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#41
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Tannoy Reveal and LM3886 power amp IC
On Wed, 26 Mar 2008 21:59:32 +0000, Eeyore
wrote: Wink wrote: I'm going get a dozen of these Nichicons and sell my BGs on Ebay for a grand. That's far and away the most sensible thing you've said. Graham I was serious Graham, I ordered 12. |
#42
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Tannoy Reveal and LM3886 power amp IC
"Wink" wrote in message
I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...APACITOR_.html whoops, yes All Electronics. |
#43
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Tannoy Reveal and LM3886 power amp IC
"Wink" wrote in message
Ironically, note that the Jeff Rowland amp's power supply caps are *not* Blackgates. That's because BGs are no longer made. :] They are Nichicon LQ-M series parts. I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) I'm going get a dozen of these Nichicons and sell my BGs on Ebay for a grand. Go for it! |
#44
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
On Wed, 26 Mar 2008 22:13:05 -0400, "Arny Krueger"
wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...APACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. I've resolved the voltage on the 63 V BGs torment. I ordered toroids with this sec: 50-43-0-43-50. The 43 V taps will run produce 56 V under load. A compromise value, not excessively low. Should I eject the BGs like a retching dog to Ebay hell, the 100 V winding will allow a return to 63-ish volt operation, maybe with the cool Nichicons. 212 Bucks for 2 custom wound toroids, 800 for the BGs, roughly 500 for Hilligs cards and stuff. Exicon double-current mosfets, 140. So if the amps turn ok I'll have some good monoblocks for under 2 Gs. Much less if I can the BGs and go with Nichs, or the original Chemicons. I think the Behringer Europower amp are much less. I think that's you're using, I assume to drive your Maggies, which I've never heard, by the way. Dave |
#45
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
"Arny Krueger" wrote in message . .. "Eeyore" wrote in message Arny Krueger wrote: "Gareth Magennis" wrote in "Eeyore" wrote Do both power amps run off the same supply rails ? Graham Yes. Makes sense, as an additional power supply would cost $$$$. I've seen it done otherwise with taps on the TX. Yes, that saves you the cost of the second transformer, but it still costs you diodes and a couple of caps. Space is a bit tight on a powered monitor also. Gareth. |
#46
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
Wink wrote: "Arny Krueger" wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...APACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. My advice to you is to get a larger amplifier so you're never close to clipping. I've resolved the voltage on the 63 V BGs torment. I ordered toroids with this sec: 50-43-0-43-50. The 43 V taps will run produce 56 V under load. A compromise value, not excessively low. Err .... if only life were that simple ! Capacitor input PSUs are not like resistive loads. Should I eject the BGs like a retching dog to Ebay hell, the 100 V winding will allow a return to 63-ish volt operation, maybe with the cool Nichicons. Or cool Panasonics or cool Samwhas or cool Rubycons or cool Nippon Chemi Cons ! The damn BRAND is IRRELEVANT ! Graham |
#47
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. Graham |
#48
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
Eeyore wrote:
Wink wrote: "Arny Krueger" wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...APACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. Couldn't this strategy also overwhelm the the preceeding stages (transformer/rectifier/fuse) by creating a huge inrush current upon turnon? My advice to you is to get a larger amplifier so you're never close to clipping. I've resolved the voltage on the 63 V BGs torment. I ordered toroids with this sec: 50-43-0-43-50. The 43 V taps will run produce 56 V under load. A compromise value, not excessively low. Why? With proper voltage filter caps, the original would appear to be adequate. The 63 volt rails were only--marginally--problematic to the 63 volt rated magic caps. Err .... if only life were that simple ! Capacitor input PSUs are not like resistive loads. Should I eject the BGs like a retching dog to Ebay hell, the 100 V winding will allow a return to 63-ish volt operation, maybe with the cool Nichicons. Or cool Panasonics or cool Samwhas or cool Rubycons or cool Nippon Chemi Cons ! The damn BRAND is IRRELEVANT ! Graham |
#49
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
In article , jakdedert wrote:
