Film-Tech Forum ARCHIVE: ''Load Fault'' light on DCM10D

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Posted by Anhtu Vu (Member # 7689) on 09-04-2013, 08:38 PM:

We just installed a new QSC system:

DCM10D
3 x SC423C
2 x SB5218
12 x SR8200
3 x DCA1622
1 x DCA3422
1 x DCA1824

So basically it's CP650/DMA8+ into DCM10D to amps and monitors.

Sometimes the ''Load Default'' light turns on for a split second before going off. It happens intermittently. Anyone knows what this means ??? Should i worry about it ???

On a side note, any QSC cinema experts in Montreal ??

Thx

Posted by Tony Bandiera Jr (Member # 2365) on 09-04-2013, 11:22 PM:

HI Anthu:

No, that "Load Fault" light is nothing to worry about...unless it stays on all the time. The software for that indicator is buggy..at low to moderate sound output levels it will frequently come on for no real reason.

If it DOES stay on for more than a few minutes, press and HOLD the "AMPS/PROC" button....the channel(s) with the fault will have a blinking yellow light in the AMPS row.

A fault can be anything from a short in the wiring to a blown speaker to a bad amplifier.

Another flaw with the monitor I found: If you shut down the amps you can still hear the sound through the monitor.....so be careful.

The DCM's are excellent monitors overall (and the DSP and crossovers are pretty good and versatile) but as a diagnostic tool for monitoring it gets a D- for the flaws I mentioned.

Sam from QSC pops in here every so often, and I have mentioned those issues to him..supposedly there was going to be an update to the firmware to address the Load fault and monitoring issues.

Posted by Anhtu Vu (Member # 7689) on 09-04-2013, 11:47 PM:

quote: Tony Bandiera Jr
No, that "Load Fault" light is nothing to worry about...unless it stays on all the time. The software for that indicator is buggy..at low to moderate sound output levels it will frequently come on for no real reason.

If it DOES stay on for more than a few minutes, press and HOLD the "AMPS/PROC" button....the channel(s) with the fault will have a blinking yellow light in the AMPS row.

A fault can be anything from a short in the wiring to a blown speaker to a bad amplifier.

Another flaw with the monitor I found: If you shut down the amps you can still hear the sound through the monitor.....so be careful.

The DCM's are excellent monitors overall (and the DSP and crossovers are pretty good and versatile) but as a diagnostic tool for monitoring it gets a D- for the flaws I mentioned.

Sam from QSC pops in here every so often, and I have mentioned those issues to him..supposedly there was going to be an update to the firmware to address the Load fault and monitoring issues.

Thanks a lot Tony. It's reassuring that i should not worry since, as you suggested, it's a bug. In my case the light does never stay on for more than 2-3 seconds.

How can you still hear sound through the monitors once the amps are shut down ?? This seems like a pretty serious bug!!!

Anyways, I just calibrated the system, using the QSC's software, and it sounds very good, still needs a bit more tweaking though.... in general, i find them a tad harsh in the high end.

Btw, while calibrating the levels in our room, i need to lower the output of the amps. Would you suggest doing it on the amps or leave all knobs at full and lower it in the software. I guess it should boil down to the same right ? My tech suggested the latter in case we need to swap out a bad amp, this way we don't need to remember where the knobs were set at.

Do you have Sam's (from QSC) last name and contact info ??

Thanks again

Posted by Clint Koch (Member # 1179) on 09-05-2013, 12:31 PM:

+1 (800) 854-4079
Sam Hynds

Posted by Carsten Kurz (Member # 5396) on 09-05-2013, 03:13 PM:

If you don't know the specifics of the output stage, I would usually not pull up the amps completely, but rather prefer to have the processor at around unity gain (or whatever applies) and not reduce level before the amps. Marking is no big thing.

- Carsten

Posted by Steve Guttag (Member # 268) on 09-06-2013, 01:18 AM:

The QSC DCM products depend on all amps at full. A nasty design trait of the dataport input of the amplifiers is that they put series resistors in line to force one to turn the signal up on the crossover. I've seen numerous DCMs clip out before the amplifiers...it can be quite frustrating. I can't express enough how much I HATE the design. I've never had an issue in the Basis stuff working with the Dataports...just the DCMs.

So, if you are using a DCM...turn the amps up all of the way. If you have any odd channels on an amp without any speakers...say Center on channel 1 but nothing on channel 2...then be sure to turn channel 2 DOWN all of the way or you'll get a load fault there.

On the surrounds...pay attention the series/parallel thing in the set up of the monitor. You always start with 1 of each. So...if you have two surrounds that are paralleled together...that would be 1-series and 2-parallel. If you don't get that right...you could get a load fault.

