly, the crossover circuit board I have doesn't have a fuse, I can see where it goes on the circuit diagram Steve posted but its not in the drawing I have for the crossover circuit board (B&W C279A Issue 2 (1973) but its location is right next to the resistor that shows all the casing damage that I have ordered a ceramic wirewound resistor to replace.
All the drivers seem to work independently when I test them, but the green wiring between the bass > tweeter and the tweeter > super tweeter is damaged from 25+ years stuck between the tweeter and the casing and needs replacing. I had to order up some 14 gauge wire to replace it at the weekend as per manufacturers specifications so I am going to replace that before I test the continuity. Though the wiring loom is fine I re-soldered and heat shrinked the connectors on the jones cinch plug on Sunday as the existing insulation had degraded and tested the continuity straight after.
The foam covering went from under the speaker surround and up onto the frame at the rear of the speaker, given the slackness in the bolts when I removed the bass driver from the baffle to clean out the dust it was in there more as an ersatz gasket and to stop any unwanted particles getting in the rear of the speaker from what limited documentation I have found online.
Replacing it with a flat rubber or neoprene gasket and adding some new foam should be an easy enough job, though I suspect the problems will come finding an 8" imperial gasket rather than a metric 200mm I/D gasket, but I'm going to get it working electrically first and check out the sound before order up more parts.
All the drivers seem to work independently when I test them, but the green wiring between the bass > tweeter and the tweeter > super tweeter is damaged from 25+ years stuck between the tweeter and the casing and needs replacing. I had to order up some 14 gauge wire to replace it at the weekend as per manufacturers specifications so I am going to replace that before I test the continuity. Though the wiring loom is fine I re-soldered and heat shrinked the connectors on the jones cinch plug on Sunday as the existing insulation had degraded and tested the continuity straight after.
The foam covering went from under the speaker surround and up onto the frame at the rear of the speaker, given the slackness in the bolts when I removed the bass driver from the baffle to clean out the dust it was in there more as an ersatz gasket and to stop any unwanted particles getting in the rear of the speaker from what limited documentation I have found online.
Replacing it with a flat rubber or neoprene gasket and adding some new foam should be an easy enough job, though I suspect the problems will come finding an 8" imperial gasket rather than a metric 200mm I/D gasket, but I'm going to get it working electrically first and check out the sound before order up more parts.
Probably several crossover versions. You seem to be doing alright here, Stuart.
I got lots of old wire lying about, but you could strip some mains cable off an old broken electrical gadget. Wire is wire IMO.
Might be easy enough to reflow the solder here:
The bass section will be the big coils on the left. The supertweeter will use small components. The tweeter will be the middling components.
You need to hold components down tight when reflowing. But easy enough. A cracked or dry joint is a likely culprit in an old speaker. Modern lead-free mixes well enough with the old leaded stuff. Be quick with capacitors. Not more than 5 seconds heat. Coils and resistors are tough as old boots.
I got lots of old wire lying about, but you could strip some mains cable off an old broken electrical gadget. Wire is wire IMO.
Might be easy enough to reflow the solder here:
The bass section will be the big coils on the left. The supertweeter will use small components. The tweeter will be the middling components.
You need to hold components down tight when reflowing. But easy enough. A cracked or dry joint is a likely culprit in an old speaker. Modern lead-free mixes well enough with the old leaded stuff. Be quick with capacitors. Not more than 5 seconds heat. Coils and resistors are tough as old boots.
Thanks, steep learning curve here though useful.
I don't plan on reflowing the solder unless I really have to, given the age of the board its just asking for trouble, plus I really don't like inhaling lead fumes if I can help it. I have tried to keep the soldering iron temperature as low as I can. There is a small amount of surface corrosion on the circuit tracks in one area but conductive paint will sort that out.
Given the original fault I believe (fingers crossed) that the resistor I pulled was in the circuit as a fuse and its damaged in some way, the rest is just age and a manufacturing error with the wiring being caught between the tweeter and the baffle. As for wire, I had the original spec and it seemed sensible to use it, given that a meter of that wire in green was £1.75.
I was looking for gaskets earlier for the bass driver, could I check 2 details firstly that the 8" driver goes in an 8" hole in the baffle as my digital callipers max out at 150mm, secondly should I be looking at solid rubber or nitrile?
Stuart.
