View Full Version : 4435 horn quit and it's not the horn

10-18-2006, 06:02 PM
Blasting away and then nothing. Swapped for another and nothing. Not biamped. What should I look for?


jim campbell
10-18-2006, 06:42 PM
check to see if the x over potentiometer turns freely ............if it feels crunchy its fried..........check for loose wires and isolate your pre amp and amp connections to check bad connections......sometimes the rca connectors on the back of amplifiers will loosen and twist the wire off inside the the case.i just test one component at a time to eliminate it until i root out the bug

10-18-2006, 06:58 PM
Blasting away and then nothing. Swapped for another and nothing. Not biamped. What should I look for?


Probably a faulty capacitor in the Hi-pass section of the crossover....or a fried L-Pad.

Check the crossover for burned components or broken leads, melted solder joints, etc.

10-18-2006, 07:27 PM
Click that "Int/Ext" switch back and forth a couple of times.

Try doing it with the system playing at LOW volume to see if the switch is intermittant....

10-19-2006, 09:46 AM
Thanks for the tips guys!

With known good replacement driver installed I exercise the switch and it comes alive again. Zilch hits it on the head! Re-install original driver and no workum. Hmmm... Swap spare back in and all is well. What happened to the driver?

Gotta admit I was running 100db+ with an old Sheffield Lab disc. Failure occured immediately after pulling faders down and pushing them right back up (without over-excursion)

Thinking of (fast-acting) fuse/circuit-breakers again. Amp is non-bridged K1, and that Crown protection card won't work with it.


10-19-2006, 10:56 AM
A $300.00 driver will protect a 25 cent fuse every time.

10-19-2006, 08:06 PM
A $300.00 driver will protect a 25 cent fuse every time.

:applaud: AMEN! :banghead:


10-20-2006, 07:14 AM
Should each component be protected individually, or do the whole cab?

10-20-2006, 10:27 AM
Best I can ascertain, fuses won't get it. JBL uses light bulbs in a few products, and there are a variety of relay and clamping circuits of indeterminate utility....

Mike Caldwell
10-21-2006, 08:06 AM
What era 4435's do you have? The early ones had 2421 drivers and the later ones used the 2426 driver. Good news is if yours has the 2426 drivers the diaphragms are readily available from many sources. If it's a 2421 I think you can still get original diaphragms from JBL, special order = more expensive. I don't know if the drivers/diaphragms are interchangeable between the two 4435 era speakers. The difference would be (if any) in the passive crossover doing any special tweaks for the between the two driver types. The 2421 uses a aluminum diamond surround and the 2426 is titanium diaphragm. Here is a link to JBL pro service showing the crossover with a 2426 driver, I could find no crossover showing a 2421 driver. (http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4435LR.pdf) You can put the newer titanium diaphragm in the 2421 driver. Unless something in the crossovers shorted out sending lower frequencies to the drivers my guess is that amp clipping did them in. A 100db+ while loud would not really be working the speakers that hard unless the amp was pushed beyond it's limits. The 2426 drivers can take a lot of good clean power, they do all time in my bi-amped stage monitors. Normally over powering a diaphragm or too low of frequecy crossover point will shatter the metal and one that is blown from excessive amp clipping will have a burned voice coil.

Mike Caldwell

10-21-2006, 12:02 PM
Best I can ascertain, fuses won't get it. JBL uses light bulbs in a few products, and there are a variety of relay and clamping circuits of indeterminate utility....

Could use a polyswitch. These are available cheap as surplus and are intended for use with speaker protection. I use them in my garden railroad engines to avoid wire burn-outs on derailment. I don't know if they have any sonic implications, but like I noted, they are noted for use with speakers.

Ian Mackenzie
10-21-2006, 05:12 PM
I agree it sounds like clipping and its likely to happen again at some point.

Ever thought about biamping those 4435. Not a total cure but it will prevent the clipped signal on the woofers burning out the HF driver voice coil and it will probably sound better. Surprised you aren't already if your running them that hard.

10-21-2006, 05:33 PM
The is nothing that will protect a driver of any type from the extended effects of clipping.

Current limiters, i.e. light bulbs, polyswitches, fuses, have no effect on the HF harmonic content and DC offset of a clipped signal.

The only cure is to turn it down or install a higher power amp that has at least 6dB headroom.

In the case of the 4435 you should be looking at 600 watts and above for passive operation, or 600 watts plus 200 watts for biamp mode...if you need to listen loud. The catch 22 is killing your ears in the long term.

10-21-2006, 07:06 PM
Could a steep low pass filter set at around 17Khz help or is that harmonic content within the pass range of the driver itself?


10-21-2006, 10:12 PM
Limit High Frequencies to reduce susceptibility to clipping damage?
An interesting idea.

Opinion: No.

Harmonics of clipped bass signals (20-200Hz?) would have significant energy within a passband below 17KHz... mostly odd order harmonics 3, 5, 7 with
decreasing amplitude, the higher the harmonic.


10-23-2006, 08:50 AM
Thanks some more guys!

Mike.... don't know the era, but here are the serial no's:
4435 SET 1 SN 261049 and 266112 w/2425H drivers
4435 SET 2 SN 281897 and 281905 w/2425H drivers
Can you estimate age?

A 'self-exiled' member we all miss applied his craft to all the X-overs, drivers, etc. Superb workmanship BTW.

