This is topic Right Surround channel buzzing?????? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by John Westlund (Member # 913) on 06-25-2002, 10:00 PM:
There is a buzzing coming from the right surround channel in our auditorium. I checked all the connections and they all seem to be fine. The amplifier is a Peavey CS400 and we have DTS with a CP-55. The speakers buzz even when the system is not playing anything.John
Posted by Randy Stankey (Member # 64) on 06-25-2002, 10:14 PM:
The amp is bad. You'll need to repair/replace it. This is a standard mode of failure for this model of amp. 
Look at the amplifier for your subwoofer. I expect it is the same model. If so, take out the bad amp and put the one from the subwoofer in its place.
Make sure all the switches on the back are set the same as the original and double check the wiring to be sure you got it right. This will get your surround channel working again until you can get the dead one repaired. You don't need the subwoofers as much as you need the surround. Provided everything else in your system is working correctly you will be able to get by without it. Most people probably won't even notice. If this is an important movie or if it's in your best house take the subwoofer amp (if it's the same) from another smaller house or less important movie.
Take the bad amp write down the model and serial numbers and call your service department, warehouse or technician. Have them get you a P.O. and send the thing off to be repaired. In a few weeks you'll get your old amp back, all repaired (or refurbished). Reverse the procedure to put everything back where you found it. You're back in business! 
Posted by John Westlund (Member # 913) on 06-25-2002, 10:17 PM:
The amplifer for the subwoofer is different. It is a QSC 1500a. I also cant take an amplifier from another house because this is a single screen 
. The surrounds were working last I checked but just buzzing very loud.
Posted by Randy Stankey (Member # 64) on 06-25-2002, 10:42 PM:
Damn! If it was the difference between a 400 and an 800 I'd say you could substitute but going up to 1500 would be pushing it. Is there any any other way you could creatively rearrange things?Is this the first time this amp has done this?
It's common for them to exhibit the symptoms on an intermittent basis. It'll do it when it's hot, for instance, but it will be okay after you turn it off for a while. It could last for a few minutes, hours or even weeks until it does this again. As time passes it will occur more frequently until it gets to the point where it won't go away.
On one occasion I got peeved off, shouted some choice words and gave it a thump on the side. The noise stopped immediately and didn't reappear for over a month! (Fonzie Power! 
)
Posted by Paul G. Thompson (Member # 655) on 06-25-2002, 10:43 PM:
I have a PeeVee CS-400 sitting on my pile of junkers. It has been sitting there for a month now. One of these days I'll rent a forklift and move it to a bench to see if it is worth saving.
Posted by John Westlund (Member # 913) on 06-25-2002, 10:48 PM:
I dont think this is going away anytime soon. It doenst have to be hot for it to buzz. It will buzz as soon as you turn it on even after sitting overnight. Sounds like it may have to be replaced.
Posted by Darryl Spicer (Member # 711) on 06-25-2002, 10:52 PM:
Take some compressed air and blow out the fan. Do this on a regular basis. The fan may not be working fast enough to keep the unit cool. By blowing it out with air you can get rid of some of the dust buildup around the heatsinks inside. Next I am assumiong you are feeding the imputs to this amp with phonoplugs. Pull these out and make sure the shield that covers the wiring conection is not loos turn it till it is tight. Next clean the phone plug connection with some rubbing alcohol to clean off any residue on the conectores.
Posted by Darryl Spicer (Member # 711) on 06-25-2002, 10:59 PM:
Hey Paul, you don't need a forklift to move the 400's. You need it to move the 800's.
Posted by Daryl C. W. O'Shea (Member # 1303) on 06-26-2002, 12:39 AM:
John,Assuming nobody likes to play inside of your rack Randy is probably right about the amp needing repairs. Just to be sure though, disconnect the inputs to the amp and see if it makes any noise. This will tell you for sure whether or not it's a wiring problem like Darryl mentioned (actually to be totally sure connect the high and low ON THE INPUT ONLY together and see if it still makes noise).
On a few occasions I have had ground hums appear out of nowhere after years of clean audio. I've also had auditorium dimmers (and stage dimmers) start to cause ground hums (and loud buzzes) in a system before. Best way to do it, shut EVERYTHING off but the processor and that single amp and see what happens. Who knows you might get lucky and the amp might be OK.
But like Randy said the amp's probably in need of repairs.
Also don't forget to make a note of the settings on an amp that you may 'borrow' from another channel so that you can restore it to its original setting when you put it back.
Good luck!
Daryl
Posted by Paul Cassidy (Member # 951) on 06-26-2002, 01:00 AM:
I had this problem once trying to locate a hummmmm coming from the speakers or so it seemed ,until I powered everything down and had a good listen around the speaker platform ,because it was intermittent and it was coming from a set of Cool store fridges in a Store on the other side of the cinema wall 
------------------
A KIWI eats,roots & Leaves.
Posted by Gordon McLeod (Member # 33) on 06-26-2002, 09:36 AM:
Since it appears that it is in only one channel of the amp swap the channels with the input connectors (probably phono jacks) and see if the problem moves
If it does it is in the monitor or the processor if it stays in that group it is the amp or a shorted groud in the speaker wireing
I had a system once where the low side of one of the surrounds got nicked with a drill and was shorting to the steel studs in a wall and was creating an interesting ground loop
Posted by Jesse Skeen (Member # 586) on 06-26-2002, 12:35 PM:
Is there a hearing-impaired system installed? I worked at one theater that had this problem and turned out to be interference from the FM transmitter- we re-aimed the antenna on the device and the buzzing went away.
Posted by William Bunch (Member # 1040) on 06-27-2002, 12:56 AM:
Hmmm, Did he say he was using a CP-55 ?? I had the very same problem in one of my theaters that had me in and out for several weeks. At first I thought it was an amplifier and swapped it out with spares. The buzzing would go away. Then they would call back a few days/weeks later with the same problem on the same channel!! After a long day with a soldering iron and a good magnifyer I found an intermittent short of some kind in the TEST plug on the back of the CP-55. Whenever I tapped or flexed the board in that location I could make the buzz stop or reappear. I tried resoldering all the connections but that did not work. The only way to stop the erractic thing as to completely remove the jack. No more buzzing and that was over a year ago and no callback. (knocking on wood)Bill BuncH
Misawa, Japan
Posted by John Westlund (Member # 913) on 06-27-2002, 01:07 AM:
Got the problem fixed tonight for the most part. I found that the right channel negative had never been hooked up to the outputs on the CP-55. The buzzing has mostly stopped but there is still a slight buzzing coming from all the speakers.