Audiokarma.org
Audiokarma Featured Sponsor

Go Back   AudioKarma.org Home Audio Stereo Discussion Forums > Speakers


We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 06-26-2010, 12:44 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
Acoustic Research Potentiometer Restoration Guide



NOTE: I tend to take WAY TOO MANY photos. Sorry.

INTRODUCTION
So you've picked up a pair of original Acoustic Research speakers. Congratulations! AR speakers are among the most cherished of the classic "east-coast" speakers of the 1960s and 1970s. Excited, you go to hook them up and - what's this? There's a surprising lack of high end... Hmm, maybe it's just that east-coast sound. Hopeful, you put your ear up to the tweeter and-- WHAT!? It's dead! There's no output. Frantic, you wonder what you're going to do about these dead tweeters that you just bought.

Fear not! There is a 90% chance that your tweeters are still very much alive and well. What has gone bad in your AR speakers are what are called the potentiometers. If you look on the back of the speaker, you will see a small knob that says "DECREASE - NORM - INCREASE". This is the potentiometer - it varies the tweeter's output level as you turn it. However, over the years, the potentiometer has corroded and can no longer carry an electric signal.

This is where you come in! Your job is now to open the speaker and clean the potentiometer and protect it from future corrosion. This guide will assist you, through the use of detailed explanation and helpful photos, to do just this, as well as a few other key items in any basic speaker restoration process. Let's get to work!

DISCLAIMER: The processes described in this guide are based on MY experiences, and MY experiences only. I realize that there are other methods by which to accomplish many of the things that I describe in this thread. I have described everything to the best of my ability. If you find that any process is not satisfactory for your standards, I am in no way stopping you from doing it your own way. However, following my guide will result in a good, listenable speaker.

The information in this thread may be used as a general guide for the restoration of all classic AR speakers with potentiometers (including AR-2, AR-3, AR-4, etc). I am in no way responsible if you mess up your speakers because they are not exactly the same as the AR-4x that I based this thread on.
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 08-23-2013 at 01:15 PM.
Reply With Quote
  #2  
Old 06-26-2010, 12:50 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

TOOLS OF THE TRADE
For this restoration project, you will need many things. Here's a list:



• Power drill
• Respirator mask
• Latex gloves
• Soldering iron
• Solder
• Cup
• Wire nuts
• Red, black, green, and yellow wire (16 gauge)
• Dremel tool or equivalent (with soft wire brush)
• Latex gloves
• Wire strippers
• Wire cutters
• Needle-nose pliers
• Long-blade flathead screwdriver
• Red and black Sharpie markers
• Brown paper grocery bag (not pictured)
• Fiberglass scratch brush (not pictured)

CHEMICALS OF THE TRADE

CAUTION! Some of these chemicals can be very harmful if used incorrectly. Please exercise caution with all of them, and refer to the product label and the particular step in this guide for further safety instructions.



• White vinegar
• Iodized salt
• Howard's Restor-A-Finish
• Howard's Feed-N-Wax
• DeoxIT D5
• 3M Strip-Calk (not pictured)
• Permatex Silicone Spray 80070 (not pictured)
• Dish soap (not pictured)

(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 08-23-2013 at 01:16 PM.
Reply With Quote
  #3  
Old 06-26-2010, 01:06 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP ONE: OPENING THE SPEAKER

We need to get to the speaker's insides if we want to repair it!

Removing the Grille Cloth
Chances are that nobody has removed the grille cloth since the speaker was at the factory, and, as such, it will still be glued onto the front of the speaker. Take your putty knife and stick it in between the grille cloth and the wood. Make sure you put a small rag on the wood side of the putty knife so that you don't damage the wood of the speaker. Slowly and gently pry up around the entire grille cloth until you feel that the glue spots have snapped apart. Be careful not to pry too hard or else you risk snapping the frame of the grille.

(NOTE: I don't actually own a putty knife, so I had to use a long-blade flathead screwdriver. Do not do this - get a putty knife.)

