AR4x Crossover Rebuild Check

[Coleman4130]

Hello All,

I have a pair of AR4x speakers with the cross-hatched woofers and crossover with 20uf and 24uf capacitors.  I now have new caps, hookup wire, hardwood boards, etc. ready to completely rebuild the crossovers.  Attached is a pic borrowed from a post by ra.ra. showing the diagram for speakers S/N 386xx, and a pic I drew to help organize the location of everything for my rebuilds.

Does anyone see any errors or problems with my diagram?  I just want a second opinion before I begin assembly.  Thank you! -John 

 

[ra.ra]

Hi Coleman,

RoyC helped me confirm the accuracy of that crossover schematic, and although it's not a bad sketch, it was sort of stupid the way I drew that 24uF cap - - - it looks more complicated than it should. Instead, I should've sketched it so that the 24 cap is simply connected in parallel across the woofer terminals. In fact, I think that is how I built it, with the 24 cap attached to the woofer magnet instead of to the cabinet bottom (back). Either method of installation is fine - - an important thing to note, which both of our sketches show with a dot - - is to ensure the three-point connection where the coil, the 24 cap, and the woofer common wire are joined.

Your sketch looks just fine. The only thing I did not understand is the comment "Bypass to 1".

Your speakers look great, and this two-capacitor version of the AR-4x (with the AR-4 woofer) is somewhat rare, and they all tend to fall in that ± 28K to 42K range of serial numbers. In fact, yours might be even more peculiar than most because of that tweeter, which looks more like the AR-4 tweet (3.5" cone) than the AR-4x tweeter (2.5" cone). 

Can you please help confirm more about this tweeter? Could you post a pic of the entire crossover to confirm the tweeter cap value (20uF, I presume?), and also include close-up pics of the tweeter, especially the backside? And measure the diameter of tweeter magnet? Since these speakers tend to suggest the production line transition between the AR-4 and the AR-4x models, I have a suspicion that your tweeters may be the 2.5" tweeter used in the 4x, but with the protective screen and partial fiberglass damping found on the 3.5" tweeter of the AR-4.

You have a very interesting pair of speakers. I hope the cabinets and grilles are in good shape as well. I suspect you'll be installing new caps, but you'd be well-advised to also to re-furbish the control pots or replace them (with A-P pots from other AR's or L-pads) and perhaps also apply a light coat of Roy's butyl dope to the woofer surrounds if they feel stiff. Your particular version of 4x shows up very infrequently, and one of the few identifications I've seen of this specimen is from a document sent to me by JKent a few years ago, as shown below.

 

 

[Coleman4130]

Thank you for responding! I learned here that these are an older design and am now interested to know/contribute more about their place in AR history.

The cabinets have significant (impressive?) sun damage from sitting in the same position for decades but are are solid. The drivers are well preserved. The grill cloths are old and funky but I have removed one from it's frame to attempt cleaning. 

Ah I see how running the 24 cap in parallel to the woofer simplifies things. 'Bypass to 1' is my understanding of how to bypass the potentiometer. I soldered up the crossover earlier and all seems to check out with the multimeter. I hope to have everything else together for a listen on Sunday.  

I didn't get a chance to take detailed pics of the tweeter but I will as soon as I can; i am curious to learn more!

I refurb one speaker at a time so if all goes well on Sunday Ill open up the second speaker and attach pics of an original crossover too.

Thanks again! -John

[ra.ra]

Sounds like you're well on your way already. Looking forward to future progress reports.

Re: grille cloth, it is very typical for the original cloth to have some degree of discoloring, but just one word of caution - - if you have removed it from the grille frame, and then subject it to moisture, subsequent shrinkage is most likely to occur upon drying, which might make it very difficult to re-stretch and staple over the original frame. Other members have various methods for cleaning the linen, but link attached shows my experience:

Re: cabinets, great to hear that the veneer is in good condition, and re-finishing of the walnut is fairly forgiving for even the weekend hobbyist. Within limits, the veneer successfully accepts efforts to lighten or darken or modify the coloration.

