JBL 4312A speaker crossover recap

[doji]

I picked up a good shape pair of JBL 4312A speakers. And I want to recap the crossover.

I found the parts list at this thread: https://audiokarma.org/forums/index.php?threads/jbl-4311s-system-complete-for-now.106180/

CAPS FOR REBUILDING A PAIR OF JBL 3112 NETWORKS YEILDING "IMPROVED ORIGINAL" SOUND
4 x AUDIOCAP PPT THETA .010µF-600V FILM/FOIL CAPACITOR Part Number 027-700
2 x DAYTON PMPC-3.0 3.0µF-250V PRECISION AUDIO CAPACITOR Part Number 027-220
4 x DAYTON PMPC-4.0 4.0µF-250V PRECISION AUDIO CAPACITOR Part Number 027-226

CAPS FOR REBUILDING A PAIR OF JBL 3112 NETWORKS YIELDING A "BRIGHT" SOUND
2 x SOLEN 3.0uF-400VDC POLYPROPYLENE CAPACITOR Part Number 027-542
2 x SOLEN 8.2uF-400VDC POLYPROPYLENE CAPACITOR Part Number 027-564


My question - why for the first 'Imprved original' sound , needs 4 x Dayton 4.0 uF caps? But in Solen set just one 8.2 uF cap? I find Dayton also has 8.0 uF caps on PartExpress, why can't I just use two of 8.0 than four of 4.0 uF caps? Any sound quality difference at all?

Also, the crossover - why 3112A, B, C schematic doesn't have the air coil inductor at all ? Only shows on 3112D.

 

[jobrewer1983]

I picked up a good shape pair of JBL 4312A speakers. And I want to recap the crossover.

I found the parts list at this thread: https://audiokarma.org/forums/index.php?threads/jbl-4311s-system-complete-for-now.106180/

CAPS FOR REBUILDING A PAIR OF JBL 3112 NETWORKS YEILDING "IMPROVED ORIGINAL" SOUND
4 x AUDIOCAP PPT THETA .010µF-600V FILM/FOIL CAPACITOR Part Number 027-700
2 x DAYTON PMPC-3.0 3.0µF-250V PRECISION AUDIO CAPACITOR Part Number 027-220
4 x DAYTON PMPC-4.0 4.0µF-250V PRECISION AUDIO CAPACITOR Part Number 027-226

CAPS FOR REBUILDING A PAIR OF JBL 3112 NETWORKS YIELDING A "BRIGHT" SOUND
2 x SOLEN 3.0uF-400VDC POLYPROPYLENE CAPACITOR Part Number 027-542
2 x SOLEN 8.2uF-400VDC POLYPROPYLENE CAPACITOR Part Number 027-564


My question - why for the first 'Imprved original' sound , needs 4 x Dayton 4.0 uF caps? But in Solen set just one 8.2 uF cap? I find Dayton also has 8.0 uF caps on PartExpress, why can't I just use two of 8.0 than four of 4.0 uF caps? Any sound quality difference at all?

Also, the crossover - why 3112A, B, C schematic doesn't have the air coil inductor at all ? Only shows on 3112D.

To be honest, most of the times Dayton caps are used to save $$. They are good caps, but I don’t think you will get a better sound stage out of the set. It’s a lateral move at best.

I’ve used many Dayton caps for XOs and they do bring them back into spec, but sound a bit flat.

Look up Jantzen Cross caps and Jantzen Z-Cap standards.

On the AudioCap Theta... yes get them they will 100% for sure add some sparkle to the top end and warmth too.

On your question, you can use any amount of caps you want as long as the vale is what was required. I tend to run them in parallel and build up to the correct uF. I feel it helps can’t explain why but it sounds better to my ears. I don’t go to crazy usually split the value in 2 or 3 caps.




^^ that is 7uF, a 7uf solan cap would measure the same...


Good luck on the project

 

[doji]

Thanks.

Just ordered the Dayton caps set for my project, plus a desoldering pump for **** happen fixes.

One subwoofer cone got a crack (looks like hit by something during move), I am thinking of recone it but the white color Auqaplas kit is a bit expensive.. Maybe I can just use some glue to fix the crack first and see how it goes..

 

[doji]

question about the crossover - why 3112A, B, C schematic doesn't have the air coil inductor at all ? Only shows on 3112D? Is 3112D better than the others?

 

[jobrewer1983]

question about the crossover - why 3112A, B, C schematic doesn't have the air coil inductor at all ? Only shows on 3112D? Is 3112D better than the others?

I have no idea why the difference, or why they were built like that, the air coil is probably a better designed crossover, who knows.

 

[RTally]

One subwoofer cone got a crack (looks like hit by something during move), I am thinking of recone it but the white color Auqaplas kit is a bit expensive.. Maybe I can just use some glue to fix the crack first and see how it goes..

Need pics. Crack or a rip/tear?

Generally, cones can be repaired by glueing a piece of a coffee filter on the back side. Use a PVA glue like Ailene's Tacky glue.

 

[doji]

I have no idea why the difference, or why they were built like that, the air coil is probably a better designed crossover, who knows.

If I add a air coil to the LF circuit , will it get cleaner and better bass? As the 3112 crossovers are all a direct pass on LF, so it's a full range signal in the LF part anyway.

 

[toxcrusadr]

Small cone tears are very fixable. Diluted glue, a small paintbrush, and a piece of white tissue paper, or some use teabag material or coffee filter. From the back of the cone if you can access it. Wet the area with diluted glue, apply the patch, paint a bit more glue to make sure it's saturated. Look at the front to make sure it's joined as invisibly as possible before it dries. Voila!

BTW that's a woofer, not a subwoofer.

 

[jobrewer1983]

If I add a air coil to the LF circuit , will it get cleaner and better bass? As the 3112 crossovers are all a direct pass on LF, so it's a full range signal in the LF part anyway.

Yes, but make sure you used a good gauge, 18-20awg will be an upgrade. I just used the Jantzen 18awg shunts on my 4301B and it really cleaned up the bottom end. I have used the 20awg on many sets and really do like them.

 

[toxcrusadr]

DC resistance of the inductor has to closely match the original or changes in the volume of the driver can result.