Insane ground loop; anybody wanna try?
Unplugging the sub has little effect ....Is the sub connected at speaker level (to the amps) or at line level (to the preamp)? And if the latter, is it connected to the preamp via XLRs, while the power amps are connected to the preamp via RCAs as you stated? In any case, if you already haven't, try disconnecting the sub from whichever component(s) it is connected to, in addition to unplugging it from the AC. Regards, -- Al |
Great — again, indebted to all of you for taking the time. Please don't apologize for asking basic questions. I agree that it's easy to overlook something obvious and I take no offense. It also occurs to me that I never actually tested the outlets with a receptacle tester. I'll do that as well — having met the previous owners of this house, anything is possible. I got the preamp a while ago and honestly don't remember if it ever played nice, though obviously Rowlands have a reputation for being pretty tightly engineered. I like the earlier suggestion to try it elsewhere and I'll figger how do that tomorrow. The preamp has one RCA and one XLR output (one pair of each, but you knew that's what I meant). The amps are connected to the RCAs; the sub is connected to the XLRs via adapter and then by RCA cables. I'll disconnect it from the preamp and try again — another good suggestion — and I'll try switching the two sets of outputs. There is no CATV in the house at all. (I have two teenagers. They think I'm Stalin.) |
the sub is connected to the XLRs via adapter and then by RCA cables.I wouldn’t be surprised if that turns out to be the key to the problem. While the post I made earlier today in this thread addresses a somewhat different situation, it provides what may very well be relevant background. The following paragraph in that post may be particularly relevant: Most XLR-to-RCA (and RCA-to-XLR) adapters short the inverted signal on XLR pin 3 to ground (XLR pin 1), although I believe Cardas can supply adapters on special order that leave pin 3 unconnected. Shorting XLR pin 3 to ground is appropriate when adapting RCA outputs to XLR inputs, and may be appropriate when adapting a transformer-coupled XLR output to an RCA input. However, at best it is poor practice when adapting an actively driven XLR output to an RCA input. And while many and perhaps most components would be able to tolerate that, with some designs shorting that signal to ground may result in major performance issues (see this thread, for example), or conceivably even damage, eventually if not sooner.The likelihood of a problem arising as a result of shorting an output signal on XLR pin 3 to ground with an adapter figures to generally be greatest when the output impedance of the circuit providing the signal is low. That is the case with your Capri preamp (80 ohms balanced output impedance, presumably corresponding to 40 ohms for each of the two signals in the balanced signal pair). In the case of the thread linked to in the paragraph I quoted above the result was buzzing, but hum seems very conceivable as well. Regards, -- Al |
