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JBL 4311's = system complete... for now.

Great thread, I've referred to it a few times now. Is anyone aware of spl/frequency response charts comparing the stock crossover with the .01uf bypass cap mod?
 
Asilker, I would be shocked (shocked, I say) if, all else being equal, adding .01 bypass caps measurably affected either the output levels or the frequency response.
 
Shocked you say????

So I assume the idea is that the small value allows a better texture through on "crucial" frequencies? So in theory the NPE or whatever would take the majority of crossover duty but the tiny expensive cap would add some sparkle or something?
 
I've read several different theories. This thread here discusses some of them, along with a separate topic (biased networks):

http://www.audioheritage.org/vbulletin/showthread.php?3555-Bypassed-and-Biased-Capacitors

But now I see there's not much discussion there. Here is a critique:

http://www.critesspeakers.com/frequently-asked-questions.html

Q: What do you think of using "bypass capacitors" in a crossover circuit?

A: Not much. The theory is that you can use cheaper caps in the crossover circuit and then use a high quality cap of about 0.01uF to "bypass" that cap and impart the "goodness" of the 0.01uF high quality cap into the circuit counteracting the "badness" of the lower quality crossover cap. First, I really don't like that someone in the cap selling business hijacked a perfectly good electronics term (bypass capacitor) and decided to redefine it's meaning. A bypass capacitor in electronics is a cap used to bypass AC around a DC circuit. Now it is being used to describe this idea of bypassing AC around an AC circuit.

Anyway, at the audio frequencies we use in crossovers and the impedance of the circuit, none of the frequencies we can hear would actually go through that .01uF cap. So, what could that cap do to the circuit? I think the obvious answer is "nothing". Good news is that this would not hurt anything. I have never heard any reasonable and coherent explanation using real electronics terms of how this cap could help anything. I think the whole idea was created to sell more caps. Yes, I am aware that JBL used this trick in a few speaker crossovers for a brief time. But they were selling speakers. Some speaker manufacturers set up their speakers in certain ways just because some they sell them to expect it. Like bi-wiring perhaps.
Click to expand...
 
Hello everybody, before starting a new thread I wanna check if it is possible to resume this one, long story short, I own a couple of JBL4311B since I was a teen, bought with my first summer job, at close to 50 I still listen to them but am figuring out I could tweak the filters to give them new breed, read a little of this long post and trying to figure it out where to start from.

I seem to remember there is no filtering on the woofer, does it make sense to use two couples of plugs for bi wiring or better just to change the original plugs (ouch...) with better ones?

Curious to read about your opinions and experiences with these speakers.

Thank you

Giovanni
 
As far as you have gone in disassembly I would go ahead and recap (if for no reason than age) today's cap are much better than the vintage. I have used clarity (just my choice ) and have been very pleased. But I have a completely different speaker sound than the JBL. Might as well upgrade the wiring as well (in for a penny, in for a pound.). Good luck and enjoy.
 
I remember attempting to remove the woofer many years ago but it wouldn't come off, seems to remember it was kinda glued but I read somewhere else it takes to remove either the tweeter or the midrange first and then leverage behind the woofer frame to push it out, is that correct?

Once I menage to remove the woofer what are the easiest steps to take to recap? Is there a known source for new components you are aware of here in EU (it would be better in Italy but I know I will have to look outside our borders...)? What about cable plugs, is it easy and worth the pain changing them (the standard ones are a pain to pull cables in)?

thank you

Giovanni
 
First off....THANK YOU FOR THIS THREAD!!! Now, with that out of the way, I am on it once again because I am confused about recapping my 4312's and hope I get some advice. I opened mine up and discovered those bypass caps. I think they say .01 on them. But, mine are not wrapped together with the larger caps as seen elsewhere on this and other AK threads. As you can see in the pic, they occupy there own little place in the lines. Is this a mistake? Also, do I really need these at all? I didn't order replacements. I hope to just remove the old ones and go with only the two larger caps. But, it looks to me like the bypass in mine are in the direct line to the L pads, so cutting them out would also cut the connection entirely, yes? Finally, if folks here warn of the need for those bypass caps, could I get away with using the old ones? They seem so, I don't know, peripheral to the overall crossover, but hey, I'm no tech. Oh, should mention that I'm using Solen metal/propalized blah blah caps. Whatever that actual name is....
 

