ooteedee Posted December 18, 2004 Share Posted December 18, 2004 I have a crossover network that uses a 27w/12v automotive dome lamp as a fuse. There are actually two on each network. One for Mid and one for High. What's the purpose of using a lamp instead of a typical fuse? Quote Link to comment Share on other sites More sharing options...
sfogg Posted December 18, 2004 Share Posted December 18, 2004 The lamp acts as a limiter. When it heats up its resistance increases, that acts to burn up (glows) some of the power going to the driver to try to protect it. If you keep turning up the power the bulbs resistance will continue to increase and it will glow brighter. When you turn the volume down the bulb cools and full power to the driver is restored. A fuse is a one shot thing... it will just burn out when it is overloaded and that driver will stop playing all together. Shawn Quote Link to comment Share on other sites More sharing options...
Deang Posted December 18, 2004 Share Posted December 18, 2004 Which reminds me. What the heck is #561 bulb, and where do you get one? Quote Link to comment Share on other sites More sharing options...
WMcD Posted December 19, 2004 Share Posted December 19, 2004 Yeah, I'd seen this from decades ago. I suppose it could be some protection if the lamp is small enough and the issue is that you're alway flirting with the long term thermal limits of the driver. If you're doing this, though, you need a bigger driver and the common sense which God gave a goose, not a protection scheme. The real problem is that the lamp, or more appropriately a fast blow fuse, will not act quickly enough to protect the voice coil. The voice coil and the feed wires are about the same size as the fuse. So the voice coil burns out to protect the fuse from damage. Smile. I'm not saying that a fast blow fuse is a bad idea. Getting into a situation where you're relying on them shows there is a bigger problem. Gil Quote Link to comment Share on other sites More sharing options...
3dzapper Posted December 19, 2004 Share Posted December 19, 2004 ---------------- On 12/18/2004 11:52:41 PM DeanG wrote: Which reminds me. What the heck is #561 bulb, and where do you get one? ---------------- Just go to NAPA or AutoZone. It is an automotive dome light bulb. Rick Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 19, 2004 Share Posted December 19, 2004 In my studio recording class we had a pair of speakers with the light bulb fuse. We were always told that using a lightbulb instead of a normal fuse gives the operator a visual signal that he's overdriving the speaker. I know JBL uses this (or did at one time) in a lot of their PA equipment as well. It was a way of "blowing the fuse" without losing sound which would be a very bad thing to happen live (been there done that). Quote Link to comment Share on other sites More sharing options...
djk Posted December 19, 2004 Share Posted December 19, 2004 The lightbulb solution is faster than a fuse or polyswitch, and less invasive of the sound. If you want the ultimate tweeter protection get the EV STR and do the lightbulb mod. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=47092&item=3769716750&rd=1&ssPageName=WDVW The light bulb mod is described on an addendum sheet and also covers modding the STR for use with the 1823/24 midrange drivers. For out interests though, all that need be done is slap a #561 in parallel with the relay contacts. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted December 19, 2004 Share Posted December 19, 2004 Quote Link to comment Share on other sites More sharing options...
ooteedee Posted December 19, 2004 Author Share Posted December 19, 2004 Cool. Thanks for all the replies. My Dad says it's used as a slow burn fuse. And that I could probably replace it with a 10 watt bulb of similar style. The crossover was from a 200 watt speaker. The amp I have for the barn is 100. So....I should be safe with a 10 watt bulb. Besides, the two bulbs are for the mid and high circuit. Which don't draw as much. Quote Link to comment Share on other sites More sharing options...
WMcD Posted December 19, 2004 Share Posted December 19, 2004 Just keep in mind that a tweeter takes about 5 watts before going into self distruction. Also "wattage" depends on the voltage applied and the resistance of the unit. We could do the math. But it seems to me that an automotive bulb is not going to be enough protection. Gil Quote Link to comment Share on other sites More sharing options...
MacKevin Posted December 19, 2004 Share Posted December 19, 2004 It would seem to me that inserting a Light bulb into the circuit would cause a power loss to the Tweeter which would affect the sound considerably. Worse than that is the fact that the Crossover is a carefully tuned RLC network that would be affected by the introduction of the lightbulb's resistance. I bought LaScala's because PWK put a lot of time and attention into tuning his designs. Any alterations to that would be a shame. Kevin Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 20, 2004 Share Posted December 20, 2004 When the tungsten is cold, it has very low/close to zero resistance. It stays out of the way until needed. Quote Link to comment Share on other sites More sharing options...
Deang Posted January 9, 2005 Share Posted January 9, 2005 The zeners still look like the best solution to me -- think I'll start using them again. Quote Link to comment Share on other sites More sharing options...
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