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are some phono stages more resistant to hum?

After a tonearm upgrade, which mostly involved "improved" shielded cable, it now hums with tube phono stage (upgraded AR PH3-SE)but no hum with backup ss device (DB Systems). It appears the hum originates with the new wiring, but why would one phono stage be impervious to the hum? Do phono stages have different grounding schemes, making them more compatible with certain tt/tonearm/wiring combos in unpredicable ways? Are ss phono pres less susceptible to hum? Have you ever changed phono pre to cure a hum incompatibility? I see from forums that tt hum problems are common and sometimes difficult to solve. Shouldn't a shielded cable be more immune to hum, not less?
128x128lloydc
roscoeiii's avatar
roscoeiii
1,155 posts
 
Something that worked for me with a P75 phono stage was running a wire from the ground post of my phono preto the chassis of my preamp
lewm
13,256 posts
 
Dear Dhl, If the phono circuit has a balanced topology, then the cartridge may be connected in balanced mode, and believe me there is CMR for the phono signal which does cancel hum along with other noise common to both halves of the signal. You can get a true balanced connection no matter how the cable is built, because the cartridge per se has no true ground, but it is indeed better if the cable provides identical conductors for the pos and negative halves of the signal, and a separate ground wire that generally grounds the tonearm body only. I don't know why you seem to think that is a problem or not available.
rtilden
156 posts
 
Lloydc:
I am wrestling with a similar condition after replacing my ss pre with a tube unit. Are you sure that your problem is a 'hum' and not a 'buzz'? Mine is definitely a buzz (heard only in the tweeter), and my current thinking is that it relates to external circuit noise which is induced into the system and picked up by the tubes and sent through the rest of the system. I must admit that I am early in my process of diagnosis, but nearby lighting dimmers cause similar a similar buzz when activated. Anybody else have comments on that line of thinking?
lewm
13,256 posts
 
Rtilden, Check to see whether any of your ICs, particularly the one from tonearm to preamp, are running parallel to or anywhere near an AC cord or a PS umbilical. I had an identical buzz that drove me a bit nuts until I noticed that my phono cable was running near to BOTH the AC cord from the turntable AND the PS umbilical from the phono stage PS. Re-routing it made a huge difference. Sometimes we lose track of what's going on with all the spaghetti hanging down at the rear of our system shelves.
rtilden
156 posts
 
Thanks, Lewm. I will check out that possibility in my next step.
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