I stood up an old receiver next to my rack for its radio, connected it
to two channels of my mixer and sometimes get hum. The mixer is
powered by an external transformer; the receiver power cord has no
ground. They are both plugged into the same power strip. When I
reverse the polarity of the receiver power cord plug, the hum is
louder when it is present.

Sometimes the hum is loud and at other times barely audible until it
gets on your nerves. Everything about this situation is intermittent.
I can usually get the hum to stop if I repeatedly rotate and reinsert
the connectors on both sides.

I also had this problem with a tuner (still on a rack shelf) which
progressed over a couple of years to the point that I dragged out the
old receiver to use instead. The tuner also had a problem with the 75
ohm lead from the attic antenna, which I fixed by adding a 300 ohm
transformer. Is this tuner likely fried? If my next tuner has a
three prong plug, will this solve the problem? Do I need special
audio cables?
Bob

--
Bob Simon
remove both "x"s from domain for private replies

"Bob Simon" wrote in message
...
I stood up an old receiver next to my rack for its radio, connected it
to two channels of my mixer and sometimes get hum. The mixer is
powered by an external transformer; the receiver power cord has no
ground. They are both plugged into the same power strip. When I
reverse the polarity of the receiver power cord plug, the hum is
louder when it is present.

Sometimes the hum is loud and at other times barely audible until it
gets on your nerves. Everything about this situation is intermittent.
I can usually get the hum to stop if I repeatedly rotate and reinsert
the connectors on both sides.

I also had this problem with a tuner (still on a rack shelf) which
progressed over a couple of years to the point that I dragged out the
old receiver to use instead. The tuner also had a problem with the 75
ohm lead from the attic antenna, which I fixed by adding a 300 ohm
transformer. Is this tuner likely fried? If my next tuner has a
three prong plug, will this solve the problem? Do I need special
audio cables?
Bob

--
Bob Simon
remove both "x"s from domain for private replies

Sounds like one or more bad patch cords to me.

Mark Z.

"Bob Simon" wrote in message
...
I stood up an old receiver next to my rack for its radio, connected it
to two channels of my mixer and sometimes get hum. The mixer is
powered by an external transformer; the receiver power cord has no
ground. They are both plugged into the same power strip. When I
reverse the polarity of the receiver power cord plug, the hum is
louder when it is present.

Sometimes the hum is loud and at other times barely audible until it
gets on your nerves. Everything about this situation is intermittent.
I can usually get the hum to stop if I repeatedly rotate and reinsert
the connectors on both sides.

I also had this problem with a tuner (still on a rack shelf) which
progressed over a couple of years to the point that I dragged out the
old receiver to use instead. The tuner also had a problem with the 75
ohm lead from the attic antenna, which I fixed by adding a 300 ohm
transformer. Is this tuner likely fried? If my next tuner has a
three prong plug, will this solve the problem? Do I need special
audio cables?
Bob


Tuner is probably OK, the RF balun at the antenna end has zilch to do with
AF o/p.
That receiver exit *may need* a series blocking capacitort, as there may be
DC present with ripple leaking out of it.

Check integrity of all audio connects. The equipment which is amplifying the
source signal should have the best ground (ie, its metalwork is grounded),
and,
if your leads are unbalanced, it is best to tie destination screen to
ground, and float it at source end when/if connected to a device's
unbalanced
device o/p.
Of course, if the source signal is balanced, then use both core and screen
of jumper lead to transfer the audio.
But, in the worst case, the hum may only disappear when an audio isolation
1:1 xfrmr is introduced between source and next stage.
Jim