Subwoofer noises with 1067

[Bostonears]

I'm experiencing two (probably unrelated) noises with the subwoofer output from my 1067:

1. With digital audio output from a Motorola Cable TV set top box, when I change TV channels, I get a momentary thump through the subwoofer. I have tried both the coaxial and optical output connections between the STB and the 1067, but the thump is there both ways.

2. My subwoofer output is routed through a Marantz MA700 mono amp to a passive subwoofer. The MA700 has a voltage trigger input connection to turn it on and off. When I hook this up to the trigger output from the 1067, the MA700 switches on and off correctly, but whenever it is on, I get a disturbing continuous buzz through the subwoofer. I'm guessing it's at 60 Hz, but it's raspy (not like a smooth hum). When I disconnect the trigger cable, it's gone.

Neither of these problems existed with my previous pre/proc (Marantz AV9000).

Anybody else experience either of these problems? Any idea how to make them go away?

[Aussie Geoff]

Bostonears,

I haven't got a RSX-1067 but here's some idea's. The kind of subwoofer thump and the buzz you are talking about can both easily be caused by what's known as a ground loop or earth loop, which is where there is a small mismatch in the ground voltage between two items connected to your Receiver / Amp etc. Now - one of the most common ways of getting this is through your cable - since that is grounded a far way from your HT power outlets. The way to test for this is to unplug the connection(s) from you cable box from the RSX-1067. If the thump and hum goes away - there's your source. If it stays there - unplug everything else from the RSX-1067 and if the hum goes way add them back one at a time - when the hum comes back - you have the culprit.

Let's just say it is the cable (90% of the time it is) then you need one or both to get a line isolation transformer OR have the ground in your cable box connection to the house checked. Do a search on Hum and several members have bought the isolation devices for prices <$20.

If you still get the hum / buzz with nothing plugged into your RSX-1067 then try unplugging the RCS cable to your sub woofer amp – if the buzz stays then it’s in the Sub amp – if it goes then take the RSX-1067 to the dealer and try it on one of their subs - just in case it has a fault somewhere.

Geoff

[Bostonears]

Geoff,

Thanks for your suggestions. Giving this some additional thought, I can devise a few experiments which I will try.

For the thump when changing TV channels, if I disconnect the Cable TV wire from the set top box to check for a ground loop there, the STB won't be able to tune in anything, and I won't actually be able to change channels, but I'll see what happens.

In listening last evening, I have now noticed that the thump also occurs when the RSX-1067 switches inputs (e.g. from Cable TV to DVD). I am now inclined to think that this is related to the item on the Wish List V4 described as Extended Digital Signal Lock, that is, it thumps when a digital signal is momentarily lost then re-acquired. I can test this theory by trying analog connections between the STB and 1067.

On the continuous buzz from the subwoofer when using the trigger cable, the problem might be a ground loop between the 1067 and the sub amp, where one ground is through the analog interconnect and the other is through the trigger cable. I will test this by disconnecting the shield portion of the trigger cable, so that the cable makes the 12V contact only at the center pin. (The sub amp should still complete the circuit via the shield of the analog interconnect.)

I'll post my findings when I've had a chance to try all this.