Eeyore wrote: Wink wrote: "Arny Krueger" wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...F_80_V_ELECTRO LYTIC_SNAP-IN_CAPACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. Couldn't this strategy also overwhelm the the preceeding stages (transformer/rectifier/fuse) by creating a huge inrush current upon turnon? Thats why some amplifiers have a slow start circuit. Also, while monitoring the rails at the circuit, any fluctuations are caused by the wiring and power supply. Any changes with various capicitors can be monitored here. If there is no change, I don't think there is any way the output could change. greg My advice to you is to get a larger amplifier so you're never close to clipping. I've resolved the voltage on the 63 V BGs torment. I ordered toroids with this sec: 50-43-0-43-50. The 43 V taps will run produce 56 V under load. A compromise value, not excessively low. Why? With proper voltage filter caps, the original would appear to be adequate. The 63 volt rails were only--marginally--problematic to the 63 volt rated magic caps. Err .... if only life were that simple ! Capacitor input PSUs are not like resistive loads. Should I eject the BGs like a retching dog to Ebay hell, the 100 V winding will allow a return to 63-ish volt operation, maybe with the cool Nichicons. Or cool Panasonics or cool Samwhas or cool Rubycons or cool Nippon Chemi Cons ! The damn BRAND is IRRELEVANT ! Graham |
#50
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
"Wink" wrote in message
I think the Behringer Europower amp are much less. Lots. The A500 is $200, the EP1500 is $280, and the EP2500 is $350. But I personally own none of the above. A close friend owns 4 EP2500 for his subwoofers. I think that's you're using, I assume to drive your Maggies, which I've never heard, by the way. The Maggies aren't mine, they belong to a (different) close friend. He still uses the Hafler amp with them, AFAIK. |
#51
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
"Eeyore" wrote in
message Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. As we both know, they are QSC clones. Very precise clones, down to an amazing level of detail. They pass stright wire bypass tests, though. |
#52
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
Arny Krueger wrote: "Eeyore" wrote Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. As we both know, they are QSC clones. Very precise clones, down to an amazing level of detail. They pass stright wire bypass tests, though. I'd like to hear that for myself. Some earlier QSCs sounded distinctly less than pure to me. Graham |
#53
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
"Eeyore" wrote in
message Arny Krueger wrote: "Eeyore" wrote Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. As we both know, they are QSC clones. Very precise clones, down to an amazing level of detail. They pass stright wire bypass tests, though. I'd like to hear that for myself. Some earlier QSCs sounded distinctly less than pure to me. Given Graham that you are in the UK, and I am in the Midwest US, you're pretty much on your own! ;-) You could warm up with the USA 850 - generated files from the PCABX web site. |
#54
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. My advice to you is to get a larger amplifier so you're never close to clipping. Not going through that again. I've resolved the voltage on the 63 V BGs torment. I ordered toroids with this sec: 50-43-0-43-50. The 43 V taps will run produce 56 V under load. A compromise value, not excessively low. Err .... if only life were that simple ! Capacitor input PSUs are not like resistive loads. Huh? 43 x 1.414 = 60.8 V No load condition of course. With this particular amp, PSU components, and biased to 350 mils, That 60.8 drops to 56 volts. The correction factor is .921 I approached this multiple ways actually. I empirically comfirmed my calculations by setting the Variac to produce 86 AC no load volts at the xfmr secondary. I then measured that voltage under load -- minimal change, as you would expect, still ~ 86 Vac. This produces +/- 56 volts DC rail voltage under load. (Of course the AC mains voltage is varying slightly the entire time. Insignificant) The Grand Unification coefficient for predicting DC rail voltage under load for a given xfmr secondary output is 112/86 = 1.302 That's with 10,000 ufd BGs. The stock Hafler xfmr's sec output is 97 volts @ 120Vac mains input. With the 27 kufd Chemicons I just pulled, this produces +/- 63 Vdc at 350 mils bias -- yes, idling, not dynamic conditions. 126/97 = 1.298 1.302 1.298 Looks like you're right, it isn't a resistive load, but about as predictable. Yes I know I've included too many significant digits, or digits that are not significant. The idea is to moderately under-rate the caps without going to excessively low voltages. Not terribly critical as Arny et al have delicately expressed. Should I eject the BGs like a retching dog to Ebay hell, the 100 V winding will allow a return to 63-ish volt operation, maybe with the cool Nichicons. Or cool Panasonics or cool Samwhas or cool Rubycons or cool Nippon Chemi Cons ! The damn BRAND is IRRELEVANT ! Yes it is. |
#55
