source for inductors?

billbillw

Just did a re-build on my Mirage crossovers. Changed all the caps and resistors (about 21 parts in each crossover!)

Before the rebuild, I noticed the response out of the woofers was not the same, one woofer was passing noticeably more midrange. I figured the coils don't go bad, gotta be the caps, might as well change them all, along with the resistors, that way everything is fresh and to spec. Well, I gave them a listen last night and I'm still hearing more midrange out of one woofer than the other. When I test this, I only have the woofer attached (removed bi-wire jumpers).

The network for low-pass is a simple 2nd order, with a single laminated I-core inductor (4.2mH) and a total 85uF in shunt capacitors. I think the driver measures 4 ohm with a multimeter, but the nominal value may be higher since the whole system is supposed to be a 6 ohm nominal speaker.

So, its gotta be a bad coil in one, right?

So, the original schematic from Mirage shows a laminated iron core inductor, 4.2mH and ~0.6ohms resistance, pretty sure its 18awg. I'm having a helluva time finding a replacement. Nothing available from Mirage, especially now that Klipsch has absorbed API.

Any ideas on where to find a suitable replacement?

I've thought about putting 2 in series to obtain the correct inductance value, but then I read about "mutual inductance" if they are placed close together. Is this something I should be concerned about?

I was thinking a 4.0 I-core and a .2 air core (or something along that line).

Or, if anybody has the modeling capabilities, could you tell me how much the crossover frequency would change if I went with a 4.0mH or 4.5mH coil?
.

Systems

Humm,I doubt the coil is bad but if you can find someone with an LCR meter you could verify they both have the same value.Are you certain the shunt cap is connected?If it wasn't then that would give more midrange output.Did you try swapping woofers to see if it follows the driver.?

ben62670

You are looking at about a 1% difference using just the 4.0. Most inductors (especially the lower cost iron cores) are 5% tolerance. I would just get the 4.0 air core from Parts express, and be done with it. I would get the Erse 18ga perfect layer's for $18.42 a piece . The DCR is very low for an air core which helps keep your crossover in spec, and they are 2% tolerance.

Serendipity

I would try Parts Express.

billbillw

Thanks for the ideas guys.

Humm,I doubt the coil is bad but if you can find someone with an LCR meter you could verify they both have the same value.Are you certain the shunt cap is connected?If it wasn't then that would give more midrange output.Did you try swapping woofers to see if it follows the driver.?

Ok, GV, If you see my original post, I just replaced all the caps in the crossover, so yes, the shunt caps are connected, no doubt. I actually moved the crossover from one side to the other (easier than swaping the woofer, and the problem definetly follows the crossover, so its not the woofer or any internal cabinet wiring either.

I originally thought there was no way a coil would go bad, but if you think about it, if they overheat from excess current, and the varnish burns off, the coils get shorted, the current path is changed, and the inductance value would change. In this setup, there really is no other explanation.

I would try Parts Express.

Appadv, Of course, that was the 1st place I looked. THey have 4.0 and 4.5, but no 4.2.

You are looking at about a 1% difference using just the 4.0. Most inductors (especially the lower cost iron cores) are 5% tolerance. I would just get the 4.0 air core from Parts express, and be done with it. I would get the Erse 18ga perfect layer's for $18.42 a piece . The DCR is very low for an air core which helps keep your crossover in spec, and they are 2% tolerance.

Ben, I think your math is off. A 4.0 would be 4.8% difference. Yes I know they are 5% spec'd, but you will find that in practice, they are usually much closer to the spec'd value. Also, I don't have room for a 4.0 air core, they are much to large to fit in this crossover. See the pic for an idea of how tight things are. The dimensions of the board fit exactly within the base of the speaker and have no room to go outside the footprint. That's probably why they went with the iron core in the first place. The Erse aircore is 3" diameter, compared to the original, which is about 1.5"

I think you will find that iron core coils will have a lower DCR due to a shorter length of coils. They are more efficent for a given winding.