Am still unclear about your "bypass" remarks. Your wiring sketch looks correct, and appears to keep the control in the tweeter circuit as intended. IMO, you want the potentiometer in the circuit for two reasons: [a] it is beneficial to have the variable control for tweeter output to respond to speaker placement and specific room acoustics; and even at full tweeter output, the pot provides a bit of necessary resistance.

Great project - - - take your time, document carefully, and report back when you can.  

 

[Coleman4130]

Thank for the grill cloth link and advice. 

Ive had great luck with Howard's Restor-a-finish with light use of OOOO steel wool.  One cabinet has been refinished and looks pretty nice, other than sun faded diagonal line across the sides...  If I get it buttoned up Sunday I will have 1 re-finished speaker and one original for A/B preview before tackling the second. 

I pulled the crossover board from completely and replaced it with hard wood so these will not be restorations; I find it so much easier to work out of the speaker box!  The 'bypass' is how my research led me to believe one can run the pot at max but keep it in the circuit for resistance.  The internals of this pot are clean but it still crackles and cuts out.  I do plan to attempt cleaning again and or replacing but for now it is 'bypassed'.  Also my hard wood boards are just too thick to thread the nut on the back of the pot.  I can drill a recess no prob' but again, another time.

I took some pics of the tweeter this morning.  It is dated Jan 27 1966.  Im not sure how to measure the cone but it can't be bigger than 2.5".

When I open up the second speaker I will take a pic of the original crossover.  The caps are unlabelled in a wax block with 3 leads; only my research here gave me the 20uf and 24uf values.

Thank you again, -John

[ra.ra]

Agreed, the Howard's products can work very well for cabinets that do not require further treatment. And the 1966 dates on yours make perfect sense when compared to the dates and serial numbers noted on my schematic sketch.

Thx for the additional tweeter pics, and as suspected, the magnet seems to confirm this hybrid. What you have is indeed the AR-4x tweeter, but with the added metal cage and (partial) fiberglass damping associated with the earlier AR-4 tweeter. Yes, this is associated with the 20uF capacitor, and your wax cap block, like mine, has no identifying labels, which is where RoyC bailed me out.

Pic attached shows front and rear of 3.5" AR-4 tweeter on left; and 2.5" AR-4x tweeter on right. Note the difference in magnet diameters.

 

[Coleman4130]

Yes it appears I have a hybrid of the two as you have described.

With a bit of work last night and this morning I was able to complete the crossover and reassemble the first speaker.  Listening results are far from subtle.  It's too early still to crank 'em up but listening to a bit of classical this early morning I am pleasantly surprised with the improvement. 

Thanks to all at classicspeakerpages for the information needed to make this possible!

Tan line pictures attached.  I didn't take a picture of my crossover but I will of the second, assuming it will be prettier...

[rebelliondog]

Well....I see that this is an old thread, so I’ll see where this goes....

i was using these diagrams to rewire my AR 4x’s.....something went wrong.  I have very little output through the woofer.  However, the Tweeter livened up and I now have control (new control knob).

i guess I did not understand the connections to the pot and then out to the tweeter....first.  And then the placement of the 24uf capacitor.....

i became frustrated put it all away a few days ago.....I would like to get back to it as soon as possible.

actually was just wondering if either of these two posters are still around to help.

 

[ra.ra]

20 minutes ago, rebelliondog said:

...if either of these two posters are still around to help...

Hey R-dog, I just happen to be lurking here today....so welcome to the forum.

Not sure what's going on with your speakers, but I hope you understand that the dialog in this thread is specifically targeted to the oddball version of AR-4x that uses the older AR-4 woofer, has two capacitors, and the 265-turn coil. Unless you have this semi-rare version of AR-4x, this dialog, these sketches, and the photos shown here do not apply to the more typical AR-4x. Please confirm your speaker serial numbers and post a pic or two and you'll get plenty of help here.  

[rebelliondog]

I have the 265 coil, two capacitors in the little ‘wallet’ underneath it all.

