Another Acoustic Research AR-4X Refurb

[Tim D]

I keep adding to my queue and I'm not working them off fast enough. Recently my daughter asked if it was possible to convert some KLH surround speakers into something nicer. She had bought a house that had these cheapy tiny KLH surround speakers hanging on the wall and was apparently thinking about some KLH 17's that I did for my son about a year ago. (Jealously maybe?) Anyway I was thinking about how to address what she asked and along came a set of AR-4X's in CL that I just couldn't pass up. I'm going to do these quickly for her for Christmas present as a surprise (or her birthday on Jan 1 if I can't get them done on time.) 

The speakers are in very good unrestored condition. Original grills. Original Xover (I'm pretty sure). Original Lpads (no scratchiness during a brief listen before buying). Original badges. Original papers on the backs. The woofers seem to have a date of Oct 28 1972, but they have fabric surrounds (not sure if that is strange or not.) And the drivers all work! For the most part they seem to just need service and some cabinet work. Here's what I think I need to do, but I'll have some questions of the experts.

- Need to recap. It seems to have some huge blue Sprague caps that are strapped in with what look to be original rivets. They look rather strange for original caps, but the way they are installed makes me think they are original. The strap appears to be covering the value, but I'm hearing it should be 20uF. I've got a meter and can give them a measure to see if they are close to that value.

- Need to inspect the Lpads a little closer. I've opened them up to take pics and inspect. The Lpads seem to be original. I'll close them up and hook them up to my Marantz 2220B to have a listen and verify they are problem free.

- Lpads don't have knobs on them. I'll need to verify that the originals are the same as I recently picked up from geekyshrink for my KLH Fives. If so, then I'll borrow from that project.

 - Need to dope the cloth surrounds. I have the stuff from vintage_ar already. The dust cap is fabric too and I can see through it. It doesn't look like it was originally doped. Should I put dope on the dust cap (or maybe just use any sealant since it doesn't need to be pliable?) Is the usual push test sufficient to check the seal?

 - Should I strip and sand the cabinets or just sand, fill some divots, and refinish. On other projects I've done the full strip, filled divots and used Danish Oil (Dark Walnut). Not sure what others might suggest. There are the usual scratches and corner chips and such, otherwise the veneer isn't too bad and appears very restorable.

 - The grill cloths are yellowed and stained but otherwise in decent condition. I've seen posts (ra.ra maybe?) where a bleach solution (sprayed on) brightened and removed most of the stains. Maybe I should gently go that route?

 - The badges are the original screw in type, but seem to be discolored and a bit scratched. Not sure if a cleaning will help. I'll get some pics later and share.

 - Face on the tweeters is surface rusty. I'll have to deal with it somehow. I have some satin spray paint (rustoleum I think) I could use once they are cleaned of rust.

 - Need to get some velcro for the grills. I might have some on hand, but will need to check.

 - The original foam gaskets seem to be kind of ok. Need a recommendation as to whether I can reuse them. Maybe wait on the push test to determine?

- The fill seems to be chopped up. Is this fiberglass or rockwool? I'm used to seeing batting, but this seems to be small pieces. It was stuffed pretty full too. Not used to it being packed in so tight.

- I have two tiny speaker hangers on the back of each. Did they come this way or can I assume they were added by a previous owner? (See pics of serial numbers where the hanger is shown.)

Here are some initial pics.

Oh, btw I paid $75 for them. I felt that was an excellent deal.

 

[Tim D]

 

Ok. Some more information....  And more questions.

The caps are original. There are other pics on the internet of the exact same caps. I measured them and they have drifted downwards. One is about 11uF and the other is 17uF. I'll be ordering new ones soon. I normally go with Daytons, but I'm open to suggestions if anyone has had good luck with others.

I put them back together and I'm doing a listen right now. The Lpads aren't as good as I hoped. In running them I'm finding that they are crunchy when I turn them and they do cut in/out a bit. Definitely need service or replacement. Any suggestions which way I should go? I can get the replacements from PE suggested in other threads, but if the thought is to just fix the originals I can do that. I'm not afraid.