(Thanks to member Zilch for the putty knife/rag suggestion.)





Removing the Woofer
Once the grille cloth has been removed, you will be presented with a sight like this:



Take your power drill and find a drill bit that will fit the screws that hold in the woofer. Begin to unscrew them - don't press down too hard or you risk dislodging the T-nut that the screw goes into, and these are a complete pain to replace (I have not successfully replaced one to date).



Put the screws in a labeled cup, so that you can both keep track of where they are and know what speaker they came from.



Once all the screws have been removed, start to pry the woofer out with your screwdriver.



CAUTION! The wires that connect to the woofer are VERY SHORT. If you pull the woofer out too far too fast, you risk damaging the wires or (more likely) the terminals they connect to on the woofer. These are not easily replaced. Make sure to pull the woofer out only as far as it wants to go, and then set it face down on the front of the speaker.



(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 11-03-2010 at 10:10 AM.
Reply With Quote
  #4  
Old 06-26-2010, 01:24 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP TWO: DESOLDER THE WOOFER

DANGER. Soldering (pronounced SAW-durr-ing) is a very dangerous activity which involves extreme heat that comes very close to your hands. I am in no way responsible if you burn or otherwise injure yourself while soldering. I have burned myself a couple times (once quite severely) while soldering, and it is NOT something you want to do. Please use common sense and utmost caution while soldering to avoid being injured.

Knowing your target
The woofer has two terminals on it - one for each polarity. In this case, the wires are red and blue.



Make sure to keep track of which side is red - this is your "positive", or "hot" wire. In almost all instances, there will be a red "X" on the side where the red wire connects - this was done by AR at the factory so they could keep track of it too.

Desoldering 101
Fire up your soldering iron and let it heat up for about 5 minutes or less. Keep in mind that the tip of the iron is the hottest part. Take the tip and put it beneath the location where the red (or blue) wire connects to the woofer terminal. Heat rises, correct? This placement, along with making as much contact between iron and wire/terminal as possible, will ensure that you spend as little time as you have to wielding this dangerously hot instrument.



Once you see the solder become shiny and start to melt, or "flow", use your needle-nose pliers to pull the wire out of the terminal. You may need to use more force than you think here, but be careful not to break the terminal off.



Ta-da! Rinse and repeat for the other wire.



Set the woofer aside for now.

(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 01-29-2014 at 06:41 AM.
Reply With Quote
  #5  
Old 06-26-2010, 01:40 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP THREE: UNSTUFFING THE CABINET

Take It All Out
See the piece of flimsy-looking fabric that is sitting below where the woofer goes? That's called the "shroud". It protects the woofer from the insulation beneath it.



Time to get out your latex gloves - the stuff inside the speaker will make you VERY itchy if you touch it with your bare skin.



Take the shroud out, being very careful not to rip it (it is extremely fragile), and set it aside for later.



Eugh... What IS this stuff?



The answer is rock wool. In the 1960s and 1970s, when wool was scarce due to the Vietnam War, "rock wool" was created as a substitute. It contains all sorts of impurities and nasties that you don't want touching you. One paper grocery bag will hold the rock wool for one speaker.

(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 11-03-2010 at 10:10 AM.
Reply With Quote
Audiokarma
  #6  
Old 06-26-2010, 01:57 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP FOUR: REMOVING THE POTENTIOMETER

Snip Snip!
Now you will be able to see inside the cabinet and take a look at the crossover.



Not much here - an inductor, a capacitor (in that large box under the inductor), and the potentiometer.

Our job is simple - cut the potentiometer out. First, make a diagram like I did of the potentiometer's connections, so you don't confuse yourself later.





Your pair of wire cutters will do the job. Try to cut as close as possible to the terminals on the potentiometer - this will save you a lot of hassle later.



(NOTE: Some AR speakers have a small piece of black caulk that goes around the potentiometer - mine didn't, but yours may. Simply pick it off and throw it away - it serves no real purpose.)

