Recap Your Speakers Like a Boss, Part 1

Wigwam Jones

Caesar non supra grammati
HOW TO RECAP YOUR OWN SPEAKERS LIKE A BOSS

What is recapping?

Speakers generally have more than one driver in them. When they do, they often have what is known as a 'crossover' in them to ensure that the appropriate frequency ranges get sent to the correct driver. Crossovers can be active or passive, and they can be simple or complex. I am just going to deal with a simple passive, 3-way speaker design of the sort commonly found on vintage speakers. In this case, I am going to replace the capacitors on the crossover network of my Realistic Nova-8 speakers. This is known as 'recapping'.

Why recap?

Passive speaker crossovers are generally made of one or more of the following electronic devices: capacitors, inductors, resisters, and variable resisters, commonly known as "L-Pads" for adjusting individual drivers to your own taste (these are the knobs that stick out of the back of your speakers). Generally speaking, the resisters and inductors do not go bad and do not need to be replaced. But the capacitors are different; they are made up of a chemical paste inside, and over the years, the chemistry changes, and the capacitors stop working within the parameters they were designed for. This can harm drivers in the worst cases, but even if it doesn't damage them, it can ruin the sound of an otherwise excellent set of loudspeakers. So it is quite common to 'recap' a set of vintage speakers, and it quite often improves the sound quality very much.

What do I need?

You need your speakers, of course. And you will need have opened them up (some open from the back, some by taking out one or more of the drivers, such as the woofer) and you'll have to identify the values of the capacitors inside. Presuming that you are doing a 1-for-1 replacement of matching values and not fiddling with the values to create a different sound, you'll want to order replacement capacitors of the same value.

Capacitors are available in a variety of types, and from a variety of vendors. With speakers, the capacitors used in the crossover should be non-polarity (also known as NP) and the voltage should be the same or higher than the capacitors you're replacing. Other than that, it is a matter of taste and budget; there are inexpensive capacitors and expensive capacitors. They are made of a variety of materials. Ask questions, look at prices, decide what you want to spend. In the end, it's your decision. As long as the values are correct and they are non-polarity and the same voltage or higher, you're good as far as having them work for you. Some people feel that more expensive capacitors sound better; your call on that.

You will also need a soldering iron. These are available very inexpensively from places like Radio Shack and lots of mail order places. You don't need to spend much on this; it does not have to be fancy at all. You will not be soldering extremely temperature-sensitive materials.

You'll need some solder. Rosin-core solder is common and inexpensive. Some people prefer to use silver solder. It costs more and is harder to use for some people; the choice is yours.

You'll need some common tools like screwdrivers, needle-nose pliers, wire snips, and that sort of thing. Nothing weird or expensive.

You'll need some sealant of some sort for various things. For example, something to stick the crossover network back down again after you've pried it out of the back of the speaker cabinet. Perhaps some kind of sealant to seal the woofer if you have to take it out and the material used to seal it in place is ruined in the process. You can buy that commercially, some people like to use the stuff used to seal doors in houses, it's a type of rope caulk that you can mold with your fingers. Your choice, but if your speakers are 'sealed' and not 'vented' then you do want a nice tight seal when you put them back together.

Some words of warning!


Soldering is done at a high temperature. You can burn yourself badly. You can start a fire. Please use precautions. Have a fire extinguisher handy. Keep the soldering iron on a stand designed for that purpose when it is not in your hand. Do not breathe solder fumes; they're nasty and bad for you. Just use common sense and be careful and go slow.

Let's get started!


Here is what I'm working on today. A vintage Realistic Nova-8 set of speakers. Classic 3-way design with a woofer, two midrange drivers, and a tweeter.


100_3749.JPG by Wigwam Jones, on Flickr


100_3750.JPG by Wigwam Jones, on Flickr

There are two connectors for speakers on the back, plus an RCA jack (common on Radio Shack speakers, you can ignore it) and a pair of L-Pads for adjusting the mid-range and treble to your taste.


100_3751.JPG by Wigwam Jones, on Flickr

Step One: Remove the woofer

First, I laid my speaker down across two chairs so that I could work on it. I used a Phillips screwdriver to remove the four screws holding the woofer in and gently pried the woofer out and turned it over.


100_3753.JPG by Wigwam Jones, on Flickr

The speaker wires are connected by press-on connectors, they pull off. Notice that there is a 'plus' and a 'minus' sign next to the connectors. The black wire is 'minus'. That's important when you put the speakers back together later. If you get them backwards, you won't damage the speakers, but you might end up with them out of phase that was intended by the crossover designers; this can cancel out frequencies that were meant to be heard, resulting in unsatisfactory sound. If two speakers are out of phase with each other, it can cancel out the bass, which never sounds good.

So keeping in mind which wire goes where, pull off the connectors.

Once the woofer is out, you'll notice the cabinet is full of stuffing. This is generally fiberglass, just like the stuff used to insulate homes. I use a plastic bag to pull this out; it doesn't bother some people but it makes me all scratchy. So I pull it out with a plastic bag like I was picking up dog poop, you know what I mean. Set it aside, it goes back in later.