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. Couldn't this strategy also overwhelm the the preceeding stages (transformer/rectifier/fuse) by creating a huge inrush current upon turnon? Well, the caps I pulled to make room for the now infamous 10,000 ufd BGs were 27,000ufd. Never a problem. I've resolved the voltage on the 63 V BGs torment. I ordered toroids with this sec: 50-43-0-43-50. The 43 V taps will run produce 56 V under load. A compromise value, not excessively low. Why? With proper voltage filter caps, the original would appear to be adequate. The 63 volt rails were only--marginally--problematic to the 63 volt rated magic caps. I was getting new xfmrs anyway. So I selected voltages that allow a return to the original config with proper voltage caps, like Arny's Nichicons. (Brand matters Graham), and avoid the marginal problematics should I decide to stick with the BGs. Why not? I had the option of getting any voltages I want at a price comparable to Parts Express pricing on Avel Lindbergs. Dave ----------------------- The damn BRAND is IRRELEVANT ! Yes it is Graham, so is Can colour. Are you in Liverpool? Graham |
#56
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
Wink wrote: On Thu, 27 Mar 2008 09:54:31 -0400, "Arny Krueger" wrote: "Eeyore" wrote Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. As we both know, they are QSC clones. Very precise clones, down to an amazing level of detail. They pass stright wire bypass tests, though. I heard they're very good. I am curious - amazing detail compared to what? He means that Behringer copied the QSC design very accurately. The electronics is as close to a perfect clone as you'll get. Even the general mechanical design is very similar. http://www.live-audio.com/messages/archive7/91505.html Graham |
#57
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
On Thu, 27 Mar 2008 11:18:35 +0000, Eeyore
wrote: Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. Graham They sound different from more refined amps? |
#58
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
On Thu, 27 Mar 2008 09:54:31 -0400, "Arny Krueger"
wrote: "Eeyore" wrote in message Wink wrote: I think the Behringer Europower amp are much less. They're not exactly a refined design by a LONG way. Fine for rock and roll sound reinforcement though. As we both know, they are QSC clones. Very precise clones, down to an amazing level of detail. They pass stright wire bypass tests, though. I heard they're very good. I am curious - amazing detail compared to what? |
#59
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
GregS wrote:
In article , jakdedert wrote: Eeyore wrote: Wink wrote: "Arny Krueger" wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...F_80_V_ELECTRO LYTIC_SNAP-IN_CAPACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. Couldn't this strategy also overwhelm the the preceeding stages (transformer/rectifier/fuse) by creating a huge inrush current upon turnon? Thats why some amplifiers have a slow start circuit. Also, while monitoring the rails at the circuit, any fluctuations are caused by the wiring and power supply. Any changes with various capicitors can be monitored here. If there is no change, I don't think there is any way the output could change. Hopefully he's reading this. It's a 'good' amp that the OP has frankensteined into 'something' else. Based on what he's said here, it may or may not have startup current limiting. I don't believe the original Hafler on which it is based did. It wasn't originally intended to have 20,000uf hanging off the bridge.... jak greg |
#60
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Tannoy Reveal and LM3886 power amp IC
On Thu, 27 Mar 2008 21:50:03 -0500, jakdedert
wrote: GregS wrote: In article , jakdedert wrote: Eeyore wrote: Wink wrote: "Arny Krueger" wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...F_80_V_ELECTRO LYTIC_SNAP-IN_CAPACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. Couldn't this strategy also overwhelm the the preceeding stages (transformer/rectifier/fuse) by creating a huge inrush current upon turnon? Thats why some amplifiers have a slow start circuit. Also, while monitoring the rails at the circuit, any fluctuations are caused by the wiring and power supply. Any changes with various capicitors can be monitored here. If there is no change, I don't think there is any way the output could change. Hopefully he's reading this. It's a 'good' amp that the OP has frankensteined into 'something' else. Based on what he's said here, it may or may not have startup current limiting. I don't believe the original Hafler on which it is based did. It wasn't originally intended to have 20,000uf hanging off the bridge.... Nope, no current limiting at all. I'm using Ixys FRED 600V, 12 amp diodes in the bridge. I had 27,000 hanging off that bridge for several years. No deaths. However -- this is not a desirable situation. I'm now using only 10,000uf Black Gates, but am going to install a soft start circuit of some type. I've had Haflers for 25+ years. They are good amps, but can be improved upon. A stock Parasound HCA1000a creams a stock 200 or 220 Dave jak greg |
#61
Posted to rec.audio.tech
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Tannoy Reveal and LM3886 power amp IC
