Most Effective Tweaks?

papermill,

There was no noticeable hum or noise prior to adding the step up transformer to better match the MM level phono pre-amp in my ARC sp16 when I bought it.  So I knew adding the step up xformer introduced the hum somehow.

First I determined hum was related to EM field by moving the stepup xfermer around and noticing changes in hum levels at different locations which gave me info about location of the source of EM.

Then I bought enough flexible sheet mu metal foil from an online source (do not recalll which, but a simple google found it at the time) to form a cylindrical container (open on both ends which did not matter in my case) that I could slide the step up xformer into easily to form an encompassing cylindrical shield.

This worked like a charm in my case. The key is knowing the location of the EM source by istening to noise levels as device is moved around, picking an optimal location with lowest noise possible then applying the mu metal so that it shields device from EM source. I can share a picture if desired. Not pretty or elaborate in my case but effective.

if noise is from RF, shielded ICs may help. in my case it was EM noise being picked up by my step up transformer directly. The ICs I use from step up xformer to phono input are unshielded mainly because I like those specific ICs, but using shielded ICs in all cases is probably safest. Each case could be different in many ways so you have to be able to determine the cause.

Hum in a phono setup is commonly due to ground issues. If ground is good, nothing else may be needed. Lower level devices like low output MC carts (a Denon Dl103R in my case) and step up transformers are most susceptible to external noise sources. Higher output MC or MM phono carts and line level devices are less affected. YMMV for sure in cases like this.