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Old 8th Jan 2019, 5:16 pm   #14
snowman_al
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Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
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Default Re: EL34 power amp reworked as a stereo amplifier

Just thinking out loud here....

If you short the inputs individually - silence.
When you connect any input source you get hum.
Is the common factor that the 'sources' have their grounds connected together? So as you have effectively two mono blocks, when you plug the sources in you short the two RCA outer rings, and hence the ground paths of each mono block, together. That might be the loop?

What happens if you add a 10 ohm resistor to the ground path of one of the inputs? (In the green lead, between the RCA ground ring terminal and the common point on the tag board.)

Alan
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