I've pretty much gotta find an iron core. Either I will have to settle for a 4.0 or 4.5, or I'll have to put a small air core in series.

ben62670

billbillw wrote: »

Thanks for the ideas guys.
Ben, I think your math is off. A 4.0 would be 4.8% difference.

Me fail math that unpossable:o

Systems

Are there any other components such an RC combo across the voicecoil?If not then it has to be the coil.here is a link that may be helful. http://www.madisound.com/cgi-bin/index.cgi?exact_match=yes&product=SL&cart_id=8856312.12379

jcaut

The inductors would be one of the last things that would be damaged, just because of the time required to heat them up so severely, so I seriously doubt that you have a bad coil. I re-read, and now see that the problem existed before the initial rebuild, so I don't know what could be causing it.

If you need to replace the 4.2, buy a 4.5, find someone with an LCR meter, and unwind until you get to 4.2. I'm pretty sure Madisound will still wind you a custom coil, also.

Jason

billbillw

jcaut wrote: »

The inductors would be one of the last things that would be damaged, just because of the time required to heat them up so severely, so I seriously doubt that you have a bad coil. If it was okay before the initial rebuild, then something else is causing the problem, IMO.

If you need to replace the 4.2, buy a 4.5, find someone with an LCR meter, and unwind until you get to 4.2. I'm pretty sure Madisound will still wind you a custom coil, also.

Jason

Jason,
The problem was there before the rebuild; it was the main reason I decided to go ahead with the rebuild.
Unfortunately, the problem is still there after the rebuild. I've replaced all the other parts in the Low pass circuit (which is wired independent of the mid/high crossover), the problem is not with the woofers or the cabinet wiring, therefore, there is nothing else that could possibly be wrong. Believe me, I tried everything else, short of testing the coils with an LCR meter. The coils are not producing the same inductance value for whatever reason. They are cheap enough, its a fairly simple swap.

I should mention, this is not a drastic problem. The speakers sound great, but like most of us, I'm a perfectionist and knowing that the woofers are not producing the same response on each side is driving me batty. I just want them to sound as good or better than the original designers at Mirage intended.


I did some modeling today using some software and there really isn't much of a difference by using the 4.0mH coil. I'll probably go with the Erse Super Q from P.E.

jcaut

Bill,

Sorry, I must have looked again at this, just about the time you posted. I see that this was the problem you were trying to fix in the first place.

You're probably right that the 4.0mH would be fine. I presume that you'd replace the inductors on both speakers? If it were me, I'd be tempted to try and measure the inductors that are there first, just to see if they are the same, within spec. You know, just to see what's going on. Maybe I'm cheap, but I'd hate to spend that much on inductors without proof that one was bad. Even if they're just at opposite ends of tolerance, if you had an LCR meter available perhaps you could unwind one of them to match the other. Have you tried measuring resistance across the coils on each crossover? I would think that a problem great enough to change the inductance enough to be audible would cause a measurable change in DC resistance.

Those Super Q inductors are quite large, also, so check to make sure they'll fit.

Jason

billbillw

Jason, I edited my post and added some interesting photos. I haven't bothered to measure the resistance. I may do so next time I have them appart, but that will probably be when I replace the with the new parts, and of course, YES, I will be replacing both. That's another reason why I did the rebuild of the crossover. I noticed some of the caps were not the same one each side. One cap in the tweeter had been replaced with a different type of cap and virtually none of the low pass shunt caps were the same. I couldn't tell what was original and what wasn't. This is why I thought at first that the woofer problem was due solely to the shunt caps not being matched. I was wrong about that.

jcaut

Sorry about all the editing.

Wow. I see. Somebody's been blowing up some capacitors.
Looking at that, there's no telling just what's going on there. I still think it'd be awfully difficult to hurt the inductors, but who knows? Good luck with it!