I do not have caged tweeters....or markings across the woofers.

i think if I fully understood the diagram.....it will work fine.  Or....maybe I followed it properly and it won’t work.  Honestly not sure....

i cannot post pictures....I’ll figure out how and post some.

Thanks for the response..

[ra.ra]

1 hour ago, rebelliondog said:

I have the 265 coil, two capacitors in the little ‘wallet’ underneath it all.

OK....good to know....I just had to ask before going further....and I like that term "little wallet". My cap assembly was just a mashed-up bundle of wax with three protruding wires. Pic attached shows mine in original state - - no caged tweeters, but I do have the tic-tac-toe on woofers.

Posting pics here is simple - - a digital image, jpg format preferable, 100KB maximum.

2 hours ago, rebelliondog said:

....maybe I followed it properly and it won’t work...

Probably not, but once you post pics with descriptions, this should get figured out with some patience.

[rebelliondog]

[ra.ra]

Thanks for posting the pics....just to confirm, could you also report the serial numbers as found on the rear labels? From everything I can see, you do not have the two-cap "oddball" version of the AR-4x - - - instead, what you have is the far more typical version of the 4x.

Your woofer - - with fully circular basket frame - - is clearly different from the one found in the 4x speakers shown here by Coleman and myself. And your crossover shows a #5 coil atop the wax block capacitor which I suspect is a single 20uF cap with two wires (green, blue). Also, it appears that the potentiometer has been re-wired in an attempt to bypass this variable control.

If my assumptions are correct that you have the typical AR-4x, you will only need the 20uF cap and will not need the 24uF caps. The attached schematic should be your basic wiring guide, and you can see that the woofer and tweeter are wired with opposite polarity - - the positive red wire from the woofer connects with the #2 terminal, while the positive yellow wire from the tweeter connects thru the control and then to the #1 terminal.

Using new L-pads is a good idea, but you will also need some additional member help here regarding the specific wiring to this device, and whether or not an additional resistor is required. Be patient and work slowly - - you've got a fine pair of speakers worthy of your restoration efforts.  

[ra.ra]

Just for posterity in this thread, I'm posting a pic of original crossover (two cap with three wires) found in the "oddball" version of AR-4x that uses the woofer from the AR-4.

[JKent]

Hey dog

Ra.ra is right. Those are "regular" 4x's and my guess is that's the problem--you used the wrong schematic.

I also see you used the 50w L-pad. The one we use is 15w but I don't think this is a problem. The 50w is bigger but you're only using 1 per box so size should not be an issue. The wiring is the same. And no--don't use the resistor.

Below is a photo of the correctly wired L-pad. So on yours remember L-pad terminal 1 corresponds to 2 on the original pot, 2 corresponds to B and 3 corresponds to 1.

Kent

[JKent]

Here is a helpful photo labeled by John O'Hanlon. "Zen" in the pic refers to the 20uF cap.

[ra.ra]

Thanks, Kent, for providing the L-pad terminal wiring yet again. And R-dog, you should probably have enough information now to get your situation straightened out. Still, this excellent thread would be worth consuming - - it includes L-pad installations in multiple AR-4x projects with and without the added resistor; and yes, your 50W L-pads will work just fine.

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/9871-another-acoustic-research-ar-4x-refurb/

 

[rebelliondog]

....when I first got these speakers, I bypassed the treble pot.  One tweeter didn’t work at all, the other was in and out.  Worked ok then.  Used the speakers in my bedroom for a while....then on to the parts / equipment room.  A couple years later (having forgotten all I researched two years ago) I decide to rebuild / upgrade them.

I thought that the waxy  “wallet” with the wires sticking out meant that there were two capacitors used in the design.

The diagram(s) I was following used two caps....one of them has 265 written on the inductor coil..

One of my speakers, I believe, has 265 written on the inductor coil (of course, the one in the picture I uploaded has a 5).....which is another reason why I thought I was in the right ballpark in my research.  The two woofers in mine look very different.  

