Members Art Flood Posted February 13, 2015 Members Share Posted February 13, 2015 The voice coil on one of my fold back wedges got fried last night. It is still under warranty but I can't afford the down time it takes to send it away for a claim so I plan on just replacing it myself. It looks pretty straightforward to replace but I thought I'd post in case there are complexities I am not aware of (this is actually the first HF driver I have burned out in more than 30 years). I did check the crossover and it looks (and smells ok). BTW it think it was a burst of high frequency feedback that fried the coil (bugger). Any advice appreciated. Thanks Link to comment Share on other sites More sharing options...
Members Audiopile Posted February 14, 2015 Members Share Posted February 14, 2015 Advice: If it doesn't work out that you can get the HF device functional by the time you need to use the wedge, you could likely get-by running full range with the functional cone driver (direct wiring the cabinet input to the cone driver) ... it might sound a little muffled, but would likely be preferred with the cone driver wired direct rather than the crossover in-line with a dysfunctional HF driver. Link to comment Share on other sites More sharing options...
Members dboomer Posted February 14, 2015 Members Share Posted February 14, 2015 The voice coil on one of my fold back wedges got fried last night. It is still under warranty ... BTW it think it was a burst of high frequency feedback that fried the coil (bugger). Interesting. Except for a very few, manufacturers warranties are for "manufacturing defects" and not for dumb errors on the part of users. Nice that you are doing the right thing and fixing it yourself. Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 14, 2015 Author Members Share Posted February 14, 2015 Interesting. Except for a very few, manufacturers warranties are for "manufacturing defects" and not for dumb errors on the part of users. Nice that you are doing the right thing and fixing it yourself. Yeah I can't blame the manufacture for this one. The real interesting bit was that the driver that fried was not on the send the caused the feedback. That is, it was the lead sings microphone that caused the problem - his wedges survived but one of the backup singers cooked. I am scratching my head to work it why - I know it was ok 10 minutes prior to the event (because I had just sound checked it myself). Cheers Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 14, 2015 Author Members Share Posted February 14, 2015 Advice: If it doesn't work out that you can get the HF device functional by the time you need to use the wedge' date=' you could likely get-by running full range with the functional cone driver (direct wiring the cabinet input to the cone driver) ... it might sound a little muffled, but would likely be preferred with the cone driver wired direct rather than the crossover in-line with a dysfunctional HF driver.[/quote'] Good idea. It certainly sound muffled with the crossover in the circuit. I've got a back up but its active and I really like keeping the foldbacks all the same. Link to comment Share on other sites More sharing options...
Members StratGuy22 Posted February 14, 2015 Members Share Posted February 14, 2015 I've fried a HF diaphragm in one of monitors. It was a $30 part. I ordered 2 to have a backup on hand. Now I'll probably never blow another. It was pretty easy to swap out if you're handy with a screwdriver. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted February 14, 2015 Members Share Posted February 14, 2015 What cabinet and what HF compression driver? Is the gap filled with ferofluid? Make sure you clean the gap out real dam good. Fold masking tape with sticky side out over a card or thin piece of cardboardand scrape out the crud/metal shavings out of the voice coil gap. Inspect with a flashlight. Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 14, 2015 Author Members Share Posted February 14, 2015 Thanks for the tips. Bad news is I discovered that I actually have two speakers with blown HF drivers. I didn't notice the second one until last nights gig (it was being used in a pair the previous night when the damage was done). Bugger! Pro Sound Guy - its an Australian made speaker similar too a SRX 712. I am pretty sure it's not filled with ferofluid - but I haven't had time to do much with them - hopefully find time today. I haven't even checked out the diaphragm yet - does this normally get damaged when the voice coil burns out? Cheers Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted February 14, 2015 Members Share Posted February 14, 2015 Sounds like you smoked the diaphragms. Are these JBL clone compression drivers?Put a 1.5 volt AA battery on the positive and negative of the compression driver input.If you do not hear anything then the diaphragm is shot. Clean out the gap and put a new diaphragm/s in.Welcome to the world of OH Sh&t...I smoked a diaphragm...chick ching. (I have to add bypass passive xover for battery check.) Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 15, 2015 Author Members Share Posted February 15, 2015 Thanks Pro Sound Guy. I posted a picture as this is my first ever issue with a compression driver. Both failed the battery test which i expected as their resistance is way out of spec - one is a couple of hundred kilo ohms and the other is open circuit. They both smell burned. So the coil and diaphragm are the one part? It looks very simple to change on this one. Hopefully they will be in stock and I can be up and running for next weekends gigs. Cheers Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted February 15, 2015 Members Share Posted February 15, 2015 Looks like B&C diaphragm. However, suspension does not look B &C easy to change. Make sure you clean out the voice coile gap. Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 15, 2015 Author Members Share Posted February 15, 2015 Thanks again Pro Sound Guy. I'll certainly clean the gap. Cheers Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 15, 2015 Members Share Posted February 15, 2015 Similar to the SRX-712? Certainly not in the weight department... What is the diameter of the voice coil? How much do the cabinets weigh? The real SRX-712 HF driver is very, very difficult to damage (umless you are an idiot), I wouldn't expect the same from what you have. I would also check to be sure there was no damage to the crossover as well. Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 15, 2015 Author Members Share Posted February 15, 2015 Similar to the SRX-712? Certainly not in the weight department... What is the diameter of the voice coil? How much do the cabinets weigh? The real SRX-712 HF driver is very, very difficult to damage (umless you are an idiot), I wouldn't expect the same from what you have. I would also check to be sure there was no damage to the crossover as well. G'day Aged - I posted about these when I purchased them. They have a 3" voice coil and weigh in at around 50lb (23 Kg). I am a bit surprised they were damaged as the seller recommended them as being bullet proof (well I proved him wrong). They copped some feedback at I'd guess around 8khz - I was setting up lights so it took me a few seconds to get to the mixer. I'll be sure to check the crossover out, THanks Link to comment Share on other sites More sharing options...
Members Audiopile Posted February 15, 2015 Members Share Posted February 15, 2015 Thanks Pro Sound Guy. I posted a picture as this is my first ever issue with a compression driver. Both failed the battery test which i expected as their resistance is way out of spec - one is a couple of hundred kilo ohms and the other is open circuit. They both smell burned. So the coil and diaphragm are the one part? The coil is glued/adhered to the diaphragm... it's a package deal. (The coil itself is "not replaceable") Judging by what I can see in your picture... all aspects of the diaphragm look to be in excellent (pristine) condition, however your picture is of the exit (phase plug) side of the diaphragm... the voice coil part would be "underneath" in your picture... you'd need to remove the diaphragm from the magnet structure to examine the voice coil portion. However, if the coil is truly burnt, there's generally some discoloring visible on the phase plug side where the surround meets the diaphragm... and I don't see any sign of the tell-tale discoloring in your picture. Generally a cooked diaphragm coil... the coil is visably burnt... a dark tan/ brown to black color. Typically the glue adhering the voice coil to the former will be failing... bubbled or worse. In extreme cases the windings of the voice coil will be partially or nearly completely separated from the former (the "former" is what the voice coil is wound on). Also, the diaphragm will likely have suffered damage... cracked or completely shattered... as too the surround would likely be failing. The surround is the swirl pattern around the diaphragm... the surround is the "flex" the allows the diaphragm to travel in the voice coil. Judging by your picture, I suspect there's an "open" somewhere in the electrical connection... not necessarily burnt "fried" but a clean/acute "open". Oftentimes when this happens, it's at the junctions of the lead-in (tinsel) wires and the voice coil. Typically there's a couple small flat copper (?) "tabs" at that junction point. The copper tabs typically have a 90 degree bend in them. If that 90 degree bend is a sharp square bend (not rounded), the bend is likely work hardened and failure prone. I have successfully soldered some failed ones of these little tabs... but doing so is a bit of a "cheap fix" (results vary). Other times, if the voice coil isn't globally burnt, but has an acute open, it's right at the junction point of a transition tab and the start of the winding... failure there suggests less than good electrical joint construction by the diaphragm manufacture (possibly a sub vendor). It could be that the driver otherwise shouldn't' have failed... but did fail due to "manufacturing techniques". Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 16, 2015 Author Members Share Posted February 16, 2015 Thanks Audiopile, You and others here are so generous with your knowledge - I really appreciate it. It would be nice if it was just a broken connection but I fear not as the dreaded burned out component smell is definately present and the coils do look lightly tanned. I managed to order a couple of diaphrams today - they were $90 (Australian) each so not cheap, but not too bad. If I can repair one of the failed diaphrams I'll have myself a spare for next time. Cheers and thanks so much. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted February 16, 2015 Members Share Posted February 16, 2015 Sounds like these boxes could be "ancient Chinese secret" Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 17, 2015 Members Share Posted February 17, 2015 Indeed, look like something it's not! Link to comment Share on other sites More sharing options...