Next step is to mask off the front baffle and back panel so I can work on the veneer. Any suggestions on chemical strip and sand; or just sand?

 

[ra.ra]

Hi TimD. You've got a nice pair of 4x's there, and everything looks original and complete - -  great deal for $75. The only thing that looks curious is that curlicue thingy which appears to connect terminal 1 and B on the back of the control pot (BTW, these are original Aetna-Pollak potentiometers, not L-pads). What is that thing-a-ma-bob? Am I seeing this correctly?

You'll get all sorts of  advice about the cabinets, but those should clean up real nice. It's just a matter of how much time and work you want to invest - - just refresh the existing finish, or sand/remove and then apply new oil finish. Just my opinion - - I like the Danish oils a lot,  but I tend to avoid the Dark Walnut - - I like it when the walnut shows an occasional blond streak, and also like to highlight the reddish tones that are in some pieces of veneer. And yes, those grille cloths will also clean up nicely - - while I've had good results with diluted bleach applications, others have shared other successful methods for restoring these to a lighter shade.

Can't quite tell from your pics, but if your badges are the incised type with the reddish "AR", they are easy to polish and restore. If they have the "AR Inc" in black - - this version is more delicate and are difficult to brighten without damage to the lettering.

Woofers look good, and cloth surrounds with semi-transparent dust cap is all normal. Tweeters look good, and some rust on face plate is also normal. These can clean up easily. For my own projects, I typically remove most everything and work on the various components separately - - cabinets with no drivers; and drivers and pots removed from the cabinets

Tightly packed fiberglass stuffing in wads is also normal, and the tissue-like separation sheet under the woofer looks to be in good condition - - it merely keeps the FG from getting into the back of the woofer.

The speaker hangers are indeed original parts supplied with the speakers for use as an owner option - - I used them once for a wall-hanging installation and they were sufficiently capable. Just remove them if they will not be used this way. And I don't think the 4x was ever furnished with knobs on the control stem, but they could always be added - - my early AR-4's have knobs, but I've never seen them on 4x's. Also, your pot control stems are the metal version, which is slightly preferable to the plastic ones. These pots will need to be disassembled in order to evaluate them properly - - then you'll be better informed on whether to restore the originals or find replacement parts. 

I've re-built several pairs of 4x's but never with s/n's as high as yours, and have never encountered that exact capacitor. The Sprague Compulytics tend to be very good and often hold their value even 45 years later, but they need to be measured "out of circuit", and it is more typical for aged caps to increase in value. You can always just replace them anyway, but you may want to re-measure before deciding to do so. Yes, 20uF is the correct value, and if you do opt for replacement, you will get many opinions and suggestion for replacement caps.

Lastly about the cabinet sealing. It is not generally necessary to dope the surrounds of the 4x woofer, but if you use the correct sealer, it will not hurt to do so - - I tend to apply a light application as I feel it helps to refresh the pliability of the cloth surround. Those white foam gaskets might be suitable for one more install, but you'll feel better if you use fresh material when re-installing the drivers - - there are several good options for doing this, but I don't like seeing these gaskets squish out beyond the driver perimeter. Pic attached is my pair of 4x using the same woofer as yours.

I hope some of this is helpful. Your daughter's gonna love these - - what a great gift! Good for you, Dad.

 

[Tim D]

Hi ra.ra,

Thanks for all of the great information. That is so very very helpful.

They do indeed have the badges with the red lettering. I've attached a pic. What is the best to clean it with? Maybe Brasso?

I'll have to look at the curly Q's next time I open them up, but I think the manufacturer was just getting crazy wrapping the wire around one of the terminals on the pot.

I've ordered the LPads from PE that were mentioned in one of Kent's threads on the AR-4x along with a set of Dayton caps (my usual standby). I'll step back and revisit your mention that these are pots before I do an install/replace. At least I have some parts coming just in case the originals aren't salvagable.

I just finished masking off the front and back panels (see pics). I'm going to chemical strip them next and start sanding. I'll take your tip on the dark walnut under consideration. It's going to take some time and work before I have to make that decision.

