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4313B
07-12-2003, 11:53 PM
As per a member's request -

The following capacitors in the JBL Model 5234A can benefit from 0.01uF poly film and foil bypass capacitors:

C1, C2, C3, C4, C5, C6
C101, C102, C103, C104, C104, C106

The schematic is located in the back of the manual which can be downloaded here:

http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/JBL-5234A%20manual.pdf

Here is the voltage drive of the 18dB/octave 51-5145 crossover card designed to be used for the 4344, 4345, and 4355 Studio Monitors. Also included is the voltage drive of the 12dB/octave 52-5140 card designed for the 4343 and 4350 Studio Monitors. The 51-5145 is ~ 3 dB down at ~ 290 Hz and the 52-5140 is ~ 4 dB down at ~ 255 Hz:

4313B
07-13-2003, 12:09 AM
Once biamplification has been implemented, switching the remaining portion of the passive networks to charge coupled capacitor technology isn't nearly such a daunting task from a monetary standpoint. As always, I don't advocate extensive modifications to the stock networks. Building new, bi-amp only, passive networks for the 4344 and 4345 (in the same spirit as the bi-amp only 4355) would be my recommendation.

boputnam
07-13-2003, 07:59 AM
Thanks, Giskard!

That clever listing of the involved caps is easier than trying to draft the little buggers onto the schematic!
:spin:

4313B
07-13-2003, 08:57 AM
Yeah, I started to go that route and then decided the schematic was simply too large and lacked the necessary resolution in one shot.

The 5234A circuit board is plainly labeled so finding the capacitors is quite easy. The 0.01uF poly film and foil bypass caps are physically the same size as the 100 uF electrolytics !!! so you can imagine what's going on here... :)

boputnam
07-13-2003, 08:49 PM
Ha!

So, might you have any pictures laying about that represent a bypass cap in position, so us novies at this can get a better handle on the physical positioning of it all?

Pretty please?

:yes:

Don C
07-13-2003, 09:34 PM
This is what mine look like. This is not DIY, this is how JBL did it.

4313B
07-14-2003, 04:58 AM
And here's a custom 3113B. I'll post a 5234A picture later today.

boputnam
07-14-2003, 06:22 AM
Wow, nice clean job. Something to admire.

And, I gotta say, that my 3113B's look NOTHING like that. That's a beauty. Those inductors (and caps, too...) are cherry better than than the original. Dang it! I see yet another project coming.

If only you'd do this commercially... :D

Hey DonC - which network is that?

Thanks for the pics - very helpful.

Don C
07-14-2003, 06:41 AM
It is N240Ti

boputnam
07-14-2003, 07:32 AM
Giskard...

I'm thinking part of why this 3113B looks so dang clean (irrespective of your enviable soldering (and layout) skills... ;) ) is that the signal paths not to/from the Lpad before leaving the network, but exits the network, goes through the Lpad and then goes directly to the transducers - correct? You have commented on the merits of that, before.

You inspire me to redo my 3113B's nearly entirely before/during the bypass cap episode. Is there any rudimentary schematic that you made-up for your effort, that helped with the layout? I'm thinking ahead to the 5234A's too...

PSS AUDIO
07-14-2003, 08:10 AM
Originally posted by Don C
This is what mine look like. This is not DIY, this is how JBL did it.

May I give you an advice?

Remove those two electrolytic non polarized capacitor and replace them with whatever you want (polypropylene is the best) but change them and you will hear a new speaker!

Don C
07-14-2003, 10:33 AM
Originally posted by PSS AUDIO
May I give you an advice?

Advice is always welcome, Thanks!

PSS AUDIO
07-14-2003, 01:38 PM
Originally posted by Giskard
And here's a custom 3113B. I'll post a 5234A picture later today.

May I give you an advice too?

Remove the screw placed to fix the coil as it changes its value.

