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Old 13th July 2003, 07:39 AM   #1
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Default Ground loop problems - looking for opinions

Hello everyone,

Just finished building this 6BM8 amp, sounds very nice when every channel is tested separatly, but when connected together one channel sounds 40% louder then the other and the lower one is distorted. I suspect the grounds to be the problem because when I disconnect the ground wire it is OK. I have builet separate power supplies but the ground is still connected via the tuner I am using. Decupling the ground solves the problem.

What I do not understand is why connecting the R and L grounds creates the problem and how can I solve it without using a transformer in the input.

http://www1.odn.ne.jp/~ces58160/tube...m8/6bm8pp.html

Thank you very much.

Glass_painter
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Old 13th July 2003, 09:59 AM   #2
EC8010 is offline EC8010  United Kingdom
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There's nothing in the circuit to diagram to suggest that there should be a problem, so I think you are looking for a wiring error. Check your DC voltages when you connect the grounds together.
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Old 13th July 2003, 10:18 AM   #3
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Default Ground loops?

Hi,

Yes, this was my guess as well so I looked at the DC volages, they do change but very little and all values are in spec (connected or not). I even took the power supply apart and built a dubble PS separate for aech side, now the only mutual wire is ground.

Any other ideas?

Thanks.

Glass_painter
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Old 13th July 2003, 10:22 AM   #4
EC8010 is offline EC8010  United Kingdom
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If you have an oscilloscope, remove the NFB and apply a sinewave from an oscillator or test CD to both channels and look to see if it's the input stage or just the output stage that is distorting/changing level.
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Old 13th July 2003, 11:16 AM   #5
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Thanks, I will try it tonight and let you know.

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