tourmax Posted March 6 Report Share Posted March 6 You may have noticed my recent thread about the tweeters in a set of AR4X's being damaged by a high freq feedback squeal when a microphone was plugged into my Sansui 8080DB. It's not something I do (was bud "jacking in") and there were a few other things that conspired to make the loud feedback squeal. It now appears it broke/melted the voice coil wire to the terminal in at least one of the tweeters. I'm currently using a second set of AR4X's I had in storage. I seldom have "Big Suey" much over 25% volume, 50% being a rare occurrence because the pressure level in the room at that volume is just not enjoyable for me (room is only 10x10). As we all know, these speakers are becoming hard to come by and I seem to prefer the AR4X's over most other speaker sets I've tried, so I'd like to protect them from unexpected "spikes" if I can. Specifically, I'd like to protect the tweeters from the type of feedback "spike" they experienced and damaged them. I don't plan on doing anything that would have a possibility of damaging them, but I wasn't expecting someone else over for a visit to do something like jam a mic in at volume before I could do anything about it. I suppose there's also the specter of a fault in the amp taking them out too as 1970's SS electronics won't really do a lot to protect components downstream if it has an internal fault. Would there be any sense to "fusing" the AR4x's? Perhaps fuse the tweeters separately (ie: inside the box) from the main input on the back? I've seen the AR scan on this site's repository, but it seems to mainly talk about a whole speaker protection fuse. I don't have an issue with placing a fuse internally to the box to protect the tweeter if that need be. Opening them up to check/replace a fuse is infinitely preferable to me than having to repair/replace a near "unobtanium" tweeter. Another quick question: is it possible the caps in the speakers need to be replaced? I would have though they would have taken the hit instead of the tweeters if they were still in good shape. As far as I know, they are originals (IE: the big "wax box"). Maybe I should just replace the caps on "spec".... Quote Link to comment Share on other sites More sharing options...
newandold Posted March 6 Report Share Posted March 6 2 hours ago, tourmax said: You may have noticed my recent thread about the tweeters in a set of AR4X's being damaged by a high freq feedback squeal when a microphone was plugged into my Sansui 8080DB. It's not something I do (was bud "jacking in") and there were a few other things that conspired to make the loud feedback squeal. It now appears it broke/melted the voice coil wire to the terminal in at least one of the tweeters. I'm currently using a second set of AR4X's I had in storage. I seldom have "Big Suey" much over 25% volume, 50% being a rare occurrence because the pressure level in the room at that volume is just not enjoyable for me (room is only 10x10). As we all know, these speakers are becoming hard to come by and I seem to prefer the AR4X's over most other speaker sets I've tried, so I'd like to protect them from unexpected "spikes" if I can. Specifically, I'd like to protect the tweeters from the type of feedback "spike" they experienced and damaged them. I don't plan on doing anything that would have a possibility of damaging them, but I wasn't expecting someone else over for a visit to do something like jam a mic in at volume before I could do anything about it. I suppose there's also the specter of a fault in the amp taking them out too as 1970's SS electronics won't really do a lot to protect components downstream if it has an internal fault. Would there be any sense to "fusing" the AR4x's? Perhaps fuse the tweeters separately (ie: inside the box) from the main input on the back? I've seen the AR scan on this site's repository, but it seems to mainly talk about a whole speaker protection fuse. I don't have an issue with placing a fuse internally to the box to protect the tweeter if that need be. Opening them up to check/replace a fuse is infinitely preferable to me than having to repair/replace a near "unobtanium" tweeter. Another quick question: is it possible the caps in the speakers need to be replaced? I would have though they would have taken the hit instead of the tweeters if they were still in good shape. As far as I know, they are originals (IE: the big "wax box"). Maybe I should just replace the caps on "spec".... All the tweeters in my system are protected by self resetting “by stable resistors“. They open if things get too hot and then come back when things cool off. I had only one that I can recall over the years doing its job. These are Allison tweeters not AR Roy Allison worked for AR, and was the design way back when. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 6 Report Share Posted March 6 IMO, yes, those caps need to be replaced if original. A fuse could be added, but putting inside the cab would be a pain to replace if you blow it. I’d put it outside on the terminal plate with a fuse holder clip. Some audiophile purists would say to never use a fuse in a tweeter circuit; but these aren’t $100,000 Wilson Audio speakers, either. Quote Link to comment Share on other sites More sharing options...
