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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#2
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![]() "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. |
#3
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"Gareth Magennis" wrote in message
... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. |
#4
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![]() "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. |
#5
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Gareth Magennis wrote in message
... "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. So it may be an effect of work hardening , relative increase in the effect of imperfections/micro fractures or some other metallurgical effect. Mackie speaker voice coil failures due to this flattening/ribboning process to make the tails to the outside world. Previous failure at the juncture of round to flat (0.07mm round to about 0.02 x 0.2mm) so at the peak stress point. This one along the length of the ribbon section, but the whole 50mm or so run was brittleised and disintegrated on touch, not the slightest sign of overheating on the remaining 25 turns of round wire. broken end marked B on this pic http://home.graffiti.net/diverse:gra...ckie_horn1.jpg http://home.graffiti.net/diverse:gra...ckie_horn2.jpg Cannot expore the metallurgy as that curve of "wire" as totally disintegrated to dust. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#6
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"Gareth Magennis" wrote in message
... "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. The shape of the cross section can change to virtually any dimension so long as the length remains the same. IOW, if you squeeze a bar of 10mmx10mm down to 2mmx50mm, its cross sectional area stayed constant (only the shape of the area changed). Its length will remain the same, since the volume didn't change; hence, its resistance will remain the same. So long as material is not added or removed, the volume will remain the same. The formula says that the ratio of length to cross-sectional area must remain the same in order for resistance to remain unchanged. If cross sectional area is changed, the length must change to maintain the ratio. The volume must remain constant. -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. |
#7
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On Dec 12, 11:55*am, "DaveM" wrote:
"Gareth Magennis" wrote in message ... "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. *If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged *The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. The shape of the cross section can change to virtually any dimension so long as the length remains the same. *IOW, if you squeeze a bar of 10mmx10mm down to 2mmx50mm, its cross sectional area stayed constant (only the shape of the area changed). *Its length will remain the same, since the volume didn't change; hence, its resistance will remain the same. So long as material is not added or removed, the volume will remain the same. The formula says that the ratio of length to cross-sectional area must remain the same in order for resistance to remain unchanged. *If cross sectional area is changed, the length must change to maintain the ratio. *The volume must remain constant. -- Dave M MasonDG44 at comcast dot net *(Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes.- Hide quoted text - - Show quoted text - What I believe Norm is questioning/proposing is that the wire may have been made more "dense" by being compressed without lengthening, and that would probably decrease its resistance. Bob Hofmann |
#8
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On Fri, 12 Dec 2008 14:50:40 -0800 (PST), "hr(bob) "
wrote: What I believe Norm is questioning/proposing is that the wire may have been made more "dense" by being compressed without lengthening, and that would probably decrease its resistance. IMHO, if the wire is squashed it will defin8itely get work hardened and this will mean an increase in resistivity -- Thanks for your time Archer |
#9
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Ardent wrote in message
... On Fri, 12 Dec 2008 14:50:40 -0800 (PST), "hr(bob) " wrote: What I believe Norm is questioning/proposing is that the wire may have been made more "dense" by being compressed without lengthening, and that would probably decrease its resistance. IMHO, if the wire is squashed it will defin8itely get work hardened and this will mean an increase in resistivity -- Thanks for your time Archer I think a little experiment is in order. A length of fine wire, measure R and diameter , then squash between shim spaced flats and re-measure R and dimensions. Whether work-hardening (xtal structure change ?) or micro-fractures or whatever does not really matter , just some data on resistance change. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#10
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Needs repeating with a proper milli-ohm set up rather than DVM 0.1 ohm
resolution or preferably actively with some higher current through it. Probably really only becomes manifest close to the current carying limit of the original round wire, replicating the problem in speaker voice coil production and use. Tried about 1m of 0.09mm (including varnish) wire around a 15mm a side flat and squashed between 2 flats in a protected vice and made no difference to 4.0 ohm, despite 32 theoretical, not obvious, flats. Repeated with just a single 15mm length of that 1m long wire, reducing 0.09 mm to about 0.03 mm , and repeated further along, so 2 squashed bits of 15mm .. May have increased to about 4.05 ohm overall but not as obvious a change as I was expecting. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#11
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Again 1m length , ps set for constant voltage and unlimited current.
Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no change ie less than 0.01 amp change, if any. Set to give 1.7 amp and varnish burnt off. So no further forward. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#12
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"N_Cook" wrote in message
... Again 1m length , ps set for constant voltage and unlimited current. Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no change ie less than 0.01 amp change, if any. Set to give 1.7 amp and varnish burnt off. So no further forward. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ All your testing seems to have verified that the formula for resistance vs. cross-sectional area does work. No matter how many 'flats' you make on the wire, you haven't changed its resistance. The small amount that it changed can easily be contributed to variations in meter connections and/or minute changes in length due to the squeezing of the wire to make the 'flats'. Barring any crystalline structure changes in the metal itself, so long as the cross-sectional area and length doesn't change, the resistance doesn't change. I suggest that the speaker winding that you're trying to diagnose failed because of metal fatigue, possibly due to loose mounting, broken adhesive or just an imperfection in the coil at manufacture. Time to move on? -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. |
#13
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DaveM wrote in message
... "N_Cook" wrote in message ... Again 1m length , ps set for constant voltage and unlimited current. Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no change ie less than 0.01 amp change, if any. Set to give 1.7 amp and varnish burnt off. So no further forward. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ All your testing seems to have verified that the formula for resistance vs. cross-sectional area does work. No matter how many 'flats' you make on the wire, you haven't changed its resistance. The small amount that it changed can easily be contributed to variations in meter connections and/or minute changes in length due to the squeezing of the wire to make the 'flats'. Barring any crystalline structure changes in the metal itself, so long as the cross-sectional area and length doesn't change, the resistance doesn't change. I suggest that the speaker winding that you're trying to diagnose failed because of metal fatigue, possibly due to loose mounting, broken adhesive or just an imperfection in the coil at manufacture. Time to move on? -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. If it was just a one off , then fair enough. But 2 separate Mackie amps with the same problem in the same 2 squashed percent of the wire of the speaker voice-coils ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#14
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![]() N_Cook wrote: DaveM wrote in message ... "N_Cook" wrote in message ... Again 1m length , ps set for constant voltage and unlimited current. Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no change ie less than 0.01 amp change, if any. Set to give 1.7 amp and varnish burnt off. So no further forward. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ All your testing seems to have verified that the formula for resistance vs. cross-sectional area does work. No matter how many 'flats' you make on the wire, you haven't changed its resistance. The small amount that it changed can easily be contributed to variations in meter connections and/or minute changes in length due to the squeezing of the wire to make the 'flats'. Barring any crystalline structure changes in the metal itself, so long as the cross-sectional area and length doesn't change, the resistance doesn't change. I suggest that the speaker winding that you're trying to diagnose failed because of metal fatigue, possibly due to loose mounting, broken adhesive or just an imperfection in the coil at manufacture. Time to move on? -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. If it was just a one off , then fair enough. But 2 separate Mackie amps with the same problem in the same 2 squashed percent of the wire of the speaker voice-coils ? Poor quality control, or a defective manufacturing process. -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy. |
#15
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Michael A. Terrell wrote in message
m... N_Cook wrote: DaveM wrote in message ... "N_Cook" wrote in message ... Again 1m length , ps set for constant voltage and unlimited current. Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no change ie less than 0.01 amp change, if any. Set to give 1.7 amp and varnish burnt off. So no further forward. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ All your testing seems to have verified that the formula for resistance vs. cross-sectional area does work. No matter how many 'flats' you make on the wire, you haven't changed its resistance. The small amount that it changed can easily be contributed to variations in meter connections and/or minute changes in length due to the squeezing of the wire to make the 'flats'. Barring any crystalline structure changes in the metal itself, so long as the cross-sectional area and length doesn't change, the resistance doesn't change. I suggest that the speaker winding that you're trying to diagnose failed because of metal fatigue, possibly due to loose mounting, broken adhesive or just an imperfection in the coil at manufacture. Time to move on? -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. If it was just a one off , then fair enough. But 2 separate Mackie amps with the same problem in the same 2 squashed percent of the wire of the speaker voice-coils ? Poor quality control, or a defective manufacturing process. -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy. Its more than that. In both Mackie cases the main active coils showed absolutely no overheating let alone burning. In all other odd o/c speakers I've poked my nose in, have had large sections of charring or completely burnt and broken coil formers. Not failure in the tail sections because they are usually different / larger conductors soldered or welded to the main coil. These Mackie tails are acting as fuses, protecting the voice coil, which is ridiculous. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#16
