AR 2ax new L-pad installation

ozmoid

ozmoid

Lunatic Member
<EDIT> WARNING!The 8 ohm L-pad used in this project is very different from the AR pot we are replacing. If you can find a 16 ohm 20 watt potentiometer or rheostat, use that instead. The L-pad WILL WORK, and can approximate the values of the AR pot in a narrow response range. For the full explanation, go to post #27 in this thread. I have left the L-pads installed in these speakers, with the right wiring/setting, they sound great, and are about 1/10 the cost of a "proper" replacement part.<END EDIT>

The purpose of this post is to help anybody hesitating about breaking into an AR to be confident about diving in! I know there is more than one way to do this, but I've developed a "method" that eliminates doing anything inside the cab that you can't do blind.

First get the speaker on a table that has a comfortable working height for you. Be aware we are going to roll the speaker over in the middle of this project, so you need to be able to get above it and get leverage.
attachment.php


Remove the woofer, and pull enough insulation out to access the crossover. Use whatever safety gear you think you need to protect against the insulation. Ventilation doesn't hurt either.
attachment.php


Here's your approach! If you have not replaced the caps, this is the time to cut the old cap block loose and replace it with modern caps. You'll need to cut it loose for the next step regardless.
attachment.php


Roll the speaker up on its side, being careful of the loose woofer. I did not unsolder the woofer for this project. Take the old L-pads and the "1" and "T" posts loose, and pull them back inside the cab. Roll the speaker onto its back.
attachment.php


Take a piece of board (I use foamcore) and place it over the woofer opening, and bring the entire "mess" of crossover parts up out of the cab. Now you can trim and solder to your heart's content without trying to cram your head and one arm into the woofer opening! One reason I used foamcore for this project is you can take a "Bic Stick" and punch a couple of holes in the board to hold the L-pads still while you work.
attachment.php


More to come, we're not done yet...
 

Attachments

  • dcp_2464.jpg
    dcp_2464.jpg
    58 KB · Views: 1,426
  • dcp_2470.jpg
    dcp_2470.jpg
    22.1 KB · Views: 1,414
  • dcp_2471.jpg
    dcp_2471.jpg
    69.1 KB · Views: 1,451
  • dcp_2472.jpg
    dcp_2472.jpg
    36.4 KB · Views: 1,413
  • dcp_2473.jpg
    dcp_2473.jpg
    27.5 KB · Views: 1,901
Last edited:
Register to hide this ad
Part II

There is a little "yoke" connecting the "T" post to the L-pads. It is too short for this project, go ahead and make up a longer one. I used a scrap of speaker wire.
attachment.php


Go ahead and cut one of the L-pads loose, and wire the new pad in place. If you're using the Dayton 15w 8ohm from PE, the center tab corresponds to the wiper contact of the old L-pad (the wire that connects in the center of the old L-pad).
attachment.php


Once you're all soldered up (and I hope you took the opportunity to untangle that mess!) there's one more detail before you start putting it all back together:
attachment.php


Now you'll see why we needed the longer yoke: The tabs on the new L-pads interfere with the back of the binding posts where they pass through the cab. You have to rotate the solder tabs on the L-pads away from each other to make all this work without a short, and the original yoke is far too short to reach.
attachment.php


Tighten it all down, put the insulation back like you found it, and reinstall the woofer. If the sealant is dry around the woofer frame, put some "moretite" or other compound around the frame before you reinstall it. (Moretite is a weather stripping product, also know as rope caulk.) There is a paper/fabric/something liner behind the woofer to prevent the loose insulation from contacting it, be sure you put that back as well!

All done, and you have smooth control over the midrange and tweeter in your AR. I tackled this out of frustration with scratchy original pots that had been cleaned and re-cleaned, and still exhibited intermitent operation. My enjoyment of these speakers increased proportionally with the cessation of my frustration levels!

Now I gotta go find some knobs that fit the controls, the stock ones that come in the box are too big to go in the recess and still let me attach wire to the posts...
attachment.php
 

Attachments

  • dcp_2482.jpg
    dcp_2482.jpg
    37.7 KB · Views: 1,389
  • dcp_2481.jpg
    dcp_2481.jpg
    19.5 KB · Views: 1,372
  • dcp_2478.jpg
    dcp_2478.jpg
    54.3 KB · Views: 1,378
  • dcp_2476.jpg
    dcp_2476.jpg
    34.2 KB · Views: 1,386
  • dcp_2486.jpg
    dcp_2486.jpg
    42 KB · Views: 1,348
Last edited:
Yes, thanks! I have a set of AR3a's I want to do this to and this really helps! :thmbsp: Much appreciated!
 
The best how-to I've seen. Great pics, great instruction. Kudos to you for the hard work and patience to pull this together for other AKers.
 
