potentiometeritis

[Guest tdeutsch]

Armed with the great advice and enthusiasm from the friendly folks who frequent this site, I dug into my new (to me!) AR-4x pair this weekend. This is the first time I've ever approached a set of speakers with tools before. These belonged to my father-in-law (who stored them unused for 25-30 years) so I have to say I was a little nervous about botching the job -- even though he insists he no longer has any attachment to them. My tweeters were not making sound and the helpful folks here diagnosed it as potentiometeritis.

I used a small wedge-shaped pointed chisel to pry up the grille staples, then levered them up but not out of the grille frame. After this, removal of the grille was non-traumatic and since I hadn't entirely removed the staples, it was simple to tap them back into place when I was done.

I removed the woofer and set it on the face of the cabinet next to the tweeter -- no snipping of wires! Then I removed the cheesecloth from behind the driver [q: what is the function of this? It's so whispy, it can't have acoustic properties, can it?]. Then I connected a AA battery to the tweeter (a tip I got from a nice person here) to make sure it wasn't blown (it wasn't).

The care with which the scraps of fiberglass were arranged in the cabinet and tucked around and under the innards was amazing, although I will say one of the speakers had less insulation in it than the other.

I marked the orientation of the pot before loosening the nut and freeing it from the masonite. Again, without cutting wires, I removed the spring clip and disassembled the pot. What a mess! No wonder there was no tweeter sound! It looked like a corroded car battery terminal in there. I used a tiny brass brush on a dremel tool -- this worked really well. There were some stubborn corrosion spots which would not shine up, but after I cleaned them with a "de-ox-it" pen, the tarnish came out. After this, I sprayed the dust off with electrical contact cleaner, coated everything with di-electric grease and re-assembled.

I was glad to do all of this without cutting wires -- although it was a little awkward working inside the box, I was more afraid of damaging the wires or globbing on the solder with my poor technique.

After completing and testing the first speaker, I still had some drop-outs. So, when I did the second pot, I bent the little angled piece that turns with the knob so it would have more intimate contact. Unfortunately, when I tested it, it dropped out as well.

Still, they play, whereas before they didn't! So, I'll just set the knob and leave it and hope they hold up for a few years while I enjoy their music.

Overall, I couldn't get over the "hand-made" look of these speakers and components. The way the crossover was lovingly wrapped in cheesecloth (again...why?)...the scruffy black plywood mounting face...the ugly but functional (and still pliant!) black goo sealing the frame. The tic-tac-toe pattern "painted" on the face of the woofers with sealant (and again... why?...technician's signature?) They look more like laboratory equipment than something sold by a commercial concern. Very cool!

Thanks again for the tips!

Tom

[ar_pro]

Excellent work, Tom - it sounds like you did everything right.

Corroding pots are almost always the root of (apparently) non-functioning tweeters in the classic AR line, and can be a pain to service - congratulations on getting your speakers up & running!

[Guest dogmeninreno]

>Armed with the great advice and enthusiasm from the friendly

>folks who frequent this site, I dug into my new (to me!) AR-4x

>pair this weekend. This is the first time I've ever approached

>a set of speakers with tools before. These belonged to my

>father-in-law (who stored them unused for 25-30 years) so I

>have to say I was a little nervous about botching the job --

>even though he insists he no longer has any attachment to

>them. My tweeters were not making sound and the helpful folks

>here diagnosed it as potentiometeritis.

>I used a small wedge-shaped pointed chisel to pry up the

>grille staples, then levered them up but not out of the grille

>frame. After this, removal of the grille was non-traumatic and

>since I hadn't entirely removed the staples, it was simple to

>tap them back into place when I was done.

>I removed the woofer and set it on the face of the cabinet

>next to the tweeter -- no snipping of wires! Then I removed

>the cheesecloth from behind the driver [q: what is the

>function of this? It's so whispy, it can't have acoustic

>properties, can it?]. Then I connected a AA battery to the

>tweeter (a tip I got from a nice person here) to make sure it

>wasn't blown (it wasn't).

>The care with which the scraps of fiberglass were arranged in

>the cabinet and tucked around and under the innards was

>amazing, although I will say one of the speakers had less

>insulation in it than the other.

