Film-Tech Forum ARCHIVE: CP65 Audio Hum

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Posted by Bernie Anderson Jr (Member # 410) on 01-10-2013, 09:50 PM:

Hi Guys,

I just noticed this tonight at home. I'm running a CP65 and using a Yamaha home receiver amp with 6 channel inputs as my only amplifier. I noticed a hum tonight in the track. I first isolated it to the lamp house, but the hum was still there even after I shut it off, but a little bit less. I powered down each item in the booth one at a time and I would get a lesser hum. But again the hum still persisted. As a matter of fact, I would still get a hum even with the CP65 and SDDS off and unplugged.

Now let me tell you about the system. The CP65 is connected to a Sony SDDS 2000 via the XLR inputs. I have the ground (-) and the hot (+) wired connected only at the cp65 output and the shield is not connected at this side. From the SDDS, I'm connecting to the Yamaha from the XLR outs to RCA inputs on the 6 channel input of the yamaha. This cable is professionally made by a manufacturer and the ground (-) and the shield are connected to the ground (-) of the RCA side. So if you follow the path, (+) and (-) out of the cp65 (no shield connected) to XLR of SDDS. SDDS XLR out to RCA of Yamaha amp (shield connected to (-). Would I be correct in thinking that with the shield being connected to the RCA (-), I could be picking up outside interference? Any suggestion on how this should be properly wired? CP65 to SDDS to Yamaha? I know it has something to do with the shield. You could interject SDDS jokes if you like, it was given to me and it works.

Thanks

Bernie

Posted by Tony Bandiera Jr (Member # 2365) on 01-11-2013, 11:17 PM:

Bernie:

On the cables from the CP-65 to the SDDS, are the shields connected at the SDDS end at least? If not try that first. Next to try is connect ONE of the shields to an "E" terminal at the CP65 end.

From the SDDS to the Yamaha, the best connection setup in most cases is to connect the shields at the RCA (unbalanced) end and float them at the SDDS end. The cables you have should work, but first correct the CP-65 cabling, and if the hum is still present, then disconnect the shields of the SDDS/Yamaha cables at the3 SDDS end ONLY.

One or both of those suggestions should clear up the hum.

Posted by Alban Birch (Member # 4121) on 01-12-2013, 04:14 AM:

Try connecting the Cp65 directly after the NR in Stereo to your Yamaha and let your Amp do the decoding. I did this on a CP55 using Pin 15 and 2 (RT and LT) on J18, these are called Pre-decode out. I then removed all the cards except Preamp, NR, Automation and Power supply after that the CP ran much cooler

Posted by Bernie Anderson Jr (Member # 410) on 01-15-2013, 06:37 AM:

As a follow up, I solved the problem. I grounded all the components together using a grounding wire to chassis, basically daisy chaining them together. Each connection made the system more and more quiet. The only thing left that I have to connect is the DA20, you can hear a slight click when it goes in and out of digital to SR (almost like a static pop). Other than that, the hum is nonexistent at normal volume levels.

Thanks again, everyone