Step Two: Remove the Crossover

You can see the crossover network below inside the speaker cabinet. It is very common for the crossover to be mounted here, since that's where the L-Pad and speaker connectors are located anyway. You won't be able to reach down inside there and solder on things, so it it going to have to come out. Chances are it is both screwed and glued to the inside of the cabinet.


100_3755.JPG by Wigwam Jones, on Flickr


100_3754.JPG by Wigwam Jones, on Flickr

So, I unscrewed it, then I used a very small flat-blade screwdriver to gently pry it out of the speaker cabinet. Some crossovers take more force than others; on some, I've had to get busy with a screwdriver and a hammer to get the things out. Just be careful and don't damage your crossovers or speaker cabinets.


100_3756.JPG by Wigwam Jones, on Flickr


100_3757.JPG by Wigwam Jones, on Flickr
 
Recap Your Speakers Like a Boss, Part 2

Step Three: Pry up the capacitors

The old capacitors are generally glued down to the crossover plate. That's to keep them from moving around and breaking the mechanical or electrical connection, and also to keep them from vibrating and creating buzzing noises inside the speakers when you're cranking out the Van Halen - and you know you do.


100_3758.JPG by Wigwam Jones, on Flickr

This is a good time to identify your capacitors and other components. In my Nova-8 speakers, I have the following:

33 uf 50 volt capacitor
3.3 uf 50 volt capacitor
6.8 uf 50 volt capacitor
10 ohm resistor
(2) 10 ohm variable resistors (L-Pads)
1.0 mH inductor
0.1 mH inductor

Now, I am old and I have bad eyes. Even my bifocals need bifocals. So I am going to put on my cheaters before proceeding.


100_3770.JPG by Wigwam Jones, on Flickr

If you don't need cheaters, good for you. You'll get old someday and I'll have my revenge, you young whipper-snapper.

Step Four: Remove and Replace the capacitors


So now I am going to use my soldering iron. I've had it running for awhile, it's nice and hot. I will bring my soldering iron tip to the end of my first capacitor (the 33 uf one) and heat up the connector. Do not grasp the capacitor you're removing by that wire with your bare hand, it heats up faster than you can imagine. Try using a pair of needle-nose pliers or grasp the body of the old capacitor, just not the wire itself. If it just won't come out after you've melted the old solder, you may have to use your wire snips to cut it off. No biggie either way. You should end up with something that looks like this.


100_3760.JPG by Wigwam Jones, on Flickr

So here is my replacement. In my case, I bought very inexpensive (like fifty cents each) replacements from Parts Express, but you can buy them anywhere. They are 33 uf, and they are non-polarity, but they are 100 volts. That's no problem. In it goes.


100_3761.JPG by Wigwam Jones, on Flickr

Once I have it soldered in, I use a little glue to stick it back down again, just like the old one was.


100_3762.JPG by Wigwam Jones, on Flickr

I used 'Gorilla Glue' because that's what I have. You could use hot glue, or whatever you think would work well.

By the way, I unsolder an old capacitor, remove it, and then solder in the replacement, because not only are my eyes old, but my memory sucks. So I just do one at a time. It also helps to have taken some photos first. I am ashamed to admit I've had to refer back to my own photos to figure out how to put things back together, but at least I had them, eh?

By the way, I can't teach you how to solder, but it's not hard. The main thing is to heat up the work, not the solder. Put the iron on the terminal where the capacitor wire will be going. Let it get hot; you'll see the old solder turn molten and start to sag. Shove your capacitor wire through there while it's molten, pull your iron off, and blow on it (don't inhale the smoke, though). It will cool down quickly. Don't hold that capacitor by the lead wire, you'll be sorry if you do. Hold the cap by the body or use something to hold with lead wire with, like pliers. A good solder joint is shiny and bright. If it's dull and scabby, it's not good. Solder joints are to provide mechanical and electrical connections, so take your time and do them right. I generally do not have to add much, if any, solder to old joints; but a few drops of fresh solder is generally not a bad thing.

Now, for my next trick, I had to make a substitution. My old capacitor was rated for 6.8 uf. As it turned out, I didn't have a 6.8 uf capacitor. Dang. But I did have a 5.6 uf and a 1.0 uf capacitor. When hooked up in parallel, they make a 6.6 uf capacitor, which is .2 uf off. That's far less than the margin for error on these anyway (10 or 20 percent typically), so I'm good. In they go.


100_3764.JPG by Wigwam Jones, on Flickr


100_3765.JPG by Wigwam Jones, on Flickr

Then I glue them down like before.


100_3766.JPG by Wigwam Jones, on Flickr

I had the same problem with the last capacitor. It was a 3.3 uf, and I only had a 4 uf. That's .7 uf off, which is 20% error. Ummm, don't do what I did. Get the right value, OK?


100_3767.JPG by Wigwam Jones, on Flickr

Step Five: Replace the crossover

Time to put the crossover back in. I use the glue to recreate the seal, then I screw it back down again. Remember to put it in right-side up, or your connectors and L-Pads will be upside down when you're done. Do not ask me how I know this.


