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I have a set of JBL control monitors and I enjoy the sound for their size, but I always felt like something was missing as far as dynamic "punch". I recently upgraded their woofers to an optional woofer JBL offers that has a larger magnet, better surrounds, and longer excusion, but it still seems like something is holding them back.On each of their crossovers there is a lightbulb for over-current protection and I was wondering if bypassing this would give an improvement in dynamics or just mess things up? I don't play my speakers too loud and I have a good amp that can easily take their load so I am not worried about needing the protection, but I don't know how necessary they really are to the crossover design.
Follow Ups:
The crossover has been designed with the protection light bulb IN CIRCUIT, shorting it out would probably cause the crossover to no longer work as intended, and the tweeter sound to get bright, and this not something you would want to do with most JBL monitors from the old style. They were known for their bright and forward sound in the treble.RE crossover tweaks, you could replace the electrolytic caps with some film caps, but be sure to get film caps that are considered "warm", or they will brighten up the sound too much as well.
Be sure to use some good solder, such as 63/37 Kester with the 44 rosin core, or Ersin multicore 63/37, and you might want to consider replacing the 'zip cord' type cables used inside these kinds of JBL/s too while you are in there.
Jon Risch
I did notice the cabling inside and considered some kind of better wire and some point to point soldering instead of the crimped spade thingies that are used.I agree about the brightness and would not want them to be any brighter... but I know little about caps in general, and could you give me some suggestions on what brand or type of caps that would be good to try (IE what caps are considered "warm"?)
Do I use the same uF value caps as the old ones?
What sort of sound improvements do better caps yield?
" ....what brand or type of caps that would be good to try (IE what caps are considered "warm"?)"
For film caps, in general: Cardas, Auricaps, Solen; these are all PP, metalized film types.
For some of the other exotic caps, the entire realm of paper in oil types, foil and paper, etc.
"Do I use the same uF value caps as the old ones?"
Yes, as close as possible to the RATED capacitance of the old part, as printed on the cap body. The electrolytic may have shifted in value, and the two channels may no longer match either.
"What sort of sound improvements do better caps yield?"
While it is ironic to replace electrolytics and try to 'avoid' getting more harsh or bright using film caps, in most cases, aside from any tonality changes that might accrue due to the inherent roll-off of HF's of the electrolytic caps compared to the film caps, a lot of the electrolytics sound grainy and hashy compared to film caps, and the better PP metalized caps can have more detail and better clarity, while not sounding any "brighter" or more "forward".
Usually it is well worth the upgrade. If you want to see what it could be like, you could try some inexpensive mylar film caps, realizing that they do not have quite the clarity or warmth of the PP caps, however, they are a lot cheaper and easy to try.
Jon Risch
Maybe you amp(s) are out of oompf for that particular speaker? Tried some other amp?
Nah... actually after a long break in period, everything is sounding pretty damn good. I would even venture to say it is now nearfield bliss.These monitors really are gems. They kick the pants off every other bookie I auditioned for nearfield. Polk, PSB, Monitor Audio, various others made for nearfield and not... These JBL monitors are very impressive... it is no wonder JBL's were the standard in recording studios for so long.
The sound is both accurate but non-fatiguing. I decided to wire them out of phase and place them facing each other so I could blast them and really get the new woofers broken in. I turned off the tone defeat on my NAD integrated so I could turn the bass up even more. After a bunch of hours of this, these speakers sound better than I would have ever imagined.
My amp seems to be a good match, actually. There is no shortage of power, and with a few tweaks, it is certainly articulate enough for me.
I actually find my old NAD/PSB combo to be a little dark, or at least a little boring, but the NAD with these little studio monitors is pretty damn musical, and I find the urge to find a permanent spot in the closet for the PSBs. I am dusting off albums I haven't listened to in a while because they are so much fun on these little guys.
Anyway, Appreciate the help... My next step is considering crossover modifications... with parts 15 years old or more, I am sure I could breathe even more life by replacing old caps, but I know little about that kind of stuff.
All the crossovers I have see with something like this it was a neon lamp or some other type gas discharge device.These are an open circuit until the voltage reaches a point high enough to ionize the gas inside and cause current to flow through the gas, much like an open air spark gap. The gas mixtures can be varied to adjust and give a more consistent flash over point.
So really under normal listening conditions they should not effect the sound.
The bulb in my crossovers appear to be a lightbulb that has a filimant much like what is in auto tail light bulbs, but shaped like what is in the link.From the design, I figure that it must be wired in series and limits the current by becoming more resistant as the power increases... I understand that audibly this compresses dynamics as you get louder and use more power.
I am not worried about over-current problems and I don't run them near loud enough for the protection to matter, I want to know if it is safe to bypass it by way of bridging the terminals. That is, if it is indeed wired in series.
I don't know for sure, that is why I am asking.
- http://www.speakerrepair.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=55-001&Category_Code=jj_jbl_xover (Open in New Window)
That is a 561 automotive dome lamp. Bose and Boston Acoustics use exactly the same part.The cold resistance is about one half of an ohm.
If you don't play it loud you could try jumping it out, but the level of the tweeter will go up a small amount.
The 561 takes a fairly long time to heat up and compress the signal. Short transients will not heat the bulb up enough to affect the sound.
You could add a relay to short out the bulb until high levels are reached.
http://archives.telex.com/archives/EV/Miscellaneous/STR Service.pdf
Thankyou for the help, I am not too interested in making the tweeter hotter than it already is.These are good speakers, the tweeter is one used in many of JBLs later studio monitors (44xx series), but I don't have a crossover adjustment knob on these like many others have so I can't dial down the tweeter if it gets too bright.
I have broken in the new woofers a bit and things aren't too bad, I will probably leave things alone if it isn't going to help dynamics on the lower end of the spectrum.
Half an Ohm isn't much at all, so I suppose it is more trouble than it is worth.
They use noral light bulbs, I have never seen what you described.
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