"Wink" wrote in message
... On Thu, 27 Mar 2008 21:50:03 -0500, jakdedert wrote: GregS wrote: In article , jakdedert wrote: Eeyore wrote: Wink wrote: "Arny Krueger" wrote: "Wink" wrote in message I see some 3,300 uF 80 volt Nichicon LQ-M caps for sale on the Active Electronics web site for less than $1.60 each... ;-) Did you mean All Electronics? http://www.allelectronics.com/cgi-bi...F_80_V_ELECTRO LYTIC_SNAP-IN_CAPACITOR_.html whoops, yes All Electronics. It turns out they're a very good size. I probably can pack 20-ish kufd a side in there, but would start at 3300 and experiment. I ordered a dozen. Well ..... you may not like how 20,000 uF sound ! It will change the clipping behaviour agin. Couldn't this strategy also overwhelm the the preceeding stages (transformer/rectifier/fuse) by creating a huge inrush current upon turnon? Thats why some amplifiers have a slow start circuit. Also, while monitoring the rails at the circuit, any fluctuations are caused by the wiring and power supply. Any changes with various capicitors can be monitored here. If there is no change, I don't think there is any way the output could change. Hopefully he's reading this. It's a 'good' amp that the OP has frankensteined into 'something' else. Based on what he's said here, it may or may not have startup current limiting. I don't believe the original Hafler on which it is based did. It wasn't originally intended to have 20,000uf hanging off the bridge.... Nope, no current limiting at all. I'm using Ixys FRED 600V, 12 amp diodes in the bridge. I had 27,000 hanging off that bridge for several years. No deaths. However -- this is not a desirable situation. I'm now using only 10,000uf Black Gates, but am going to install a soft start circuit of some type. I've had Haflers for 25+ years. They are good amps, but can be improved upon. A stock Parasound HCA1000a creams a stock 200 or 220 Dave jak greg How does it do that? Does it have flatter frequency response, lower distortion, lower noise that aren't already below the threshold of hearing? Unless you can quantify the differences, statements like "creams a stock 200 or 220" are not only meaningless, but come across as uninformed and audiophoolery. S. -- http://audiopages.googlepages.com |
#62
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Tannoy Reveal and LM3886 power amp IC
"Serge Auckland" wrote in
message "Wink" wrote in message ... I've had Haflers for 25+ years. They are good amps, but can be improved upon. A stock Parasound HCA1000a creams a stock 200 or 220 Dave How does it do that? Perception and sighted listening tests. I've heard them both. They are both very good. Does it have flatter frequency response, lower distortion, lower noise that aren't already below the threshold of hearing? Nope. Unless you can quantify the differences, statements like "creams a stock 200 or 220" are not only meaningless, but come across as uninformed and audiophoolery. If Wink ever did a proper listening test and believed the results, he'd have a lot to think about. But he already laid out the logic-proof box he's worked himself into, right near the start of the thread. He doesn't believe in AB tests. |
#63
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Tannoy Reveal and LM3886 power amp IC
On 2008-03-26, Don Pearce wrote:
Although they are small, tweeters need just as much power as bass drivers on average music material. But they are going to get a great deal more upset than a bass unit when asked to mop up a lot of DC. Why ? Because they cannot dissipate heat as effectively ? Or because they somehow have more power to dissipate ? -- André Majorel URL:http://www.teaser.fr/~amajorel/ (Counterfeit: ) "I drink, I smoke, I gamble, I chase girls--but postal chess is one vice I don't have." -- Mikhail Tal |
#64
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Tannoy Reveal and LM3886 power amp IC
"Andre Majorel" wrote in message
On 2008-03-26, Don Pearce wrote: Although they are small, tweeters need just as much power as bass drivers on average music material. But they are going to get a great deal more upset than a bass unit when asked to mop up a lot of DC. Why ? Because they cannot dissipate heat as effectively ? Yes. Tweeter voice coils are usually designed to have as little weight as possible. Or because they somehow have more power to dissipate ? No. |
#65
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Tannoy Reveal and LM3886 power amp IC
On Apr 1, 2:36 pm, "Arny Krueger" wrote:
