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AR90 Crossover rebuild


rrcrain
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I'm in the final planning phase before I restart to rebuild the crossovers in a pair of AR90s. I've planned to replace all of the capacitors with Solen poly caps and the inductors with Solen Hepa-Litz coils. I'll use Kimber speaker wire for all of the point to point wiring.

With this in mind, I have two questions;

1. Considering that I've never used the cut switches on the speaker, should I leave them or replace them during this operation

2. What else should I consider doing to the speaker while I am rebuilding the crossovers?

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>>With this in mind, I have two questions;

1. Considering that I've never used the cut switches on the speaker, should I leave them or replace them during this operation

2. What else should I consider doing to the speaker while I am rebuilding the crossovers?<<

1. I’m working on a pair of AR-90s for my brother. I’m permanently removing the “cut switches” to make room for new (larger sized/same value) caps. It also simplifies the wiring.

I’ve already removed them in one speaker. Desolder the wires and caps connected to the PCB, remove the three nuts in the back holding the switches to the crossover board -- the switches, PCB and resistors come out in one piece. Easy to reinstall if you decide to keep them in the speaker.

2. Consider:

- Add additional bracing and/or damping material to interior of the cabinet

- Add binding posts and wire your crossover for biamping

- Add spikes to anchor the speaker to the floor

- Refinish or at least apply Boiled Linseed Oil and wax the walnut. Touch up the black areas

Rich

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Guest dogmeninreno

>I'm in the final planning phase before I restart to rebuild

>the crossovers in a pair of AR90s. I've planned to replace all

>of the capacitors with Solen poly caps and the inductors with

>Solen Hepa-Litz coils. I'll use Kimber speaker wire for all of

>the point to point wiring.

>

>With this in mind, I have two questions;

>

>1. Considering that I've never used the cut switches on the

>speaker, should I leave them or replace them during this

>operation

>

>2. What else should I consider doing to the speaker while I am

>rebuilding the crossovers?

Why replace the inductors? The seldom go bad and were built well by AR? Your choice of course. Dale in Reno.....

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I decided to replace the inductors as well in order to bring all of the crossover components to current standard. Also, given the size differential between the electrolytic caps and the poly caps I'm installing, it appears that it will be easier simply to build a new crossover from the ground up rather than to try and squeaze in the near coke can sized poly caps in the current layout.

Concerning damping, where in the AR90 case would one place additional damping material? The cabinet is totally packed above the twin woofers, and one of the two crossover boards is mounted to the back of the cabinet, the bass, lower mid crossover is on the floor of the cabinet. As far as additional bracing, I can perhaps see an additional brace about midway up the case from side to side.

I definitely agree with rewiring the crossover for bi-amping and actually did that last summer to the current/old crossover. This helped in making the speakers a bit brighter among other things. Perhaps this is due to the age of the electrolytics in the crossover, but it did have a noticeable impact.

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Okay. I just noticed that the layout print and the schematic for the AR90 do not agree on all cap values. The schematic shows a 40uf cap in the upper mid circuit, but the layout print shows it as a 4 uf cap. I've not pulled the old crossover out of the cabinet as I was hoping to have all of the proper value caps and coils on hand before I started this project.

Does anyone out there know which value is correct? Are there any other descrepancies that I've not yet noticed?

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What I listed in my previous post were possibilities I considered for the AR90s I’m working on. The owner’s desires and budget dictate what upgrades will be done.

>> I decided to replace the inductors as well in order to bring all of the crossover components to current standard.<<

My $.02 -- As Dale said, “Your choice of course.” But, I have to agree with him on a cost/benefit basis. Most bang for the buck is in upgrading caps and wire.

Are you replacing the 2 resistors that must stay in the crossover network?

>> Also, given the size differential between the electrolytic caps and the poly caps I'm installing, it appears that it will be easier simply to build a new crossover from the ground up rather than to try and squeeze in the near coke can sized poly caps in the current layout.<<

I know what you mean. The 100 uF caps I use are the same size as an empty TP roll and I parallel another cap with them to get the value I need. I had great success on my AR 11 project building the crossover on a larger piece of pegboard and then gluing it to original board inside the cabinet that I had removed all the components and hot melt glue from. I aligned the binding post and switch holes to keep them in same position as original.

