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Old 30th September 2007, 08:01 PM   #1
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Default Fix a ground loop!

I've got horrible wiring in my dorm room and the most ridiculous kinds of feedback, hash and ground loops. If I plug my three-pronged printer cable into my power strip, I get a ground loop from that through to the USB connection in my laptop, and back out to my tube amps which are grounded. Rather than keep breaking the grounding pins off of all my computer equipment (my monitor was horrible with noise until I did this), is there a more convenient way?

My thought was to try and find an external sound card that might break the ground loop. I know that my amps are wired well enough because at home, they exhibited almost none of the problems they've been having here. Maybe a bumpy car ride to college with them in the trunk with tubes plugged in didn't help, but I've replaced the rectifiers and power tubes, and the drivers are 6SN7's (should be sturdy enough). My question is whether other people have had this problem, and whether getting an external sound card, powered or not, helped the problem?
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Old 30th September 2007, 08:06 PM   #2
tade is offline tade  United States
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lol, and I thought that I was the only one to pull the; break the ground pin off of all my equipment... Better not let the UL find out!

I am sorry that i don't have any advice for you, seeing as that proved to be the best solution to my problem. i am quite interested in our other forum member's opinions.

Hummmmmm
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Old 1st October 2007, 06:39 AM   #3
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I actually just cut the copper bus bar from the ground connector lug on the IEC inlet on each amp and there's still hum, albeit less. My amps didn't use to hum so I figure it isn't a wiring job. They use two 1N4007's per leg in place of a 5U4, soldered right across the pins (from 6 and 8 to 2 or something).

Other than that the only tubes that have been in the amp while it was being driven in a car are some 6SN7's. One of the coin base RCA's is microphonic but that's only in one amp, not both.. The KT77's are biased at around -34V each with a 470 ohm 5 watt MF resistor, and a 464V B+/ I figure around 72mA per tube, dissipating around 30W total. A tiny bit over the limits but plates aren't red and I doubt this is contributing to hum.
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