Put the speaker upright and look at the back plate. There are two terminals marked "1" and "2", and a knob (usually red, sometimes black) that says "DECREASE - NORM - INCREASE". The "DECREASE - NORM - INCREASE" knob is actually the opposite side of the potentiometer that you just disconnected inside the cabinet.



(NOTE: Some AR speakers, such as the AR-3a, have a third screw terminal, labeled "T", on the back, with a jumper in between the "2" and "T" terminals. This is what powers the high frequency driver(s) of the speaker, and, if removed, converts the speaker to woofer-only operation.)

Take your needle-nose pliers and start to unscrew the nut that holds the potentiometer on - once you turn it a little bit you can do the rest with your fingers.



Here's an idea - put the nut and spacer in that cup you put the screws in earlier.



Push the potentiometer through.



Voilį, you have successfully taken out the potentiometer. You may ignore the rest of the speaker for a little while.



You'll notice that there's a very thin metal piece that looks like a giant staple - this holds the two halves of the potentiometer together.



Take your needle-nose pliers and pull both ends of it out.



This is what your potentiometer looks like on the inside. You'll notice the corrosion - this is what was preventing your tweeter from working.



We don't need the half with the red (or black) knob in it - put it in your parts cup, along with the metal "hold-it-together" piece we just took out.



Now onto the cleaning!

(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 02-17-2011 at 01:24 PM.
Reply With Quote
  #7  
Old 06-26-2010, 02:16 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP FIVE: CLEANING THE POTENTIOMETER - PART ONE

Soak City
These are the two parts of the potentiometer that we want to clean.



Time to get out the vinegar and the iodized salt - we're gonna cook up a homemade recipe.



CAUTION! Vinegar is an acid. It will rust anything metallic it comes in contact with. Make sure you are using WHITE VINEGAR, as any other vinegar can be dangerous to you as well.

Pour enough vinegar into a cup that the large part of the potentiometer will be completely submerged.



Now pour A LOT of salt in. That's right, GRATUITOUS AMOUNTS OF SALT. I was very surprised at just how much salt would dissolve into the vinegar.



I used the end of an old toothbrush to stir up this concoction - I didn't want to mix it with anything metallic, or else it would rust.



Plop the two potentiometer parts into the mixture. You'll notice in seconds that the heavily corroded areas start to turn a salmon-ish color - this is a layer of copper. Copper is good - it is one of the best conductors of electricity.



Let the pot soak for about one hour. Afterward it should look much better.



Take the pot out (I just stuck my fingers in and then washed my hands afterward) and set it out to dry. Pointing a fan at it wouldn't hurt.



(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 11-03-2010 at 10:11 AM.
Reply With Quote
  #8  
Old 06-26-2010, 02:35 AM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP SIX: CLEANING THE POTENTIOMETER - PART TWO

Ridin' Spinners
Time to break out the DeoxIT D5 and your Dremel tool (with soft wire brush attachment). If you're poor and have no money, a simple soft wire brush and some elbow grease will be okay.





Take the large part of the potentiometer and grab onto one of the terminals with your needle-nose pliers. Now take the DeoxIT and spray it on the metal circles in the center, and on the wire coil on the outside. Don't press on the dispenser too much - DeoxIT bottles spray pretty fast.



Turn the Dremel tool on and begin to polish the metal parts you just sprayed - don't be afraid to push against them relatively hard. Try to keep a balance between pressure and the speed of your tool - too slow a speed and it won't polish well, and if you push too hard it won't polish well.



Polish until all of the metal is nice and shiny.



Rinse and repeat with the other, smaller metal piece. Be careful not to push against this too hard, or else you risk bending it out of shape.



It's a good idea to also brush the pot with a fiberglass scratch brush to get into places where the Dremel tool won't reach. You can order one here: http://www.contenti.com/products/brushes/150-040.html

(Thanks to member gkimeng for this suggestion.)