JKent Posted March 6 Report Share Posted March 6 I agree with Bill about replace those ancient wax caps. When I got my AR-3s the tweeters were shot (so was one mid) so I converted them to 3a's and because of that experience with tweeters I added the recommended Buss Fusetron Dual Element FNM 1-1/4 fuses. For your 4x's, AR recommends FNM 6/10. That document is in our Library. My only comment is these fuses and fuse blocks are clunky and a little hard to find. I wonder if there are other options. http://www.classicspeakerpages.net/library/acoustic_research/special_sections/additional_ar_documents/fusing_ar_speaker_systems_1/ Quote Link to comment Share on other sites More sharing options...
tourmax Posted March 6 Author Report Share Posted March 6 Thanks gents. I’ll get on those caps. I’ve seen the scans of AR recommendations for fusing in the library section. I’ve also seen the “signal loss” argument on the internet in places. I’m more concerned with protecting these old speakers than I am loosing any signal. It’s not like I’m building some competition sound system or anything like that. It’s just a simple home system, so I’m willing yo give up a little something in order to possibly save them this type of damage if it ever happens again in the future. whats the difference between the suggested brand fuses and a commonly available “fast blow” fuse? Quote Link to comment Share on other sites More sharing options...
JKent Posted March 6 Report Share Posted March 6 Take a look at this old thread Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 7 Report Share Posted March 7 On 3/6/2024 at 3:58 PM, tourmax said: Thanks gents. I’ll get on those caps. I’ve seen the scans of AR recommendations for fusing in the library section. I’ve also seen the “signal loss” argument on the internet in places. I’m more concerned with protecting these old speakers than I am loosing any signal. It’s not like I’m building some competition sound system or anything like that. It’s just a simple home system, so I’m willing yo give up a little something in order to possibly save them this type of damage if it ever happens again in the future. whats the difference between the suggested brand fuses and a commonly available “fast blow” fuse? I don’t think a fuse would have protected your tweeters from the sudden *thump* of a mic input: Quote Link to comment Share on other sites More sharing options...
RoyC Posted March 7 Report Share Posted March 7 1 hour ago, ReliaBill Engineer said: I don’t think a fuse would have protected your tweeters from the sudden *thump* of a mic input. Interestingly, back in the shop we also saw more fried woofer voice coils than tweeter voice coils...which had been protected by its crossover components. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 8 Report Share Posted March 8 Which I guess speaks well for the durability of the woofer mechanics. The voice coil can’t shed heat fast enough, and 30-1000 Hz is where the majority of music power is. Looking at the suggested wiring of the fuses, it doesn’t protect the tweeters by themselves. The fuse is seeing the total current fed to the loudspeaker. So is it going to protect the tweeter? Kind of doubtful. It’s a crapshoot whether enough current still passes to the tweeter to blow its VC before the fuse blows. Quote Link to comment Share on other sites More sharing options...
RoyC Posted March 8 Report Share Posted March 8 3 hours ago, ReliaBill Engineer said: Looking at the suggested wiring of the fuses, it doesn’t protect the tweeters by themselves. The fuse is seeing the total current fed to the loudspeaker. So is it going to protect the tweeter? Kind of doubtful. It’s a crapshoot whether enough current still passes to the tweeter to blow its VC before the fuse blows. Agreed. Quote Link to comment Share on other sites More sharing options...
tourmax Posted March 8 Author Report Share Posted March 8 16 hours ago, ReliaBill Engineer said: I don’t think a fuse would have protected your tweeters from the sudden *thump* of a mic input: You're probably right, But I'd like to try and protect these old speakers as much as I can. I was planning to fuse the tweeter and woofer separately so I can use different values for each. Might be an exercise in futility, but if it saves them just once from an abnormal condition, it's worth it to me. I'm not really worried about a fuse impacting a signal path "sonic-ly". Not many fuses are as thin as those fine wires crossing the basket to the voice coil gap. Hmmm.....which sort of shoots down the argument for including a fuse when I think about it....lol! Quote Link to comment Share on other sites More sharing options...
RoyC Posted March 8 Report Share Posted March 8 It's not unusual for some old "vintage" amps to send very destructive DC to speakers when failing (at any volume level). It can't hurt to use a basic 2 to 3 amp fast blow fuse in an inline fuse holder as some protection insurance with these systems. https://www.parts-express.com/In-line-AGC-Fuse-Holder-070-609?quantity=1 Quote Link to comment Share on other sites More sharing options...
newandold Posted March 8 Report Share Posted March 8 MDX-2 is the way to go for external fusing. …..Still have some will post a pic later. Great choice protection for the original AR lineup. Quote Link to comment Share on other sites More sharing options...
newandold Posted March 8 Report Share Posted March 8 2 hours ago, newandold said: MDX-2 is the way to go for external fusing. …..Still have some will post a pic later. Great choice protection for the original AR lineup. Quote Link to comment Share on other sites More sharing options...
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