KanedaK Posted March 12, 2011 Share Posted March 12, 2011 I've finally bought a second-hand set of ALK universal networks to replace the old AAs in my LS. They're on their way, and I'm very excited to hook them up! I've been wondering if the fuse in those networks would protect my beloved speakers in the event of a sudden DC burst at the amplifier output? Both my preamp and power amp are direct coupled designs, and tho the sound is great I'm always a little bit worried. The preamp is a DIY kaneda, and the power amp is technics SE-A5, wich supposedly has sofisticated protection in case of DC output, but it's 30years old and I don't wanna check if that protection still works... now I didn't buy the ALK networks for that particular reason, but it would be a welcome side benefit and would bring me a certain peace of mind! regards, François Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 12, 2011 Share Posted March 12, 2011 You should send Al of ALKEng an email with your question. He designed the crossover. The only insight I can offer is to the complexity of your question. It does not take much DC to damage a speaker. The lower the input frequency to the speaker , the lower the power handling is. A difficult concept for many. To expect that a fuse designed to protect speakers for program music will protect speakers for DC is an obvious incorrect assumption, which you understand since you asked the question. You're going to get lot of incorrect response by folks who may not really understand, that it only takes a few milliamps at DC to burn out the average speaker. Of course, relying on a fuse to protect from DC would render the speaker useless since the needed rating of the fuse to protect from DC will blow the fuse under normally operating conditions. fuses can't be tuned to a frequency. It would take a very large capacitor to block DC (about 40,000 uf). A 4000uf cap will roll off at 10hz, and offer some protection. A DC protection circuit, would be better. Quote Link to comment Share on other sites More sharing options...
djk Posted March 12, 2011 Share Posted March 12, 2011 "it only takes a few milliamps at DC to burn out the average speaker." Are you sure? The spec sheet for the LaScala industrial claimed it would handle 40W of DC. Most prosound amps that have DC crowbars are set to trip around 8V DC, about 16W at 4 ohms. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 12, 2011 Share Posted March 12, 2011 here's one that says 25 watts from 0 to 40hz. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 12, 2011 Share Posted March 12, 2011 hmmm.....wonder how we can test this... Quote Link to comment Share on other sites More sharing options...
mark1101 Posted March 17, 2011 Share Posted March 17, 2011 You shouldn't be able to get DC through a capacitor. There are caps in line on all the filters (tweet, mid, woof). You should be OK. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 17, 2011 Share Posted March 17, 2011 you are right that an inline cap would block DC, but there are no caps in line in the woofer circut....just an inductor....the below circut board based protection circut would be much cheaper that the large film capacitor that would be needed in the woofer circut (almost 2000uf ) Quote Link to comment Share on other sites More sharing options...
mark1101 Posted March 17, 2011 Share Posted March 17, 2011 Yes I see that now. Well, I suppose we have all been at risk all along. Ha ha. This is the last thing I would ever worry about though. The poster admits his amps have protection anyhow. My system is active and I have all amps connected directly to all the drivers with no components in between. My mids are TAD 4002s and onlt cost me around $2100/pr. I'm still not the least bit worried and my amps are Mac 250s and 2100s....around 40 years old but rebuilt by DeWick. Quote Link to comment Share on other sites More sharing options...
djk Posted March 17, 2011 Share Posted March 17, 2011 Those McIntosh are not DC coupled, and cannot pass DC to the woofers. Relays may not open with DC (contacts weld shut). Crowbar circuit works. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 17, 2011 Share Posted March 17, 2011 Mark, I understand. Just as a point of reference, it's very common for SS amps to be out of spec and have excessive DC offset and it's really a very common cause of SS gear fault circuit activation and channel cut outs. Most speaker manufacture instructions for wiring their speakers in bi-amp mode emphasize not to by pass the crossover networks, which as you indicated will protect mids and tweets, just not woofers. Exceptions would be if you use a sub woofer which has a passive xover and the common setup of main in from your amp and sat out to your speakers. These have a lo pass and a hi pass section in them with the hi pass section going to your main speakers. This would protect the woofers in your main speakers, but not in your sub. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 17, 2011 Share Posted March 17, 2011 Thats true...funny that for true DC protection if using a DC amp is converting a direct coupled SS amp to a capacitance coupled one Quote Link to comment Share on other sites More sharing options...
mark1101 Posted March 18, 2011 Share Posted March 18, 2011 I forgot to mention the MACs are pushing my HF and MF horns. I have QSC PLX2 1104 pushing the MWMs and QSC PLX2 1804 pushing the subs. Still nothing in between amps and drivers. Maybe someday I'll have an issues but not so far, and I don't worry about it either. Quote Link to comment Share on other sites More sharing options...
djk Posted March 18, 2011 Share Posted March 18, 2011 The QSC PLX series have a DC sense circuit that shuts off the power supply, it looks like it should work (protect the speaker). Quote Link to comment Share on other sites More sharing options...
KanedaK Posted March 19, 2011 Author Share Posted March 19, 2011 Thanks folks for all the input... as I understand it in case of DC only the woofers go "smoke", but in the case of the universal network the fuse is in the woofer section... maybe for that reason? anyways, my networks didn't arrive yet... they are stranded at the customs, for some reason (I live in Belgium). Twenty times a day I check on the USPS website with the trcking number, but nothing seems to move since monday. GRRRRR!!!! I just hope it's the normal delay, I'm probably just too impatient. I've been dreaming about those networks for YEARS, without being able to afford them. And now they're stuck because some custom officers don't do their job efficiently enough, or are being paranoid about what's in the box. At least it didn't get lost by the postal service like my power amp was, last summer (two months to travel from centre of France to Brussels), or as I recall ten years ago this Technics preamp that, coming from a city in the north of Belgium, went all the way to Toulouse (south of France) and finally back to me (Brussels). fingers crossed. I'll post a full listening test when (if) they arrive. Quote Link to comment Share on other sites More sharing options...
KanedaK Posted March 28, 2011 Author Share Posted March 28, 2011 Great... 13 days stranded at the customs, and my networks are finally back in the mail delivery circuit... it's gonna cost me 130$ import taxes! I really don't get how they calculate it. Last year I bought a plate amp for my subwoofer in the US, it went through the customs TWICE since the first one was defect and got returned, and I only paid around 15$! And it was a new, more expensive device, and more heavy! and they ask me 130$ for a pair of used, second-hand universals.... my guess is there's absolutely NO logic behind the amount they ask you to pay, and it's just pure luck... anyways, I should get them in the next 48hours; I'll be finally able to listen to them and put some comments... Quote Link to comment Share on other sites More sharing options...
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