PDA

View Full Version : 4315A crossover problem



johnaec
04-09-2005, 07:23 PM
Ever since I picked up my 4315A's last year, one 2405 HF unit has been way down in level, (15 - 20 db down) - I've been compensating in the meantime with EQ, but even that can't really compensate.

I finally dug into them today and determined the 2405 itself is fine - 5.3 ohm DCR, and I even plugged in a brand new 2405H with exactly the same result. I double checked all the accessible connections, and the level control *does* have an effect, ('smoothly raises and lowers the level, albeit at that way reduced level). There's just almost no signal apparently coming from the crossover. I even removed the perforated crossover cover but nothing appears amiss at all, at least at the board level.

I don't have an image file of the network schematic or I'd post it, but here's the PDF for reference: http://www.jblproservice.com/pdf/Network%20Schematics/3114A%20Network.pdf

Does anyone have any idea how I might narrow down the problem more, without trying to tear the crossover completely apart? I've got another old beater 3114A network kicking around that came all unglued inside, but when they're in otherwise good shape, you can't hardly get to the transformers and caps behind the main board, (they're glued to the bottoms of the cans), because the connecting wires are too short to lift the board out without unsoldering everything!

Any suggestions 'greatly appreciated!

John

GordonW
04-10-2005, 10:34 AM
I'd have to say, probably a bad cap. Happened to me a few times, on other speakers, with similar symptoms.

May be time to just bite the bullet and tear into the crossover...

Regards,
Gordon.

johnaec
04-10-2005, 11:22 AM
I'd have to say, probably a bad cap. Happened to me a few times, on other speakers, with similar symptoms.

May be time to just bite the bullet and tear into the crossover...Yeah, at least I've got an additional old beater I can raid for parts. There's also one on eBay I'm looking at.

Any suggestions on "ungluing" if it looks like one of the big caps glued in the bottom has to be removed?

Thanks - John

4313B
04-10-2005, 11:25 AM
Why don't you just have me build you a new pair of networks John?

It would only take me about six to twelve months to do it though. :biting:

johnaec
04-10-2005, 11:34 AM
Why don't you just have me build you a new pair of networks John? :biting:I'd LOVE to - we'll have to talk later, (after income taxes, property taxes, etc...). I'm seriously interested, though.

What I'm really going to need networks for in the future are my Sub1500, 2012H, 2105H, 2405H cabinets , once completed. (I know - 'less than optimal component combinations, but hey - it's mostly for fun... 4315's on steroids...:) ) Until I get passives together for those, I'll have to use active crossovers/EQ, (and a pile of amps...).

John

johnaec
04-10-2005, 02:57 PM
It appears I was lucky! There are two 1.5 mf caps in the UHF circuit, and they're right on the top of the board. I replaced both of them with caps out of the spare 3114A and my UHF is back! ('Knock on wood - I still need to remount the drivers.) But open air on the UHF is the same from both cabinets now.

Thanks, Gordon, for the suggestion to go for the caps. And Giskard - I'll definitely be in touch on some network stuff in the future. If nothing else, I have questions on how to go about your recommended bypass procedures on these 3114A's. I've searched a bunch of past threads, and it seems like .01 mf caps are mostly used? Would all the caps get these, or only some of them? I'll do a little more reading...passive crossovers are still mostly a mystery to me...

John

4313B
04-10-2005, 03:02 PM
You could put one of these in parallel with every stock capacitor.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=027-700

I've finished doing just that to two 4430 networks and four 4435 networks recently (also getting Ti Series Monster Cable).

(Left was in progress, right was still stock.)

johnaec
04-10-2005, 03:26 PM
Thanks Giskard - 'gotta run right now, (late for a date...)
John

aust-ted
04-10-2005, 09:22 PM
You could put one of these in parallel with every stock capacitor.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=027-700

I've finished doing just that to two 4430 networks and four 4435 networks recently (also getting Ti Series Monster Cable).

(Left was in progress, right was still stock.)

Giskard They look like great caps. Just one concern, surely adding the .1ufs would affect the xover freqs, especially for the smaller value caps? I note you have completely replaced one of the tiddlers. Do you have a rule of thumb on when to add or to to simply replace?

Regards
Ted

4313B
04-10-2005, 09:32 PM
They are 0.01 uF.

So a 1.0 uF on a 2405 becomes a 1.01 uF.

Yes, I completely replaced all of the stock 0.01 uF metalized polypropylenes with these film and foil AudioCaps. :)

aust-ted
04-10-2005, 10:10 PM
Giskard

My apology I should have written "0.01 uf"

Regards
Ted

4313B
04-11-2005, 07:38 AM
No problem. It's good to double check stuff.