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AR-2AX External Crossover


Guest baumgrenze

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Guest baumgrenze

I am in the process of rebuilding a pair of AR-2AX speakers I bought from AR, mail-order, in 1967. Bill at Millersound in Lansdale, PA reattached the spider on one of the woofers for a very reasonable price.

As I worked on the speakers, I decided that it would be far more convenient to make future repairs on the crossover network if the components were mounted outboard on the back of the speaker cabinet.

I carefully removed the component parts of the crossover, tagging each connection with a string tag.

I cut a 5" square of hardened Masonite from an old kitchen cabinet door. I centered it on the inside of the cabinet over the original terminal opening and marked the three terminal bolt holes and drilled them out. I also marked the location of the holes for the two Pollack pots so that I could carefully seal them with Ace rope caulk weatherstripping (recommended elsewhere in this forum as a sealant for speaker remounting.) I drilled 3 more holes in my Masonite in a triangular array, using the original bolt to bolt distance and carefully avoiding the original AR marking for the pots on the outside of the crossover board, mostly for sentimental reasons. I now had 6 terminal posts, the requisite number for the unique connections made in the crossover.

After drilling out the remaining holes, I placed rope caulking around the edge and around each bolt (and the pot holes)(see photo) and bolted down and screwed down the new terminal board. I put terminals on the speaker wires, removed each bolt, and attached the speaker leads either to the original terminal posts or to one of the new terminal posts on the inside of the cabinet. I put a washer, lock washer, and nut on each on the outside to fix the bolt in place. I reassembled the crossover on the back of the cabinet (see photo) being very careful to replace the original aluminum inductor mount with a brass screw and washer so as not to change the character of the inductor.

I can now clean (or bypass at will) the Pollack pots whenever I wish. I have not yet concluded whether or not I need to install new capacitors. I do know that a Fluke Model 87 multimeter cannot put sufficient charge on a 50 V capacitor to test it. Technical support at Fluke confirmed my observations. I'm now trying to negotiate capacitor testing by a friend with EE expertise.

How many hackles have I raised as a result of my unorthodox mounting of the crossover?

These speakers are mounted in openings in a bookshelf that were created to fit them. If they fit any tighter the cabinet would be mounted in acoustic suspension fashion in the shelf. I see no reason to cover the back.

I'm also working on a pair of AR-5's from late 1972 that I bought at an estate sale. For these I may cut some black walnut stock I have so that I can extend the cabinet back a couple of inches and provide a false back to cover the crossover.

baumgrenze

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Guest baumgrenze

I've satisfied myself that the original capacitor packs for these speakers are probably ready for retirement. At least the 4 micro farad capacitors (and those in my AR-5's) could not be measured using a Fluke Model 87 multimeter. When a friend checked them using his HP200 oscillator and a resistor, they all read 20% or more above 4 micro farads. The Fluke appeared unable to provide charge fast enough to get a reading, even though it should read automatically up to 5 micro farads.

My question is, did you use caps that 'came close?' At Parts Express I find Solen's with values of 3.9 and 6.2. These are within +/- 10% of the original values. The spec on the Solen's appears to be 5%. Are these the ones to use?

Thanks,

baumgrenze

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>I've satisfied myself that the original capacitor packs for

>these speakers are probably ready for retirement. At least the

>4 micro farad capacitors (and those in my AR-5's) could not be

>measured using a Fluke Model 87 multimeter. When a friend

>checked them using his HP200 oscillator and a resistor, they

>all read 20% or more above 4 micro farads. The Fluke appeared

>unable to provide charge fast enough to get a reading, even

>though it should read automatically up to 5 micro farads.

>

>My question is, did you use caps that 'came close?' At Parts

>Express I find Solen's with values of 3.9 and 6.2. These are

>within +/- 10% of the original values. The spec on the Solen's

>appears to be 5%. Are these the ones to use?

>

>Thanks,

>

>baumgrenze

If you worried about accuracy, Parts Express offers their brand (Dayton) precision 1% tol. caps.

They list 4 and 6.2 uF MPP rated at 250 VDC. They are a little more expensive than the Solens but you may find the extra cost justified.

These sould work just fine.

It's all about the music

Carl

Carl's Custom Loudspeakers

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