Jason

ben62670

Its real hard to find a cheap MM that will read inductance. You could measure the ohms, and that would give you a fair idea. Or just buy new inductors. I really would try to make the air cores fit. At anything but a sub woofer frequency air cores are better IMO.

billbillw

ben62670 wrote: »

Its real hard to find a cheap MM that will read inductance. You could measure the ohms, and that would give you a fair idea. Or just buy new inductors. I really would try to make the air cores fit. At anything but a sub woofer frequency air cores are better IMO.

It seems that some schools of thought have changed in regards to using aircore, especially when compared to the ERSE Super Q.

VMPS claims to use them in their speakers, read the "crossover" section at this page:

http://www.vmpsaudio.com/technical.htm

jakelm

Did you try swapping the woofers? Or did I miss that post?

billbillw

jakelm wrote: »

Did you try swapping the woofers? Or did I miss that post?

You missed it above. I actually swapped the crossover from one side to the other and the problem followed the crossover. This eliminated both the woofer(s) and possible cabinet wiring problems.

jakelm

billbillw wrote: »

You missed it above. I actually swapped the crossover from one side to the other and the problem followed the crossover. This eliminated both the woofer(s) and possible cabinet wiring problems.

It is just so rare that an inductor goes bad. I have seen a burned board where there was a short which cause the tweeter to be much louder. The short actually bypassed the resistors on the board, thus giving a non resistive signal to the tweeter. I'm sure the same could happen with the midbass. Or even a bad solder joint, or a solder that touched 2 parts of the board.

But I'm sure you checked the board already.

Jockos

Not to hijack your thread but I have a similar problem with my 5b's. One of the inductors was repaired about a year ago but the speaker sounds thin and shrill compared to my other one. Tried swapping another spare tweeter but same result. Sounds like my 6 in driver is putting out too much highs. I'm going to recap. the x-over and see if that helps. Parts express does sell a LCR meter for $95. I'll be watching your situation closely.

Jockos

billbillw

Well, it took awhile to finish up this project, but today I finally got around to replacing the inductors on my Mirage crossover's low pass filter for the bass driver. After the change, it was clear that the inductors were definitely the problem. After replacement, both channels sound identical now. I ended up using the Erse SuperQ in a 4.0 mH size. Now I can finally enjoy the M3 sound as they were meant to be. I'm sure the entire crossover needs to be burned in, so there should only be better things to come. But, I can already say that the midrange is much cleaner. Previously, with one of the bass drivers passing too much midrange, there was some harshness especially on piano that is now gone.

In hindsight, I can see that one of the old inductors looked a little brown and some of the glue had turned dark as if it was over heated. The board on that inductor came from showed some browning too. Its odd, the tweeter section on one side was burned out, and the bass on the other channel was burned. They must have been bi-amping and ran into some problems.

Systems

Great to hear you got them fixed.They are great sounding speakers and along with their big brother the M1 were ground breaking products when they were first introduced.A few other companies started to copy their bipole design.

PoweredByDodge

digikey.com

billbillw

PoweredByDodge wrote: »

digikey.com

???? Thanks for the insightful post.

If you read the thread, you'd see the problem was already solved. Also, Digikey does not have a 4.2mH iron core inductor that is designed for a crossover. I checked there long ago.

PoweredByDodge

read the first page, not the whole thread... ''' ooo bad me '''

however now that you mention what you were exactly searching for, why a ferrous core? if its a space / packaging issue, then it makes sense, but otherwise the best thing you can use (and really isn't any huge price difference) is an air core.

billbillw

PoweredByDodge wrote: »

read the first page, not the whole thread... ''' ooo bad me '''

however now that you mention what you were exactly searching for, why a ferrous core? if its a space / packaging issue, then it makes sense, but otherwise the best thing you can use (and really isn't any huge price difference) is an air core.

Again, read the thread before you post. Smallest aircore was 3", I only had 1.5" to work with.

PoweredByDodge

Kim, $20 for a 16 awg air core ... that's a SUPERB price.

**adds solen to his list of 'places to get stuff'**