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You can't go wrong keeping them in circuit. If you don't have a tester, replace them if you can. Otherwise leave them in. Good luck! Great speakers.
 
Thanks oldsmobuick. The surgery shall begin shortly. If I can ever get the control knobs off first! I think they have been glued.
 
Ha. I need a pair of those. Well, don't underestimate detoxit, mine were like new after a few sprays. And they were AWFUL to start with. All four were perfect after, I bought L-pads but didn't even put them in.
 
oldsmobuick said:
Ha. I need a pair of those. Well, don't underestimate detoxit, mine were like new after a few sprays. And they were AWFUL to start with. All four were perfect after, I bought L-pads but didn't even put them in.
Click to expand...
I tried to save them. So far I've opened the one's seen in the pic and both actually had parts of the wiring broken and unraveled and was being dragged along as you turned the knob. The ones on the other speaker might be better. The problem is that these speakers were owned by a heavy smoker. The knobs moved as if they had honey inside. The once white woofer is now the color of a used cigarette filter.
 
Not sure if this thread is still active but there is no way I would have undertaken this project without having seen this thread. That said, here is my experience with tuning up the crossover network in a pair of old JBLs.

Recently my dad gave me his pair of 4311Bs that he bought before setting off for college in 1980. Cosmetically they are in pretty darn good shape. Some scratches here and there but nothing too major. A couple of the mids and tweets have pooched dust caps but the woofers are pristine. Functionally all drivers seemed to be working, until I messed with the L-pads. At best they would crackle and at worst they sometimes cut out altogether. Certainly they weren't actually attenuating anything. Even with my ear pressed up pretty close to the tweeter it was hard to tell how much sound they were even generating and I started to suspect that something could be amiss. Some googling led me here. Now I've never actually taken a speaker apart before, much less one that has a significant amount of sentimental value, but I like to think of myself as a decently handy guy so here we go.

4MafdMq.jpg


I decided to go with the "improved original sound" caps and new L-pads. The Theta 0.01uF I couldn't find in stock so I went with something that's hopefully similar. I don't really understand why the bypass capacitor is needed anyway but I digress. As it turns out, the hardest part of this job, by far, was actually getting the drivers out of the cabinets. It was hard to believe that there was not an adhesive in there and that they were only held in with the screws. Damaging the baffle boards and having to paint them was really not something I wanted to get into, so the solution was a plastic putty knife thing with sort of a chisel tip that I tapped under the mids and twitters. I was able to stick my arm through the tweeter mounting hole and lift the woofer out from underneath.

H0uaC4e.jpg


Removing the foilcal was a step that I was dreading, I'm not know for my patience or delicacy and I was certain I would mangle these things. Not so fast, wide flexible spackle knife and a hair dryer as recommended did the trick.
mUgUZAM.jpg


Crossover network came right out next. I was a bit relieved to see it followed the 3112B schematic and not the 3112C schematic as the driver wiring color indicated it was going to be. I took the relatively lazy route and decided to snip the wires right off the old caps and just re-use all existing wiring. Sprayed the hell out of the L-pads with some De-Oxit and then Fader Lube. Based on how freely and smoothly they were now turning I took the gamble that they'd be OK and didn't need replacing after all. That was a gamble I won. Used Epoxy to put all the new caps on the board (would not recommend, what a mess), twisted the leads together, tinned them up and then heat shrinked them. Forgot to get a picture of the board with the new caps installed and wired but it was a pretty clean job actually (by my standards).

a0uJacG.jpg
1MnLEe3.jpg


Everything went back together nicely, just have to get some kind of spray adhesive to put the foilcals back on. I anxiously fired them back up, decided to spin the MoFi pressing of Dylan's Blood on the Tracks and it sounded like someone had taken a blanket off of the mids and his. Huge improvement sonically. I'm also now able to actually fiddle with my attenuator knobs with real results. Big thanks to everyone that had so extensively documented the process in this thread dating back to 2007(!).

P.S. Not sure I handled the image embedding properly. Also somewhat scared to hear what I did terribly wrong. I'd like to eventually re-finish the cabinets but I have ZERO experience in that arena. If anyone can point me in the right direction there I'd appreciate it.
 
