AR90 restore project

[Mr. Weather]

I started sanding the second speaker last night. It had some gouges in the top that required deeper sanding but fortunately I did not sand through the veneer.  This second speaker had drips of grey paint on the back and brushed-on black paint over those, so I ended up sanding the entire back.   So the second speaker has been sanded entirely except the front black.

Also, great news, the base of the second speaker has far less damage than the first speaker.  The base is pretty much entirely entact, and now I can see that the bulging button of the first speaker is just water damaged MDF.  The second speaker does not have this problem.  The second speaker does have some damage at the corners but this is minor.

I didn't get an 'after' photo of the second speaker but overall it sanded well.

I am still waiting for the epoxy, capacitors, and other parts to arrive for this project.

On the first speaker, I need to sand the entire back.  The test spray of black paint was good but all of the original black paint will need to be removed from the back to ensure an even looking new black spray.  This is not surprising as a paint job is only as good as the surface that's being painted.

Right now I have 2 hurdles:

First, the plastic grill peg sockets/holes are in the way of complete sanding on the sides. Removing the sockets by pulling them out damages the veneer, however I can use a die grinder to remove their plastic to the point where they should come out without a fight. However before I do this, I want to make sure that the new plastic sockets on order will fit correctly.  So I need to wait for those to arrive.

Second, the walnut veneer is damaged on the first speaker near the bottom.  A thorough repair job should really include fixing that.  To fix veneer, the damaged and missing veneer can be filled in with epoxy and sanded.  This will result in a non-matching spot.  The better method is to cut out the damage veneer and replace it with new veneer.  This results in a less obvious repair and shows an attempt at a correct repair.  Either method, done properly, should help stop the veneer from continuing to peel off.  I ordered some walnut veneer to make a proper repair.

My test panel with 4 coats of Danish Oil on walnut wood looks great.  4 coats applied over 4 days gives the most sheen and depth to the wood.  I polished it with XXXX steel wool after day 3, and then polished it with a clean cloth after day 4.

On the Advent forum, I have a thread going for a local set I found that needs some love.  So I'm re-foaming those today.  The worst things I've found so far are the incorrect use of gaskets between the speakers and baffle board, and a replacement tweeter wired right to the woofer's positive terminal.

[Mr. Weather]

Work is still moving along:

1. I epoxied the bottom of the speaker that had damage to the MDF.  This worked well although I could have used a second box of epoxy. Having done this once, I got a great appreciation for the process and I could do it again better on another pair of these.  However this is a very good solution for the damaged MDF.
2. The black backs of both speakers have been sanded bare and repainted in a matching black.
3. I cut a new bottom base for the cabinet that had the MDF damage.  Instead of using 3/8" MDF or particle board, I used 1/2" plywood.  Additionally, I added a 1/4" layer of oak around the perimeter of this new piece.  I will add the same oak boards to the bottom of the other cabinet and this should help prolong the original MDF there.  The oak will provide a strong surface for mouting metal feet or felt or whatever may be needed in the future.  No photos of this yet.
4. I was able to remove the plastic "poly grill guide" sockets from the cabinet sides using a die grinder to remove the plastic material from the inside of each socket. This weakened them and allowed me to pry them out without pulling up the veneer.  This enabled me to sand the veneer surface completely. I got replacement grill guides from Parts Express to ensure these will work before removing the old ones.

I'm still waiting on the walnut veneer. Should be here in 2 or 3 days.  Today I will ge the new footer boards installed and get some photos.

[DavidR]

Looking goood!

[johnfalc]

These are lucky speakers to have found you!

[Mr. Weather]

20 hours ago, DavidR said:

Looking goood!

16 hours ago, johnfalc said:

These are lucky speakers to have found you!

Thanks!  It's been a fun but slow project. I ordered another kit of epoxy and will use that to get the base totally flat and to attach on the new plywood and oak bottom piece, shown below.

Still waiting on the walnut veneer.  That's the main hold up right now.

[Mr. Weather]

It is cold and rainy here in Houston.  Perfect weather to stay inside.  I started on the crossover work.

I will use standard NPE capacitors all around, with the addition of 0.01 uF poly capacitors in parallel to the 4, 6, 24, and 80 uF capacitors, with the goal of revealing a bit more sound detail without affecting performance.

