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Discussion Starter · #1 ·
My system has been setup for almost two years, and I haven't reconfigured anything for months. Until yesterday, there was absolute silence from all channels when no source was playing. Now I get a hum/buzz (more of a buzz) from the front right channel only. I have tracked down a few ground loop problems in other systems, and the sound is very familiar. The difference is that my previous experience with ground loops caused a buzz in all channels. This time, it is only affecting one channel. Does this sound right? My area did have two days of thunderstorms prior to the new noise, but I unplugged everything before both storms. The only thing I'm not sure about is whether I unplugged the cable before both storms.


My system:

Krell TAS 5-channel amp (on a dedicated 20-amp circuit)

Rotel RSP-985 processor

Tuner

DVD

HTPC

Cable

Subwoofer

Everything but the amp is connected to a Brickwall surge protector which has another dedicated 20-amp circuit


At first I thought that something might have fried one channel on the amplifier, but the buzz goes away if I disconnect the audio interconnects from the amplifier. I also tried to move some of the wires around, but that didn't change anything. I didn't get a change to really try a bunch of things last night because my wife wanted to watch something. Before I start changing things around tonight, I wanted to get some opinions from the experts.


Anyone have any suggestions before I start unplugging the world? It seems odd to me that a ground loop would suddenly appear only on one channel.
 

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Discussion Starter · #2 ·
I did some more testing of the buzz. I followed the instructions in the FAQ.


With everything except speakers disconnected from the amp, I still have a buzz, except now the buzz is in the two surround speakers. Yesterday, when I disonnected things I got no buzz at all.


Any ideas where I might look some more? Until two days ago, I had a silent system. Now I have a buzz.
 

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Can you short the amp inputs and try again? I think the Krell has shorting inputs, but there might be a problem with them. Then if it still buzzes, it's a dead cert that the problem is in the amp, sorry to say. :(
 

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Discussion Starter · #4 ·
I'm currently using the RCA inputs on the Krell, and the balanced inputs all have the shorting pins in them. I can try and short the RCA inputs tonight and see what happens. This morning, I tried two other tests:


1. With everything connected and only the amp on, I get a buzz from the right front. There is a very faint hum/buzz in the surrounds.


2. Leave all the interconnects alone and unplug the Rotel processor, and now I get a distinct ground loop hum from the surrounds, and the front right gets a lot quieter.


Is it also possible that the two thunderstorms messed something up with my powere? Remember, the amp was unplugged for most of the time. Both thunderstorms were really bad, and they when right over my area.


Very strange...
 

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Discussion Starter · #5 ·
With all inputs shorted (XLR using the Krell-supplied pins, and RCA using shorted pugs), my system is absolutely silent again.


Does this mean I have a power or EMI problem? It concerns me that it showed up after two years of silence.
 

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Neither. It probably means you have a flaky shield ground somewhere above the amp. Maybe in a cable or processor switch. Start by reseating all cables to the amp. If you still get buzz, remove and short the far end of the cable to the amp. If the system remains quiet, then you're pretty well assured that it's somewhere in the processor or before.


Does it happen with all inputs to the processor? Only with one?
 

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Discussion Starter · #7 ·
"Does it happen with all inputs to the processor? Only with one?"


It depends. When connected to the processor, the buzz is much more pronounced in the front right. You can hear and localize the front right from 20ft away. The other channels are very faint. I have to put my ear right up close. If I unplug all the interconnects to the amp, then it is all channels. However, the sound changes pitch.


Regarding the flaky shield ground, I'm curious where this could be. I have three dedicated 20 amp circuits for my system. One for the amp, one for the projector on the ceiling, and one for all the remaining equipment. I unplugged everything but the amp, and I shut off the circuit breakers for the other plugs, and I still get the buzz. Could my noise be coming from elsewhere? Also, I used a ground check plug (passed), and I got out a volt meter. All plugs read 120v on the hot wire and 30-40mv on the other. For grins I checked the chassis and the rack for any charges, but all were 0.


I will try shorting the ends on my interconnects. I also want to make up 14 shorted RCA plugs for all the remaining inputs on my processor. If all that fails, my dealer suggests bringing the amp in.
 

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I don't mean to hi-jack, but I have 2 quick questions - I've heard it's a good idea to plug any unused RCA connections on a receiver/processer with shorted RCA interconnects, is that true? If so, how do you make them?
 

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Discussion Starter · #9 ·
At the recommendation of my dealer, I brought the amp to the store and connected it up. Of course, the amp was silent. My dealer suggested a few more tests.


1. Float the ground on the amp. I wouldn't leave it like this, but I tried it. No change. There still is a buzz in the RF speaker.


2. Use a long extension and plug the amp in somewhere else. In this case, the noise got MUCH worse.


3. Short all the inputs on the processor. This made it a little better, but there still is an audible buzz in the from the RF.


4. Shut off every breaker in the house except the one for the amp. I still had a buzz, but one breaker did cause the buzz to change.


My next step is to have someone check out the circuits and the ground.


Eventually, I will probably send it back to Krell because the dealer thinks something may have caused the amp to be more prone to noise. My concern is that it will get to Krell and be perfectly quiet.


Any other suggestions?
 
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