Make sure all of the impedances for your designated speakers are correct too. When in doubt...measure them yourself.

Posted by Marco Giustini (Member # 4544) on 09-06-2013, 11:44 AM:

Steve,

I've noticed that problem numerous times. Why QSC would design such a feature on purpose?

Posted by Steve Guttag (Member # 268) on 09-06-2013, 05:21 PM:

I don't know but I've been VERY vocal to them about my displeasure about the dataport design. One thing I've noted with QSC...their gain structure is all over the place and they don't do much to manage it. When you combine that with the lack of tools to be able to set it up yourself, you get one piece clipping before another.

Posted by Marco Giustini (Member # 4544) on 09-06-2013, 05:23 PM:

I've struggled in the past to avoid clipping at the DCM. I thought they'd have solved the issue with the new DCM 10/20/30 but it does not look so and the DCP series also seems to follow the same criteria.

Posted by Steve Guttag (Member # 268) on 09-07-2013, 08:23 AM:

I've put in a handful of DCP300s now. Thus far, while there are gain structure issues I've yet to have it clip out before the amps. One has to really watch themselves on the input side to get everything right. QSC gets so many things right in their upper-end DCP stuff like the Basis and now Q-Sys...but on the cinema DCP solutions...it just makes me scratch my head on how some of it makes it to production the way it is.

One thing I have also done is just skip the Data port crap and wire straight to the Phoenix connector. You can run the monitor lines to the Dataport if you want the load sensing or possibly the "Amps On" feature but if you skip the dataport, you'll not have gain structure issues anymore. Set your inputs right and you'll have plenty of gain...then use the amps inputs (as one should) to get the gain structure on the output right...you'll never clip the DSP that way.

I might just make a board that allows one to use the data port cables but breaks out the audio lines to feed the amps via the Phoenix connectors. It wouldn't be too hard and it would eliminate this annoyance.

Posted by Marco Giustini (Member # 4544) on 09-07-2013, 01:52 PM:

That's a great idea, thanks.

So you're saying that the resistors are on the dataport inputs of the amps?

DCA and ISA amps do have gains on the back or protected on the front, it is easy and safe to adjust the levels on the amps themselves. Amps are also quite reliable, the replacement issue is so rare that I'd rather have the proper gain structure.

Thanks again
Marco

Posted by Steve Guttag (Member # 268) on 09-07-2013, 02:43 PM:

Yes, the resistors are on the amplifiers.

Posted by Marco Giustini (Member # 4544) on 09-07-2013, 06:23 PM:

Thanks. That helps quite a lot.

Posted by Anhtu Vu (Member # 7689) on 09-10-2013, 07:43 PM:

I finally got a chance to talk to Sam @ QSC. Hopefully, he can drop by to answer some of your questions.

Basically, he suggested to wire all surrounds in parallel, no need for series-parallel. He also explained the reason why the data port was design that way.

Anyways, I rechecked my set up and everything was done up to specs for the exception of one loose wire on one of the surround. Hopefully the load fault was caused by that.

So far, aside from the ''load fault'' coming on once in a while, i've never experienced clipping from the DCM and the system sounds great after further adjustment.

Posted by Steve Guttag (Member # 268) on 09-11-2013, 06:24 AM:

With respect to the dataport wiring (series resistors)...he is just putting lipstick on a pig...it was a bad design, period. The number of clipping systems (easily proven) goes to prove it. It, without a doubt, raises the noise level of the system too.

Posted by Marco Giustini (Member # 4544) on 09-11-2013, 09:46 AM:

To be fair, you won't see clipping if you run your films at a low level. 99% of cinemas run their films below 6.0 (most below 5.0), and with those levels anything will do.

Posted by Anhtu Vu (Member # 7689) on 09-11-2013, 10:27 AM:

quote: Marco Giustini
To be fair, you won't see clipping if you run your films at a low level. 99% of cinemas run their films below 6.0 (most below 5.0), and with those levels anything will do.

We run our film at 7 and no clipping whatsoever.

Posted by Steve Guttag (Member # 268) on 09-12-2013, 09:34 AM:

Really? With DCinema, you should be able to hit 105dB per screen channel. See how loud you can go before clipping...you'll likely not hit 105dB or 103dB, for that matter. Make your own custom cables and have the channel 1 and 2 feeds to the amps go straight to the phoenix connectors...you'll make it and have a quieter system too.

Posted by Anhtu Vu (Member # 7689) on 09-16-2013, 10:27 PM:

Btw, can overloading the inputs of the DCM10D activate the fault load light ???