Serial numbers are  fx343364 and fx331864.

i am again having trouble uploading photos....unsure why.

i will try to use the diagram posted by jkent with only the 20uf cap and see how it goes.

The way I wired it this time brought out the highs.  To me the tweeter sounds great....and wide range of control now with the 16 ohm / 50 watt l-pad.  Woofer volume is super low....

[JKent]

If the "wallet" has just 2 wires it's a single capacitor. If there are 3 wires it's double. 

If one of your inductors has 265 turns, and the 2 woofers look different (from each other) is it possible you have 1 common 4x and 1 of the rarer ones? Ra.ra may be able to offer a guess based on the SNs but of course it would be best if you could post photos of the front and the crossover of the other (possibly dual-cap) speaker. But if the dual-cap ones were very early I doubt it. I've worked on SNs ranging from FX18817 to FX262765 and never saw the dual caps. Your SNs are from later in the production run.

I don't know what resources you have but as mentioned the photos should be resized to about 100-200KB each. I use Photoshop Elements, resize the photo to about 6" wide, Resolution about 100 and a Quality of 8.

[ra.ra]

55 minutes ago, JKent said:

If one of your inductors has 265 turns, and the 2 woofers look different (from each other) is it possible you have 1 common 4x and 1 of the rarer ones?

This is exactly the first thought I had, and confirmation will be dependent upon having comparative pics of both speaker assemblies. And Kent is correct about the number of caps and number of wires - - this has already been confirmed by the photos in this recently revived portion of this thread .

From R-dog's serial numbers, I would guess these 4x speakers might date from late 1970 or early 1971 (320XXX is april 1970; 383XXX is october 1971), and I would assume the original AR-4 woofers had most likely been depleted by then. As mentioned far earlier in this thread, all 2-cap and 265 coil 4x's I've seen have been in the range of s/n 28,000 to 42,000, but perhaps we have yet another outlier here.

Re: posting pics - - whatever you did in previous post was perfect: jpeg files under 100KB.

[lARrybody]

This is a drawing I made of my AR4x recap.

Here is the finished version.

One set of my 4x's has smooth cones, another set has ribbed cones like yours. My Ar4's have the cross hatch pattern on the woofers. They all have cloth surrounds.

[jviss]

Gee, I hope you folks are still here monitoring this thread!  I have two pair of AR4x speakers, plus a pair I gave to my son.  I'm just starting my refurb/restoration.  The first pair I will work on was purchased new by my Dad, approximately 1969.  Serials FXI76350 and '356.  Only real prob now is low/no output from one tweeter; could be the crossover network.  I am replacing the nicotine-stained grill cloth with cross-stitch linen I got at Michael's.  I have a couple of new rheostats on hand if needed.  I'm assuming I'll be replacing the caps.  

Wish me luck!  

 

[JKent]

Luck! 😁

Yes. Definitely replace the 20uF caps. That along with the new pots should fix your tweeter problem. 
Like your dad, I bought mine new in 1970 (ok—one year later). They were my first speakers and, about 20 years ago, my first restoration. Not difficult at all and truly well worth the effort. 

[RoyC]

4 hours ago, jviss said:

I have a couple of new rheostats on hand if needed.  I'm assuming I'll be replacing the caps.  

Wish me luck!  

 

Corroded level controls are the most likely reason for tweeter output issues, though it is always prudent to replace the capacitors when you are doing that work.

Also, take a look at the perimeter of the tweeter cone. It is not unusual to find it to be separating from the basket due to degraded adhesive.

Roy

[jviss]

Wow, thanks @JKent and @RoyC!  So glad you experts are on here, and helping.  

 

I really have to dig into these.  I love them!  I replace the grill cloth today, with this stuff from Michael's:

https://www.michaels.com/product/loops-threads-aida-cloth-cross-stitch-fabric-oatmeal-10357727

 

They still sound great, but as I said, the right tweeter is about silent.  I'm going to open both of them and rebuild the crossovers and test the whoofers and tweeters.  As I mentioned, I have a couple of new rheostats, so perhaps I'll swap those in, too.  

Cheers,

jv