I'm also going to try the bleach thing on the grill cloth but with 2 parts water and 1 part bleach. Gotta go to the store because the Misses is out of bleach.

I'll skip the knob then unless someone can claim to know that they actually came with one. That way I still have parts for my KLH Five project.

BTW, I was playing them on my Marantz and without being serviced they do sound pretty decent. I have to believe that after a recap and light seal they'll be even better.

 

[ra.ra]

New L-pads will work just fine if you do choose to go that route, and Dayton caps are a great choice. Re: L-pads in vintage AR's, sometimes an added resistor is advised, but I cannot remember the conventional wisdom advice for the 4x with an L-pad - - but I'd think you probably want to get all of the HF output you can from these relatively reticent tweeters.  Pics attached show: original control knob from earlier AR-4 model; and badge cleaning process. I use Noxon metal polish, but Brasso will probably be very similar - - simply rubbing the badge on a small scrap of cotton flannel will remove all of the tarnish, and turn up as verdigris. To preserve the brass color, I like to use a light spray of satin lacquer.

I use chemical strippers sometimes, and they can be very effective, but in your case there is not much to "strip", but you'll still probably pick up some residual unwanted color if you are intending to try to re-finish from bare wood. Fine steel wool (or better yet, bronze wool = non-magnetic) will dig out the old finish from the deeper woodgrain, and sandpaper will be required to smooth out the outer veneer surface. 

For the grille cloth, I'd suggest starting off with a slighter more diluted solution, say, maybe 1:3. I use a spray bottle and a cheap natural bristle brush (see pic) to work it into the fibers. Don't be alarmed if it looks yellowish at first - -  it will fade as it dries - - allow them to dry in ambient air (no hairdryers), and also be forewarned that this process may require more than a single application in order to achieve the desired effect.

[RoyC]

8 hours ago, ra.ra said:

 The only thing that looks curious is that curlicue thingy which appears to connect terminal 1 and B on the back of the control pot (BTW, these are original Aetna-Pollak potentiometers, not L-pads). What is that thing-a-ma-bob? Am I seeing this correctly?

The wire on the pot is a jumper between 1 and "B", which is a quick fix for a corroded, non-functional pot. It by-passes the series leg, maintaining the parallel resistance of the pot in the circuit. It is not original, so someone had opened the cabinets once before. It is the best way to by-pass a pot.

Try the new L-pads as is. If the tweeters' output seems too strong in the midrange, solder a 25 ohm resistor across their terminals. This will make the L-pads' effect similar to that of the pots at typically used settings.

Roy

[ra.ra]

Thanks, Roy. Helpful diagnosis and explanation, as always, and good advice to the OP.

[Tim D]

I'm going to try cleaning the pots. I found an older thread in this forum where Roy had posted some pics of the pot disassembly. I didn't realize these were so serviceable.

Here is the thread for others benefit in the future.

 

[lARrybody]

My AR 4X's had the Chicago Industrial wax block capacitor with the inductor coil mounted on top. I discontinued it and pushed it back slightly to make room for a 20uf Dayton polypropylene capacitor.  I installed new L-pads with the 25 ohm resistor. 

 

 

I wound up installing new linen grill cloth. Used Parts Express caulking strips to seal the tweeter and woofer. Did not touch the cabinets for they were in excellent shape. Both warranty cards are still attached.  Drivers dated 1968. 

What a wonderful gift. Truly a gift that keeps giving. 

[Tim D]

Well, I tried the bleach thing on the grill cloth but with 2 parts water and 1 part bleach it lighted both the stain and the cloth so the two still had the same contrast. I changed to 50-50 mix and that brightened and removed the stain, but I had to re-apply a few times. There is definite shrinkage and the fabric started separating in one area. I had to stop. Good enough! I'll get some pics and post soon. One thing to mention though that even after it dried for day there was a funky smell coming from the cloth like B.O. Yuck! I hope that goes away.

I cleaned the badges with Brasso. That made a difference. See for yourself.

Been busy at work so I haven't continued on the cabinets. Maybe tomorrow.