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![]() N_Cook wrote: Michael A. Terrell wrote: Poor quality control, or a defective manufacturing process. Its more than that. In both Mackie cases the main active coils showed absolutely no overheating let alone burning. In all other odd o/c speakers I've poked my nose in, have had large sections of charring or completely burnt and broken coil formers. Not failure in the tail sections because they are usually different / larger conductors soldered or welded to the main coil. These Mackie tails are acting as fuses, protecting the voice coil, which is ridiculous. No, it isn't. Who would manufacture speakers that way for Mackie? If they did, all of them would fail. They would have to pay extra, and get no warranty. It sounds like the tinsel wire was the wrong type for the power level and was likely got through due to poor QC. Poor quality tinsel wire also suffers from work hardening, and broken strands. When enough break, the rest burn. Also, if they are a few percent too short, they get more mechanical abuse, which destroys them. Since you didn't see them when they were brand new, you have absolutely no idea what really happened. I have worked in failure analysis in electronics manufacturing, and I can tell you that production people can be some of the biggest idiots in the world. Monday mornings they have hangovers, and Fridays they don't give a damn what they do, as long as they can leave on time to drink their paychecks. -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy. |
#17
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Michael A. Terrell wrote in message
m... N_Cook wrote: Michael A. Terrell wrote: Poor quality control, or a defective manufacturing process. Its more than that. In both Mackie cases the main active coils showed absolutely no overheating let alone burning. In all other odd o/c speakers I've poked my nose in, have had large sections of charring or completely burnt and broken coil formers. Not failure in the tail sections because they are usually different / larger conductors soldered or welded to the main coil. These Mackie tails are acting as fuses, protecting the voice coil, which is ridiculous. No, it isn't. Who would manufacture speakers that way for Mackie? If they did, all of them would fail. They would have to pay extra, and get no warranty. It sounds like the tinsel wire was the wrong type for the power level and was likely got through due to poor QC. Poor quality tinsel wire also suffers from work hardening, and broken strands. When enough break, the rest burn. Also, if they are a few percent too short, they get more mechanical abuse, which destroys them. Since you didn't see them when they were brand new, you have absolutely no idea what really happened. I have worked in failure analysis in electronics manufacturing, and I can tell you that production people can be some of the biggest idiots in the world. Monday mornings they have hangovers, and Fridays they don't give a damn what they do, as long as they can leave on time to drink their paychecks. -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy. The problem is not at the tinsel wire, ie the flexible bridge. But before that, a flattening of the voice coil wire into ribbon. Production seems to be a precise length of say 2.5m with the ends squashed giving some precise run of round voice coil wire. One end has the ribbon fixed to the tinsel in the ideal spot but the other end arrives at maybe half a turn from ideal and has to make a half turn to join the tinsel for the other termination. Tinsel ribbon is presumably higher current carying than the crresponding voice coil wire, so no problems there. This Mackie problem is something to do with a run of same gauge but squashed wire. Remember the whole half-turn of ribbon disintegrated so not due to a nick or rubbing on metalwork. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#18
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Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#19
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N_Cook wrote:
Perhaps it is chemistry . Bear in mind that the wire is silver and not copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are copper coated btw. Ron(UK) |
#20
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Ron Johnson wrote in message
... N_Cook wrote: Perhaps it is chemistry . Bear in mind that the wire is silver and not copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are copper coated btw. Ron(UK) The voice coil remains unaffected, do you know of a simple test for silver v aluminium ? I would say it looked brighter, more silvery indeed, than aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al wire or silver wire for that matter. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#21
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N_Cook wrote:
Ron Johnson wrote in message ... N_Cook wrote: Perhaps it is chemistry . Bear in mind that the wire is silver and not copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are copper coated btw. Ron(UK) The voice coil remains unaffected, do you know of a simple test for silver v aluminium ? I would say it looked brighter, more silvery indeed, than aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al wire or silver wire for that matter. Are you saying that the part of the coil which failed is a separate wire from the actual voice coil or in some way 'free floating'? In most speakers - of the single rear suspension type, the v/c is wound on the former with the ends coming up the cone on the inside then soldered to the pigtails where they pass through the cone. The tails of the v/c and soldered joints are glued to the cone inside and the pigtails glued on the outside. All this is usually covered on the inside by the dust dome. There should be little fatigue of the v/c wire anywhere as it should be secured to the v/c former or cone. The pigtails and often silvered and do fail either through gross overexcursion or fatigue leading to overheating. I`ve seen pigtails melted where the voice coil is intact. You can sometimes rescue a speaker from this condition with some new pigtails and a dust dome. At one time you could buy pigtail wire from Goodmans, you probably still can from Wembley Loudspeakers if you ask nicely. A speaker which has been seriously overdriven often shows no voice coil damage other than an obvious open circuit in the 'straight' part of the v/c winding. Chances are, your customer was pushing the amps well into clipping and simply overcooked the voicecoils which melted at the weakest point. Wembley Loudspeakers will repair the drivers at a reasonable cost no doubt. Ron |
#22
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Ron Johnson wrote in message