>> Concerning damping, where in the AR90 case would one place additional damping material? … As far as additional bracing, I can perhaps see an additional brace about midway up the case from side to side.<<

You might try contacting Sean about the additional bracing he did to his AR 9 and AR 90 cabinets. ( #3181, "RE: AR9 owners, what are your preferences?" )

The “damping material” I’m referring to is not the Dacron polyfill. Don’t add any more of this. I was suggesting you “consider” applying spray on or brush on damping material, or adhesive backed damping sheets to the interior surfaces of the cabinet to “deaden” (minimize resonance) of the cabinet.

Rich

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Given the existing resisters are ceramic non inductive wire wound , I had planned on recycling them.

I'm a bit ashamed to admit this, but I am not familiar with the term or phraose of bypassing in reference to caps. Might someone elaborate on this concept and then explain the whys of doing it?

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>>Given the existing resisters are ceramic non inductive wire wound , I had planned on recycling them.<<

I was just curious. I plan on recycling also. My only concern is if I have to rebuild the upper crossover on a new board, the leads on the 6 Ohm resistor on the upper board are very short.

>>I'm a bit ashamed to admit this, but I am not familiar with the term or phrase of bypassing in reference to caps. Might someone elaborate on this concept and then explain the whys of doing it?<<

Don’t be ashamed. That’s why we have this forum. To ask questions and share knowledge. Rather than plagiarize, here is a web site that explains the hows and whys of bypassing, including cascade bypassing: http://www.northcreekmusic.com/Bypassing.html

I used North Creek Zen caps (no bypassing) on my AR 11 project. I might try bypassing at a later date on a different project. IMHO - It can get very pricey when you start experimenting with numerous brands of exotic bypass caps.

Rich

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I have one of the upper crossovers on the bench at the moment and have been experimenting with component layout the last two evenings. So far, I've left the resistor where its at and believe that I'm ready to start hot glueing components in place. So far, it looks good that the crossover can be wired component to component without the need for additional wire AND have the new coils in the original configuration.

I've one unplanned change of design that didn't thrill me. My local supplier was supposed to have ordered the Hepa-Litz inductors, but discovered the US supplier doesn't carry them. They also discovered that the import duties and freight in getting directly from Canada was going to be excessive, so they ordered the standard 14 gauge Solen inductors instead. The US supplier does carry aplha-core copper foil inductors, which is what I now have for the tweeter section.

For the bass, I'm using a Solen 200 and 150 poly paralleled to get the 350 uf needed for the circuit. Thank God room in the case isn't a factor.

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  • 2 weeks later...

The crossover rebuild, the task is done.

All capacitors were replaced with Solen Poly caps, even the 350uf in the bass section. I did have to use a 150 and 200uf cap to get the proper value in this circuit. All of the inductors were also replaced with Solen 15 gauge except for the .1uh coil in the tweeter section where I used an AlphaCore copper foil inductor. All wire was replaced with Kimber TCX 15 gauge copper with Teflon insulation and the speakers are bi-wired. Several of the replacement cap and coil values were close but not exact replacement values. Given the old parts were rated plus/minus 10% and the replacement values were no more than 4% off and rated plus/minus 5%, it was felt by Solen and myself that this would have minor if any impact in performance.

Also, I did remove the attenuation switch assembly. It's not missed!

The changes I'll try to describe are due as much, or moreto the condition of the old capacitors as it is to the quality of the new components.

The most dramatic change is the upper mid range driver now being a major contributor to the sound stage. Previously, it was nearly silent with the lower midrange driver performing 80 percent of the work. Female voices are now primarily reproduced by the upper midrange, male voices are mixed equally between the upper and mid. Female voices, such as Shania Twain no longer eminates from the bass section. Overall definition and soundstage has dramatically improved with quite a bit of high frequency detail now reproduced that had been missing.

