tube pre-amp

Matthewong · 10th June 2005, 05:42 PM

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?

Simpleton · 10th June 2005, 05:46 PM

Do you have it's schematic, together with the PSU? it would help a lot.
Could be a faulty ground connection, filaments(?), ....

SY · 10th June 2005, 06:36 PM

There's a 99% chance that you've got a ground loop.

kmtang · 11th June 2005, 04:47 AM

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

Matthewong · 12th June 2005, 04:54 PM

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.

sklimek · 12th June 2005, 05:14 PM

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

10th June 2005, 05:42 PM	#1
Matthewong diyAudio Member Join Date: Jun 2005 Location: KL	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?

10th June 2005, 06:36 PM	#3
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	There's a 99% chance that you've got a ground loop. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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10th June 2005, 05:46 PM	#2
Simpleton diyAudio Member Join Date: Jan 2005 Location: Lisboa	Do you have it's schematic, together with the PSU? it would help a lot. Could be a faulty ground connection, filaments(?), ....

11th June 2005, 04:47 AM	#4
kmtang diyAudio Member Join Date: Nov 2004 Location: Vancouver	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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