Film-Tech Forum ARCHIVE: CP-500 Popping noise

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Posted by Chad M Calpito (Member # 3736) on 09-21-2006, 12:43 AM:

I had a question. Recently, while opening the projection booth for #1 & #10, I would hear low popping noises coming from the booth monitor & from the auditorium upon turing on the equipment via the Circuit Breaker Panel. After the CP-500 unit completes it's boot sequence, there are no other problems. Everything runs fine. Is this normal? I don't know if it's the amps themselves or the actual Dolby Digital CP-500 unit. I am using 19 QSC Amps of various models. Sorry, I don't have the actual model numbers for the amps handy. Also, would this popping affect the speakers in the auditoriums over time?

Posted by Cameron Glendinning (Member # 3516) on 09-21-2006, 01:11 AM:

Sounds like you should turn on the amps after the processer. what else is on the same circuit breaker? something like an air conditioner would do the same thing.
Many cinemas turn off each amp then the circuit breaker for the processer. One cinema that I worked in had a problem with the individual amp switches then breaking!
As for damage, how many years has this been happening?

Posted by Michael Schaffer (Member # 1204) on 09-21-2006, 01:20 AM:

If the sound is also heard on the booth monitor, it probably doesn't come from the amps - unless the amp is wired up and set to monitor the amp outputs, of course. If so, the next step would be to check if the sound can also be heard when the processor output is monitored. That should clarify whether it is the processor or amps. I do seem to recall a problem like that with CP500s, but it was many years ago and I can't quite remember.
Maybe it will come back to me. In the meantime, it should be checked if the sounds are coming from the processor or the amps by monitoring them accordingly during the boot sequence.
If it turns out to be the amps, see if you can narrow it down to one. In that case, you don't have to reboot everything. Just switch off the amps and then switch them on one by one, listening for the sound.

Posted by Chad M Calpito (Member # 3736) on 09-21-2006, 10:07 AM:

Thanks for the tip, Michael. I'll check it out this morning when I open. And, to answer your question Cameron, it just recently started doing this. When I started in this booth, it didn't make the popping sound and that was in February when I started in this booth. So, it's something new.

Posted by Jason Setzer (Member # 3949) on 09-21-2006, 09:39 PM:

Well there is a couple issues here.

1)Popping noise can permantly damage the speaker cone/voice coil
2) Popping noise is usually accredited to amplifiers, typically it is a power supply issue with one of your amplifiers
3) As Cameron stated something with a large inductance ie air conditioner could also cause the "popping" sounf coming from the speakers. But as you stated is hasnt always had the popping sound it sounds like a degraded power supply.

They are both absolutely correct about turning the amplifiers off and always booting the processor first, in car audio for example the head unit has a couple second delay so that it always powers up first and then the amp(s) power up afterwards(was the easiest example I could think of).

Posted by Chad Souder (Member # 343) on 09-22-2006, 01:17 PM:

We had this problem awhile back and as others have already stated, just shut the amps off before you turn off the breakers and turn them on after you flip the breakers on the next day and you should be fine.

Posted by Kevin Raisler (Member # 1761) on 09-22-2006, 06:54 PM:

Iv'e had this problem too based on my experiences the problem has always rested in the 684 board. next time your tech is present have him check it.

Posted by Gordon McLeod (Member # 33) on 09-22-2006, 09:21 PM:

I usually heve the processing equipment on a UPS powered up 24 7

Posted by Adam Martin (Member # 641) on 09-23-2006, 04:11 PM:

Circuit breakers are not designed to be power switches. [Mad]

And what Gordon said.

Posted by Phil Hill (Member # 371) on 09-23-2006, 04:34 PM:

Actually there are "switch duty rated" circuit breakers. ALL booth subpanels should use them.

Posted by Steve Guttag (Member # 268) on 09-23-2006, 05:20 PM:

Actually Adam...if you read the typical duty rating on the non-switch rated breakers...you'll find that you can switch them on/off once per day for over 10-years. Compre that with switching individual components or with dirt build up in components that have fans and it really starts to become a wash.

A big problem I find is that there are only two decent load centers in the US for 120/208 service...Square-D and Cutler-Hammer. The rest...GE and such are complete JUNK and should be specifically excluded from use. Those breakers fail right out of the box...forget about switching them.

Steve

Posted by Adam Martin (Member # 641) on 09-23-2006, 05:29 PM:

Huh. Interesting.

I still like the idea of leaving the sound rack on 24/7 with a UPS. It seems like it's better for the circuitry with regard to the on/off heat cycles.

Is there any equipment that has a fan that cycles on/off or high/low depending on the need? If not, there should be.

The first person to complain about wasting electricity gets banned. [Big Grin]

And just so I'm on-topic, I agree with having the amps off or muted until after the processor has finished its power-up routine in order to protect the speakers.

Posted by Chad M Calpito (Member # 3736) on 09-25-2006, 11:17 PM:

Well, here is an update. I followed the instructions and I found out that it was the CP-500 Digital Processor. I was hoping to see my technician today, but, he wasn't at the theater when I arrived. But, I will tell him of the situation whenever I see him next. Anyway, thanks to all of you for your input and information. You are all most kind. [Big Grin]

Posted by Louis Bornwasser (Member # 3063) on 09-26-2006, 04:25 PM:

We have always used the Ashly amps which have built in input muting to eliminate pops on start up. Some processors (Smart) pop on shut doen and this is a real problem. Louis