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Old 10th June 2005, 05:42 PM   #1
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Default tube pre-amp

I've built a tube pre-amp using 2 6sn7gts. I'm facing a very big problem now and hope that someone out there can help me. My pre-amp will come out humming aound, and have tried a lot of methods, but still there the humming. Can anyone tell me how to solve it?
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Old 10th June 2005, 05:46 PM   #2
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Do you have it's schematic, together with the PSU? it would help a lot.
Could be a faulty ground connection, filaments(?), ....
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Old 10th June 2005, 06:36 PM   #3
SY is offline SY  United States
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There's a 99% chance that you've got a ground loop.
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Old 11th June 2005, 04:47 AM   #4
kmtang is offline kmtang  Canada
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Do you use DC for the filament? Also, you need to raise the potential filament supply to approximately 80-100V in case the last stage is a cathode follower.

Of course, the ripple level of the B+ could induce in lot of hum as well.

Please post your schematic and picture of your amp so that we could find whether there are anything we could see.


Johnny
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Old 12th June 2005, 04:54 PM   #5
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Default Humming

Thanks all of you. I've tried everything I could to reduce the hum, but the hum still there. From voltages to ground looping, everything I've tried. First I thought It was bacause the heater voltage. But after some modification, the hum only reduce a little bit, the hum is still there. I've attached the schematic, hope you all can help me. Thank you.
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File Type: jpg 6sn7pre.jpg (11.1 KB, 209 views)
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Old 12th June 2005, 05:14 PM   #6
sklimek is offline sklimek  United States
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Default Re: Humming

Quote:
Originally posted by Matthewong
Thanks all of you. I've tried everything I could to reduce the hum, but the hum still there. From voltages to ground looping, everything I've tried. First I thought It was bacause the heater voltage. But after some modification, the hum only reduce a little bit, the hum is still there. I've attached the schematic, hope you all can help me. Thank you.
Schematic? Sometimes when you attach a file and 'preview' before sending you need to re-attach the file before sending.

if that's what happened.

Stan
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