... N_Cook wrote: Ron Johnson wrote in message ... N_Cook wrote: Perhaps it is chemistry . Bear in mind that the wire is silver and not copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are copper coated btw. Ron(UK) The voice coil remains unaffected, do you know of a simple test for silver v aluminium ? I would say it looked brighter, more silvery indeed, than aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al wire or silver wire for that matter. Are you saying that the part of the coil which failed is a separate wire from the actual voice coil or in some way 'free floating'? In most speakers - of the single rear suspension type, the v/c is wound on the former with the ends coming up the cone on the inside then soldered to the pigtails where they pass through the cone. The tails of the v/c and soldered joints are glued to the cone inside and the pigtails glued on the outside. All this is usually covered on the inside by the dust dome. There should be little fatigue of the v/c wire anywhere as it should be secured to the v/c former or cone. The pigtails and often silvered and do fail either through gross overexcursion or fatigue leading to overheating. I`ve seen pigtails melted where the voice coil is intact. You can sometimes rescue a speaker from this condition with some new pigtails and a dust dome. At one time you could buy pigtail wire from Goodmans, you probably still can from Wembley Loudspeakers if you ask nicely. A speaker which has been seriously overdriven often shows no voice coil damage other than an obvious open circuit in the 'straight' part of the v/c winding. Chances are, your customer was pushing the amps well into clipping and simply overcooked the voicecoils which melted at the weakest point. Wembley Loudspeakers will repair the drivers at a reasonable cost no doubt. Ron This is a high power horn so tinsel ribbon instead of pigtails. Instead of the voice coil of round wire going from one tinsel to the other there are short runs of flattened wire. Unnecessary here , assuming it is to save overlap, so fouling the gap in the magnet, because the magnet is milled out on both sites of the lead-in and lead out tinsels. In pics of earlier post. If the wire had not been flattened it would not have failed, at least as how it was being used, is what I am suggesting. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#23
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![]() N_Cook wrote: Perhaps it is chemistry . Bear in mind that the wire is silver and not copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. Why would they use silver? It is very soft, and malleable. More than likely it is aluminum, or bright tin plated copper. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. If the piece cracked, it could have arced and heated. That can spread and damage the surface. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. -- http://improve-usenet.org/index.html aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy. |
#24
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Posted to sci.electronics.repair
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N_Cook wrote:
Ron Johnson wrote in message ... N_Cook wrote: Ron Johnson wrote in message ... N_Cook wrote: Perhaps it is chemistry . Bear in mind that the wire is silver and not copper and the surface area of a squashed wire is more than when it was round and any corrosion on that surface will have proportionally more effect on the thin flats than the bulky round. The voice coil wire looked like copper because it was under a coppery brown lacquer. But, before it disintegrated, the ribbon section was darker brown than the round section. Now if air could get under the lacquer and tarnish the silver to black copper sulphide, or whatever that blackening is, then that would explain it. Unfortunately none of that section remains as it literally turned to dust after photographing it, you could not pick it up even with fingers, it was little more than a wraithe. Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are copper coated btw. Ron(UK) The voice coil remains unaffected, do you know of a simple test for silver v aluminium ? I would say it looked brighter, more silvery indeed, than aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al wire or silver wire for that matter. Are you saying that the part of the coil which failed is a separate wire from the actual voice coil or in some way 'free floating'? In most speakers - of the single rear suspension type, the v/c is wound on the former with the ends coming up the cone on the inside then soldered to the pigtails where they pass through the cone. The tails of the v/c and soldered joints are glued to the cone inside and the pigtails glued on the outside. All this is usually covered on the inside by the dust dome. There should be little fatigue of the v/c wire anywhere as it should be secured to the v/c former or cone. The pigtails and often silvered and do fail either through gross overexcursion or fatigue leading to overheating. I`ve seen pigtails melted where the voice coil is intact. You can sometimes rescue a speaker from this condition with some new pigtails and a dust dome. At one time you could buy pigtail wire from Goodmans, you probably still can from Wembley Loudspeakers if you ask nicely. A speaker which has been seriously overdriven often shows no voice coil damage other than an obvious open circuit in the 'straight' part of the v/c winding. Chances are, your customer was pushing the amps well into clipping and simply overcooked the voicecoils which melted at the weakest point. Wembley Loudspeakers will repair the drivers at a reasonable cost no doubt. Ron This is a high power horn so tinsel ribbon instead of pigtails. Instead of the voice coil of round wire going from one tinsel to the other there are short runs of flattened wire. Unnecessary here , assuming it is to save overlap, so fouling the gap in the magnet, because the magnet is milled out on both sites of the lead-in and lead out tinsels. In pics of earlier post. If the wire had not been flattened it would not have failed, at least as how it was being used, is what I am suggesting. It`s more likely to fail on the straight, horn drivers usually do, either because it`s that part of the winding isnt in the magnetic gap or there`s nothing close by to help sink the heat away - Eitherway it almost certainly failed due to being overdriven, maybe a burst of loud feedback or the internal amp being driven into clipping. Are you sure that the v/c is round wire with only the leadouts being flattened? Most half decent speakers these days are wound with flat wire anyway. Of course, being Mackie, anything could happen! Ron |
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