Overall, this was a project well worth the effort and price paid.

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Guest Brian_D

Overall, this was a project well worth the effort and price paid.

Come to that... what did this rebuild cost you, and what parts did you reuse? (I need to build one from scratch for a center project)

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>Overall, this was a project well worth the effort and price paid.<

Thanks for coming-back and reporting your results. I've been contemplating changing caps in a pair of 90s (of a friend's) or my 9s or the 10pi project I'm still waiting to complete.

It seems to me that if I bought a 1968 Camero and I were driving it every day, I may well want to upgrade the shock absorbers and tires even if I were to keep the rest of the car stock. It should ride and corner better, right?

Have I then insulted the integrity of the overall design and build of the car? I don't think so, though some might disagree.

Now, if I started putting Firebird body panels on it or installed a larger Ford engine from a Mustang, well, now I have "destroyed" the original design intent.

So, while I'm not going to replace my drivers with KEF ribbons, I'm thinking I might do a capacitor upgrade on the upper cabinet (although I'll likely leave the inductors alone).

As I understand it, AR was big, big, big on lab tests and measurements. Seems to me if I don't change the value of the capacitors I'm not really changing those measurements and any changes would be subtle and in theory should allow only better information of the same type and amount through the component.

So I ask you; although obvious, do you find the overall effect "subtle" or "startling." I ask because I don't want startled.

Bret

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The effect was a bit of both. The detail is vastly improved as well as the over all clairty. I wasn't aware that I could not clearly hear the lyrics to some music until I after the upgrade and I was hearing it clearly for the first time. Increased detail, openness and clarity were the subtle changes. The major changes were due to simply to having decent caps in place that now prevented information from going to the wrong section; such as female voices coming out of the bass drivers.

Given the effect of replacing the lower mid and bass caps, I do recommend replacing the caps on the lower crossover as well. I did have to use a 200 and 150uf cap in paralell to get the 350uf for the bass section, plenty of room in the cabinet. Tighter bass and precise midrange will be what you get.

I've driven these speakers bi-amped with the old crossover and was very pleased with the sound; Brighter and a detailed sound stage. I'll be bringing my bass amp home tomorrow night (power spike took it out) and will see what the speakers sound like bi-amped with the updated crossover.

Total cost for the upgrade with new caps, inductors and wire was around $300

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>The major changes were due to simply to having decent caps in place that now prevented information from going to the wrong section; such as female voices coming out of the bass drivers.<

Yeah, it really sounds like your 90s might have had some serious "issues." Do you have any idea how the caps might have ended-up being so wrong? Too many years playing Parliment and Funk-A-Delic at earsplitting volumes or maybe just age or, whatever?

The reason I ask is that if it is just age, then there are a lot of us who may be suffering the same thing and don't know it.

Bret

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I purchased the AR90s new and know exactly how they have been treated; Used but never abused.

I didn't realize that the bass crossover was "leaking" high frequencies until after I had rewired the speakers for bi amping. I hooked up one section at a time to proof out my wiring job and heard Shania Twain's voice coming out of the bass section, abet very softly. Simply put, the old caps leak rather badly from age. Also, they flat out will not hold a charge.

My bet is that most of the existing AR90s have worn out caps in them by now simply due to age.

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Bret,

When I replaced the caps, wires, and resistors in my AR11s, I “prototyped” a crossover. I used the original inductors and attenuation switches. I used all new caps. I found 10uF and 40uF caps- no problem. I had to parallel a 100uF and a 20uF cap to get 120uF for the woofer. I replaced the (cheap and thin) original wire with Teflon insulated 14 AWG silver clad OFC to mid and tweet and 10AWG OFC to woofer. I replaced the resistors because some of the originals looked like they had been cooked. I had no intention and believe it sacrilege to replace the original drivers with anything non-AR.

I built one crossover, installed it, and tested it against a “stock” AR11. The difference between the two was “subtle” but obvious and noticeable. Its not like they were very different speakers. There was no change in the “AR signature”, but one was “cleaner” than the other. The difference is very much like your description of your experiment with the power cords.