>I marked the orientation of the pot before loosening the nut

>and freeing it from the masonite. Again, without cutting

>wires, I removed the spring clip and disassembled the pot.

>What a mess! No wonder there was no tweeter sound! It looked

>like a corroded car battery terminal in there. I used a tiny

>brass brush on a dremel tool -- this worked really well. There

>were some stubborn corrosion spots which would not shine up,

>but after I cleaned them with a "de-ox-it" pen, the tarnish

>came out. After this, I sprayed the dust off with electrical

>contact cleaner, coated everything with di-electric grease and

>re-assembled.

>I was glad to do all of this without cutting wires -- although

>it was a little awkward working inside the box, I was more

>afraid of damaging the wires or globbing on the solder with my

>poor technique.

>After completing and testing the first speaker, I still had

>some drop-outs. So, when I did the second pot, I bent the

>little angled piece that turns with the knob so it would have

>more intimate contact. Unfortunately, when I tested it, it

>dropped out as well.

>Still, they play, whereas before they didn't! So, I'll just

>set the knob and leave it and hope they hold up for a few

>years while I enjoy their music.

>Overall, I couldn't get over the "hand-made" look of these

>speakers and components. The way the crossover was lovingly

>wrapped in cheesecloth (again...why?)...the scruffy black

>plywood mounting face...the ugly but functional (and still

>pliant!) black goo sealing the frame. The tic-tac-toe pattern

>"painted" on the face of the woofers with sealant (and

>again... why?...technician's signature?) They look more like

>laboratory equipment than something sold by a commercial

>concern. Very cool!

>Thanks again for the tips!

>Tom

Tom, I suggest you apply some dielectric grease to the pots..Works great for me every time!! You can get it at almost any auto parts store..Good lock, Dale in Reno

[mrbruce4]

Your description of working on the pots without disconnecting the wires was very similar to mine. I have 2 pair of the 4x speakers and after I had to resolder one set of connections (to correct for a bypassed pot), I decided I would avoid cutting wires and resoldering in the box if at all possible.

I had my significant other to help and we did the other 3 relatively quickly but it was a challenge and I'm glad it's over. Like you, I was surprised at how corroded the contacts were.

I also redid the putty sealer around the woofers to try to make the cabinets airtight. Was reasonably successful.

I think the most impressive thing is to listen to these 35+ year old speakers and realize how good they still sound. None of mine have had capacitors replaced, I don't think. I don't feel I'm proficient enough to take this on, so for now, I'll enjoy them as bedroom system speakers.

[tysontom]

Great job! Your description of the care in the work done is an example of the proper way to go about restoring these older AR speakers. The fact that you still have a few "drop outs" from the level controls is normal, and there is no reason to fret over that. It isn't possible to completely eliminate some slight dropouts even with a brand-new Pollock level control.

The only thing you have left is to lightly sand the cabinets with 600-grit sandpaper and apply some Watco oil (or boiled-linseed oil) to the cabinets to bring them back to their original appearance. For best results, follow the oiled-walnut refinishing directions that can be found elsewhere in The Speaker Forum.

The cris-crossed pattern on the woofer cone was put there for damping purposes to make the 8-inch woofer flatter and smoother in response, and to make it less likely to have cone "break-up" nodes in the higher frequencies.

--Tom Tyson

[Guest tdeutsch]

"The cris-crossed pattern on the woofer cone was put there for damping purposes to make the 8-inch woofer flatter and smoother in response, and to make it less likely to have cone "break-up" nodes in the higher frequencies."

That is an amazing level of attention to detail. I'm not equipped to either buy OR doubt that statement, but it demonstrates that the AR folks were indeed speaker junkies of the highest order. A less brilliant speaker company would have tried to solve that sonic problem with electronics, or a more expensive driver. But their solution, to everyone's benefit, was to just paint a tic-tac-toe board across the driver. That just cracks me up.

So, if I look at other speaker cones, would I see a similar pattern painted on them? Or maybe a parcheesi board pattern works better?

Also you mentioned the cabinet. I have rarely seen a bevel and fit as precise, and as well-matched from panel to panel, as is on my walnut 4x's. No filler and the seam is nigh invisible.

