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   Home » Analog Playback» 834p modding..."humming" along a bit too much... (5 posts, 1 page)
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06-11-2020 Post does not mapped to Knowledge Tree
keithiopian
Posts 4
Joined on 06-11-2020

Post #: 1
Post ID: 25864
Reply to: 25864
834p modding..."humming" along a bit too much...
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
06-11-2020 Post does not mapped to Knowledge Tree
rowuk


Germany
Posts 354
Joined on 07-05-2012

Post #: 2
Post ID: 25865
Reply to: 25864
Does it hum without the step ups?
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. 


Whenever I feel blue, I start breathing again.
06-11-2020 Post does not mapped to Knowledge Tree
keithiopian
Posts 4
Joined on 06-11-2020

Post #: 3
Post ID: 25866
Reply to: 25865
Tried your method
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.
06-11-2020 Post does not mapped to Knowledge Tree
keithiopian
Posts 4
Joined on 06-11-2020

Post #: 4
Post ID: 25867
Reply to: 25866
Pics = 1000
reference on current state
http://tempuri.org/tempuri.html

Scope on the power supply out seems pretty steady...
06-11-2020 Post does not mapped to Knowledge Tree
keithiopian
Posts 4
Joined on 06-11-2020

Post #: 5
Post ID: 25868
Reply to: 25867
Confirming hum
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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