Very nice presentation! Makes me want to pull my AR-2axs out of the attic and replace those crappy old l-pads. Well done!
 
Nothin' like making photographs while you're actually fixing stuff there Oz! I can't hold the solder, the iron, AND my beer if I'm busy taking pictures! :D Good job Bubba!
 
Nothin' like making photographs while you're actually fixing stuff there Oz! I can't hold the solder, the iron, AND my beer if I'm busy taking pictures!

Kind of like smoking a cigarette and passing a beer while driving a 4-speed in the snow! :smoke:

Shacky
 
Thanks

Thanks to everybody posting here!

I really did this for 2 reasons:

There's been a lot of discussion about whether those particular L-pads would fit without moving the mounting holes. They do,and the pictures above put paid to that little mystery.

I put off digging into these speakers because I was afraid - too complicated, what will it look like, what if I can't get them back together in working order? I lost a lot of good enjoyable listening time because there wasn't anything like this on AK.

And now there is.

In other threads, there has been some discussion about non-original parts changing the "AR Sound", or affecting the value of the speakers. I did NOT buy these things to look at or trade - I bought them to LISTEN TO! Changing the L-pads really increased my enjoyment of these speakers. :thmbsp:
 
TECH Update 7/14/06

Pot vs L-pad comparison

attachment.php


The original AR part is a 15.7 ohm (fixed resistance) potentiometer/rheostat.

In the case of the PE L-pads, the outer resistor (3) is 8.8 ohms, the inner resistor (1) is 40.0 ohms. That's how I got the crossover leveled out - I metered the L-pad across 1 and 3, then adjusted it until I got 15.7 ohms to match the fixed resistance of the AR pot. Since the lowest possible Ohm setting on the L-pad is 8.8, it will never show the amp a lower load than that. I don't think the amp sees a constant 8 ohm load, just 8 ohm as a maximum load.

For the L-pad to have a constant resistance from terminals 1 to 3, the two resistors would have to be identical. If you do that, you just need the one resistor anyway, and you now have a potentiometer! (or rheostat, if you like.)
 
shacky said:
What about terminal 2 on the PE L-Pad. Does the resistance here make a difference in the crossover?

I know we are thinking about this way too much but I'm still confused about all this pot/lpad stuff.

My older 2AX's still sound great with the original pots back in. I have the mid and hi pots tunred up ~ 90% and it still is way more laid back than with the PE l-pads. L-Pads made it bright sounding and now matter what I did I didn't get the blooming bass I'm getting now. Could be I did something wrong or could be that the later model crossovers are less impacted by the 8 ohm PS L-Pad.

Thoughts?

PS I've never had speakers that sound so good at low to moderate listening levels. I still have them on the floor because I like that bass that you can feel in your butt. No distortion and no boomy ported sound. Just pure bass that makes classic rock sound rich. I'm now listening to the newish Matt Bianco with Basia CD. This Disco-Jazz (my discription) goes way down. The AR's go right down there with a guteral feeling - no distortion. Amazing. Hi's and mid's are great but not in your face. I remember another Ak'er mentioning - "did they know how good they had it in the 60's with this old technology?"
Click to expand...
Shacky, the difference in the original AR pot and the PE L-pad is two-fold:

1. The AR pot has a FIXED resistance across terminals 1 and 3 of 16 ohms. No matter where you move the control (wiper), this reading remains constant.

The L-pad varies resistance across terminals 1 and 3 as you move the control. Resistance will vary from 8 ohms at min to 40 ohms at max.

2. The AR pot output on terminal 2 varies from 0 ohms to 16 ohms as you move the control. this is the ONLY terminal affected by the control on the AR pot.

The L-pad varies terminal 2 output as you move the control from .5 ohms to 40 ohms.

These resistance changes are certainly changing how the crossover sounds, and is affecting the "voice" of the speakers. The easy solution with the L-pads is to just mark the point where terminals 1 and 3 read 16 ohms, and leave it there. At that point, terminal 2 is reading about 10 ohms - this is very close the "sweet spot" on the original control.

I have now measured over half-a-dozen AR pots, and the resistance varies from 15.5 to 17.3 so far. So if we have gotten within "an ohm or two", we are within the same tolerance AR used for the part.
 
Thanks, Jim.

If shacky had not questioned the "sound" of the L-pad, I never would have explored this further than "Oh, everybody says use the L-pad."

I am NOT an electronics expert, I am still learning how crossovers work and how the values are set by the hardware. It obvious to me that the L-pad is SO different from the original part mechanically that it will never accurately replicate the AR pot. The bad news is that a new set of rheostats/pots is going to run about $100+, if you can find them in stock anywhere. The 2ax regularly sells at auction for about that price.

So big question is can you live with the sound of the L-pad? How close is close enough for you?
 
You must log in or register to reply here.
Back
Top Bottom