Actually, the reason the transformers hum is because DC is getting on the primary of the transformer.
Here is a little quote by the one and only Nelson Pass (my hero) :
"If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.
The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.
You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +."
If you trace the hum to the transformer you may want to give the above suggestion a try. I insert two back to back electrolytics on the primary in every amp I build as a matter of design, so I never have to worry about this type of caveat.
Here is a little quote by the one and only Nelson Pass (my hero) :
"If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.
The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.
You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +."
If you trace the hum to the transformer you may want to give the above suggestion a try. I insert two back to back electrolytics on the primary in every amp I build as a matter of design, so I never have to worry about this type of caveat.