[Tim D]

Caps and Lpads arrived yesterday. Going to go inside and pull the old pots for an inspection. I have a concern with the Lpads I ordered per my inspection of the values and how it changes the impedance of the tweeter circuit. I think the DCR is too low at 8 ohms. I also noticed this thread where others are calling the 8 ohm Lpad into question. Hopefully I can restore the originals and not have to deal with this topic.

 

[JKent]

Tim

Too much reading on this subject will drive you batty. A little background: johnnieo (John O'Hanlon) is a very knowledgeable EE professor. He approaches this from an engineering perspective. I have great respect and fondness for John but the person who has done the most experimenting with pots and L-pads, from an audiophile/music lover's perspective, is RoyC. Both John and Roy (and a couple others) authored the AR-3a restoration guide.

My understanding of Roy's work in this area (which is an evolving thing) is that L-pads are fine, trouble-free replacements for the troublesome pots. I put L-pads in my AR-4x's. They were my first speaker project and I bought "replacement pots" from Vintage AR. They're the same L-pads you bought from PE.

In the thread you linked to, John mentions several possible causes for the problem Shacky encountered, including poor or incorrect soldering.

My advice is; don't fret over this. The L-pads will work perfectly IF they are wired up correctly. If you want to add the resistor, go ahead. Here is something Roy wrote a few years ago. Please see the third post, with pictures:

 

[Tim D]

Thanks Kent. Looks like I can save the original pots..... They aren't bad at all.

In the process of sanding the cabinets and trying to clean up the drivers now. I'll be working on the pots tonight. Only one pot was jumpered. The other was in better shape electrically. I'll check them with my multimeter to be sure there isn't any hidden issues.

 

Here's some pics of the worst one.

 

 

[RoyC]

10 hours ago, Tim D said:

Caps and Lpads arrived yesterday. Going to go inside and pull the old pots for an inspection. I have a concern with the Lpads I ordered per my inspection of the values and how it changes the impedance of the tweeter circuit. I think the DCR is too low at 8 ohms. I also noticed this thread where others are calling the 8 ohm Lpad into question. Hopefully I can restore the originals and not have to deal with this topic.

 

Tim,

The L-pad and AR pot are both variable attenuators, but are different animals. The "8 ohm" designation of the L-pad has a different meaning than the "15 ohm" designation of the AR potentiometer.

The "8 ohm" L-pad, in fact, presents a higher total parallel resistance to the circuit then the 15 ohm pot. For every position of the L-pad, the parallel resistance is higher than that of the pot in relation to the series resistance. The L-pad's "8 ohm" designation means it is designed to provide attenuation in such a way as to keep an 8 ohm driver as close to 8 ohms as possible at each setting. The pot's "15 ohm" designation is simply the total of the series and parallel resistance at each setting. For example,  when the 15 ohm pot is set so the series resistance is 3 ohms, the parallel resistance is 12 ohms. When the 8 ohm L-pad is set to 3 ohms in series, its total parallel resistance is near 30 ohms. This is why we recommend using a 25 ohm parallel resistor when using an L-pad...to reduce the (parallel) resistance, and therefore shunt more current past the driver to emulate the characteristics of the AR pot. (Placing resistors in parallel reduces the total resistance.)

The bottom line is there is no practical reason not use an L-pad, especially when replacing crusty, corroded pots. (For the record, this is not an "evolving thing". It is why we included it in the 3a restoration guide. I think Kent was referring to the tweaking of the HiVi tweeter/capacitor combo.)

The pot shown in your photo would be sent to the trash bin in my shop, though I would save the shaft, spring clip, and (possibly) the wiper for the parts bin. I only retain and clean pots with tarnish, not crusty corrosion. There are always pits under the corrosion, which translates into dropouts and questionable future reliability.

Roy

[lARrybody]

Use the L-pads. Make the crossover like this. Easy Peasy

[Tim D]

Ok. You guys have me convinced to go with the Lpads. It's Christmas Eve though and I don't have the 25 ohm resistors. I'll see if the local parts house is open today. If not I may try w.o.