TheCasual said:
Not sure if this thread is still active but there is no way I would have undertaken this project without having seen this thread. That said, here is my experience with tuning up the crossover network in a pair of old JBLs.

Recently my dad gave me his pair of 4311Bs that he bought before setting off for college in 1980. Cosmetically they are in pretty darn good shape. Some scratches here and there but nothing too major. A couple of the mids and tweets have pooched dust caps but the woofers are pristine. Functionally all drivers seemed to be working, until I messed with the L-pads. At best they would crackle and at worst they sometimes cut out altogether. Certainly they weren't actually attenuating anything. Even with my ear pressed up pretty close to the tweeter it was hard to tell how much sound they were even generating and I started to suspect that something could be amiss. Some googling led me here. Now I've never actually taken a speaker apart before, much less one that has a significant amount of sentimental value, but I like to think of myself as a decently handy guy so here we go.

4MafdMq.jpg


I decided to go with the "improved original sound" caps and new L-pads. The Theta 0.01uF I couldn't find in stock so I went with something that's hopefully similar. I don't really understand why the bypass capacitor is needed anyway but I digress. As it turns out, the hardest part of this job, by far, was actually getting the drivers out of the cabinets. It was hard to believe that there was not an adhesive in there and that they were only held in with the screws. Damaging the baffle boards and having to paint them was really not something I wanted to get into, so the solution was a plastic putty knife thing with sort of a chisel tip that I tapped under the mids and twitters. I was able to stick my arm through the tweeter mounting hole and lift the woofer out from underneath.

H0uaC4e.jpg


Removing the foilcal was a step that I was dreading, I'm not know for my patience or delicacy and I was certain I would mangle these things. Not so fast, wide flexible spackle knife and a hair dryer as recommended did the trick.
mUgUZAM.jpg


Crossover network came right out next. I was a bit relieved to see it followed the 3112B schematic and not the 3112C schematic as the driver wiring color indicated it was going to be. I took the relatively lazy route and decided to snip the wires right off the old caps and just re-use all existing wiring. Sprayed the hell out of the L-pads with some De-Oxit and then Fader Lube. Based on how freely and smoothly they were now turning I took the gamble that they'd be OK and didn't need replacing after all. That was a gamble I won. Used Epoxy to put all the new caps on the board (would not recommend, what a mess), twisted the leads together, tinned them up and then heat shrinked them. Forgot to get a picture of the board with the new caps installed and wired but it was a pretty clean job actually (by my standards).

a0uJacG.jpg
1MnLEe3.jpg


Everything went back together nicely, just have to get some kind of spray adhesive to put the foilcals back on. I anxiously fired them back up, decided to spin the MoFi pressing of Dylan's Blood on the Tracks and it sounded like someone had taken a blanket off of the mids and his. Huge improvement sonically. I'm also now able to actually fiddle with my attenuator knobs with real results. Big thanks to everyone that had so extensively documented the process in this thread dating back to 2007(!).

P.S. Not sure I handled the image embedding properly. Also somewhat scared to hear what I did terribly wrong. I'd like to eventually re-finish the cabinets but I have ZERO experience in that arena. If anyone can point me in the right direction there I'd appreciate it.
Click to expand...
looks like you did great work.

I used minwax on my 4311b's and it came out great. However, the pair i had needed a serious refinish. They were in bad shape. If you're look even halfway presentable, get some walnut Howard's "Restore-a-Finish". that stuff is magic
 
How did you handle the deep scratches? Did you sand the whole things down and then stain?

Mine have a few scratches that make it through the veneer, particularly on the corners. Think I'll try to track down some of the Howard's you mentioned. I'm not trying to go crazy with the cabinet restoration, just clean them up a bit and let them keep some of their used character.
 
Nice work on the 4311B's and welcome to AK!

You will be coming back and acquiring more gear now, guaranteed :D You can find Howards Restore-a-Finish just about anywhere, Home Depot, Lowes, ACE etc.
Great stuff, you will see a big difference immediately without going crazy on the veneer. You can always sand later if you need to.
 
Nice work!!!

It's been a while since I visited this thread. Got to tell ya I got a pair (two actually) of Jubals, a couple L-300 and I'm restoring a 4333 - but I still love those 4311 monitors. They're very very nice speakers and my mod'ed XO, very much the same as yours, gives them life and charm. :thumbsup:
 
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