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Author Topic: STX825 blown HF drivers  (Read 12437 times)

Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #10 on: March 30, 2013, 10:11:06 pm »

Hello David!

That is correct, did not realize that an offline device file without channel names will not overwrite channel names on the ITech. And as you can tell, these amps were deployed for Vertec v4 duty till the very recent upgrade to HD. but what's in a name ?

I can assure you the presets were working as desired, and sounded very good!

Bob, what you are seeing is not correct.
This device file has no bi-amp settings. And I have tried and find it pointless running any of the JBL portable boxes biamp'd.

Regarding the RMS limiter. The RMS limiters have a very slow attack time, 4seconds. And if the amps see a continuous signal above they engage. So far I have rarely ever seen that happen, maybe with some really loud metal acts belting it out. I think its a safe area to be in, if the programme material is really compressed, then the drivers should be able to handle that at 1/3rd rated power over a much longer time than at their full rated continuous power.
Especially since I don't do EDM or the likes. Mostly.

Regarding the Peak limters, set to 100v in this case, I think its moot.
The ITech 4000 is rated 2000watts into 4ohms, which, by my calculation translates to bout 90volts. So I don't see how setting it at 100volts would ever allow them to engage without the amp clipping first.

Unless of course I am totally off on how these limiters work.

None the less, as mentioned before, the limiters were not being put into action, so that should give us all a very real idea of how easy the mix was.

Regards,
Sidhu
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Greg Cameron

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Re: STX825 blown HF drivers
« Reply #11 on: March 30, 2013, 10:56:27 pm »

And I have tried and find it pointless running any of the JBL portable boxes biamp'd.

Though you may not find an overall sonic reason to run bi-amp as opposed to passive, there may be another - steeper crossover slope for better HF driver protection. The JBL specs don't specify the filter order, but I suspect their only 2nd order, maybe 3rd order filters. External bi-amping means you'll probably be using a 4th order LR filter which means not working the HF driver as hard in it's lower range and possibly smacking the diaphragm on the phase plug. I'll be curious to know the mode of failure, but I'll submit that bi-amping at minimum will increase HF driver safety & clarity compared to running passive mode. And I'll also submit that if you do tend to push the rig, bi-amp will sound better.
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Bob Leonard

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Re: STX825 blown HF drivers
« Reply #12 on: March 31, 2013, 01:10:31 am »

Dave, Nitin, thanks. I'll run the settings again tomorrow and see what SA say's again.
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Art Welter

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Re: STX825 blown HF drivers
« Reply #13 on: March 31, 2013, 12:21:19 pm »

Regarding the RMS limiter. The RMS limiters have a very slow attack time, 4seconds. And if the amps see a continuous signal above they engage. So far I have rarely ever seen that happen, maybe with some really loud metal acts belting it out. I think its a safe area to be in, if the programme material is really compressed, then the drivers should be able to handle that at 1/3rd rated power over a much longer time than at their full rated continuous power.
Especially since I don't do EDM or the likes. Mostly.

Regarding the Peak limters, set to 100v in this case, I think its moot.
The ITech 4000 is rated 2000watts into 4ohms, which, by my calculation translates to bout 90volts. So I don't see how setting it at 100volts would ever allow them to engage without the amp clipping first.

Unless of course I am totally off on how these limiters work.

None the less, as mentioned before, the limiters were not being put into action, so that should give us all a very real idea of how easy the mix was.

Sidhu,
The presets show almost a 6 dB boost up high.
The driver is not padded in the high frequency, and the nominal impedance is 8 ohms, though the DC resistance is quite low (4+ohms IIRC).

30 volts or so of feedback could take out the HF drivers.
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Bob Leonard

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Re: STX825 blown HF drivers
« Reply #14 on: March 31, 2013, 12:23:24 pm »

Bob, I attached a screenshot of what I am seeing. Both channel 1 and 2 appear to be the same.

I have the correct file now Dave. Quick question would be why no LP filter below 20khz, maybe at 17-18khz, and why the 6db of gain in the upper regions.
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Bob Leonard

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Re: STX825 blown HF drivers
« Reply #15 on: March 31, 2013, 12:24:48 pm »

Same questions at the same time. Great minds think alike.
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Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #16 on: March 31, 2013, 12:51:33 pm »

Same questions at the same time. Great minds think alike.

 :)

As mentioned before, eq presets copied over from the STX tunings as provided by Harman for the XTI boxes.

Image attached.


« Last Edit: March 31, 2013, 12:53:51 pm by Nitin Sidhu »
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Art Welter

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Re: STX825 blown HF drivers
« Reply #17 on: March 31, 2013, 01:23:47 pm »

:)

As mentioned before, eq presets copied over from the STX tunings as provided by Harman for the XTI boxes.

Image attached.

And as mentioned before, limiters set to protect a woofer won't protect a HF driver rated for 75 watts IES.
The limiter settings offer no protection to the HF when you are using them in the passive mode.
Remember, you are boosting 6 dB in the high end, and there is no attenuation up real high in the passive crossover.

When you inspect the diaphragms to see if they look burnt, also check to make  sure they were the correct impedance and original JBL equipment, and there are no obvious burnt resistors or blown capacitors in the passive crossover.

Good luck sorting out the problems!

Art
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Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #18 on: March 31, 2013, 01:32:58 pm »

And as mentioned before, limiters set to protect a woofer won't protect a HF driver rated for 75 watts IES.
The limiter settings offer no protection to the HF when you are using them in the passive mode.
Remember, you are boosting 6 dB in the high end, and there is no attenuation up real high in the passive crossover.

When you inspect the diaphragms to see if they look burnt, also check to make  sure they were the correct impedance and original JBL equipment, and there are no obvious burnt resistors or blown capacitors in the passive crossover.

Good luck sorting out the problems!

Art

Hello Welter!

Thank you. I understand what you are saying.

We will inspect the HF drivers and revert. I have been told that drivers were inspected and were found to be dead. So the crossover should be good.

This would however put me in a very peculiar dilemma. We have never in the past longest time blown an HF driver. We have worked with the 725/932 for many years now, and it has always been good.

Sidhu
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Nitin Sidhu

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Re: STX825 blown HF drivers
« Reply #19 on: April 01, 2013, 11:53:34 am »

Here are some pictures. Thank you.

Strange thing is that the one HF that is left working measures in at 4ohms exactly on the multimeter, instead of 8. The service centre says that's cause it too is damaged.






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