Film-Tech Forum ARCHIVE: Lots of noise when hooking up mics to CP650

This is topic Lots of noise when hooking up mics to CP650 in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Joe Redifer (Member # 3) on 04-10-2009, 07:36 PM:

We are doing some theater rentals soon for business meeting types and when we hook up the wireless mics we get a lot of noise (re: buzz, ground loop, etc) coming through the speakers. It doesn't matter if the microphone is on or off. We have tried going straight into the RCA jacks for Non-Sync 2 as well as directly into the XLR input for the PA on the CP650 (which was even worse, lots of hiss regardless if the mic is on or off). The rental company gave us a cable which has XLR on one end and RCA on the other. They also gave us a long XLR-only cable which we used for the PA connection.

My question is this: I am assuming the problem is before the 650 (I hope). OK that's not really a question, I just want to make sure that the problem is with the rented equipment and not ours (the regular Non-Sync music sounds fine). I am 99.762% sure it is hooked up properly (it also came with a mixing board). Hints, tips or suggestions?

Posted by Tony Bandiera Jr (Member # 2365) on 04-10-2009, 08:53 PM:

Hi Joe:

First off: I would make sure the mixer and wireless mic unit is plugged into one of the same receptacles in the rack that the CP-650 is. Biggest possibility is AC ground loops from the equipment being fed from separate circuits..

Second, the rental company should have available "Direct Boxes" which can provide isolation and if need be ground lift of the audio lines.

Make sure the wireless receiver is as far away as possible from the CP-650, any dimmers or booth lights, etc..anything that can possibly induce noise.

Without actually seeing the rental gear involved, those are the things I can come up with.

Posted by Joe Redifer (Member # 3) on 04-10-2009, 11:42 PM:

God damn it, I posted this in the wrong forum! How the hellz did I do dat?

Anyway, I'll see what we can do, but we have a fairly limited space and no room in the rack to plug the mixer into the same set of receptacles as the 650.

Posted by Pete Naples (Member # 761) on 04-11-2009, 02:45 AM:

Mic gain on the CP650 may be turned up WAY too high, try turning it down to minimum and increasing to the correct level.

If phantom power is on for a mic that doesn't need it, and wireless receivers generally don't [Wink]

, that can make 'orrible noises. It shouldn't matter with good quality professional mics but it's not unheard of with less than teh best of microphones. I've known the off cheap hand held mic to get warm when phantom powered un necessarily.

I've often had to install a pair of isolating transformer between non-sync inputs and other equipment such as mixers.

I'd be checking the mains earthign and amplifier wiring shielding arrangements on that CP650 too.

Posted by Scott Norwood (Member # 30) on 04-11-2009, 07:41 AM:

Since the microphone input on the CP650 is balanced, make an XLR cable with pin 1 (shield) disconnected at the CP650 end. This will solve a ground loop issue. Make sure that the wireless receiver is configured to output a "mic" level signal, not a "line" level signal (most can be set up to do either).