Help with apparent RFI interference?
Right, looking for a little help with what appears to be RFI interference. Pardon the length, but I want to provide as much info as possible – any help or pointers would be very much appreciated.
I am running a pretty standard set-up with a blended two-channel and HT system. CDP, preamp, monoblocks on the one side, and a HT receiver running the center and surrounds with the main preouts into the bypass loop on the preamp for the HT side. The stereo preamp and monos are new to the system, and that’s when the issue arose for the first time.
HT receiver is a Marantz SR 7000 and the preamp is a Rowland Concerto. They are connected via a RCA to XLR cable made by Bettercables (which may be the issue, but bear with me) because the preouts are RCA-only and the bypass loop on the Rowland is XLR-only. I originally tried some RCA-XLR converter plugs and a completely unshielded, braided silver interconnect. Noise was really bad. So, I tried the Bettercables (better shielding) cable. Noise persists. Hence, I ask my questions. Imperfect, but no reason it shouldn’t work….
Independently, everything connected, the stereo side is dead quite (and sounds wonderful). Check. (It's wired balanced from start to finish, if that matters).
When by bypass loop is engaged and the HT receiver is off, dead quiet.
But, when the HT receiver is on, bypass loop engaged, there is an unacceptably loud, white-noise-ish, background hiss on the mains. But, not always. (Here’s where it gets a touch more complicated). When the DVD is selected (on or not on) at the HT receiver, but is not passing an audio signal (video is no problem, strangely), dead quite. When it is passing an audio signal, however, noise begins. Thus, you would think, something to do with the DVD player? Not so.
When any other input is selected at the HT receiver, whether or not there is something connected to it, noise. (Actually, there is nothing connected to the majority of the inputs, which are all noisy. The only other one busy is a second digital in from the HD-DVR. Not sure whether there is a hiss from that when it’s off, forgot to try and it basically never is off, but definitely noisy when it’s on.)
Couple of possible culprits immediately come to mind. Well, two potential, really. One usual suspect: the RCA-XLR cable is not shielded enough and the noise is coming in there (which seems not unlikely, considering the rat’s nest it’s running through and the fact that it's going from single ended to "balanced", lord knows how). The fact that the noise stops with the whole system on so long as the DVD is selected and not passing a signal seems to suggest that’s not the problem, though. Other possible guess is that the RFI is leaking into the HT receiver through the open / uncapped RCA inputs, and that is somehow canceled when the DVD circuit is selected (but then not canceled as soon as the DVD begins passing an audio signal?!?). Both seem unlikely to me for various reasons, but I’ve got no other ideas. And, besides, I refuse to buy caps for all of the RCA inputs on the HT receiver – too damn many – so I prefer to think that’s not the problem.
I’ve been running this same set-up for many years, without issue, with the only new addition being the Rowland (previously into the HT bypass loops of a VTL pre, then a Rogue pre, and then into a regular input on a Plinius pre – which didn’t have a bypass loop). May be that the Rowland is simply that much more sensitive (which is certainly is) and that the issue has always been there, but simply not at noticeable levels. Can’t say.
Finally, it’s not a ground loop. That’s a battle I’ve fought and know well. Too well. This is something else. I’m moving soon and will clean, rub, recheck and reorganize everything in the process. In the meantime and as I go – any thoughts on what I should be looking for or thinking about.
Many, many thanks.