Below I have the white 0.01 uF CornellDublier 940C caps glued and soldered to the NPE caps.  I got the 940C from Mouser and the NPE caps from Madisound and Parts Express.

I also ordered a new set of Pomona "minigrabber" test clips for my Fluke 115 meter in hopes of getting more accurate capacitance readings, especially from the old caps.  So we'll see if that makes any difference.

I recently successfully replaced all of the capacitors, inductors, and resistors in a pair of Original Large Advent (OLA) cabinets without removing the crossover boards from the cabinets. That worked well enough but those crossover boards are less cluttered than the AR-90 ones. However that gave me some confidence that I can replace the AR capactitors with the boards in place without too much grief. I am using my son's Haiko soldering station which is quick and powerful.  The main hurdle is my old eyes.

 

[DavidR]

For me the 6uF was the only difficult one to solder, especially the side that goes to the blue wire. I got a battery operated light in there, cut a length of solder approx 18" and used it like a welding rod. Then I got the (cold) soldering pen in place, turned on the juice and used my other hand for the solder. Crammed.

[Mr. Weather]

6 minutes ago, DavidR said:

For me the 6uF was the only difficult one to solder, especially the side that goes to the blue wire.

Yep, that one is on the top of the rear board and looks to be a stretch.  I took one photo and couldn't even see the dang thing. However later I realized if I go in from the other side it's more visible.

[DavidR]

If you have a Harbor Freight store in your area pick-up one of these lights.

 

 

 

 

[Mr. Weather]

45 minutes ago, DavidR said:

If you have a Harbor Freight store in your area pick-up one of these lights..

Yes those are handy.  I ended up using a compact gooseneck desk light that worked well.  The caps are all swapped on one speaker.

The uppermost cap is a real bear.  Not easy to get the soldering iron and solder up that high while trying to see into the cabinet.

For some of the replacements, I ended up leaving some of the old capacitor wire in place, bending that into a tiny hook with needle nose pliers, making the same hook on the new capacitor wire, and then hooking the two together.  Then the new one stays in place for soldering.

[DavidR]

3 minutes ago, Mr. Weather said:

For some of the replacements, I ended up leaving some of the old capacitor wire in place, bending that into a tiny hook with needle nose pliers, making the same hook on the new capacitor wire, and then hooking the two together.

Yup, many times I'd leave the old wire/lead to make it easier to connect the new cap.

[DavidR]

Make sure the 350uF is wired correctly. It may just be the camera angle making it look like the red wires/coil and one side off the cap (POS) are connected to the green/white/ black/resistor cluster (NEG). They should NOT be connected. Make sure they can't touch if jostled about and/or insulate the exposed metal.

ar90 xoverschematic.pdf

[Mr. Weather]

1 hour ago, DavidR said:

Make sure the 350uF is wired correctly. It may just be the camera angle making it look like the red wires/coil and one side off the cap (POS) are connected to the green/white/ black/resistor cluster (NEG). They should NOT be connected. Make sure they can't touch if jostled about and/or insulate the exposed metal.

ar90 xoverschematic.pdf 54.75 kB · 2 downloads

Good catch.  Fortunately, as you mentioned, this was the angle of the photo. Here is an overhead shot.  I did glue down the new components (and the 1 ohm resistor) to ensure no shorting.

That is a fantastic schematic.

[DavidR]

AHhhhhh, that's better. I sometimes add electrical splicing tape over exposed areas that are close.

Better to be safe than sorry; but that's just me.

[Mr. Weather]

All of the capacitors are replaced.  I got more accuate measurements of the old caps this time and some of them are still in spec. The last 40 uF broke when I took it out, so I did not measure it.

 

 

[AR surround]

Those original 6 uF caps in my AR90's were yellow mylar types.  I'm assuming that they are the same in your pair.   The highs with the series tweeter caps as the original 4 uF Callins and the 6 uF mylar sounded like a "chuh" compared to a more pleasant "shhhh" after I replaced them.   

Here were mine for reference. Some  values were remarkably close to yours.

[Mr. Weather]

24 minutes ago, AR surround said:

The highs with the series tweeter caps as the original 4 uF Callins and the 6 uF mylar sounded like a "chuh" compared to a more pleasant "shhhh" after I replaced them.  