100_3768.JPG by Wigwam Jones, on Flickr

Step Six: Replace the woofer

Shove the fiberglass batting back in (I use a plastic bag to keep from getting all itchy and scratchy, you do what you want) and hook the woofer wires back up. Remember to get the polarity correct; black is minus.


100_3769.JPG by Wigwam Jones, on Flickr

Step Seven: Hook them babies up, and PARTAY!

Hook your speakers up and give 'em a listen. If you did everything right, you're done. If not, don't panic. Anything you did can be redid. Just take it apart again and go through everything slowly. Sometimes when you're working on crossovers, wires come unsoldered or unplugged from drivers because you're twisting and pulling on the thing. Check 'em out, make sure you don't have any dangling wires or bad solder joints. Check one driver at a time.

In my case, I discovered that when I was done, my tweeter didn't work!

My first thought was that I had done something wrong, of course.

But, I removed the tweeter, and I hooked up a known-good tweeter to the wires. Music! OK, so the crossover is at least passing signal. I then hooked the suspect tweeter directly up to the wires from the stereo (don't do this much, but it works for testing). No sound! That's one dead tweeter son. I later did some Googling and found out that this particular tweeter is known for being blown on the Nova-8 speakers. The other one is dead too, so I need two new tweeters. But otherwise, I'm done, I'm good to go!

That's it, folks. Hope you find it useful. Just remember, you too can recap your speakers. It's not hard; it's kind of fun in fact. And you'll be glad you did it if you have classic old vintage speakers. The change in sound is almost always a serious improvement.
 
Nice work Wiggy! Thanks for posting. Did you deox those pots while you had it open? :)
 
Fantastic Tutorial WW!

I am planning on diving into a set of speakers I have and even though I figure it will be pretty straightforward, detailed info like this is invaluable to those of all experience levels.

One can never read or learn too much.

Thanks!

Brian
 
Fantastic Tutorial WW!

I am planning on diving into a set of speakers I have and even though I figure it will be pretty straightforward, detailed info like this is invaluable to those of all experience levels.

One can never read or learn too much.

Thanks!

Brian

Thanks, Brian, that's gratifying to hear! I know there is a wealth of information on AK; and everyone has been so generous with their time and help for me; I wanted to give something back. I thought the photos might be helpful to someone just doing it for the first time. It's only my third or fourth set of speakers myself. Good luck with yours!
 
Thanks for the very well-written tutorial!

Might be a German-language thing, but around here these caps are called bi-polar electrolytics.

In my personal speaker experience I've yet had to encounter a crossover that was glued down - screws only so far, and one completely floating crossover. My dad's speakers (homebrew KEF BBC monitor clones from the early 80s with B110 SP 1003 woofer/midrange and Isophon SKK 10 tweeter) have an L-pad screwed through the back and two flying caps soldered directly to the woofer terminals - that's it! Replacing a woofer on those was a bit tricky - my dad refused to have them recapped, so I used the original caps, which boiled down to two caps paralleled, i.e. 3 wires to solder to each terminal at once.
 
Oh, be sure to plug that RCA jack with an unused plug or something. The box "sees" that as an air leak and the bass performance can suffer as a result.
 
Oh, be sure to plug that RCA jack with an unused plug or something. The box "sees" that as an air leak and the bass performance can suffer as a result.

Indeed! I only left it out because I thought it had less to do with recapping than with my individual speakers. But yes, I plugged the holes. I also need to go back and reseal the woofers as well; I reused the seals that came with the woofers and I think they could be better done.

I've also considered replacing the dead tweeters with the 8-ohm versions and then entirely rebuilding the crossovers using the VL mods. I might end up doing that, but this simple stock rebuild cost me less than $5 in parts so far. That's bang for the buck, you know?
 
I should say this is a very good thread for the first timer who's read about recapping but may be apprehensive about trying it.

IIRC, the VL mod on a Nova 8 (where the tweets need to be replaced) cost about $80 in parts. That is a complete crossover change the replaces the existing crossover.
 
It's threads like these that make me feel all warm and fuzzy inside. Excellent work, sir. Really. :thmbsp:
 
Outstanding job! Great pics. You really look the part of the Techie Master in those cheaters. This labor of generosity certainly deserved to be added to the reference guide. :thmbsp:



The only nit-picky comment I'll make (and this is really being nit-picky) is that it might sometimes be better to completely remove the old solder (use a desoldering gun, solder-sucker or wick) and re-do the connection with fresh, new solder, instead of recycling the old solder. I'm not sure whether it would really make any difference, but it just seems like it might be a better approach. I might be completely wrong about this, though.
 
Leave it to a photographer to put together such a slick tutorial! (And leave it to Mr. Jones to inject it with so much humor and personality!) I also like the early Halloween costume. Nice job!

You might note that when you recap you're primarily looking for electrolytics. As you noted, they are the ones with the goo that dries up. Also you can construct a non-polar electrolytic cap from two regular electrolytics: Get two regular electrolytics with the same or greater voltage tolerance of the original, but double the capacitance. Tie their positive legs together, and use the negative legs as leads for your new non-polar cap.
 
Back
Top Bottom