I did actually install them and try them out they are a bit scratchy even after cleaning. I have some pretty cool stuff that takes off all of the oxides called "Krud Kutter". I picked it up from Wally World. It did actually remove all the oxidation and rust, but it does feel smooth and it is a bit scratchy. I'll pull them and put in the Lpads. Once out I'll take some pics of the old pots and post for the record.

[JKent]

1 hour ago, Tim D said:

Ok. You guys have me convinced. It's Christmas Eve though and I don't have the 25 ohm resistors. I'll see if the local parts house is open today. If not I may try w.o.

I think it will be fine. As I said, when I did my 4x's I did not use the resistor. That''s actually what I was referring to when I said that Roy's thinking was evolving on this subject. Maybe not--it was John who advised me, over a decade ago, to use  a Zen film cap and an L-pad. No mention of a resistor at the time. 

So put 'em together and enjoy some Christmas music!

-Kent

[RoyC]

7 hours ago, JKent said:

I think it will be fine. As I said, when I did my 4x's I did not use the resistor. That''s actually what I was referring to when I said that Roy's thinking was evolving on this subject. Maybe not--it was John who advised me, over a decade ago, to use  a Zen film cap and an L-pad. No mention of a resistor at the time. 

So put 'em together and enjoy some Christmas music!

-Kent

Kent,

Perhaps it was an oversight...John never questioned the 25 ohm resistor/L-pad combo, and, in fact, verified it before we wrote the guide. Page 15 of the 3a restoration guide was written by him with my input. (Btw, it is easy to verify with a simple ohmmeter.)

In my opinion, the only valid reason not to use the resistor is when trying to eek out a bit more output from an old 3a style 3/4" dome tweeter. John was dismayed when he discovered the AB Tech "AR" level control replacements were, in fact, ordinary  8 ohm L-pads. It was the primary motivation to come up with a way to bring the influence of the L-pad closer to that of the original pot.

Roy

[Tim D]

Ok. The Lpads are in and I've got Christmas music running through them. I put them together without the resistors for expediency. They are closed up now - maybe for good. I've got several days of veneer and baffle cleanup and I need to seal the woofers, but they are electrically done. My daughter is coming for Christmas dinner but won't know that these will be hers on her Birthday on January 1.

Larry's diagram was invaluable, but one small thing was that the 1 and 3 terminals on my Lpads were reversed. I followed his numbering without paying attention to the actual positioning on the diagram and found the Lpads were working backwards. Once I assumed that his numbering was backwards from my Lpads I made the correction and it worked. They sound great! The Lpad in full increase might be just a little too bright. That's good because it will allow the fine control to back it off to where she likes it.

Here are some pics of my Lpads where you can see I've hooked them up per his diagram (by ignoring his numbering which is reversed from my Lpads). You can see where mine are numbered in reverse order from his diagram. I.e. Mine are numbered 1, 2 3 clockwise - his is 1, 2, 3 counter-clockwise. I abandoned the old cap in place. Didn't want to drill out the old rivets.

[Tim D]

 

Had a day yesterday playing Christmas music through them. Had two goof-ups.

 - My wife broke the surprise. She didn't know we were going to wait until her birthday. Oh well. I committed to getting her a stop-gap turntable and receiver since she doesn't have anything to drive it with right now. Eventually I plan on getting her a Heathkit AR-13 and a Dual 1226 waiting in the queue to go with the AR-4X's. For now I'll get her something to get by from the collection.

- After everyone went home I was trying to press on the knobs that came with the Lpads just to see how they'd fit. They took a little more effort than I liked and then suddenly the terminal plate broke loose! Ouch! Now I need to glue it back on.

I also found out that the grill on one of them is very very tight. Not sure if it swelled or what. Not sure how to deal with that.

Anyway. Here's what's left to do.