I am not surprised to hear this. Seems like a reasonable difference.  It's a piece of evidence to support the idea that it is difficult to find the authoritative source of truth with sound.  While people can agree on technical standards such as flat frequency responce, high dynamic range, low distortion, or perhaps replacing worn, old, or faulty electrical components, I am reminded that everything in the electrical paths can potentially make a differnece, audible or not, measureable or not.  When you add in the decisions of the musician, recording engineer, music producer, or author of the recording software or designer of the studio monitor speakers, or the team who designed the home listener's audio amplifier, there are countless variables.

I was reading about the history of Rudy Bozak. After years of successful work and products, he was reluctant to adopt acoustic suspension designs.  The man spent a lifetime designing speaker drivers and experiementing with materials.  He thought things should be a certain way and that's how he designed them. 

I mention that because like any endeavor, I think it's great that people can have a discussion about the finer points.  While audio might seem like a straightforward science, it's far more complex than that when you go down the rabbit hole.

[Mr. Weather]

Does anyone have any thoughts on the side grills for the AR-90?  I have always thought these looked odd and have never cared for the look.  I suspect their bulky presence was designed to draw attention to the woofers on the sides of the cabinets which may have been unusual at the time. AR wanted people to notice them.

Anyhow, I keep pondering the prospect of reproducing the side grills, but making them much more slim.  Each grill assembly about 1-1/8" thick and protrudes about 1-1/4" from the side of the cainet.

It seems like it would be possible to build one that was no more than 1/4" thick and maybe protruded only 3/8".  This could be done with pine boards cut down to 1/4" thick and maybe 1-1/5" high, and joined at the corners with a glued half lap joint. Paint them black.  Install mounting pegs. Staple on black fabric.

[Aadams]

1 hour ago, Mr. Weather said:

Does anyone have any thoughts on the side grills for the AR-90? 

I don't think you will solve the problem with thickness.  It is more an issue of overall proportion.  The AR9 and 90 woofer grills have identical measurements.  Aside from the obvious height difference, their cab depth and width vary by around a 1/2 inch in both dimensions, virtually indistinguishable to the eyeball.  

This is a good thread if you haven't seen it.

 

[Mr. Weather]

27 minutes ago, Aadams said:

I don't think you will solve the problem with thickness.  It is more an issue of overall proportion.

My theory is that thinner side grills would be less distracting looking.  But it could be true that any grill on the side would be distracting looking, and shaving 1 inch off the grills wouldn't make any real improvement. I feel compelled to at least make one and see how it looks.

Good thread.  Great that the OP got the AR-90's for $125 in 2010.

[DavidR]

What many AR9 and AR90 owners say > "If you want this sound you have to accept the looks that comes with them."

[Mr. Weather]

46 minutes ago, DavidR said:

What many AR9 and AR90 owners say > "If you want this sound you have to accept the looks that comes with them."

Seems reasonable.  As I've gotten old I've realized that the looks of something may fall in and out of favor over the decades.  Could be the same here.  Ultimately the quality of the sound is what matters most here.

[Mr. Weather]

I applied a second batch of epoxy and used that to attach the new base.  Next major work is the walnut veneer repair after it arrives.

[Mr. Weather]

I made a great deal of progress tihs weekend.  In review:

1. The rear of the cabinets posed a challenge. The bare MDF soaks up paint like a sponge, and the high porosity and varied condition of the wood means that the painted finish is uneven and splotchy, even with 3 coats of paint.  Rattlecan paint is splotchy enough anyhow.  Probably I should have used a primer.  However, I settled on this formula:  3 coats of paint over an hour, let it dry for a couple of days, then sand with 320 grit, wipe down with alcohol, then apply a single, even final coat working as carefully as possible, and don't mess with it.  I think the resulting sheen is greater than the factory paint, but it's totally acceptable.

2. The bases worked out well.  One cabinet of course didn't need much work.  The other one needed a new base which I replaced.  Both cabinets got a 1/4" solid oak footer, kind of like a horse shoe, to protect the base panels and provide a strong attachment point for feet or whatever. In the cabinet with water damage to the MDF, I applied 2 coats of epoxy and then stuck on the new plywood base.  At some point I masked the cabinets with plastic and tape (yet again), and used the same black paint on bases to match the factory paint, however I did not paint the surface of the oak that contacts the floor because there's no reason for that to be painted.

