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Johnconnon

AR 4XA tweeter control issue

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Hey guys, first post here so please bear with my ignorance. I have recently purchased a pair of 4xa's and seem to have an issue with the tweeter dial at the back. Specifically with one speaker, it crumbles when turned and I can't get it to sound like the speaker isn't playing within itself if that makes sense? Any quick fix ideas, I haven't opened her up yet as don't want to potentially worsen the situation. 

Thanks!

 

John

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The tweeter-control issue is very common with AR speakers of this vintage; as long as the drivers are undamaged, you're in good shape.

If you'd like to do the repairs yourself, download & read "Restoring The AR-3a", which will provide valuable information on how to proceed.

http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_schematicss/restoring_the_ar-3a/

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Hi John

Welcome to the CSP!

Your problem is with the potentiometers, or "pots", which are notorious for becoming corroded and not working. The 4xa speakers are from the same era as the 3a. If you download the 3a restoration guide you will find valuable information about the control pots. The easiest fix is to replace them with L-pads, available from Parts Express. While you're in there you should replace the capacitors so order those as well. PE also has nice foam gasket tape for re-installing the woofer.

The 3a booklet will also guide you in removing the woofer, protective paper (Kimpac) and fiberglass stuffing.

CSP member ra.ra. is quite knowledgeable about this model and will probably chime in. I restored one pair but I don't have an accurate record of the crossover caps. The 4-x used a 20uF cap but the 4-xa used a different value--10uF IIRC (but see what ra says). The 4-xa was/is an excellent speaker and well worth restoring.

A possible "quick fix": Rotate the control fully clockwise and counterclockwise several (many) times. The idea is to try to scrape off some of the corrosion. Then listen to music while rotating the control and you "may" find a good spot. This is just a quick and dirty temporary fix and not the permanent solution.

-Kent

Here are the L-pads: http://www.parts-express.com/speaker-l-pad-attenuator-15w-mono-3-8-shaft-8-ohm--260-248

Here is the speaker gasket: http://www.parts-express.com/parts-express-speaker-gasketing-tape-1-8-x-3-8-x-50-ft-roll--260-540

Here are 10uF caps: http://www.parts-express.com/dayton-audio-dmpc-10-10uf-250v-polypropylene-capacitor--027-428

or these http://www.parts-express.com/sprague-441p-220-ac-@-60-hz-10uf-capacitor--029-104

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Thanks both, really appreciate the quick advice. So kind of you. Will digest all your thoughts and in the meantime it might be worth me sending you the eBay link as quite a bit of work went into restoring them already. But I imagine there is still an issue with tweeter control beyond that. Any further thoughts extremely welcome. 

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=131784615334&category=14990&pm=1&ds=0&t=1463428579079

best

john

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That IS helpful.

The good news: The sealant on the woofers is the correct stuff (made by our own RoyC). You'd be surprised what some people put on there!

The caps have been replaced with very good quality caps. So I think the only culprit is the pots, even though the seller says they were thoroughly cleaned. Have you contacted the seller to ask about this?

Also, could you maybe explain what you mean when you say it "crumbles" and sounds like the speaker is "playing within itself"?

Be sure to try the back & forth thing I suggested.

Maybe other members have some thoughts?

-Kent

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Hey Kent,

I've not yet contacted the seller yet but will do. With regards to the sound, it feels like there is very little treble and bass, as if the speaker is pointing backwards into the box. When I twist the knob little changes, but occasionally a bit of treble will break through sporadically and then go as if the connection is weak. Does that help?

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Hi John, and welcome! The 4xa is unfortunately often overlooked because, despite it being an excellent speaker product, it gets shoved aside like a neglected stepchild and was overshadowed by the larger and "newer" models which were being marketed during the same time period. Your specimens are undoubtedly UK models as evidenced by the paper tags and the brown painted backs. Also, they just might be reasonably early Euro releases, as evidenced by the pot control (instead of switch), cloth surrounds (not foam), and front (not rear) wired tweeter.

Kent is correct to note that use of the appropriate woofer cloth sealer and high-quality replacement caps are extremely fortunate additions to your renewed speaker purchase. Not sure what is going on with your muffled speaker - - does the other one sound fine? When that tweeter and control are working properly, there should be a world of difference with regards to tweeter output when the control is manually turned. 

Your original crossover appears to be wired correctly with the woofer and tweeter sharing the same polarity, but can you confirm that the "new" crossover has been similarly wired? 

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Yes, welcome John.

The AR-4xa is a fine speaker when it is performing correctly.

Sounds like one of the pots maybe not be working correctly which should not be difficult to correct.

Never seen that particular capacitor brand before but they look like they are designed for high voltage due to their physical size. Are you located in Europe?

If the drivers ohm-out correctly you will need to have a closer look at the pot -- fix, find a replacement or substitute with an L-pad/resistor combo is the usual procedure.

That is a very nice grain pattern on those British cabinets.

Interesting to note the 300K+ consecutive serial number range on these. There is an orphan 4xa from 1974 Norwood production here that uses the three position switch crossover and has rear-wired tweeters and a smooth woofer cone with a serial number in the 15K+ range.

AR-4xa.2016.05.16.01.jpg

AR-4xa.2016.05.16.02.jpg

RogerAR-4xa.2016.05.16.03.jpgAR-4xa.2016.05.16.04.jpg

Edited by owlsplace
added photos

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Thanks again guys. Hi ra.ra here is are two photos of the wiring on the tweeter of the faulty speaker (can't seem to attach photos to this) https://we.tl/paIuB0M5Wk. I think there may be an issue with the woofer as well as it is also underperforming when compared to the adjacent speaker using the balance knob on my Marantz amp. I wonder if there is a problem with the connection of the tweeter control at the back which is why little happens when turned? Though people have also pointed out a potential problem with the pots. Maybe I should just follow the AR3 guide and open her up to get a better look?

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John,

To attach photos you can drag them to the area next to the paper clip in the Reply box or click on "choose files" and select them from your hard drive. Optimal size is probably about 6 to 8" wide and about 100KB or so.

Here are your photos. I also noticed "jpg" file extension seemed to work better than "jpeg"

2.jpg

1.jpg

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Thanks, Kent, for attaching the pics within this post, and I agree with you about the 100KB file size being more than adequate for most images. Also, thx for the reminder about using the paperclip feature.

I have a pair of these exact same tweeters in a very early pair of AR-6 speakers, and yes, somewhere underneath the black tape lies this splice between the hairlike tinsel wire (left, in your pics) and the braided copper tinsel wire (right, in your pics). My tweeters date from January 1971, and the DCR measures at 4.9 and 5.8 ohms, but the original tape is still tenaciously bonded to the front plate of the driver such that I am hesitant to dissect this piece of assembly in order to observe this delicate connection. In other words, I am not familiar with how this splice should appear, but yours does look like a very tenuous attachment and I would suggest measuring the DCR of your drivers.

Having said that, before we start blaming a faulty pot or tweeter or woofer, you may want to first confirm the output of your Marantz amplifier to see if both channels are performing. Unhook the speakers from the amplifier and re-connect them to the opposite channels (i.e., move the one from left channel to the right channel and vice versa) to see if the problem stays with the amp channel or with the speaker cabinet.

Edit: Oops, I did go back and look at your photo link and I now see the pic of the "new" x-o with installed Sonicap - - the wiring looks fine, but it is impossible to know the condition of the pots. Still, I suggest you check the amp first. 

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