After you've finished polishing the pot, it's time to get all of the vinegar and salt deposits out of it. Fill a tub with water, add some dish soap, and swish and scrub.







Let the pot dry for about an hour - I put it on a soft cloth under a slow-speed fan.



(Thanks again to gkimeng for the suggestion.)

Coating the pot with something dielectric will help prevent future corrosion. I used Permatex Silicone Spray 80070, which both lubricates the pot for smooth operation and coats it with a dielectric compound to protect against corrosion. You can find this Permatex product here: http://www.advenquest.com/gear/produ...nt-2-Pack.html



Spray the whole pot with the solution until it's covered in foam, then pick it up (or tilt it over on its side) and let the foam slowly run off.





After most of the foam is gone, go ahead and pat it dry with a cloth.

(Thanks to gkimeng for the dielectric suggestion.)

Congratulations, your potentiometer is now clean and protected! Now it's time to put everything back together.

(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 11-03-2010 at 10:12 AM.
Reply With Quote
  #9  
Old 06-26-2010, 05:19 AM
barebones's Avatar
barebones barebones is offline
AK Member
 
Join Date: Oct 2008
Posts: 533
Bravo.....
__________________
til' death do us art....
Reply With Quote
  #10  
Old 06-26-2010, 06:20 AM
Andyman's Avatar
Andyman Andyman is offline
Scroungus Stereophilus
 
Join Date: Apr 2003
Location: 15 miles North of Canada, East of Grumpy. West of Kegger
Posts: 25,151
Nice write up on a very common, oft discussed repair. It should get stickied somewhere.

It's too bad your pots weren't nastier looking though. The ones I've cleaned were loaded with that nasty green fuzz corrosion
__________________
"Do or do not. There is no try"

- Yoda
Reply With Quote
Audiokarma
  #11  
Old 06-26-2010, 08:53 AM
pioneervato's Avatar
pioneervato pioneervato is offline
Happy Halloween!!
 
Join Date: Nov 2006
Location: The Arizona Desert Between Phoenix and Tucson
Posts: 12,724
Very nice and detailed tutorial. I cleaned up my pots on my AR2ax's in a very similar manner a couple years back. Now that you have her undressed this would be a good time for a re-cap job as well. Great job!
__________________
Reply With Quote
  #12  
Old 06-26-2010, 12:00 PM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP SEVEN: REWIRING THE POTENTIOMETER - PART ONE

Snap It Into Place
Retrieve the other pieces of the potentiometer from your parts cup. Put the small metal piece on the red (or black) knob like so. It's designed to only fit one way, so don't worry about putting it on in the incorrect orientation.



Fit the two halves together again - you'll notice that there are three "nubs" on the dark half. These are also only designed to go in one way, so if you don't have it, keep rotating it around until you find the orientation that works.

(NOTE: Make sure that the red (or black) knob is lined up correctly when putting the two halves back together. As long as the metal piece inside is touching any part of the wire coil, it's fine.)


A Lengthy Solution
While your soldering iron is heating up, go find some green and yellow wire, and that diagram you made earlier. Get your wire cutters and cut three pieces of green wire and one piece of yellow wire, each about 3x the length of your pointer finger.



(NOTE: If you don't have green and yellow wire, red and black will be fine. Red = yellow, and black = green.)

Get your wire strippers and strip the wires to about this length.





Set these wires aside for now - we'll use them in just a minute.

(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 11-03-2010 at 10:12 AM.
Reply With Quote
  #13  
Old 06-26-2010, 12:15 PM
istariknight's Avatar
istariknight istariknight is offline
AK Member
 
Join Date: Feb 2008
Location: UK
Posts: 148
Superb guide ! Unfortunately couldn't revive mine (Looked like someone put 1000v through them!) had to replace them with L-Pads from Vintage-AR. For what its worth, they function just the same & sound no different at all so don't despair if you can't fix yours people =)
Reply With Quote
  #14  
Old 06-26-2010, 12:24 PM
bluesky's Avatar
bluesky bluesky is offline
AK Member
 
Join Date: Feb 2007
Posts: 5,908
Excellent...worth of a sticky!