I believe my test was validated when my 13 year old daughter walked in on one of my tests and asked me what I was doing. I told her I was testing the speakers to see if they sounded different. She did not know which was which and after standing in front of each one of them for just a few seconds she pointed to the “restored” speaker and told me it sounded better. I asked her if she was sure. In a teenager talking to parent voice she replied, “can’t you hear the difference.” A budding audiophile.

When I had both restored AR11s completed the “subtle” became “startling”. As startling as what your heard with a change of power cords. But also in a good way. As I described in another thread, I heard things – instruments, notes from instruments, vocals, inflections, ambiance, … I didn’t hear before restoring the AR11s. And something else. A “blackness” between the notes that I’ve read about and now can say yes, I know what they mean, because I’ve “heard” it too.

I’m doing something similar to a pair of AR90s. Replacing caps and wires only, and removing the attenuation network. Original inductors, drivers, and resistors – no biamping. I believe I’ll have comparable result to rrcrain’s.

As far as the cap values – Since space is not an issue, if I can’t find an exact value match, I plan to parallel two or more caps to get an exact value match.

Rich

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>My bet is that most of the existing AR90s have worn out caps in them by now simply due to age.<

I appreciate the response. Just age, no 130db KISS sessions. . .hmmmm. That's really bad news. I was hoping that you didn't know the full history of the speakers and maybe, just maybe, all my speakers didn't need new crossovers.

Between your description of your 90s and Rich's experience with the 11's *now* I'm going to feel like I could "do better" by rebuilding my crossovers.

Bret

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I suppose this could be viewed as a positive or a negative effect of the crossover rebuild. The new crossover revealed that one of my upper midrange drivers appeared to be dead. My first thought was that I had made some sort of wiring error and spent quite a bit of time going over and over their wiring. After I was convinced the crossovers were correct, I decided to order and install a new driver, and original parts are indeed available. Once installed, the new driver had a startling effect, working as designed. Since the old driver is unrepairable, I carefully unassembled it to determine what had happened. What I discovered should NOT be an issue with other speakers (hopefully). The dome had two creases in it directly opposite of each other, probably from a moving accident, that had deformed the voice coil to the point it had popped out of the magnet groove. This defect was not audible with the old crossover since the driver in the other speaker was all but totally dead.

Having the upper midrange drivers actually working makes these old AR's sparkle.

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  • 1 month later...

This post is a partial reply to Richard (Timbertop) on a question he asked me about in a different thread.

>>I am interested to hear about the results from the AR90s you are currently testing. Would you be able to describe the capacitance test you used, indicating what equipment? And indicate what recordings you are using as the listening test.<<

Richard,

I remove the capacitors from the crossover and then test them with a capacitance meter. It is a time consuming operation because I de-solder the capacitor leads and usually some other components or wires from a connector. I do it this way in case I have ot reassembly the crossover with the original parts. Whoever assembled these AR-90s went crazy with the hot melt glue gun. It was caked on everything.

I use this capacitance meter from Parts Express:

http://www.partsexpress.com/pe/showdetl.cf...tnumber=390-735

It is the only one they sell with a high enough range to test the big woofer caps in AR crossovers.

I’ll post again about results and recordings used after I finish final assembly on both AR 90 crossovers and get an initial listening test of both speakers with new crossovers. Hopefully in the next day or two.

BTW I found 3 more “bad” capacitors in the second AR90.

Rich

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Brian, my apologies for not having answered your question sooner.

The only parts in the speakers I recycled were the two resisters. New caps, new inductors and wire. The inductors were all 15 gauge copper wire except for the tweeter where I used a Goertz 15 gauge copper foil inductor.

Cost wise, the total project was over $200. I paid $200 up front to the local shop to order the parts and over 2 months after the fact, I have yet to be handed a bill for the remainder. Best guess is the total project was done for around $300. I've mentioned this issue to one of the co owners and he wasn't concerned about it.

