New LS90s have some issues

saabracer23

Hello all, I'm back into the Polk game. I found a pair of LS90s for what I hope is a decent price, $150. They are doing something weird. When they start playing they sound great but after a minute or so the sound extremely distorted. I switched out sources and amplifiers but nothing helped. I pulled all of the drivers (because they all sounded horrible) and measured impedance and played them fullrange and they're all great. This has got me thinking it may be the caps in the crossover? It's weird both speakers have the problem.

So since I'm thinking I'll have to fix the crossovers I did a search to see upgrades but came up empty handed. Are there upgrades to the crossovers? What over upgrades to bring these to their full potential? I have read someone put the two midrange drivers on top and the bass drivers on bottom? Clearing out some of the stuffing? I checked the coils onthe crossovers and it looks like there is a 4mH and a 1.55mH I believe. Is this the updated one?

Any advise on these would be greatly appreciated, I know there was plenty to do on my old sda 2s

Thanks
Dan

ohskigod

both channels?, odd.

swap speaker cables by chance? worth a shot if you didnt. Incidentally, 150 for the pair is damn good, so if you gotta put money into them you got the room to do so and still be ahead.

I would say pull the crossover and use another driver on them (low volumes of course) to see if it distorts on other drivers. if both are gone, someone probably played them REAL loud, as I used to pummel the bejesus out of mine and they just took it in stride.

see if there is a fuse in the crossover or something maybe? just throwing out ideas, let some others chime in here too.

EndersShadow

The LS90's I see around me are going for 500+ so you made a very nice score, even if like ohskigod said you need to drop a little cash into em..

vc69

I have never had x-overs out of mine, so I cannot be of much assistance. I will congratulate on your purchase though. I have close to $500 in mine and they are worth every penny.

I too am very interested in doing upgrades to the x-overs so I am waiting with much anticipation, and in fact would be willing to trot down this road with you if we can get some help. I have zero experience in these types of things.

saabracer23

Thanks for the suggestions, any suggestions on crossover upgrades or driver rearranging? Vc69, were you looking for port dimensions? I think I read a thread where you were looking for them

Dan

cokewithvanilla

someone has one sale pending for 485 on the gon... 150 ain't bad

saabracer23

Well I replaced the caps in both crossovers and....nothin. So I auditioned each woofer again carefully and it so happens it was woofer, it buzzes. So if anyone has a mw7100 laying around I'll take it from you. I'm also still interested in hearing about upgrades.

Dan

vc69

saabracer23 wrote: »

Well I replaced the caps in both crossovers and....nothin. So I auditioned each woofer again carefully and it so happens it was woofer, it buzzes. So if anyone has a mw7100 laying around I'll take it from you. I'm also still interested in hearing about upgrades.

Dan

I have purchased 2 replacement drivers from Polk CS. Give them a call and mention being a member here for a discount. I replaced 2 to retain mirror imaging, but I have to say I could not hear a difference. Honestly, I didn't try very hard . These speakers sound great.

I would still LOVE to try to upgrade the xovers with high end parts. Problem is I am not interested in trying it myself. I have considered getting Ben to give it a shot.

saabracer23

Do you remember the pricing on them by chance, I would like to purchase one, but the dust caps are different. Man I remember getting tons of tips on upgrading the sda series I had, but nothin on the ls90?

Dan

saabracer23

Ok it looks as though I have the earlier version with the 4mH inductor, is layout the same, just different values?

Dan

vc69

saabracer23 wrote: »

Do you remember the pricing on them by chance, I would like to purchase one, but the dust caps are different. Man I remember getting tons of tips on upgrading the sda series I had, but nothin on the ls90?

Dan

Seems like it was about $55 with the discount. The dust caps are different, but I have not noticed any difference in the sound of the drivers. I replaced the topmost driver in each speaker which carries the lowest frequency from the xover if I am not mistaken. These are a weird cascaded xover configuration.

Again, I have never pulled the xovers out. I need to replace binding posts, so it will happen, but I wish I could get them completely rebuilt with Sonicaps and Mills or some such at the same time. I think we are in uncharted territory at that point though. I have found one or two threads where Geppy (?) did some tweaking, but nothing like a rebuild, just monkeying around with the cascade i think.

Polkie2009

vc69, you may not have to replace the binding posts, I believe there is a nut and washer on the other side of the plastic cover that secure the threaded binding post. I had one get loose and thought the same thing,darn, the post is jacked up, but no_, I was able to fix it:)

vc69

Polkie2009 wrote: »

vc69, you may not have to replace the binding posts, I believe there is a nut and washer on the other side of the plastic cover that secure the threaded binding post. I had one get loose and thought the same thing,darn, the post is jacked up, but no_, I was able to fix it:)

Thanks, but in my case one of the posts threads have been stripped. I want to go with some really nice posts whenever I dig into the xover. I like banana's, but I might want to go "spades" someday.

vc69

vc69 wrote: »

Thanks, but in my case one of the posts threads have been stripped. I want to go with some really nice posts whenever I dig into the xover. I like banana's, but I might want to go "spades" someday.

correction:

Bananas will work on my current "injured" posts. I can't screw the binding nuts down tightly on one of the four posts on one of my speakers, thereby prohibiting the use of spade terminated cables.

After re-reading my previous post, I felt compelled to correct myself. Jeez, I am glad I am off work tomorrow. I'm slipping away....

Polkie2009

Lol, I could follow what you were saying vc69. Dan, I had to replace a mw7100 in my LS50's due to one of the drivers sounding fuzzy on certain frequencies. I found that by gently pushing the driver in, it would sound fine for a day or so,but the problem would come back. I finally found someone here on CP that had a couple of used mw7100 drivers so I R+R one in it's place. Fixed the problem immediately:)

saabracer23

R+R?

