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Posted by keithiopian on
06-11-2020
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So I decided to try some of the mods mentioned to my semi-recent 834p w/ MC step-ups. It all started with C1 and C7...but then i got into RIAA, upgraded diodes and filter caps. Well, everything should be just stellar on paper but...now I have a hum that I can't seem to eliminate for the life of me. I didn't I have to admit, despite plenty of flux and solder sucking, due to some different lead sizes some traces didn't end up in perfect condition...but I don't think so bad that there's terrible capacitance acting as antenna...I tried shielding w/ copper tape to no avail. Oscilloscope on hand and ready for testing, just honestly not sure how best to track it down. Happy to share any photos if helpful, any advise at all more than welcome.
bestk
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Posted by rowuk on
06-11-2020
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The 834p is a tried and true circuit. It should be OK. If you have hum, I would suspect the step up transformers first and the power supply second. Maybe a ground lead is not attached?
Take it completely out of the system, disconnect the phono leads, short the inputs and check if it hums with headphones.
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Posted by keithiopian on
06-11-2020
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totally disconnected, even on different power plug. Will try with everything screwed back together in final box form to double check any EMI (and when it's not 1am). thanks for the advice. oh and it does hum with either mm or mc, just obviously harder to hear without the stepups.
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Posted by keithiopian on
06-11-2020
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tried with everything back reassembled (enclosed w/ copper shielding and such)...still a hum. Both MC and MM, slightly less on both when put in a lifted-ground japanese plug. Possibly relevant, there also seems to be a secondary noise, more of an oscillator/very slow tremolo.
(Also for now just testing with the default "selected" tubes it came with, tho i'm hoping to put in windmill raytheon 5751 eventually...worth a shot trying other new make 12ax7s?)
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