"Andre Majorel" wrote in message On 2008-03-26, Don Pearce wrote: Although they are small, tweeters need just as much power as bass drivers on average music material. But they are going to get a great deal more upset than a bass unit when asked to mop up a lot of DC. Why ? Because they cannot dissipate heat as effectively ? Yes. Tweeter voice coils are usually designed to have as little weight as possible. The answer, while technically correcvt, skips a lot of important detail. The important consideration here is the weight of the voice coil itself which, in modern direct radiator tweeters, often comprises a substantial portion of the total moving mass, so minimizing its weight is important in being able to get sufficient efficiency out of such a small radiating area. The radiating area has to be small in order to achieve a reasonable dispersion at the short wavelengths required, thus the diameter of the tweeter and hence the voice coil has to be appropriately small. Further, at the frequencies over which the tweeter works, the mechanical excursion is small and thus the voice coil is also short. All of that results in several things: 1. The voice coil, being small in diameter, short in length and light in weight, must be wound fairly small gauge wire to achieve the necessary electrical and electro-mechanical properties needed. It's not at all uncommon for the voice coil to use 36 gauge wire (a two-layer 1" coil with a length of .17" wound with 36 gauge wire will result in a voice coil with a DC resistance of just about 7 ohms and a Bl product in the realm of about 5 with typical magnet structures and weight about 0.6 grams, just about what you want for a mid-efficiency tweeter). 2. The small, low mass structures end up with low heat capaciites compared to woofer assemblies, the result being large temperature rises for the same disiipated power compared to woofers. 3. The thermal resistance of these assemblies is usually substantially higher than larger drivers, further exacerbating the temperature rise for a given input power (which, actually, is the definition of thermal resistance). 4. With no other heat transportt mechanisms, the maximum available current carrying capacity of the smaller gauge wire used in tweeter voice coils is substantially less than tthe wire found in woofers. By some standards, for example, the maximum current capacity for 36 guage wire is on the order of a few teths of an amp, while that of a 27 gauge wire of the type found in a typical 6-8" woofer is 8 times as much by the same criteria. |
#66
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Tannoy Reveal and LM3886 power amp IC
wrote in message ... On Apr 1, 2:36 pm, "Arny Krueger" wrote: "Andre Majorel" wrote in message On 2008-03-26, Don Pearce wrote: Although they are small, tweeters need just as much power as bass drivers on average music material. But they are going to get a great deal more upset than a bass unit when asked to mop up a lot of DC. Why ? Because they cannot dissipate heat as effectively ? Yes. Tweeter voice coils are usually designed to have as little weight as possible. The answer, while technically correcvt, skips a lot of important detail. The important consideration here is the weight of the voice coil itself which, in modern direct radiator tweeters, often comprises a substantial portion of the total moving mass, so minimizing its weight is important in being able to get sufficient efficiency out of such a small radiating area. The radiating area has to be small in order to achieve a reasonable dispersion at the short wavelengths required, thus the diameter of the tweeter and hence the voice coil has to be appropriately small. Further, at the frequencies over which the tweeter works, the mechanical excursion is small and thus the voice coil is also short. All of that results in several things: 1. The voice coil, being small in diameter, short in length and light in weight, must be wound fairly small gauge wire to achieve the necessary electrical and electro-mechanical properties needed. It's not at all uncommon for the voice coil to use 36 gauge wire (a two-layer 1" coil with a length of .17" wound with 36 gauge wire will result in a voice coil with a DC resistance of just about 7 ohms and a Bl product in the realm of about 5 with typical magnet structures and weight about 0.6 grams, just about what you want for a mid-efficiency tweeter). 2. The small, low mass structures end up with low heat capaciites compared to woofer assemblies, the result being large temperature rises for the same disiipated power compared to woofers. 3. The thermal resistance of these assemblies is usually substantially higher than larger drivers, further exacerbating the temperature rise for a given input power (which, actually, is the definition of thermal resistance). 4. With no other heat transportt mechanisms, the maximum available current carrying capacity of the smaller gauge wire used in tweeter voice coils is substantially less than tthe wire found in woofers. By some standards, for example, the maximum current capacity for 36 guage wire is on the order of a few teths of an amp, while that of a 27 gauge wire of the type found in a typical 6-8" woofer is 8 times as much by the same criteria. All perfectly correct, however something you didn't mention is that a tweeter is never "asked to mop up a lot of DC" unless something is seriously broken, and I don't just mean the amplifier. (but that has to be broken too of course for DC to appear at the output) With any passive crossover, capacitors will block DC from the tweeter, and in any decent active/bi-amped system, some form of DC prevention to the tweeter is considered a good idea also. MrT. |