Members Audiopile Posted February 17, 2015 Members Share Posted February 17, 2015 Sounds like these boxes could be "ancient Chinese secret" To be fair: It's pretty rare that I see cooked compression driver voice coils. Generally, in my experience, compression drivers die in one of three ways: 1) Fatigue or shattering of the diaphragm & surround... usually from sheer hours (chronic), or acute damage (when shattered). 2) An open in the electrical path... generally at one of the tinsel wire to voice coil tabs or at one end of the voice coil windings. 3) Debris in the motor area (a picture of beer & RedBull or otherwise dumped down the horn throat). I suggest that I my opinion, based on my experience, if a compression driver fails and upon examination the voice coil windings look to be well "tanned" (showing apparent signs of heat stress)... if failure of the electrical path hadn't come first, mechanical failure elsewhere should have been close behind... otherwise the engineering wasn't done right. Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 18, 2015 Author Members Share Posted February 18, 2015 Audiopile, I replaced my diaphrams last night and it looks like mine fall into your second category - they have both open circuited at the connection to coil. It will be tricky to repair but I will give it go. Thanks for you help. Link to comment Share on other sites More sharing options...
Members Audiopile Posted February 19, 2015 Members Share Posted February 19, 2015 Audiopile, I replaced my diaphrams last night and it looks like mine fall into your second category - they have both open circuited at the connection to coil. It will be tricky to repair but I will give it go. Thanks for you help. Ok, yes... trying to fix that is nothing less than tricky. In the past, I've done a number of creative things to fix that, including as I recall carefully unwinding the last coil before the break to get enough length to span the gap and/or very carefully adding a little piece of small gauge wire to span the gap. (solder doesn't span a gap unless you don't want it to)... I vaguely remember somewhere on the order of 3 decades ago buying 3 or 4 Sunn wedge monitors... pretty cheap cause all of them had dysfunctional HF drivers. As I recall the compression drivers were Fostex (410's I think), and all of them had open circuits at the connection to the coil... and I meatball surgery fixed all four... saving myself full dollars at the time with only an hour or two time investment into each fix. Last summer I was the fill-in bass player for a 40th wedding anniversary party at a church were those monitors are still being used, and all were still fully functional. Sometimes one gets lucky. (a real steady hand and a good soldering iron can help with the luck thing) Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 19, 2015 Members Share Posted February 19, 2015 If the VC is aluminum wire (pretty common ob HF drivers) then don't even waste the time trying. You can't really solder the connection, in manufacturing it's welded rather than soldered and it's tricky process with the dissimilar metals, aluminum being the issue. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted February 20, 2015 Members Share Posted February 20, 2015 Honestly, spend the money and just replace the diaphragms. They failed from wear. Link to comment Share on other sites More sharing options...
Members Art Flood Posted February 20, 2015 Author Members Share Posted February 20, 2015 Honestly' date=' spend the money and just replace the diaphragms. They failed from wear.[/quote'] I have! Even got a spare. But I am still going to fool around with the old ones - its been valuable learning so far. Cheers Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 20, 2015 Members Share Posted February 20, 2015 I don't think they failed from wear, most diaphragms don't fail from wear. They fail from "accidents", willful overpowering, corrosion from external liquids, etc. Link to comment Share on other sites More sharing options...
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