Same problem in Sansui Speakers.

Have to take one of my speaker Potentiometers apart one of these days. But it still functions in specific positions, but it is corroded for sure.

Very Very nice write-up! A keeper!

Last edited by bluesky; 06-26-2010 at 12:34 PM.
Reply With Quote
  #15  
Old 06-26-2010, 12:53 PM
tmad40blue's Avatar
tmad40blue tmad40blue is offline
"I can hear forever!"
 
Join Date: Aug 2009
Location: Ann Arbor, MI
Posts: 2,289
(Go back to TABLE OF CONTENTS)

STEP EIGHT: REWIRING THE POTENTIOMETER - PART TWO

Come Outta There!
Now it's time to get rid of those old factory connections. In order to hold the potentiometer in place while desoldering, I used a small clamp like this one.



The goal here is to clear each of the three terminals of the old bits and pieces of wire. Take your soldering iron and put it in the optimal position - just slightly beneath the area where you want the solder to melt.



Once you see the solder begin to melt, you will need your needle-nose pliers. Your goal is to get all of the little pieces of old wire out of the terminal, and to leave a nice-sized hole for the new connections. This can be one of the most frustrating steps of the process, so don't worry if it takes you a while.





Repeat this for each terminal until there is nothing left of the old connections.

Soldering 101
Time to make your own connections for the first time!

CAUTION! The entire potentiometer becomes VERY HOT when it comes in contact with the soldering iron. Exercise caution when handling it, as you can burn yourself.

Find that diagram of the potentiometer you made earlier, as well as the wires you cut earlier, and start to wire it up according to the diagram.





Take your soldering iron and place it just beneath the point where the wire meets the terminal.



In order to effectively solder a connection, you need to make sure that the solder "flows". This means that the solder should not touch the iron at any time. Instead, you want the wire to become hot enough to melt the solder on its own.



Once you have heated the wire for long enough, touch the solder to it.



If you see the solder visibly flow along the wire and onto the terminal, you're doing great! Let this happen for 5 seconds or so until the solder has flowed along enough of the connection. Then take the solder and the iron away and wait for the solder to solidify.



Ta-da! If you want to test the solidity of the connection, grasp the wire (not too close to the connection, it's still hot) and pull a little bit. If the wire doesn't budge, you've made a good connection.

Repeat this for all the connections on your diagram.



Now you've successfully completed the hardest part of the job. w00t!



(Go back to TABLE OF CONTENTS)
__________________


Thanks for the knowledge and guidance, Zilch!
--------------------------------------------------------
My systems
Home theater build
AR Potentiometer Restoration Guide

Last edited by tmad40blue; 11-03-2010 at 10:13 AM.
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 04:36 AM.



Friends of Audiokarma
We appreciate your help in keeping this site going.
Stereo Repair World
Herbies Audio Lab
Vintage Home Audio
Amps and Sound
Pro DJ Headphones - click here
Organ Donor Parts
Wargos Electronics
Parts Connexion
Sonneteer
Take Five Audio
Sound Stage Direct
Audio Salon
AudioClassics
Audience AV
AV Solutions
Simply Speakers
Tone Arm Audio
BD Enterprise
Musical Paradise
Howard Products
Classic Sound Repair
FM DX Antenna
McIntosh Cabinets
Siliconray
BOI Audio Works
Vinyl Magic Record Cleaner
Amplifiedparts
Grant Fidelity
RSL Speakers
Yesterday's Audio
Urban Antigue Radio
DeWick Repairs
Many Moons Audio
Vintage Electronics Repair
The Tube Store
Politicalchat.org
Audio Doctor
Antique Radio Classifieds
MCM Electronics
Videokarma.org
   
   
Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
©Copyright 2002-2014 AudioKarma.org, All rights reserved.