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AR 2AX l-pads


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Wanted to share my experience with changing out l-pads and caps in my 2AX - older version vintage 1965. Some folks on AudioKarma helped me out tremendously and I appreciate all the help they gave me throughout this project. I followed an AK thread that used the Dayton 8 ohm l-pads. I was a little concerned that using 8 ohm instead of original 15 ohm might effect the sound - but these were a non-working pair when I got them so I did not know what they sounded like in original form.

I replaced all l-pads, inserted Solen caps of equal values to original, used Moretite to re-seal the woofers and coated the dry surrounds with rubber cement to ensure a good air seal. They sounded great but I noticed that some music didn't sound as it "should". More like it was very different from what my ear was expected.

I've been asking around and a couple of people told me that using the 8 ohm l-pads with original value caps probably raised the crossover points - significantly. To some ears this may sound very pleasing but I kept looking for more from these aclaimed speakers.

Well I had a cherry pair of original l-pads I took out of a later pair of 2AX's and decided why not take the time to do an experiment. 4 hours actually to take them back apart, swap out the l-pads and re-seal the woofers.

The result to my ears is spectacular! I think I was missing music in the low midrange which seems to give the bass more "bloom". Music sounds more like what I exspect. Listening to Pink Floyd DSOTM and it's fantastic. Last night I listened with the 8 ohm l-pads in place and I just couldn't get the balance "right".

I don't in anyway mean this as criticism of others ideas. But to my ears the change to 8 ohm l-pads doesn't sound "right". To others it may be perfect.

Only reason I'm posting this for those considering a replacement. If you don't hear what you like with the 8 ohm l-pads you may want to keep looking for a working pair of 15 ohm. As I am just a beginer at this, please don't take my thoughts as that of an expert. Just relating what sounds best to my ears.

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Hi there;

Thank you for adding to this particularly controversial subject.

The controls in AR speakers are potentiometers or rheostats, not L-pads.

You should also find after a continuous capacitor burn-in period of about 40 hours, the mid-upper area of sound will improve.

Did you change out the bass drivers capacitor also, or just the mid and tweeters?

There is a lot of data here on this topic in the search for "L-PADS".

I did the search, but there was so much, I was overwhelmed, I did not actually find the "meat" I was looking for, or at least it may have been stretched over several threads.

My hunger for the "meat" is, what is the basic difference between L-pads and pots in form and function.

Why should L-pads not be used in place of pots?

If L-pads are ok, then what impedance should they be?

I am hoping that the technically knowledgeable members, and there is numerous, will clear this up for me, please.

Good luck.

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Only change the cap for mid and tweeter. I have no idea wha difference is between l-pad and pot. I have heard that both the original potentiometers and the Dayton 8ohm show constant ohm regardless of "volume" of pot or l-pad. So the original shows 15 ohms and Dayton shows 8 ohms all the time. I was wondering why that wouldn't change the sound of the speaker - I beleive Carl did warn me to use the originals but I wanted to obviate any problems with the old style potentiometers.

I was not happy at all with the sound from 8 ohm Dayton units. And now that I have the old 15's back in - cleaned up of course - I love these speakers. Listening to Pat Metheany - First Circle, Still Life Talking, Road to You. I know these CD's like the back of my hand. I could not get the 8 ohm l-pads to sound "right". Now that I have the 15's in place - all sounds as it should. And very nice indeed.

I was beginning to sonder if all the talk about AR's was urban legend untill I put the 15 ohm pots back in.

Glad I could add to a contoversial topic!

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I just tried to write a post and it seems to have gone off into the aether somewhere never to return. Will try again. If two versions of this note appear... sorry, like the cat--it came back.

First, there can be many reasons your L-pads did not sound as good as the original potentiometers.

-- L-pads are NOT the same as potentiometers.

-- lousy capacitor

-- cold solder joint the first go-around

-- and on and on ...

Here I want to comment only about the first issue. The attached sketch shows the innards of an L-pad, of a potentiometer and how the Pollack 15-Ohm pot is used in a typical tweeter circuit.

The function of an L-pad is to maintain constant input RESISTANCE to the pad when connected to the rated RESISTIVE load. e.g., if an 8-Ohm resistor were connected to terminals 1-2 of an 8-Ohm L-pad, the input resistance seen at terminals 1-3 would always be 8-Ohms for all shaft rotation angles.

However, the tweet and mid are not simple resistors, they are impedances (R plus L, C) whose value changes with frequency. It is likely that at some shaft position, the match with the potentiometer is good enough for some listeners, but they are not precisely the same.

The AR-3a "Limited" (1991) used L-pads, but AR designers changed the values of L, C in the mid and tweet crossovers to accomodate the differences between the pad and the potentiometer. Perhaps someone with P-spice, the correct frequency dependent models for some drivers, and lots of spare time could model these differences for one speaker of interest. Results will be speaker dependent.

Meanwhile, it is a simple task to open the potentiometer, clean out the muck, polish the surfaces, coat them with a dielectric grease and re-assemble. A lot cheaper than new L-pads, which for some cabinets are too large to fit in the original mounting holes!


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While I don't understand all you wrote this is awesome background. Somone noted to me that there are 16 ohm lpads available from Parts Express for those who have un-repairable originals. Though an l-pad it might be a better choice in a pinch.


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Hi Shacky:

An L-pad would work in a pinch, but 8-Ohm would be the choice. The drivers in most of these units (AR-2x, -4x, -3,-3a, etc. are nominally either 4- or 8-Ohm, but that value varies with frequency. I believe the 16-Ohm version would be inappropriate. Those who do install pads use the 8-Ohm version.

Seriously, try opening the existing potentiometers by removing the spring wire that holds the backside in place. Then clean their insides and re-assemble. That was a rugged design; it can take a lot of cleaning with a Dremel tool or fine emery paper. Very few are totally beyond repair--perhaps those used as decoration in an acquarium?

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The 8 ohm lpad was what started my whole journey. They did not sound "right". When I took them out and replaced with cleaned up originals - the sound is much better. I was told the 8 ohm lpad instead of the 15 ohm pot changed the crossover points significantly.


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>The 8 ohm lpad was what started my whole journey. They did

>not sound "right".

Hi Jim: Yes, I agree, as would many other folk. However there are some who substitute L-pads and are satisfied. What can one say? Good luck in restoring them to the best condition you are able!

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Thanks John. They are working "as new" with a cleaned up original set of pots. These speakers are what I was looking for. Not an in your face sound - very laid back and very good bass with great bloom. I can listen to these speakers at very low volume (with loudness on) and still hear full sound with great bass.

My wife hates loud music (which one's don't) so this is important to me. It's not that they can't crank - they can - but for everyday listneing they are great. Takes a little getting use to as they sound flat at first. They remind me of my Wharfedale w40D's my brother and I had. I would think the AR's are better but I'd love to be able to do a side by side. My brother and I had the Wharfedales in our apartment bedroom and our parents had many complaints from the neighbors:7

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