1. Glue the terminal plate back on. Ouch. Ouch. Ouch.

2. Paint the front baffle and speaker faces. Need to figure out how to mask the surrounds and cones.

3. Fill the dings with home-made filler from the dust collected from sanding the cabinets and some wood glue.

4. Seal the surrounds. Check for leaks.

5. Danish Oil. Probably the Dark Walnut I have on hand.

Some comments about the Lpads without the resistor...... I think they sound nice. Perhaps slightly bright, but there are times when I might like it this way. They have enough bass right now to be satisfying (even before I seal the surrounds.) They'll belong to my daughter, so I might not be listening to them much in the future, but it is good to know if another pair come along that I have a sound choice to leave out the resistor.

 

Thanks Guys!!!! I really really appreciate your help.

 

[ra.ra]

3 hours ago, Tim D said:

....and then suddenly the terminal plate broke loose!

That's too bad that you have to go back inside to repair this. This is somewhat unusual - - -  normally, many of us cannot figure out how best to remove these masonite panels when we intentionally want to, and yours just came loose with a bit of external pressure. Looking back on your pics, however, I see that it appears that perhaps no staples were used to secure this panel ........ glue only, it seems.

21 hours ago, Tim D said:

I put them together without the resistors for expediency.

I think this may have already been mentioned, but if you choose to add the resistor at a later time,  the easiest way is to simply unscrew the tweeter and apply the resistor directly across the tweeter terminals, then re-install tweeter. Nice project, congrats.

[Tim D]

52 minutes ago, ra.ra said:

That's too bad that you have to go back inside to repair this. This is somewhat unusual - - -  normally, many of us cannot figure out how best to remove these masonite panels when we intentionally want to, and yours just came loose with a bit of external pressure. Looking back on your pics, however, I see that it appears that perhaps no staples were used to secure this panel ........ glue only, it seems.

I think this may have already been mentioned, but if you choose to add the resistor at a later time,  the easiest way is to simply unscrew the tweeter and apply the resistor directly across the tweeter terminals, then re-install tweeter. Nice project, congrats.

 

Thanks Ra.ra,

Yes, there were no staples. The glue looked yellow translucent like modern gorilla glue. It was very brittle and I was able to use a putty knife to remove it from both the crossover plate and the cabinet in about 30 minutes. I have since re-applied it with new glue and I have a brick resting on it while it cures.

 

[lARrybody]

The crossover drawing I posted does have one flaw in the labeling of the terminals, although the wiring is correct. The 1-2-3 was meant to relate to the original pot terminals and should be labeled 1-B-2 instead. I will correct the sketch.

The knob supplied with the l-pads does not evan look like it belongs with the 4X speakers. I used these which are about 3/4 in tall and 1/2 in in diameter. They have a set screw so you don't have to push them on and it is easy to align with the shaft travel.

https://www.parts-express.com/penn-elcom-z408601-basic-amplifier-knob-black--240-208

If you really want to get authentic you can see if JKent has any of the original reproductions left. I don't think 4X's originally came with knobs, but it is a nice touch.

When it comes to the finish here is my opinion. Get a small can of the Watco Natural Danish oil finish and apply at least 2-3 coates. Its not real danish oil, but it makes a fantastic finish. I try to stay away from anything with any color added. Just my opinion.Here are some 2ax's with that finish.

[Tim D]

The glue was very brittle and didn't appear to adhere very well. Kind of like old peanut brittle and didn't stick much better than peanut brittle either. I wouldn't be surprised if this is a source of cabinet leaks for AR-4X's. It might be something to investigate - if I had another set.

[Tim D]

Very nearly done. There were a few corner dings and small chips that I filled with sanding dust mixed with wood glue along the way. I took Larry's advice and went with the Danish Oil Natural finish. So far I've got two quick coats on and might go with a third. Even though it is clear, the oil finish darkened it up anyways. All that is left is to maybe put on one more coat, dope the surrounds and maybe put on the AR knobs I have. Image 42 has both without and with the Danish oil on the two speakers side-by-side. I'm glad I did go with the natural finish because the dark walnut would have been overpowering for these small bookshelves. This is dark enough. The veneer is in good enough shape that I could go lighter and not have to hide a lot of imperfections too.

Here are some pics of the final stages. I've got to admit I'm a little jealous of my daughter now that they are almost done and looking so good. Her birthday is on January 1. They'll be done by then.