Ian.....might be time to bi-amp indeed. I followed earlier advice and tried passive first. Experience so far with bridged K1 was not good - nuked some stuff bad. Two-channel mode provides enough volume but does seem to lack robust headroom at 100+ db.

For bi-amp, what do you think about a K2 for the L/R bottom and a K1 for the tops, or would a single K1 provide a reasonable amount of additional headroom?

This gear is used in a Control Room so endless opportunities exist to push the wrong thingy - and I do! Maybe some kind of 'bypassable' fuse system of some sort might be good here?

For those interested, the diaphragms are aluminum and sound somewhat 'clinical' to me, so I may be interested in a SS amp of different flavor that sounds a bit warmer for the horns. A tube set-up is out of the question as my wallet is rather bare. Suggestions?

Also, it won't be long before I get back with the forum members that were interested in a listen. Acoustics are almost complete - it's been a slow go.


10-23-2006, 09:59 AM
Find an Ashly FET-1500 for the highs. Inexpensive used, and very well built....class A front end.

Here's a FET-1000C on eBay....seller has two removed from a church. 190watts bridged mono @ 8 ohms.

http://cgi.ebay.com/ASHLY-FET-1000C-STEREO-MOSFET-POWER-AMPLIFIER-MINT_W0QQitemZ320038912267QQihZ011QQcategoryZ23787 QQrdZ1QQcmdZViewItem

10-23-2006, 10:17 AM
This gear is used in a Control Room so endless opportunities exist to push the wrong thingy - and I do! Maybe some kind of 'bypassable' fuse system of some sort might be good here?

Limiter with "active" lights... or at least a set of meters w/ peak hold or persist, so you are
reminded when you're pushing things, might be useful... check gain structure to ensure
pre-amplifier stages are not clipping either. -grumpy

10-23-2006, 11:59 AM
Thanks grumpy and edgewound.

grumpy....I admit the last failure was a result of my pushing things a bit - and need to mind the store better indeed. But... I wish that's all there was to it. A more typical example of what could/will/did happen goes something like this: 28 channel board - has the vu's, peak lites/meters and all that. 5.1 live mix and everybodys jammin in the Control Room. Everything is direct - electronic drums, bass, keys and guitars along with an occasional drunken girl (with limiter) trying to sing. Gain structure optimized and all is well. Someone decides to turn/push the wrong knob, or what happened last nite - the drum program is accidentally switched to a different kit - with entirely different volume structure. Friend hits drum. I was fortunate.

Can't seem to cover all the potentials here. Could put limiters on 8 of the busses but ya need good ($) units to do that, and it's 8 more items in the chain. I like to stay analog when practical/possible too.

Wouldn't bother me a bit if a fuse (or something) blew and sound stopped. This is a private facility and losing a precious take is not gonna happen here.

Edgewould...would you share your experience with that amp vs. this particular horn, or is it a general class A thing that 'smooths' it?

BTW, been looking for a decent example of that plastic guitar!

10-23-2006, 12:40 PM
I don't know the sonic effects of light bulbs but I use them all the time trouble shooting. In a situation when another tech if his problem is not fixed will at least blow a fuse or breaker in a lousey place and at worst let out vast quantitys of magic smoke, all I do is lite a bulb. Tungston changes resistance radicaly with temperature. If you measure the resistance of a 100 watt light bulb you may measure 5 ohms. Now a little math will tell you that 5 ohms and 120 volts would give you 2880 watts so clearly something is happening here. As soon as you start to put current through a filiment it starts to get hot and starts to limit current and this happens fast but if you are running much less current than the filiment is rated for the filiment stays cool and the resistance stays low and it is either inperceptible or barely perceptible. Seems the only tricky part is picking the right size light bulb, and if you do, it should be pretty foolproof. Especially if your crossover includes an inductor across the line after the light bulb. I haven't done this with speakers and I haven't checked out their circuit, but I have used light bulbs as circuit protecters hundreds of times in innumerable situations and this has to be what they are doing. You could have a switching circuit around it but they say inaudible and it wouldn't be if there was any switching. If you pick a bulb designed for two much current it won't protect and if you pick a bulb designed for not enough current it will begin to light and effect the sound when their is no need for protection. If what they are doing in the pro protection circuits is different than this I'd be very surprized but if someone knows different say so. You could afford to protect a little more tightly with a light than with a fuse because if one transient was enough to have an effect it would protect softly and never miss a beat and rather than tripping because too much current whent through the driver it would prevent too much current from going through. If you wanted to look after a session and see what it had done you could hook up a DVM with a recording mode across the light at the bigining of the session and afterwards it could show you the highest voltage it had dropped (it's going to limit current by dropping voltage) or depending on the sophistication of your meter much more.

Mike Caldwell
10-23-2006, 07:15 PM
The 2425's would make at least the drivers early 1980's. You mentioned the diaphragms were aluminum the 2425's were titanium. They have either been replaced at one time or.........I am really guessing here maybe JBL put aluminum diaphragms in the 2425's to make them more comparable to the early models with the 2421 drivers....again only a big guess!

Mike Caldwell

11-30-2006, 07:13 PM
Pair of 4435's for sale for $1250 . Woofers need foam job, look and sound good, otherwise

12-01-2006, 08:43 AM
......Can you estimate age?...........

Hi SteveW,

looking through our Registry tells us your 4435 are from July to Sept 1983.
The change from 2421 to 2425 was in spring / early summer 1983.


12-03-2006, 09:42 PM
Thank you Hofmannhp.