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Old 23rd May 2013, 11:24 PM   #1
mjock3 is offline mjock3  United States
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Default Hum issue in PAS Aikido

I recently built a PAS variation. A Tubes4Hifi Aikido tube preamp made for a PAS enclosure. I am have a hum issue. I used their power supply update as well. The hum varies in how loud it is depending on where the volume is set. However every once and a while it increases in how loud it is. It stays louder for a couple minutes then dies down again to the level it was at before. I have replaced all the new 12au7's with another new set but that has no affect on the situation. I have put a cheater plug on it, reversed the way it was plugged in with no affect. All my equipment is plugged into the same power conditioner. I do not believe it is a ground loop hum. Any one out there that might be able to help me figure out where this is coming from?

Thanks,
Mark
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Old 24th May 2013, 10:37 AM   #2
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Is the hum at 60Hz or 120Hz? And do you own an oscilloscope?
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Old 24th May 2013, 03:28 PM   #3
mjock3 is offline mjock3  United States
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Hum is 60 hz, yes I have a scope. But I have only used it a few times. May I ask what does the 60 hz vs 120 hz mean?

Thanks,
Mark

Last edited by mjock3; 24th May 2013 at 03:30 PM.
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Old 24th May 2013, 03:33 PM   #4
SY is offline SY  United States
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120Hz and 60Hz hum will have different origins, so it's useful as a first step to determine which it is. 120Hz usually comes from power supply wiring and layout, especially if signal circuit grounding isn't optimal- it's the major ripple component from rectifying 60Hz. 60Hz usually comes from a ground loop or pick up of radiated hum.

What part of WI are you in?
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Old 24th May 2013, 03:37 PM   #5
mjock3 is offline mjock3  United States
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I am in Appleton.
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Old 24th May 2013, 03:50 PM   #6
SY is offline SY  United States
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Nice town, home of Harry Houdini.

We're up there every couple of weeks (just there yesterday), if we can't get it sorted out via the forum, I can walk you through it if you like. Photos of your layout and wiring would help, as would a screen shot of what the hum on the output of the preamp looks like on your scope.
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Old 24th May 2013, 04:33 PM   #7
mjock3 is offline mjock3  United States
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Sy, that would be great if you are in this neck of the woods for you to stop by. Any time even if I don't have the issue any more.
Unfortunately one of my amps went down the other day, so it may be a while before I get it back.

Been a while since I loaded an image any tips?
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Old 24th May 2013, 04:41 PM   #8
SY is offline SY  United States
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Yeah, it's pretty easy. Scroll down in the Reply screen to the "manage attachments" button. It's pretty intuitive from there. Keep the image size under 200k or so.

I see you're in the coffee biz. Excellent, I'm a bit of an enthusiast...
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Old 24th May 2013, 04:48 PM   #9
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For some reason, I could open the image from the notification mail I got . The wiring is up for some improvement. The twists on what as far as i can determine is the heater cabeling need to be WAY tighter for any EMI cancelation. The heater supply needs to be balanced as well by an (artificial) center tap. The lenghts of almost every cable could be shorter as well. I suspect this is how the 60Hz interference is getting into your signalpath.
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Old 24th May 2013, 04:56 PM   #10
mjock3 is offline mjock3  United States
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Here's what I have for pictures.
Funk1980 not sure if you got these pics if so please let me know.
Attached Images
File Type: jpg IMG_0651 (640x480).jpg (234.8 KB, 190 views)
File Type: jpg IMG_0652 (640x480).jpg (214.5 KB, 185 views)
File Type: jpg IMG_0653 (640x480).jpg (200.1 KB, 182 views)
File Type: jpg IMG_0654 (640x480).jpg (213.4 KB, 181 views)
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