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AR90 Crossover rebuild


rrcrain

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Amazingly, the local shop was able to locate a supplier that has a stock of new upper midrange drivers on hand. Unfortunately, the first replacement that arrived was bad. Based upon the dome geometry, it appeared that the voice coil wasn't in the manet groove. The second replacement was a perfect sonic match to the 20 year old driver; well as perfect as my ears can determine.

I'll see if I can hunt up the old inductors and get some reliable DC resistance measurements on them and get the measurements posted later this week.

I thought you were going to tell me the bass would become a bit over pronounced, not a dropoff in bass response. I do NOT want any more bass out of these puppies! If it's a bad recording, the bass can be unforgiving. If its a well done recording thats been well mixed, its georgeous.

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I suspect the real issue is my ears and what I've become used to hearing. I'm not yet used to precise, well defined bass with a distinct report to it when its in the recording.

As an added note.

I'm using a pair of Heathkit AA-1800 amps to drive the AR90s in a horizontal biamp arrangement. As an unscientific observation, both amps used to become rather warm at moderate listening levels, around 30 to 40 watt peaks. With the new crossovers, they are almost stone cold at the same listening level.

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I'm using a Mosfet 120 I built as a kit about 11 years ago to drive AR9s. I think it's a fine amp. It was sold by Soundvalves also known as Soundvalues in Ohio who had bought up all the old Dynaco stock. This amp was kind of a successor to the Dynaco Stereo 120 designed by Klauss and Peterson who where quite famous. It's birdgable to 240 watts mono and always seems to run cool. It has a nice big power supply and sounds excellent to my ears. I took it to a friends house shortly after I completed it and several of us compared it to many fine amplifiers he had on hand including some Haflers and it held its own without any problems. My only regret is that I didn't buy several more. At $200 a pop for a box of parts and 7 hours of very easy assembly, it was a steal. It can easily make the AR9s thunder in a room of about 4000 cubic feet.

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You'r comment got me to thinking last night about my amps and speakers. It wasn't until last summer that I had rewired the speakers to enable them to be biamped, or that I had even acquired a second amp for the purpose. The AA-1800 is rated at 250 per channel into 8 ohms, 500 watts peak per channel and a bit more than that into 4 ohms.

It's only been in the last few years that my old amp started running on the hot side and I had assumed that it was the electronics showing its age. Apparently, I was right, but it wasn't the electronic components that I had imagined. Since electrolytics do dry out with age, anyone know of an excellent cource for large electrolytic caps in the 13,000 uf range? I suspect that I should start looking for neww ones to drop in my amps.

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I'd go to a large electronics parts supply house first. Don't forget to check the dimensions of the original, diameter and height as well as voltage. I had a lot of trouble finding a suitable replacement for the caps that failed in a Dynaco SCA80Q until I ordered them from Soundvalves (no longer in existance). The originals were made in Scotland. The replacements were......Mallory. Surprise surprise. I think CRC is a large manufacturer also. Maybe Panasonic.

You might check to see if the thermal conductive grease for the output transistors has dried out too. Let me know if you replace your capacitors and it works. That wouldn't have been my first guess for overheating. In fact come to think of it, I'not sure what would cause that. Bias current drift in the output transistors??? Bias control pots can get noisy just like any other pots.

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oops! I miscommunicated here.

The issue with running hot was taken care of with the new crossovers.

I'm looking to replace the power supply caps as a preventative measure before they suffer a catastrophic failure. The rails in these amps are pos and neg 100 VDC fused at 5 amps each.

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>>I am interested to hear about the results from the AR90s you are currently testing … And indicate what recordings you are using as the listening test.<<

After a couple of late nights, I finally finished the crossover rebuild on my brother’s AR-90s. The only way I can describe how they sounded before we started this project is “inconsistent.” Sometimes they sounded OK and sometimes they sounded awful. These were an eBay purchase, so we don’t know the history of this particular pair.

