LS90 Mods

[toobwacky]

I lucked out and snagged a pair of LS90s off CL that are in excellent condition. I already had a pair of Magnepans, but at the price I paid for the LS90s I thought I would play with them for a while, sell them and recoup all my money.

I thought they sounded really good at the seller’s house and even better when I got them home. Playing pink noise through them I was surprised to find the lower 2 drivers were the ones emanating the midrange frequencies...

Anyway, I downloaded both schematics from this site (thanks!) and decided to make some further refinements to my version 2 LS90s. I moved the midrange reproducers into the top 2 positions of the cabinet and put the bass drivers in the bottom 2 positions. This involved removing all four woofers from each cabinet although I suppose the same could have been accomplished by rearranging the wiring coming off the crossover board attached to the terminal cup.

I was pleasantly surprised to find a 1”thick front baffle and 4 braces in each cabinet. Not surprising were the cost cutting measures of utilizing stamped baskets and thin guage inductors. Over all this is a very well constructed speaker. I took out the 2 layers of fibrous “door mat” type material that divided the internal cabinet volume and rearranged the stuffing to better damp the internal midrange frequencies and to stop blocking the ports. I also removed the plastic trim from the from of the baffle for diffraction reduction.

Put it all back together and...WOW! Imaging and midrange detail are GREATLY improved and the bass is a lot more focused and defined. This project was well worth the 2 hours of my time that it used and it took a speaker that I thought was already pretty darned good to an entirely higher lever.

Oh, by the way... I sold my Magnepans and am keeping the LS90s. :D

[zarrdoss]

I have some LS90 series 2 and really like the way they sound. Some of the best sounding neutral speakers I have ever owned, I was thinking of selling them but not now. I understand that all four drivers get a progressively lower cut off as you go down, I think they call it the cascade effect.
Welcome to the club!

[DaveMuell]

I'll be upgrading the x-overs in my 90's as soon as I go buy my solder sucker apparatus'. I have my caps in hand. I will let you know the results (in 20 words or less). I wouldn't mind knowing the opinion of others wether or not it is worth it to upgrade the resisters and/or the coils. So far, I have only considered the caps.

[Face]

I'll be upgrading the x-overs in my 90's as soon as I go buy my solder sucker apparatus'. I have my caps in hand. I will let you know the results (in 20 words or less). I wouldn't mind knowing the opinion of others wether or not it is worth it to upgrade the resisters and/or the coils. So far, I have only considered the caps.

Are they air core or iron/steel core? If they're air core, leave them be. If they're the other, when replace them, make sure the replacement has a similar DCR or you can throw off the speaker's balance.

Don't forget to replace the resistor while you're in there.

[toobwacky]

The stock inductors are iron core. I'm thinking about replacing them with really heavy gauge iron core inductors. I know conventional wisdom says air core sound better, but heavy gauge iron core have far lower DC resistance and will allow my amp to better damp the woofers.

Of course I'm open to contrary opinions on the matter. :)

[Face]

I know conventional wisdom says air core sound better, but heavy gauge iron core have far lower DC resistance and will allow my amp to better damp the woofers.

make sure the replacement has a similar DCR or you can throw off the speaker's balance.

;)

If you are dead set of changing the DCR, be sure to pick up a few different resistors for the tweeter to restore the tonal balance.

[DaveMuell]

I have some LS90 series 2 and really like the way they sound. Some of the best sounding neutral speakers I have ever owned, I was thinking of selling them but not now. I understand that all four drivers get a progressively lower cut off as you go down, I think they call it the cascade effect.
Welcome to the club!

They aren't really cascaded, two are in series, and two are parallel. The schematics can be found via a sticky thread in the vintage section.

[DaveMuell]

Are they air core or iron/steel core? If they're air core, leave them be. If they're the other, when replace them, make sure the replacement has a similar DCR or you can throw off the speaker's balance.

Don't forget to replace the resistor while you're in there.

As it turns out, I had ordered the Mills resistors.

At PE, I can't find air core replacements for the iron cores with the exact same values - how far off can I go, in which direction, and given this compromise is it worth the replacement?

[zarrdoss]

Dont you hate when some prior owner messes around and screws it up?, some sda srs 2.3 I have the prior owner pulled some drivers out and put them back in with the polarity backwards AAARRRGGGG!!!!!!

[Face]

As it turns out, I had ordered the Mills resistors.

At PE, I can't find air core replacements for the iron cores with the exact same values - how far off can I go, in which direction, and given this compromise is it worth the replacement?

Here are some more choices: http://www.partsconnexion.com/t/catalog/inductors.html

[zarrdoss]

They aren't really cascaded, two are in series, and two are parallel. The schematics can be found via a sticky thread in the vintage section.

I read this thread before I bought these thats where I got the idea that they were cascaded.

http://www.polkaudio.com/forums/show...highlight=ls90

[Face]

And how could I forget?

http://www.madisound.com/catalog/index.php?cPath=404_20

[DaveMuell]

I read this thread before I bought these thats where I got the idea that they were cascaded.

http://www.polkaudio.com/forums/show...highlight=ls90

You are correct, given that the definition of cascaded is two or more drivers. I stand corrected.

[zingo]

If you want an iron core inductor made for woofers, try Jantzen's 14g Toroidal Inductors. They range from 1.5mH to 18mH and handle 700w RMS. I've heard good things. :D

[DaveMuell]

The LS-90 schematics show a 1.55mH with a .28 DCR - the closest Janzten Toroidal I see is a 1.50 and a .049 DCR. That's pretty much par for the course, everything I see is quite a ways off on the DCR and geneerally at least .05 off on the mH. I need some advice on how to make something like this work. I don't want to deviate too far from spec, do I?

[GV#27]

The toroid/iron core type is only necessary fwhere or big indictance values(>2.5m)are needed.If your version of the LS90 use the 4mh for the bottom woofers then use of them.Otherwise I would suggest an air core for the the 1.0 and 1.55 mh like the Solen 14AWG.http://www.madisound.com/manufacture...perfectlay.php The DCR values are close enough at .21ohm for the 1mh and bang on .28 for the 1.5mh.Small differences in DCR and inductance will be insignificant.

[GV#27]

The toroid/iron core type is only necessary where big inductance values(>2.5m)are needed.If your version of the LS90 uses 4mh for the bottom woofers then use this type for it.Otherwise I would suggest an air core for the the 1.0 and 1.55 mh like the Solen 14AWG.http://www.madisound.com/manufacture...perfectlay.php The DCR values are close enough at .21ohm for the 1mh and bang on .28ohm for the 1.5mh.Small differences in DCR and inductance will be insignificant.

Edit:Fixed typos.

[DaveMuell]

Excellent information. Now, will replacing these inductors be worth roughly $100 in the LS-90s? That ain't much money, but if it is not an audible improvement, I will put that money towards something else.

[GV#27]

Now, will replacing these inductors be worth roughly $100 in the LS-90s?

It would depend on the quality of the stock inductors and at what power levels their core begins to saturate.If they saturate at moderate levels then yes going with air cores should bring about worthwhile audible improvements.If the core can take a lot of power before saturating then there may be little or no difference in SQ.Sorry Dave but I can't give you a more definitive answer.