In Reply to: A challenge to you all posted by SteveBrown on January 19, 2017 at 20:22:49:
Hi Steve,Hum can come in via a lot of different means, as you know. But one kind of hum I ran into was from AC line current riding in the return (shield) conductor of the input wires. You can tell this is your problem if the output is hum free until you connect the cable to the preamp, then it starts humming, or until cables from both channels are connected.
I found a way to cut that kind of hum back to very low levels with just a well placed resistor (and probably some rewiring of the input stage and input jack). John Broskie over at TubeCAD does a similar thing in some of his designs. I wrote a blog about the technique (see link). No need to read all the techie stuff in the article, but do have a look at the schematics to see.
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Edits: 01/21/17
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Follow Ups
- RE: A challenge to you all - bwaslo 13:42:30 01/21/17 (1)
- RE: A challenge to you all - SteveBrown 17:14:29 01/21/17 (0)