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Thread: sonicguard

  1. #1
    imtkjlu
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    sonicguard

    sonicguard

    How does it work ? how do I build my own ?

    Cheers /Kjell

  2. #2
    Senior Member Baron030's Avatar
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    Here is a link to get an explanation on how it works.
    http://www.jblproservice.com/general_faq.htm

    To build your own, I would start by researching several of the JBL products that have "SonicGuard". This would give you an understanding of how the LP1 and LP2 "light bulbs" are used. And who knows, you might even find a JBL crossover network design that you can include in your project. Why reinvent the wheel, when you don't have to.
    It might also be helpful to say what crossover network design you are planning on modifying and which JBL speaker components you are using in your project.

    Baron030

  3. #3
    imtkjlu
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    Ugh, what a terrible font/style i used in my question!
    Thank you for the information
    Where can I bye this "light bulbs" ?
    My interest was just general, how it works and how to build...
    Regards /Kjell

  4. #4
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    The UREI monitors also used light bulbs as fuses, mounted on the front panel for easy replacement. I was once in a studio where the light bulbs were taped over because they were distracting when they flashed to the beat.

  5. #5
    Senior Member louped garouv's Avatar
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    I have read a mentioning of using lightbulbs in a preamp's circuit as well to draw some juice to help prevent the mixer's 'output stage' (I am guessing here) from clipping...

    supposedly it was a throwback to tube audio practices...

    does anyone have a pointer to some additional reading on this topic?

  6. #6
    Moderator hjames's Avatar
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    I don't think it was to prevent clipping, rather to indicate possible clipping.
    Momentary blinks are ok, but when it is on nearly continuously, beware ...

    They are basically just a resistive load but if you load them too hard the filament would burn out. Of course the sound would presumably be overdriven and crappy before the bulb would blow ... at least thats how most peak indicators should work.

    Quote Originally Posted by louped garouv View Post
    I have read a mentioning of using lightbulbs in a preamp's circuit as well to draw some juice to help prevent the mixer's 'output stage' (I am guessing here) from clipping...

    supposedly it was a throwback to tube audio practices...

    does anyone have a pointer to some additional reading on this topic?
    2ch: WiiM Pro; Topping E30 II DAC; Oppo, Acurus RL-11, Acurus A200, JBL Dynamics Project - Offline: L212-TwinStack, VonSchweikert VR-4
    7: TIVO, Oppo BDP103D, B&K, 2pr UREI 809A, TF600, JBL B460

  7. #7
    Senior Member louped garouv's Avatar
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    Quote Originally Posted by hjames View Post
    I don't think it was to prevent clipping, rather to indicate possible clipping.
    Momentary blinks are ok, but when it is on nearly continuously, beware ...

    They are basically just a resistive load but if you load them too hard the filament would burn out. Of course the sound would presumably be overdriven and crappy before the bulb would blow ... at least thats how most peak indicators should work.

    well, i think the bulb was installed in the mixer's chassis, in the case I am referring to at least, so as a indicator -- not so much....

    from reading the post again (partially presented here), well you can all read....

    variable saturation device is today's word (for me)

    Until my retirement in 1999 I was involved with many clubs with in the USA. Back in the late 70s and until the early 90s I was flown all over the country as a trouble shooter for problems being encountered on many sound systems. I can honestly state that sound systems using the old Bozak and Urei mixers hardly ever had problems with the mixer.

    99 times out of 100 the problems were pre and post processing equipment that was installed to twist, bend, and shape the sound. A truly properly operating sound system does not require all types of extra gear if installed correctly. Keep in mind that each piece of gear you add has to put some type of noise in the chain. Also remember garbage in means garbage out in any type of sound system.

    The Bozak was never the problem in any of the systems I was evolved in, and the problem with the Urei was running out of head room that caused early distortion that was and easy secret fix. I know how you love Urei mixers so I have sent you a separate set of drawings with the Urei fix. Urei used the most advanced technology at the time that included IC chips. The problem with the chip is they do not have a high saturation point like the Bozaks transistors. By installing ............................ in the Urei circuit it acts like a variable saturation device. If you use a fixed resistor it limits the Urei from producing a higher gain output. The .............................. installed where I have shown you only absorbs the distortion and lets the mixer reach higher and cleaner output levels. This is a trick we used when we went from tubes to transistors back in the late 50s. Funny how ..........................installed properly can correct and make the Urei mixer respond and sound so much cleaner.
    after a bit of an uproar, the original poster revealed that the "........................." was a lightbulb...

  8. #8
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by louped garouv View Post
    ... some additional reading on this topic?
    Take this:
    When lightening the resitance of the bulb arises, the speaker gets relativly less voltage - sort of dynamic compressor. When the voltage is too high the bulb blows - sort of a fuse.
    (When child my father built a "lamp box" for our electric railway - no smoking transformer ever. )
    ___________
    Peter

  9. #9
    Senior Member Baron030's Avatar
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    If you do a search on the JBL part# "SK-3" the limiter bulbs are available for about $6.95 each + shipping.

    Here is a link to a well known reliable source:
    http://www.speakerrepair.com/Merchan...e=jj_jbl_xover

    Baron030

  10. #10
    Senior Member Baron030's Avatar
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    To help explain how sonicguard works, let’s take a look at the JRX115 schematic below. At low power levels, the resistance in the SK-3 bulbs is going to be very low. Having never measured one of these parts, I am going to take a wild guess and say that the resistance is about 2.5 ohms each. When combined with the R1 resistor, the signal leading to the 2412H driver is going to be attenuated by about 3.5db. But, at high power levels, the filaments will quickly heat up and the resistance rises to a point where almost all of the current is being fed through the R1 resistor only. This causes the attenuated to increase to about 9.5db.
    So, you can think of the SK-3 bulbs as a really cheap compressor with a very limited range of about a 5 or 6db. I have noticed that JBL usually mounts these lambs very near a reflex port. I am sure they do this so that the light is clearly visible, from outside the enclosure. In that way they also serve as a visual warning, when you are pushing your drivers too hard.
    Baron030
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  11. #11
    imtkjlu
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    Excellent! thank you all.

  12. #12
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    Quote Originally Posted by Baron030 View Post
    I have noticed that JBL usually mounts these lambs very near a reflex port. I am sure they do this so that the light is clearly visible, from outside the enclosure. In that way they also serve as a visual warning, when you are pushing your drivers too hard.
    I have a pair of MR922's which use a similar circuit, and on them, the lamps are mounted behind a red lens on the connector plate on the back - that way, you can see them if the speakers are mounted on stands somewhat in front of the band.

    John

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