3. Veneer repair:  This was challenging.  The basic premise worked.  I even used a piece removed from the large area of damage to repair a smaller damaged area.  But the new veneer has a more contrasty look than the original so it's not a great match.  I also had problems with the new veneer chipping at the lower edge even when I hand sanded it.  Probably I did not use enough glue.   I filled in some small areas with wood epoxy putty and those did not accept much stain and do look lighter. So, ultimately the major damage is fixed and physically tied off, but the end result is not as polished as I wanted, cosmetically.

4. I gave the factory original walnut veneer a quick once over with 320 and wiped it down with acetone and paper towels to remove any residual dust or contaminants.   The weather today is perfect with a high of about 72*, mostly sunny, and low humidity.  So the acetone flashed off quickly.  I cracked open a new can of Danish oil and started applying it with a clean used cotton rag.

All I can say is wow!  Instantly the walnut looked fantastic.  Really amazing.  Just after staring the first application and seeing how great it looked, Hotel California came on the radio. I am not superstitious but I saw this is a a good sign because it's a great song and great album, in spite of the poor folks being condemned to Hotel California for eternity.

I applied a heavy coat of Danish oil, let it soak in 15 mintues, then did a second one, let it set a while, and then wiped it down. There was not much residual to wipe off; the walnut soaked up 99.9% of the Danish oil. That was all done per the instructions on the can, and I will consider that one coat.  I dollied the cabinets back inside and they're resting.  (I must have wheeled these things in and out of the house a dozen times now.)  After about 24 hours, I will sand them with fine sandpaper (or use steel wool), wipe clean, and then do a second coat.  At a minumum I will do a 3rd coat but I don't know if a 4th will be needed.  I don't want to overdo it and somehow end up with a bad result. 

You will see in two of the photos that the lower cabinets near the woofers have a different look to the wood.  This is real, and it has always been there since I stripped them.  Whatever was done at the factory originally has caused the wood around the woofers to be lighter.  Clearly it relates to the fact that these were painted black at the factory in that area.  This was always as risk for this project so I can accept it.  I don't know if this will minize with more Danish oil, or not.  There is always a possibility to re-apply the factory black pattern of paint, although that is not my preferred route right now.

I will need to touch up the factory black paint on the fronts in some areas, but I will probably use a small paint brush to dab it on carefully.

Anyhow, I am totally jazzed that the walnut shined up like it did.  This is a great step forward.  Can't wait to get these things rocking again.

[Mr. Weather]

The Danish oil is moving along.  I applied a 4th coat this morning and that's it. It needs to cure more and then get buffed.  Maybe I will wax it, but not for several days.

I measured the threads of all of the screws while I had them out, and the measurements are in a photo below.  (spoiler, most are #10 with 24 threads per inch,  the others are 1/4" x 20 threads)  Most of the screws were showing some rust, so I brushed them with a small stainless steel brush, cleaned them with alcohol, and gave them a light coat of matte black paint on just the heads.  The screws for the LMR drivers did not need paint so I left them alone.  One of the woofers had one slightly undersized screw.  Amazingly in my random assortment of screws, I had a few that were near perfect match:  The correct threads, nearly the same head, light black in color, and only about 1/4" too long.

I hand painted a number of really tiny dings and chips in the factory black paint, and I need to do the same to some edges where the light colored particle board is visible, but I will use a brown paint that matches the valnut. You can see this on top rear corner in the photo below where the light MDF stands out between the walnut top/side and black rear.

I have not done much with the front grills, but today I washed them with soap and water.  I am not inclined to recover them as the holes are not highly visible except one pea-size hole.  The resulting wash water was filthy though: grey-brown. 

I was able to get new AR90 badges, but they do not have any backing plates.  It should be really easy to make backing plates using a small piece of sheet steel with a small nail welded or glued to the back.  Securing this in the grill mounting hole can probably be done with a small cork instead of the original metal push-on nut which is probably difficult to source cheaply and difficult to make.  We shall see.