I don't plan on reflowing the solder unless I really have to, given the age of the board its just asking for trouble, plus I really don't like inhaling lead fumes if I can help it. I have tried to keep the soldering iron temperature as low as I can. There is a small amount of surface corrosion on the circuit tracks in one area but conductive paint will sort that out.
Given the original fault I believe (fingers crossed) that the resistor I pulled was in the circuit as a fuse and its damaged in some way, the rest is just age and a manufacturing error with the wiring being caught between the tweeter and the baffle. As for wire, I had the original spec and it seemed sensible to use it, given that a meter of that wire in green was £1.75.
I was looking for gaskets earlier for the bass driver, could I check 2 details firstly that the 8" driver goes in an 8" hole in the baffle as my digital callipers max out at 150mm, secondly should I be looking at solid rubber or nitrile?
Stuart.
I presume 8" is the outer diameter of the bass driver chassis? If so the inner, or baffle hole, diameter will be smaller.
Mounting hole diameters vary among 8" drivers, so remove the bass driver to measure the particular hole diameter in this case - I would think a ruler would do the job adequately enough.
Once you are sure of the outer and inner diameter, you can make your own gaskets using a suitable thickness of cardboard. Wharfedale successfully employed cardboard gaskets in the likes of their 1970s Denton loudspeaker. Cardboard is 'squashy' enough to ensure an airtight seal.
Mounting hole diameters vary among 8" drivers, so remove the bass driver to measure the particular hole diameter in this case - I would think a ruler would do the job adequately enough.
Once you are sure of the outer and inner diameter, you can make your own gaskets using a suitable thickness of cardboard. Wharfedale successfully employed cardboard gaskets in the likes of their 1970s Denton loudspeaker. Cardboard is 'squashy' enough to ensure an airtight seal.
Good and bad news, firstly the last of the bits turned up this morning once I replaced the resistor it worked fine on test, all the tweeters are fine so all I have to do is swap out the damaged wiring and re-assemble the speaker once the foam to go over the bass driver arrives
Now for the bad news, whatever caused the resistor in the speaker to blow also took out something in the amp, left channel is totally dead on both A & B connectors. I have found the service manual online but I'm struggling to find anything in there that would take out the left side output but still keep voltage coming out and the "protection circuit" doing its self test OK, so what I am essentially asking is if anyone is any good with amps or knows of a repair place in West Sussex?
Now for the bad news, whatever caused the resistor in the speaker to blow also took out something in the amp, left channel is totally dead on both A & B connectors. I have found the service manual online but I'm struggling to find anything in there that would take out the left side output but still keep voltage coming out and the "protection circuit" doing its self test OK, so what I am essentially asking is if anyone is any good with amps or knows of a repair place in West Sussex?
So, we must return to consider more carefully what you said in post #3 - as quoted above.
My advice would be to start a new thread regarding the amp problem in the 'Amplifiers/Solid State' section of the forum, where it would attract most attention from the amp repair experts.
As an old amplifier man, I can tell you it is easier to fix a vaguely working piece of engineering than a totally dead one. 🙄
Quite honestly it is easier to buy a new one:
I think it is likely you had a problem with the transistor amplifier output stage:
It never seemed likely to me the problem was the loudspeaker crossover:
I could see nothing there that a 10R resistor fault could explain. My advice is to buy a new or second-hand amplifier. 😎
Steve
Found the problem late last night, fuse was loose in the pre-amp stage on the amp, which must have happened when I was de-fluffing the air vents under the heatsinks. Ignore that service manual its the right model, just for a later version that I think was originally for the Japanese market and was quite probably a EOL line that had a UK OEM power board fitted.
As for the 10R Resistor, the old one was still on my desk and out of curiosity I cut the heat damaged insulation off and it was quite "crispy" inside.
Thanks for your help its been very much appreciated.
Found the problem late last night, fuse was loose in the pre-amp stage on the amp, which must have happened when I was de-fluffing the air vents under the heatsinks. Ignore that service manual its the right model, just for a later version that I think was originally for the Japanese market and was quite probably a EOL line that had a UK OEM power board fitted.
As for the 10R Resistor, the old one was still on my desk and out of curiosity I cut the heat damaged insulation off and it was quite "crispy" inside.
Thanks for your help its been very much appreciated.
Well done Stuart! A triumph of persistence. You are a have a go guy, I can tell. 🙂
Visual inspection.
Why didn't I think of checking the output fuses! 😱
Visual inspection.
Why didn't I think of checking the output fuses! 😱