#67
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Tannoy Reveal and LM3886 power amp IC
On Apr 2, 12:41 am, "Mr.T" MrT@home wrote:
All perfectly correct, however something you didn't mention is that a tweeter is never "asked to mop up a lot of DC" unless something is seriously broken, and I don't just mean the amplifier. (but that has to be broken too of course for DC to appear at the output) With any passive crossover, capacitors will block DC from the tweeter, and in any decent active/bi-amped system, some form of DC prevention to the tweeter is considered a good idea also. NEVER say never! DC current through tweeters is certainly a pathological case, but that does not eliminate it from the realm of possibilities. One of the consequences is that the same DC current can often be more destructive of a tweeter than the same AC RMS current. The reason being is thatv the mechanical position of the voice coil gets prefferentially biased on one direction or another, rather than averaging around the 0 mechnical point. The result is that the thermal resistance can be increased either because it no longer sees the metal in the gap as a sink, or, in the case of magnetic fluid cooling, it actuall can move out of the fluid. There is also the issue of mechanical strain. I once was asked by a client, a US distribution arm of a French driver company, to evaluat about 1500 tweeters that were returned by a dealer as "defective," and the dealer was refusing to pay the now 120-day overdue bill. Every single one of them showed substantial thermal damage inthe form of melting in the plastic dome material where the voice coil former (aluminum) was joined to the dome. There was also some of the ferrofluid splattered on the back of the dome and around the front surface of the magnet structure. All 1500 had the same failure. When I tested unused samples of the same model, I was able to drive them to more than 4 times their rated power with in-band signals of every kind with no failures. However, if I simply hooked the tweeter to a car battery and left them there for 1 minute, I was able to EXACTLY duplicate the same appearance. The voice coil got biased enough that the majority of it was outside the fluid, withn only the rearmost portion of the former in the fluid. At that point, the voice coil was able to get hot enough to glow visibly under room light, melting the plastic on the dome and boiling the residue fluid off the voice coil spattering it around ther area. Yes, something was SERIOUSLY broken. The dealer, a car installer in the southwest, didn't have the money to pay for the order, so decided to methodically connect every one of them to a car battery, burn them up, and return them unpaid as "defective." |
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Tannoy Reveal and LM3886 power amp IC
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I once was asked by a client, a US distribution arm of a French driver company, to evaluat about 1500 tweeters that were returned by a dealer as "defective," and the dealer was refusing to pay the now 120-day overdue bill. Every single one of them showed substantial thermal damage inthe form of melting in the plastic dome material where the voice coil former (aluminum) was joined to the dome. There was also some of the ferrofluid splattered on the back of the dome and around the front surface of the magnet structure. All 1500 had the same failure. When I tested unused samples of the same model, I was able to drive them to more than 4 times their rated power with in-band signals of every kind with no failures. Hmm, sounds like some Audax tweeters I've used in the past. However, if I simply hooked the tweeter to a car battery and left them there for 1 minute, I was able to EXACTLY duplicate the same appearance. The voice coil got biased enough that the majority of it was outside the fluid, withn only the rearmost portion of the former in the fluid. At that point, the voice coil was able to get hot enough to glow visibly under room light, melting the plastic on the dome and boiling the residue fluid off the voice coil spattering it around ther area. Yes, something was SERIOUSLY broken. The dealer, a car installer in the southwest, didn't have the money to pay for the order, so decided to methodically connect every one of them to a car battery, burn them up, and return them unpaid as "defective." This sort of thing happens not infrequently, and sometimes fraud is not the reason. Most hard drive vendors demand that devices returned in warranty will have failed a diagnostic test using a program they provide. It's no secret that hard drives can easily fail in actual use, but pass the diagnostic, even when run in the failing computer. There are procedures for ensuring that the hard drive will always fail the diagnostic, none of which need be discussed right now. |
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