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Post subject: Strange Noise In My 5F6A Clone
Posted: Sun Jun 02, 2013 9:17 am
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Rock Star
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Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Lately I have been noticing a strange noise in my Weber 5F6A clone. It is sort of a rapid "pop-pop-pop" but very quiet. It only seems to affect the normal channel. No noise in the bright channel. It changes volume as the normal volume control is raised or lowered. I thought it was motor-boating at first.

I put the amp on my bench and fired her up. Turned the normal volume all the way up and the bright volume all the way down.

No popping!

I opened the back and started tapping on all the connections between the normal input jacks and V1. Nothing. Guitar plugged in .... guitar not plugged in. Just a slight hiss. So I closed her back up and set her on the floor and plugged her into my Furman power conditioner. No popping. Then I put the amp back on the cabinet that it normally sits on, just below my HDTV.

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Turned the amp on .... and the popping was back.

Put the amp back on the floor .... no popping.

Back on the cabinet .... well, you can guess what happened.

Strange thing is, the tv is turned off.

My amps plug into the Furman and the TV and DirecTV box plug into an old Rotel power conditioner. The popping seems to be something being induced into the preamp of the 5F6A. The chassis is shielded all around and the grounds are good. The AC line for the tv is several inches away. The HDMI cable plus into the tv directly behind the amp.

I'll try disconnecting the HDMI cable and moving the Rotel to another outlet. Beyond that, I don't have a clue as to what is causing the noise or how to fix it. Any other suggestions?

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Post subject: Re: Strange Noise In My 5F6A Clone
Posted: Sun Jun 02, 2013 1:49 pm
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Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
The problem appears to be solved.

It occurred to me that the noise first appeared shortly after we upgraded our Verizon Internet service to their new FIOS Quantum (50 Mbps/sec down, 25 Mbps/sec up). The Ethernet cable between the fiber converter mounted outside the back of our house to the upstairs router runs on the other side of the wall, directly behind the two amps in my photo. I don't know how well shielded the cable is. I had been using the Eurotubes preamp tube dampers on the preamp tubes of the 5F6A for some time now. I decided to remove those and put the aluminum tube shields back on the preamp tubes. The result: silence. No more popping and strange crackling. Interestingly enough, my BDRI sits on the cabinet next to my 5F6A clone, and it does not seem to have a noise problem. I also have the Eurotubes dampers on it, but the preamp tubes are sunk deeper into the chassis and appear to be partially shrouded by metal. I'm still puzzled as to why only the normal channel of the 5F6A was affected and not the bright channel. :?

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