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Old 12th July 2003, 03:32 AM   #1
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Default A/B/Y and hum in guitar amps

i had to switch to playing drums because nobody will play drums for me, so i've lent my amp to my friend so that he can play through his amp and my amp at the same time. he puts his guitar into a line6 delay modeler and plugs my amp into the left-out and his amp into the right-out. anyways, one of them amps is humming like crazy and neither of them hum that much when they are alone. could it be that the two heads are sitting on top of each other? or cos they are different impedances or what?
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Old 12th July 2003, 03:55 AM   #2
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travis you might have got it correct as all the variables of your gear are unknown
I experienced major setup problems when i was in the business with some equipment....some amps are herendous for causing problems with other equipment...if the amplifiers are fine by themselves then its an issue....but if it this happening in one location then the power feed could be it


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Old 13th July 2003, 06:42 PM   #3
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Travis,

I would suspect an earth loop introduced through the two heads being connected together through the signal earth from the line six. I would break the ground in one of the signal feeds with a isolation transformer.

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Old 13th July 2003, 07:31 PM   #4
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so if i made a buffer and connected its output to both amps, it would probably hum?

Click the image to open in full size.

i will make something like this, with three switches: left on/off toggle, right on/off toggle, and switch to turn them both on and the same time. CMOS!
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Old 13th July 2003, 07:47 PM   #5
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Hi Travis,

That is a nice buffer design! Should do the job nicely as all possible earth loops between the pieces of equipment are broken.

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Old 13th July 2003, 09:18 PM   #6
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is this how it would look with out all the extra mumbo-jumbo?
Click the image to open in full size.
i want to make sure i understand what's going on. how do i go about picking good specs for the transformers?
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Old 14th July 2003, 01:45 PM   #7
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Travis,

You have the drawing right. However for your scenario you could get away with just one transformer as you only need to break one ground connection. You would need a normal 'line level' transformer 1:1 ratio meduim impedance.

A typical broadcast line transformer would be excellent but you don't need something that fancy any standard line level transformer will work well with electric guitar. Voice or keyboards require something a bit better.

James
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Old 14th July 2003, 03:36 PM   #8
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thanks, guys.
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