4313B
07-14-2003, 01:39 PM
Thanks Yuri but it's inert :)
I checked that out twentysome years ago when JBL went from using 2.5 mH iron cores in the early runs of L96's to 2.5 mH air cores in the later runs of L96's and started running bolts through the coils ;)

4313B
07-14-2003, 03:48 PM
Here's an AudioCap 0.01uF poly and how it should go across the electrolytics. The alligator clips are used as heatsinks while soldering. These are too large and one should use smaller clips, or hemostats, but they are all I had close at hand for the photo.

boputnam
07-14-2003, 07:29 PM
Brilliant!! :bouncy:

Waiting on the 5234A,

Signed,

"Stickler"... ;)

GordonW
07-15-2003, 11:28 PM
MAN... looking at Don C's crossover pic- I haven't seen THAT many ceramic-boat resistors together in one place, since I pulled apart a McIntosh ML2C speaker system, during restoration a few years ago! :eek:

Hey, did JBL ever use a heat sink for the ceramic resistors in anything? I've seen a few McIntosh speakers that actually did that, and there's some comments from Roger Russell (Mc's primary speaker designer in the 1970s) about doing so... and how doing that improved not only reliability, but dynamic range as well in some small degree...

Regards,
Gordon.

4313B
07-16-2003, 05:52 AM
"Hey, did JBL ever use a heat sink for the ceramic resistors in anything?"

Not that I know of. The 7.5 ohm resistor in parallel with the 1.55 mH tapped autotransformer in the L300/4333 is a large 40 W resistor that is mounted alone on standoffs because it gets so hot. It's also inside a metal can/cage so it won't catch anything on fire.

4313B
07-16-2003, 06:44 AM
"If only you'd do this commercially..."

I'd build you a pair of 3113B networks Bo.
You might want to try biased instead of conventional though.
I'm not too sure if I will ever build another conventional network for my own personal use.

*****

"the signal paths not to/from the Lpad before leaving the network, but exits the network, goes through the Lpad and then goes directly to the transducers - correct?"

Yes. But biasing some networks (L212 comes to mind) wouldn't allow for that since the conjugates (which would have to be biased as well) come after the L-Pads. Ti series networks are "easy" to bias since they don't use L-Pads at all. 4313/L96/L112/L150A networks are "easy" to bias.

boputnam
07-16-2003, 07:04 AM
I'd build you a pair of 3113B networks Bo.

Be still, my heart... Re-reading, I fear the syntax is ambiguous enough to actually NOT be a firm offer! Drat! :(

More than just having them and being able to enjoy them, I wanted to study them in close range and marvel and the design and soldering.

Oh well - at least I have a good picture of your handiwork!

4313B
07-16-2003, 07:11 AM
Ambiguous in that I don't really see why you would want to rebuild a pair stock unless you wanted that "specific" sound character (which you will never get anyway since those capacitors are long ago NLA).

In other words, I'd pull the stock networks and pack them away and go with new biased networks :)

If you want a biased pair of 3113B networks, I will build them for you. If you have a different pair of JBL's you'd like to try first, I'll build them biased networks for you too.

boputnam
07-16-2003, 07:34 AM
If you want a biased pair of 3113B networks, I will build them for you.
An astonishingly generous offer - that is, so long as it doesn't cost me the 4345's as "barter"... :p

I cherish the 4313B's and can't imagine they - as such - can be much improved on. I've not yet added the bypass caps (they only arrived yesterday! PartsExpress was B/O'd). But now, I may be needing them for the 5234A's anyway! So, you bet!

:dancin:

4313B
07-16-2003, 08:24 AM
Good Grief! Those AudioCaps were B/O'd that long???

boputnam
07-16-2003, 09:12 AM
Good Grief! Those AudioCaps were B/O'd that long???
I couldn't believe it either. Made me think the order had been lost/cancelled. When it arrived, I began to wonder if PE was struggling. First orders came with Popcorn - this one in merely a plain unmarked bag.

It's tough out there...