[ninohernes]

The later AR-4x woofers used a ribbed cone insted of the "paint".

[dynaco_dan]

Hi there;

I have also seen this criss cross pattern on some KLH woofer cones as well.

The rugged T-nuts were used on all of the classic speaker enclosures.

This must have been a first back in the mid '50's, when just a wood screw would have obviously been cheaper.

An accurate pattern for drilling the holes would have been made, then the T-nuts hammered those holes before assembling the cabinets.

Heavy duty construction even down to the AR-4X speaker.

I don't know if it was Ed Vilchur's or Henry Kloss's idea, perhaps Henry's more so, but this, was not a penny pinching manufacturing method.

I do not recollect another manufacturer using the T-nuts.

Most speakers that, I have personally come across, use a Philips wood screw, and none too long either.

At our local specialty store here, is Lee Valley, they carry several different styles of T-nuts.

I found a furniture recovering or re-upholstering business here years ago, before T-nuts were popular in our local Canadian Tire Stores, and they bought T-nuts in bulk case lots and they were relatively inexpensive to buy.

[tysontom]

KLH did use a criss-cross pattern on some of their woofers, but it was first started at AR. The material was actually a rubber "glue" and was initially used by AR on the AR-2, then later on the AR-4/AR-4x. Ed Villchur or Roy Allison engineered it. Villchur and Allison were pretty much constantly measuring and improving loudspeaker performance in the anechoic chamber on the 4th floor of the Cambridge plant, and there was a persistent problem with cone breakup at the upper end of the response. The damping rings helped suppress unwanted energy in the cone. Henry Kloss also was aware of it, as he did the same thing on some of his woofers.

The T-nut construction was also a Villchur design and the first application was with the original AR-1s. Villchur insisted on this quality of construction, not because it looked better or would make repair easier later on, but because the T-nuts allowed one to torque the drivers into the cabinets properly to eliminate air leaks around the frame. Once started, AR stayed with the T-nuts, while most other companies used plain wood screws. A good example: the AR-3a used eight (8) machine screws with T-nuts to hold the woofer in place whereas the Large Advent contained four (4) smaller wood screws to hold the woofer.

Along with innovating the use of machine screws, AR also front-mounted its drivers flush with the top panel. This required cutting an inner hole for the driver as well as routing-out the hole for the woofer flange. Prior to this, manufacturers were mounting speakers to the *inside* of the speaker cabinet with wood screws.

--Tom Tyson

[ar_pro]

A very solid, and reliable method - I have seen T-nuts used with JBL and Altec systems, and in guitar and bass enclosures from Ampeg, Fender, and others.

[dynaco_dan]

Hi Tom;

As always a great clarification of this topic, thank you.

I was guessing at Henry deciding on the T-nuts, as he had the woodworking background, I believe.

No doubt this was the most practical method of strongly mounting the woofer at least, due to their weight.

One can only imagine if they had been epoxied in like some of the KLH drivers.

At the labour and parts costs to AR even, it showed they were not producing speakers at the lowest possible cost, thank goodness for us.

I haven't seen up close and personal, an AR speaker that is from the '80's or later, except a pair of AR-9's at a past customers home.

Unfortunately, I fixed his heating system too well, I was only allowed into his sound room after I got the heat on.

That was my tip, great.

I drifted away from hifi after I saw a pair of AR-3A Improved at a friends home way back in the mid to late '70's.

[Guest tgw]

I have had good results by repeatedly spraying the pots of both my Ar-4x's and AR-3's with contact cleaner and WD-40 and just working the control back and forth until I see good linear response on a VOM I attach across the terminals.

My next step is to replace the caps with new ones.

[Guest baumgrenze]

Has anyone tried this product for restoring LPads? I found it (and some very complimentary recommendations) while engagned in the restoration a 30 year old set of model trains.

http://www.aerocarlubricants.com/Trains/index.htm

ACT-3753 Conducta Lube and Cleaner - 1oz.

Cleans and lubricates commutators and brushes. Enhances performance and extends brush life. Has been found to reduce amp draw by as much as 50%. Improves current flow through brushes to the commutator. Will enhance the capabilities of DCC operations.

Baumgrenze