Originally, our intent was to keep the cost to a minimum. I reused the coils and resistors. I used a combination of mostly Dayton, with a few Solen, and North Creek Zen caps. I replaced the hook-up wire with the same type I used in my AR-11 project. The attenuation boards were removed. The 40uF Zen cap takes up most of the space where these boards were.

When I tested the first prototype against the “stock” AR-90, I was somewhat disappointed with the results. After I had already put the crossover together, Sean posted a message about not using inexpensive (Dayton) caps. Having used some Dayton caps and “hearing” them, I have to say that I agree. I discussed the results with my brother and we decided on a Zen / Solen combination.

The Dayton caps were removed and the prototype rebuilt. After a short listening test I was convinced we had the right caps.

With both crossovers rebuilt and installed, right away I can tell the sound was significantly improved. There is so much more detail and clarity. A larger sound stage in that the music seems to extend further back behind the speakers, what I call ambiance. The improved detail and clarity, dare I say accuracy, has been described as if a curtain has been removed from in front of the speakers. I believe that description fits here.

For listening tests I believe it really doesn’t matter so much what you listen to as it does listening to what you like and are familiar with.

I start with Cowboy Junkies’ “Trinity Sessions.” Mining for Gold - no instruments, only Margo Timmins singing. Listen for ambiance, timbre, and clarity. In 1 minute 34 seconds you can tell a lot about your speakers. “Misguided Angel” – right from the beginning of this track if you don’t feel the bass from the kick drum hitting you in the chest your speakers are not performing.

Linda Ronstadt’s “Greatest Hits Vol II.” The DCC Gold CD (remastered from original studio master tapes). You get Linda’s full range in “Blue Bayou.”

I recently added Nora Jones’ “Come Away with Me” CD to my listening tests. I’ve also added Allison Moorer’s, “Miss Fortune.”

For a change of pace, Pink Floyd, “Dark Side of the Moon.” For a quick test, I listen to select portions: Heart beat at beginning, alarm clocks in “Time,” cash registers in “Money.”

Fleetwood Mac, “Fleetwood Mac” album, “World Turning.” In the mid to late ‘70s this was THE track almost everyone used to test bass. The dealers just had to pull the grills off the and have you watch the woofer excursion with every beat of the kick drum.

Henry Mancini, “Symphonic Soul.” Some orchestral pop music. Listen to bass guitar solo at beginning of “Peter Gunn.” Must be able to hear both the bass guitar and the drum behind it.

Mannheim Steamroller, “Christmas Extraordinaire” Want a very quick test track? The first 30 seconds of this CD.

This is a representative list of what I used for my initial listening test. Additionally, some Sax/Jazz – Grover Washington Jr. “Winelight” and Male vocal - Marc Cohn, “Walking in Memphis”.

Rich

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Guest crazycat

I've been following several threads about upgrading crossovers for AR90 and AR9 speakers. I am in the process of upgrading the crossovers for my 9's. This is my first attempt to rebuild crossovers. I descided to go with Solens crossed with Audiocaps for the upper and mids. My question is what type caps did you use for the 2500 and 470 uF and where did you get them? Do you just parrellel enough to get the value?

Thanks-Robert

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Robert,

I have not rebuilt an AR-9 crossover - yet. The AR-90 crossover does not have 2500uF or 470uF caps.

I can tell you that “rrcrain” and I had to parallel two or more caps to get the 350uF value of the woofer capacitor for our AR-90s. I had one bad 350uF cap and the other one was marginally within tolerance. I replaced them both to restore the woofer crossover back to the original spec - 350uF. If you have to replace the 470uF cap you will almost certainly have to parallel some caps to get the correct value.

Have you tested the caps and are they degraded / out of tolerance / leaking?

If they test OK, I would leave them in the crossover. These caps are not easy to find and are going to be relatively expensive to replace. IMO - You spend the most and gain the least improvement by “upgrading” caps in the woofer section. However, if your woofer caps have degraded to the point they are out of tolerance, you will probably want to replace them.