Not included in this cost was the cost of one new upper mid driver. I discovered one was dead, and had been dead for some time. It just wasn't obvious until the new crossovers were installed.

BTW, a Heathkit IT 2250 was used to check the new and old caps.

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Having recently studied the crossover schematic and design concepts of the AR9 which Tim Holl wrote up, I decided to take a look at the AR90 just to see what differences there are. I was especially curious about the low pass section for the woofers. I would say that if you rebuild this crossover network, it is important to reuse the original chokes (inductors.) Their DC resistance and current carrying capacity are critical to the design. They also work in combination with the final mechanical system resonance point and resulting electrical impedence versus frequency curve which is dependent not only on the drivers but importantly on the internal air volume of the cabinet and its air tightness.

The design of the AR90 low pass section was surprisingly different from that of the AR9. AR9 was true to the basic concept while AR90 was much simplified not having the impedence equalization off resonance feature of the AR9. Perhaps the characteristic impedence of the drivers made that unnecessary.

Strangely, the topology of the design of the crossover circuit for the upper midrange horn dome changed as well changing the 6uf choke to 8 uf and adding a 1.37 mh choke in shunt between the 24uf cap and the 0.2 mh choke. This should have changed the overall tonal balance between the AR9 and AR90 in that range slightly. Was this done to increase the power handling capacity of the system and reduce upper midrange driver failure at high volume? Perhaps Tom or Ken could shed some light on that.

The program equalization switches used a slightly trickier arrangement using two resistors in series for the 6 db cuts where the AR9 used one resistor for -3db and another for -6db. No idea why but they are equivalent.

I would think that given how critical the realationships are for matching the crossover to the drivers and cabinet, especially the woofers, this is one series of speakers where all of the production units would be checked or at least a fair random sampling of them would have been checked in each production run to be certain that the bass response conformed to the prototype within spec. While a lesser manufacturer probably would not have bothered, I suspect, AR would have made the effort. Personally, I'm of the opinion that in this case, "don't fix it if it ain't broke."

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> Personally, I'm of the opinion that in this

>case, "don't fix it if it ain't broke."

Soundminded, your advice is valid for anything that works, including speakers. In the case of my speakers, age had taken its toll.

Once the new crossovers were installed in both speakers, it became extremely apparent that the upper midrange driver on one cabinet was dead. I first thought was that I had made an error in wiring one crossover and I spent a few evenings tracing my wiring and taking resistance measurements on both assemblies. Once I was convinced both were correct and exactly the same, I swapped the upper mid drivers, and the once dead circuit produced sound.

Since I lack a sig gen, I was stuck with having to compare the drivers and used a DMM set to the diode setting; enough voltage to produce a click and nothing more. One driver produced a click, one didn't. I did take the driver to the local shop the next day and confirmed its death. My best guess is that the driver had been dead for several years and had been damaged in one of my moves. Simply put, the voice coil had been forced out of the magnet groove and was resting on top of the magnet face.

Amazingly, the dead driver was producing just about as much sound as the good driver with the original crossover assembly. I checked the original capacitors and dicovered that they had drifted from their original value by over 20% and had a high leakage current.

Your comment on the bass section though especially caught my interest. I did replace the original inductor with a solen 15 gauge inductor, which if memory serves me correctly is one wire gauge larger than the original. What if any negative change would you expect to hear, and how would you recommend counteracting this change?

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I would compare the dc resistance of the original inductor with that of the replacement. The replacement should be lower because the wire gage is greater. If there is much difference, I would wire a precision resistor of the value of the difference in series with the replacement inductor. My hunch is that the lower resistance would lower the value of Q, the resonance magnification factor. This would theoretically cause the bass response to drop off just a small amount. Anyway, that's how I'd compensate for the difference if I felt there was one and it meant anything.

I'd be interested in your measurements if you make any and your comments. I was also hoping to get comments from Tom, Ken, or anyone else who'd care to give their thoughts about it.

BTW, did you have the driver repaired? Did you find a suitable replacement? What happened? Don't leave us hanging.

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