Dan

Ron Temple

Nothing to add to for saabs problem, but I thought I'd chime in since I've been running 90s for a few months now. I've got to say that the 90s have made me procrastinate on setting up the 1Cs in the 2 channel room. I've got the source, the pre, the amp and the room, but the last time I set them up, I just wasn't pleased. I had them in the same position I initially set them up in, but this time the room sounded echo'y, the mids bloated, the bass hard-hitting, but ill defined. In short, I retired the rig until further notice. OTOH, the HT rig featuring the 90s and 35s sounds better everyday. I haven't done too much music listening, but what I have done is more coherent than when I had both 1Cs and 2Bs sharing the load in a not optimum setup. That's not saying I don't miss them. As I've stated before, there's just some material even commercials that SDAs make you sit up an notice the awesomeness. LS90s don't do that. They sound great for everything. but a commercial sounds like a commercial, a well mastered DD TV program very nice...just not, "wow, I've got to find out the artist that did this soundtrack". BDs and music are a tossup. Audyssey sets a hell of a soundstage...maybe I'll hook the 1Cs and 2Bs back up to compare again (I'm using the 2Bs as stands right now).

saabracer23

Well it looks as though tweaking the crossover will not work, but I can improve it. The crossover pcb for the first and second version are the same, just different values on the components. First the resistor went from .8 ohms to 1.0 ohms. I'm guessing the 12w mills resistor will do. The one and only cap went from a 50v electrolytic to a 100v Mylar. Should I get a Mylar or put in a polypropylene? Then lastly the original inductor went from a 4.0 mH .55 ohm to a 1.0 mH .25 ohm. What is the ohm rating on the resistor mean, I cannot find that value when shopping.

Dan

Polkie2009

Sorry Dan,lol, I'm an old man who's worked on to many things over the years;) R+R is short for remove and replace. Polk broke the mold when they engineered these LS90's, they really are some sweet speakers.

vc69

Polkie2009 wrote: »

Polk broke the mold when they engineered these LS90's, they really are some sweet speakers.

They Sure did.

Ron, I am pleased to hear you are enjoying the 90's.

Saab, please keep us updated on the xovers. Are you going with HQ parts? What are you thinking of using?

saabracer23

Well I started another thread but I'm not getting any help there, I may end putting up a thread over at diyaudio. I'll get mills resistors, Jantzen standard z for the caps, and not sure on the coils. I'm wondering if I should go air core or iron core. Only one needs replaced, not sure if I'll gain anything replacing the others. Hmmm

Dan

Oh is there a better cap for the money? From what I have read it seems to be the best bang for your buck.

vc69

Hey Dan,

Perhaps a thread here with a "help needed" tag and "LS90 xover rebuild" in the title would get some of the more experienced DIY guys on the ball. There is certainly a bunch of knowledge here, but they are mostly SDA guys. These LS90's just haven't quite caught on to that extent. I think they may though, and if you have any luck with this endeavor then I am not too far behind. I can't help but believe that some HQ parts would make a difference. Air inductors seem to be the way to go for some reason.

I'm pretty excited about you doing this.

55LS70

I upgraded the crossovers in my LA70's with soniccaps and they sounded better than new. I should also state that I replaced the drivers and tweeters in both of them about a year before.

vc69

Any new developments?

saabracer23

No not really, I'm trying to sell a pair of acoustic elegance 18" passives to fund the project. I prefer my subs sealed. Anyway as soon as they sell I'll start ordering parts. If anyone know someone who would like almost new special order 2500g passive for $150 for the pair let me know!

Tough market!
Dan

vc69

Sure is. Have you posted in the Flea Market?

luv-my-ls50

Hi, I'm a new member here. I've got a pair of LS50s and like them a ton. One of the MW7100 drivers has developed a bad buzz where the surround glues to the cone. I've been looking all over these forums tonight trying to find one of these drivers. Somebody suggested I get one from Polk. I've been to their site but can't seem to find where to order one or even search for the part number (MW7100). Could one of you old-school Polkies tell me where/how to order one of these drivers from Polk or maybe one of you guys have one? Also, does it hurt the x-over to unplug the buzzing driver and play the speaker (at low volumes) with just one of the MW7100s? They seem to be wired in series. The other driver still works when the bad one is unplugged. If this is a stupid question, please forgive my ignorance. I am not a EE. Thanks, Dana:frown:

F1nut

Customer Service & Tech Support:
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It would probably be best to not play them until you can get a replacement driver.

luv-my-ls50

Correction: They seem to be wired in parallel. I've been looking around this forum all night and somebody suggested turning or rotating the driver 180 degrees since it has been in that position since 1993. I did this and hooked it back up. It seemed to help quite a bit. Monday I will try Polk Audio Customer Service Department at 1-800-377-7655 and see if they have a replacement driver. Thanks F1nut

quadzilla

saabracer23 wrote: »

Well I replaced the caps in both crossovers and....nothin. So I auditioned each woofer again carefully and it so happens it was woofer, it buzzes. So if anyone has a mw7100 laying around I'll take it from you. I'm also still interested in hearing about upgrades.

Dan

I had this same problem, and just found today that the rubber surround has seperated in a few places from the cone. I'm about to post a thread on what adhesive should be used to reattach it. What you're describing sounds a lot like what mine were doing.

vc69

I am interested in the answer to that question as well. I replaced the driver s I had a problem with, but one of them could be repaired. I was thinking that a 3M adhesive for rubber ought to work.

luv-my-ls50:

Polk CS sells a replacement that works quite nicely. When you call, mention that you are a Club Polk member for a discount!