>> I decided to go with Solens crossed with Audiocaps for the upper and mids. <<

Can you explain what you mean by “Solens crossed with Audiocaps for the upper and mids?” Are you bypassing Solens with Audiocaps or just using some Solen and some Audiocaps?

Rich

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I have to politely disagree on replacing the caps in the woofer section. I used a 100uf and 150uf Sloen cap to get the correct value, and the improvement in the bass response is almost beyond description. I'm not used to feeling the pressure of the peddle drum at low wattage hit me in the chest like it does now.

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Guest crazycat

Rich,

Thanks for the reply. No I have not tested the caps. I brought my 9’s out of long-term storage and was initially going to refoam woofers and mids and go with that. When I checked speakers for continuity the upper mids were blown . Having just enough understanding of crossover operation to be dangerous, I diagnosed the problem as defective caps. A capacitance meter seemed too expensive :D. Also, by this time I had come down with a nasty case of the might-as-wells.

I meant to say in my previous post that I bypassed Solens with Audio Caps for the upper and mids. Actually it is more like paralleling them, using a 3.9 Solen and a 0.1 Audio Cap to make a 4uF. I did similar for the rest, trying to match the factory values as closely as possible. The distinction between bypassing and paralleling still evades me.

Currently, I am trying to decide whether to do the same with the woofers. The thought of 5 or 6 caps in parallel scares me. That is why I’m curious if there might be an easier/simpler way (other than being logical and buying a cheap capacitance meter to test the existing caps).

Anyone have any opions/ideas?

Robert

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>>I have to politely disagree on replacing the caps in the woofer section. I used a 100uf and 150uf Solen cap to get the correct value, and the improvement in the bass response is almost beyond description. I'm not used to feeling the pressure of the pedal drum at low wattage hit me in the chest like it does now.:D (Sorry, I just couldn’t resist, LOL)

*I had my daughter participate in a “blind” listening test when I was testing the first prototype crossover with the Zen caps in woofer section, Dayton caps in lower mid, and Dayton caps with Solen 24uF in upper mid and with 6uF Zen in tweeter circuit.

Against the stock AR-90, she picked the stock AR-90 as better – except for the audibly better bass response in the prototype. She more or less confirmed what I heard. For me, sometimes the stock speaker was better, sometimes the prototype, except the prototype always had better bass. The Solen / Zen crossover was clearly superior sounding to the stock speaker in all areas.

Since Robert stated he is “upgrading” his AR-9 crossovers, the points I was trying to make:

1) Although there is a significant improvement in bass response by replacing the woofer caps, it comes at a significant cost (over 50% of the total) relative to replacing all the other caps in the crossover. It will probably be a much higher percentage of the total in the AR-9 because of the much larger cap values involved.

As an example: you buy two 200uF and 270uF Solens from Percy Audio to parallel in pairs to get 470uF caps. The cost is over $220 with shipping. I haven’t even determined a price for the 2500uF caps, but you can see the cost is already substantial.

2) I do not advocate upgrading (tweaking) by replacing perfectly good OEM caps. However, I do believe what I have read about capacitors, in particular electrolytic capacitors. While they may not “fail,” they do degrade over time and eventually need to be replaced. I also believe you and I have confirmed there is some validity to this by testing the capacitors in several speakers.

4) The only way to objectively know if your caps are degraded to the point where they are out of tolerance or significantly mismatched and are affecting the performance of your speakers is to test them. You cannot use age alone, a subjective measurement in this situation, to determine the “health” of your capacitors.

Rich

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The 4700uf monster leaves you little choice other than to use a new electrolytic. I've read some comments that the new oil filled caps are rather good. These might be an option, but I've absolutely no experience with them.

Personally, I interpet "oil filled"as "electrolytic" by another name.

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>>I meant to say in my previous post that I bypassed Solens with Audio Caps for the upper and mids. Actually it is more like paralleling them, using a 3.9 Solen and a 0.1 Audio Cap to make a 4uF. I did similar for the rest, trying to match the factory values as closely as possible. The distinction between bypassing and paralleling still evades me. <<

In one of my posts above, I referenced a web site that describes bypassing. Basically, bypassing is done by paralleling capacitors. But, all paralleling of capacitors is not bypassing. Paralleling a 3.9uF Solen and a 0.1 AudioCap is bypassing. In bypassing, you are paralleling a large (3.9uF) metallized polypropylene cap with a much smaller (0.1uF) film and foil capacitor. Additionally, your bypass capacitor will have a higher voltage rating than the larger capacitor.

Rich

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Guest Jotaeme

>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?

Hello, congratulations! Nice project. Since you may later would want to try some adjustments why not leaving the cut switches? Kimber wire and Solen poly caps are great but you might gain a lot from using Hovland poly caps instead for the tweeter section only.

Enjoy and happy listenings !

JotaM

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Well, I DID use Kimber wire throughout the project, and did replace all of the old wire. The Alphacore copper foil inductor in the tweeter section did an excellent job as well.

Some say capacitors don't wear in or break in, and I have to admit that I was in that camp myself not that long ago. All I can say is that the sound has altered just a bit as the new parts settle into their new home.

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>>Some say capacitors don't wear in or break in, and I have to admit that I was in that camp myself not that long ago. All I can say is that the sound has altered just a bit as the new parts settle into their new home.<<

Richard,

So, instead of reforming your AR-90s, you have corrupted them, turning them to a life of crime to go out and commit speaker break-in. ;-)

When I rebuild crossovers I try to play them as much as possible every day for a week to let the new capacitors “set their bias” (North Creek’s terminology) and settle in. This is part of my listening test routine for “prototypes” and after final installation of rebuilt crossovers. The Zen caps are non-polar, but directional. They have a preferred orientation with different color leads to designate “input” and “output.” Haven’t seen or read this about Solens.

I hope you are finding, as I have, the speaker’s change in sound over time is one of improvement. It gets richer, even more detailed, and deeper (more ambiance). I played the AR-90s yesterday and it was like there was a whole new dimension to the speakers.

Time for these AR-90s to go back to their owner for final evaluation.

Rich

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Guest OpusX

To all who have had the patience to follow this thread as these crossovers were rebuilt....

Looks like the AR-90s will be making a trip up to Omaha this weekend and I will get my first listen to see what Rich was able to with them and compare them to the AR-11s he did for me and the original AR-9s that I also own. Will pass on our comparisons for what they are worth to the group. What I am pleased most about through all of this is the amount of discussion and information that got exchanged and shared with respect to rebuilding crossovers which is exactly the value of this forum. Glad the speakers could serve as a testbed and I consider the money spent on the rebuild worth every penny in the information it provided to the group.

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  • 2 weeks later...

>compare them to the AR-11s he did for me and the original AR-9s that I also own. Will pass on our comparisons for what they are worth to the group.<

Enquiring minds can't wait to find-out.

Would you clarify what was finally done? I think I understand that the inductors and resistors in the 90s were NOT replaced. Did I get that right?

Bret

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>>Enquiring minds can't wait to find-out.<<

Bret,

I transported the AR-90s from Atlanta to Omaha two weekends ago. I also delivered the pair of AR-LSTs that my brother bought over a year and a half ago and had never seen or heard.

The LSTs were unwrapped and hooked up first. Unfortunately, my time in Omaha was cut short, so we did not have a chance to hook up the AR-90s while I was there. Peter will post his listening impressions as soon as he can.

>> Would you clarify what was finally done? I think I understand that the inductors and resistors in the 90s were NOT replaced. Did I get that right?<<

Yes.

The crossovers were rebuilt using the original inductors and the two resistors not in the equalization (attenuation) network. This network was removed and the switch holes filled with black plastic plugs. All wires were replaced – 14 AWG to lower mid, upper mid and tweeter; 10AWG to woofers. All capacitors were replaced with either Solen or North Creek metallized polypropylene caps.

Rich

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  • 16 years later...

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